JP2023168643A - Rational processing method of spent nuclear fuel - Google Patents

Abstract

To provide a rational high level radioactive waste processing method for converting an unnecessary radioactive nuclide which is generated in spent nuclear fuel into a short life nuclide or stable nuclide, increasing weight of reusable nuclides, and reducing the amount of waste which is vitrified.SOLUTION: A rational high level radioactive waste processing method uses: a gas tank for collecting a gas nuclide which is generated immediately after nuclear fuel extraction; a soluble substance tank for collecting nuclides which are soluble in a nitric acid after collection processing such as a PUREX method or the like; and an insoluble substance tank for collecting nuclides which are not easily solved in a nitric acid and insoluble nuclides after the collection processing. In the gas tank, after storage for a regulated period, only iodine is irradiated with thermal neutrons once, only the soluble nuclides in the soluble substance tank and the insoluble nuclides and the nuclides which are not easily solved in the insoluble substance tank are irradiated with cold neutrons, and radiation in storage for a regulated period and storage are repeated multiple times, then oxides generated in the respective tanks are converted into chlorides whose boiling points are low, then elements are separated by a fractional distillation method using a difference of the boiling points, and if necessary, isotopes are separated using a gas centrifugal separation method, for collecting radioactive nuclides and stable nuclides reusable as resources, and reducing the amount of waste nuclides being vitrified.SELECTED DRAWING: Figure 1

Description

The present invention relates to a technology for processing high-level radioactive waste using nuclear fission products.

A 1,000,000 kW class nuclear power plant uses approximately 23 tons of 5% enriched uranium fuel every year, and the fission products (FP) generated from spent nuclear fuel depend on the U235 ratio, burnup, and operation. Although the types of nuclides and the amount generated vary depending on the situation and irradiation time, it is generally said that 2 to 5% of fission products are generated from one ton of nuclear fuel.

These fission products are converted into highly active liquid waste (HALW) after recovering actinides such as uranium and plutonium through reprocessing of spent nuclear fuel based on the PUREX (Plutonium and Uranium Recovery by Extraction) method. ste) and Become. (For actinide removal, there is Patent Document 1 etc.)

This high-level radioactive waste liquid is concentrated, reduced in volume, dissolved in glass, and solidified in a stainless steel container (canister) (vitrified material). This vitrified material maintains a high temperature due to the decay of the radioactive materials inside. Therefore, the vitrified material is stored in an intermediate storage site for about 30 to 50 years, until the radioactive material is reduced and the temperature is lowered, and then the vitrified material is finally disposed of (geological disposal) in a stable geological formation more than 300 meters underground.

In such a treatment method, the amount of vitrified material increases, and there are problems such as securing a storage space and managing the vitrified material, and securing a storage space is an especially urgent issue. Therefore, elements and radionuclides in high-level waste are grouped according to half-life, chemical properties of the elements, purpose of use, etc. Long-lived nuclides are treated with short-lived or Methods of converting radioactive nuclides into non-radioactive nuclides (transmutation technology) and using more useful elements and nuclides (recycling high-level waste) are being considered. (Non-patent Document 1 etc.)

Regarding nuclear transmutation technology, there are reports of nuclear transmutation by irradiating long-lived fission products with neutrons, charged particle beams, positrons, etc., but these only target specific radionuclides and require high-level It is not related to radioactive waste as a whole. (Patent Documents 2, 3, 4)

A method has been proposed to selectively separate and recover platinum group elements, technetium, tellurium, and selenium at a high recovery rate from the nitric acid solution handled at spent nuclear fuel reprocessing plants or the radioactive process waste fluid generated during the process. These are related to recovery for reuse and are not related to vitrified solids. (Patent Document 5)

In a radioactive waste disposal method, high-energy neutrons generated by an accelerator are irradiated with high-energy neutrons generated by an accelerator to cause inelastic scattering to a group of isotopic elements containing radionuclides and having a common atomic number among fission products from radioactive waste. It is a nuclide transmutation that reduces the mass number (neutron number) by 1 or 2 by (n, 2n) reaction or (n, 3n) reaction, and differs depending on the parity of the neutron separation energy of the isotope element. Taking advantage of this, we select a neutron energy band in which the reaction cross sections of nuclides with different mass numbers differ by a factor of 10 or more, and irradiate this selected energy band with neutrons to reduce the mass number of the long-lived nuclide to be converted. A method for processing radioactive waste that converts it into short-lived nuclides or stable nuclides, and a technology for extraction without isotope separation has been disclosed. (Patent Document 6)

JP 2002-243890 A Method for separating and storing all actinides from spent nuclear fuel JP2017-198622A Method for processing long-lived fission products using neutrons Kyoto University, National University Corporation JP 2018-044851 A System for shortening the lifetime of long-lived fission products by nuclide conversion and lifetime shortening treatment method for nuclide conversion of long-lived fission products Chubu University Educational Corporation Japanese Patent Application No. 2016-544629 Method for disposing of long-lived fission products Research Organization for Advanced Information Science and Technology, etc. Japanese Patent Application No. 11-026995 Separation and Recovery Method for Platinum Group Elements, Technetium, Tellurium and Selenium Nuclear Cycle Development Institute, etc. JP 2016-176812 Publication Radioactive waste processing method, Toshiba

Atomic Energy Encyclopedia ATOMICA "Group Separation and Resource Recovery of High-Level Waste" (07-02-01-01) Summary, Japan Atomic Energy Agency (JAEA) In addition, documents referenced and cited data after the summary of the invention The original is described at the end.

However, by utilizing the fact that the neutron separation energy of the above-mentioned isotopes differs based on the parity and oddity, neutrons in the selected high energy band are irradiated to reduce the mass number of the long-lived nuclide to be converted, and the mass number of the long-lived nuclide to be converted is reduced. In a method for treating radioactive waste that converts it into stable nuclides, neutrons in a high-energy band with a reaction cross section that is more than 10 times different are irradiated, but the reaction cross section of the nuclide that is not desired to be converted is less than one-tenth, (n, 2n) reaction may occur and radionuclides may remain, making complete separation of radionuclides and stable nuclides difficult to achieve. Furthermore, there are 10 elements targeted for radioactive waste, and there is no description of radionuclides with half-lives of 10 to ¹⁰ years or more. Furthermore, there is no description of the weight of radionuclides generated or radioactivity, and there is no quantitative description.

The present invention deals with the removal of actinides such as uranium and plutonium from spent nuclear fuel generated at nuclear power plants through reprocessing such as the PUREX method, and the nuclides contained in the high-level radioactive waste liquid left behind and residues not included in the waste liquid. With regard to nuclides contained in The purpose of this study is to provide a method for treating nuclear fission products.

The present invention provides a tank (hereinafter referred to as a gas tank) for recovering and storing gaseous nuclides generated from spent nuclear fuel immediately after its removal, and a tank for recovering and storing actinides such as uranium and plutonium after a specified period of time has passed. After that, out of the FP excluding gaseous nuclides, a storage tank separates and collects nuclides that are soluble in nitric acid (hereinafter referred to as soluble nuclides) and nuclides that are poorly soluble or insoluble in nitric acid (hereinafter referred to as poorly soluble nuclides). (Hereinafter, the former of the storage tanks will be referred to as the soluble material tank and the latter will be referred to as the refractory tank.) These nuclides are irradiated with low-energy cold neutrons and their mass numbers are changed by a neutron capture reaction. A method for converting radioactive waste, which is characterized in that after irradiation with neutrons, after a predetermined time has elapsed, the method described in claims 1 to 5 is used to store the waste for a predetermined time and irradiate it with neutrons a predetermined number of times. Provide a processing method.

In this radioactive waste disposal method, after a specified t ₀ hours including the cooling period, the soluble nuclides in the solubles tank are irradiated with cold neutrons for the first time, and after being stored for the specified t ₁ hour, radioactive decay occurs. The generated gaseous nuclides are transferred to a gas tank, and the generated poorly soluble nuclides are collected into another storage tank (hardly soluble tank A) using a solid-liquid separator or the like. Thereafter, after irradiating the soluble nuclides with cold neutrons _twice and storing them for a specified time, the gaseous nuclides generated by radiation decay are collected in a gas tank, and the poorly soluble nuclides generated are separated using a solid-liquid separator. This method of processing radioactive waste is characterized in that the radioactive waste is collected in a storage tank A, and the hardly soluble nuclides are not irradiated with cold neutrons.

In the radioactive waste treatment method, after a predetermined time t ₀ has elapsed, the poorly soluble nuclide in the poorly soluble tank is irradiated with cold neutrons for the first time, and then a nitric acid solution with a specified concentration is poured into the tank, and a specified t ₁ ' After storage for a period of time, if the generated gas nuclide is a stable nuclide, it is exhausted, and if it is a radionuclide, it is collected in a gas tank, and the generated soluble nuclide is filtered together with a nitric acid solution and placed in another storage tank (solubles tank B). After the second cold neutron irradiation of the poorly soluble nuclides, the soluble nuclides and nitric acid solution recovered in the soluble tank B are refluxed to the poorly soluble tank and stored for a specified time t ₂ '. Thereafter, cold neutrons are irradiated Nj times to the poorly soluble nuclides, but the soluble nuclides in soluble tank B immediately before the Njth cold neutron irradiation are returned to the poorly soluble tank together with the nitric acid solution after the Njth cold neutron irradiation. After storage for a specified _time , if the gas generated by radioactive decay is a stable nuclide, it is exhausted, and if it is a radionuclide, it is collected in a gas tank, and soluble nuclides are collected in a soluble tank B using a filtration device, etc. However, this method of disposing of radioactive waste is characterized in that soluble nuclides are not irradiated with neutrons.

In the radioactive waste treatment method, gaseous nuclides generated in the soluble and hardly soluble tanks are collected after a specified time t ₀ has elapsed, but the soluble nuclides are not irradiated with cold neutrons. Immediately before the second time, only iodine is extracted from the gas recovered from the solubles tank and the gas present in the gas tank and stored in the iodide tank, and only the iodine is irradiated with neutrons once. At this time, the neutrons may be thermal neutrons. Gas generated in the iodide tank is collected in a gas tank. If the gas generated in the refractory tank is only stable nuclides, it will not be collected in the gas tank. After that, the gaseous nuclide is not irradiated with neutrons, and the solid nuclide generated by radioactive decay during this storage period is collected in another storage tank (solid tank), and this solid nuclide is not irradiated with neutrons. It is a method of disposing of radioactive waste.

The soluble and refractory tanks are irradiated with cold neutrons Ni and Nj times, respectively, and after being left for a certain period of several years, the radionuclides decay and the resulting solid nuclides are transferred to the soluble and refractory tanks. A. The solids tank, poorly soluble substances tank, and soluble substances tank B were collected, and the nuclides and nitric acid solution recovered in the former three were collected in chloride tank 1 (equipped with a solidification device) and the latter two. The nuclides and the nitric acid solution are transferred to a chloride tank 2 (equipped with a solidification device) and heated to drive out the nitric acid, thereby converting most of the nuclides into oxides.

The oxides generated in the chloride bath are converted into chlorides with a low boiling point. The chloride present in chloride tank 1 is put into the vaporization tank and heated in ascending order of the boiling point of the chloride, vaporized in a rectification column for each boiling point, fractionated in a condenser and extracted as chloride, and only stable nuclides are extracted. If any, they are collected into a stable nuclide recovery tank via a cooling device, and radioactive-only nuclides and isotopes containing a mixture of radioactive nuclides and stable nuclides are collected into a vitrified nuclide recovery tank. A single radionuclide that can be used as a radioactive substance was recovered, and isotopes with only two nuclides, a radionuclide that can be used as a radioactive substance and a stable nuclide that can be reused as a resource, were collected using the mass difference used during uranium fuel production. Isotope separation is performed using a gas centrifugal separator to separate light nuclides with a small mass number and heavy nuclides with a large mass number, and collect them in a light nuclide recovery tank and a heavy nuclide recovery tank, respectively. Next, the chloride tank 2 is treated in the same manner. By treating the nuclides generated in the soluble matter tank and the nuclides generated in the refractory tank separately, the weight of stable nuclides recovered can be increased, and the weight of waste nuclides that will be vitrified can be reduced.

The present invention converts unnecessary radionuclides with long half-lives into short-lived nuclides or stable nuclides, reduces the weight of nuclides in the vitrification of high-level radioactive waste, and makes reusable radionuclides and stable nuclides. It is possible to provide a rational method for processing nuclear fission products that recovers each nuclide or each element as a resource.

FIG. 1 is a conceptual diagram showing an embodiment of the present invention.

Hereinafter, an embodiment of the present invention will be described based on FIG.
The present invention is a method in which a nuclide is irradiated with low-energy cold neutrons that increase the neutron capture cross section of the nuclide, the neutrons are captured by a neutron capture reaction, and the mass number is changed to perform nuclide conversion. The cold neutron source device is equipped with a shutter that slows down the neutrons generated from the neutron source using cryogenic liquid hydrogen as a moderator, further slows them down with liquid helium, converts them into cold neutrons, and performs neutron irradiation for a certain period of time. do. For neutron irradiation, the shutter is opened only for a sufficient period of time for the irradiated nuclide to undergo nuclide transmutation. A nuclide with a large neutron capture cross section captures neutrons and its mass number increases by 1. Furthermore, if the neutron capture cross section of a nuclide whose mass number increases by 1 is large, this nuclide also captures neutrons and its mass number increases by 2.

Due to neutron irradiation, stable nuclides may be converted to radioactive nuclides, and the number of neutron irradiations and the length of time left after irradiation change the nuclides and weight produced by radioactive decay. Therefore, the weight of nuclides to be discarded can be reduced and used as resources. In order to maximize the weight of recovered nuclides, it is necessary to optimize the number of neutron irradiations and the exposure time. This will be discussed in Examples.

(Processing after removing spent nuclear fuel and leaving it for a certain period of time)
The gaseous nuclides of the FP generated from spent nuclear fuel removal are collected in a gas tank, and the nuclides other than the gaseous nuclides of the generated FP are cooled for a certain period of time and then reprocessed using the PUREX method, etc. to recover the remaining high levels. Radioactive waste contains soluble nuclides in nitric acid solution and poorly soluble nuclides such as residue.
95% of the iodine generated in the nitric acid solution is recovered as a gas during the uranium and plutonium recovery process, and the rest remains as a residue in the nitric acid solution as silver iodide and palladium iodide. Therefore, these gases generated during a certain period (t ₀ hours) are treated as the weight of the nuclide generated in the gas tank. [Reference 1; listed at the end]
Note that carbon reacts with nitric acid and exists as _CO2 , so it is treated as a nuclide that is stored in the gas tank. [Reference Document 2: Listed at the end] However, the weight indicates the value of carbon only.
The soluble nuclides and poorly soluble nuclides are stored in a soluble substance tank and a hardly soluble substance tank, respectively. A nitric acid solution containing nitric acid-soluble nuclides can be used as is, but it is first denitrified and a new nitric acid solution with a concentration of 4 to 6 mol/L is added to convert nitric acid-soluble nuclides into nitrates or oxides. This nitric acid solution containing nuclides soluble in nitric acid is collected in a solubles tank.

(Soluble tank)
After a certain period of time (t ₀ hours) after spent nuclear fuel removal, cooling, and reprocessing, the nuclides in the nitric acid solution in the solubles tank from which the soluble nuclides were recovered are irradiated with cold neutrons for the first time, and then t ₁ hour. Store. t After ₁ hour, the gaseous nuclides of helium, xenon, krypton, bromine, and iodine generated by radiation decay using soluble nuclides as parent nuclides are collected in a gas tank, but bromine, which is liquid at room temperature, and iodine, which is solid, are collected as gases. To do this, heat the solubles bath if necessary. These gases are transferred to the gas tank by a vacuum pump or the like via a backflow prevention valve.
Floating or precipitated sparingly soluble nuclides such as germanium, zirconium, palladium, indium, and tin generated by radioactive decay are collected through a solid-liquid separator into the sparingly soluble substance tank A attached to the soluble substance tank, and the soluble nuclides are filtered. is refluxed to the solubles tank together with the nitric acid solution. After t ₁ hour, the nuclides in the solubles tank are irradiated with cold neutrons for a second time and stored for t ₂ hours. If necessary, the solubles tank is heated to remove gaseous nuclides generated by radioactive decay during this storage period. is collected in a gas tank, the generated poorly soluble nuclides are collected in a poorly soluble tank A attached to the solubles tank, and the nitric acid solution containing the soluble nuclides is refluxed to the solubles tank. Thereafter, only the soluble nuclides are irradiated with cold neutrons Ni times and stored for t _i hours, and the gaseous nuclides generated by radiation decay are collected in the gas tank and the generated poorly soluble nuclides are collected in the poorly soluble substance tank A. Repeatedly refluxing the nitric acid solution containing the nitric acid solution to the solubles tank. Cold neutrons are not irradiated to poorly soluble nuclides generated during storage. This increases the recovered weight of poorly soluble stable nuclides generated by decay. Note that the nitric acid solution evaporates due to the heat generated during the collapse, so the required amount is satisfied after cold neutron irradiation and the liquid amount is kept constant.

(Hardly soluble substance tank)
After a certain period of time (t ₀ hours) after spent nuclear fuel has been removed, cooled, and reprocessed, poorly soluble nuclides are collected in the poorly soluble tank and irradiated with cold neutrons for the first time, then transferred to the poorly soluble tank. A nitric acid solution of a specified concentration is added and stored for t ₁ '. After time t ₁ ', the only gas generated by decay using a poorly soluble nuclide as a parent nuclide is stable iodine 127. In order to release iodine as a gas, heat the poorly soluble substance tank if necessary and install a backflow prevention valve. After confirming safety with a radiation monitor, the air is evacuated using a vacuum pump or other means. In addition, the nitric acid solution containing soluble nuclides such as boron, gallium, arsenic, selenium, silver, cadmium, tellurium, etc. generated by radioactive decay using poorly soluble nuclides as parent nuclides is filtered. to be collected. After the elapse of time _t1 ', the nuclide in the refractory tank is irradiated with cold neutrons for the second time, and then the nitric acid solution containing the soluble nuclide and an additional nitric acid solution are added and refluxed to the refractory tank, and _t2 ' Store time. Before the third cold neutron irradiation, the nitric acid-soluble nuclides and nitric acid solution generated during this storage period are filtered and collected in the solubles tank B attached to the hardly solubles tank. Thereafter, after irradiating only the poorly soluble nuclides with cold neutrons Nj times, the nitric acid solution containing the soluble nuclides generated by storage for _tj hours is repeatedly refluxed from the solubles tank B to the poorly solubles tank. Even after time t _j has elapsed, stable iodine 127 is repeatedly generated by the decay of tellurium 127 produced by the decay of tin 127 and antimony 127 produced by cold neutron irradiation, but it can be exhausted as described above. However, if the spent nuclear fuel is MOX, or if the uranium-235 content or burnup is different, or if radioactive gaseous nuclides are generated in the refractory tank, the gas tank should be removed using a vacuum pump etc. through a valve with a backflow prevention valve. Transfer to. Soluble nuclides generated during storage are not irradiated with cold neutrons. This increases the recovered weight of soluble stable nuclides generated by decay. Note that since the weight of soluble nuclides generated after cold neutron irradiation increases with the number of irradiations, the amount of nitric acid solution must also increase.

(gas tank)
After the spent nuclear fuel has been removed for a certain period of time (t ₀ hours), the gaseous nuclides generated are combined with the gaseous nuclides recovered from the solubles tank just before the second cold neutron irradiation into the solubles tank after t ₁ hours have elapsed. Then, the gas tank is heated to sublimate and vaporize bromine and iodine, and a cooling device installed at the top of the gas tank cools the saucer at the top of the gas tank to liquefy only the iodine, which is then transferred to the iodide tank. Iodine is irradiated with thermal neutrons to convert its nuclide. This can be done by thermal neutron irradiation because the neutron capture cross section of iodine is large even for thermal neutrons. After ₁ hour has passed, a nitric acid solution with a specified concentration is added to the gas tank and left for ₂ hours. The solid nuclides generated by radioactive decay during this storage period are the stable soluble nuclides rubidium and cesium, which are collected in a solid tank attached to the gas tank, and the gaseous nuclides generated are returned to the gas tank. The generated soluble nuclides are not irradiated with neutrons. In addition, the only nuclide generated in the iodide tank is xenon, which is refluxed into the gas tank. Thereafter, in synchronization with the cold neutron irradiation and storage period cycle of the solubles tank, the gas generated in the solubles tank is recovered, and the soluble nuclide and nitric acid solution generated by the decay are returned to the gas tank, which is repeated Ni times. . In addition, if the gas generated in the refractory tank contains other than stable iodine-127, it is synchronized with the cold neutron irradiation of the refractory tank and the subsequent storage period cycle, and is returned to the gas tank immediately before the cold neutron irradiation. let

After repeating cold neutron irradiation Ni and Nj times in the soluble matter tank and the hardly soluble matter tank, and after storage for a certain period of several years, the solid nuclides generated by the decay of radionuclides are transferred to the soluble matter tank and the hardly soluble matter tank. The nuclides and nitric acid solution recovered in tank A, the solid tank, the hardly soluble substance tank, and the soluble substance tank B are collected in the chloride tank 1, and the nuclides and nitric acid solution recovered in the latter two are chloride. When the nuclides are transferred to tank 2 and heated to drive out nitric acid, most of the nuclides become oxides. [Reference 3; listed at the end]

The oxide isotopes generated from the first three and the latter two are separated into elements using the difference in boiling points, but the boiling points of these oxides are extremely high, so they are converted to chlorides with a low boiling point. . The oxides transferred to the chloride tanks 1 and 2 are converted into chlorides by injection of a hydrochloric acid solution at a specified concentration or chlorine gas. If chlorine gas is used for nuclides that cannot be converted into chlorides with hydrochloric acid and carbon is added, chlorides will be generated in several hours of heat treatment according to the chemical formula below.
2[M]On+nC+xCl ₂ →2[M]Clx+nCO ₂
However, [M] represents a metal element, such as boron, germanium, zirconium, niobium, rubidium, ruthenium, rhodium, palladium, thulium, and hafnium. [Reference 4; listed at the end]

The chlorides (60 nuclides in the example) present in the chloride tank 1 mainly generated in the solubles tank are charged into the vaporization tank, heated in ascending order of chloride boiling point, and vaporized in the rectification column for each boiling point. It is fractionated in a condenser and taken out as chloride, and if it is a stable nuclide or an isotope that is only a stable nuclide, it is collected in a nuclide recovery tank via a cooling device, and it is collected as a radionuclide and an isotope that is only a radionuclide or isotope that is stable as a radionuclide. Isotopes with mixed nuclides are collected in a vitrified nuclide recovery tank. In addition, isotopes consisting of two nuclides, a radionuclide that can be used as a radioactive substance and a stable nuclide that can be reused as a resource, are separated by isotope separation using a gas centrifugal separator that takes advantage of mass differences. Separate into large numbers of heavy nuclides and collect them in a light nuclide recovery tank and a heavy nuclide recovery tank, respectively.

Next, the chlorides (36 nuclides in the example) generated in the refractory tank existing in the chloride tank 2 are put into the vaporization tank, heated in ascending order of the chloride boiling point, and purified for each boiling point. It is vaporized in a distillation tower, fractionated in a condenser, and extracted as chloride.If it is a stable nuclide or isotope containing only a stable nuclide, it is collected in a nuclide recovery tank via a cooling device, and is then recovered as a radionuclide or isotope containing only a radionuclide. Alternatively, isotopes containing a mixture of radionuclides and stable nuclides are collected in a vitrified nuclide recovery tank. Although details will be described in Examples, since the nuclides generated in the soluble material tank and the hardly soluble material tank are treated separately, the weight of waste to be vitrified can be reduced.

Bromine and iodine are present in the gas tank, but both are stable nuclides and can be recovered as liquid and solid, respectively, at room temperature. For gaseous nuclides with a boiling point of 0° C. or lower, the weight of radionuclides decreases, the weight of stable nuclides increases, and the proportion of radioactive gas to be discarded decreases slightly. The radionuclide iodine-129 is converted into stable xenon-130.

Before describing embodiments, definitions of terms related to the present invention will be explained. FP generated from spent nuclear fuel in nuclear power generation decays due to radioactive decay, and the nuclides are shown in the order of atomic number, element symbol, and mass number, and the decay type and half-life are shown in parentheses. If there are two types of collapse, the branching ratio is displayed as a percentage. The units of half-life are seconds: s, minutes: m, hours: h, days: d, and years: y. Note that one year is calculated as 365 days.
Types of decay include alpha decay, beta decay, and gamma decay. In alpha decay, an atomic nucleus emits a helium nucleus (alpha ray) and changes into an atom with an atomic number of 2 and a mass number reduced by 4. There are three types of β-decay: decay in which a neutron in the atomic nucleus releases one electron, converts the neutron into a proton, and increases the atomic number by 1 (hereinafter referred to as β-decay); In ecβ+ decay (hereinafter referred to as ε decay), a proton emits one positron and is converted into a neutron, and its atomic number decreases by 1, and in the other, one electron outside the nucleus is captured by the atomic nucleus, and one proton is converted into a neutron. There is a decay in which the atomic number decreases by 1 (hereinafter referred to as ec decay). In both cases, electrons (β rays) are emitted. Furthermore, there is a double β decay in which β decays occur almost simultaneously, and in this decay, two neutrons become protons, so the atomic number increases by 2 (hereinafter referred to as 2β decay). In either decay, the mass number does not change. In addition, in gamma decay, when an excited atomic nucleus transitions to the ground state, excess energy is emitted as gamma rays, and the atomic number and mass number do not change. In nuclear isomer transition (hereinafter referred to as IT decay) in which a daughter nuclide in an excited state generated by decay emits gamma rays and decays to a ground state, neither the atomic number nor the mass number changes. Nuclides with a mass number of m are nuclear isomers. Here, IAEA data were used for the decay type, branching ratio, and half-life. [Data source 1; listed at the end]
The order of decay changes from nuclides with higher nuclear energy levels to nuclides with lower nuclear energy levels. This energy level is based on data from the IAEA NDS Mass Chain Chart of Nuclides.

The time it takes for a certain nuclide to radioactively decay and reduce its weight to 1/2 is called the half-life τ, and the relationship with the decay constant λ is τ=ln(2)/λ [ln(2) is the natural logarithm of 2] ]. The radioactivity per gram of nuclide is called specific radioactivity S _R , where N _A is Avogadro's constant and Z is the mass number, S _R =λ×N _A /Z, and the unit is Bq/g.
The degree of reduction in radioactivity is expressed by the time T _0.1 to reach 0.1Bq, and if m is the weight of the radionuclide with specific radioactivity S _R after t seconds, then T _0.1 = 1/λ×{ln(10 )+ln( _SR ×m)}+t.

Since the neutron capture cross section σn of most nuclides is inversely proportional to the neutron velocity, the capture cross section σn (0.353 meV) of cold neutrons (in this case, the boiling point of liquid helium -268.9°C) is It was calculated based on the value of σn (0.0253 eV) for thermal neutrons (20°C) from the Data Research Group's JENDL-5 [data source 2; listed at the end]. The value of σn (0.353 meV) is 8.47 times the value of σn (0.0253 eV). Note that nuclides whose capture cross section is not inversely proportional to the neutron velocity are defined as having a value greater than that of thermal neutrons.

The neutron capture probability σp of a nuclide is expressed as the ratio of the neutron capture cross section σn and the nuclear cross section σ.If the mass number of the nuclide is Z, the atomic radius is R=1.25×Z ^1/3 [fm]. Given, the nuclear cross section σ=πR ² was calculated. [Japan Atomic Energy Agency: Display of atoms or atomic nuclei, number density, nuclear radius, unit system (03-06-01-03)]
If the neutron-irradiated nuclide has a σp of 1 or more, it captures one neutron and undergoes nuclide conversion, and its weight becomes 0 g.The weight of the nuclide whose mass number increases by 1 becomes the weight of the nuclide that captured the neutron. Further, if σp of the captured nuclide is 1 or more, the mass number is converted to a nuclide whose mass number is increased by 2, and the weight of this nuclide is the sum of the weights of these nuclides. If σp is 1 or less, the weight of the irradiated nuclide will be multiplied by (1-σp), and the weight of the converted nuclide will be multiplied by σp.

A radionuclide A (decay constant λ _A ) decays, and the daughter nuclides B (λ _B ), C (λ _C ), and D (λ _D ) generated one after another are radionuclides, and the daughter nuclide E is a radionuclide. Assuming that the radionuclides are stable nuclides, and the weights of the radionuclides at any time t are respectively N _A , N _B , N _C , N _D , and N _E , the following simultaneous differential equations hold true for these weights.

If the initial weight of radionuclide A is N ₀ at t=0, then equation (6) can be obtained by multiplying both sides of equation (1) by exp(-λ _A ×t) and integrating over t. The initial weights of radionuclides B, C, D and stable nuclide E are 0, and by substituting equation (6) into equation (2) and solving the differential equation, equation (7) is obtained, and in the same manner, equation ( 3) By solving Equations (5) to Equations (8) to Equations (10), the nuclide weights N _A (t), N _B (t), N _C (t), N _D at any time t are obtained. (t) and N _E (t) are obtained using equations (6) to (10) shown in [Equation 2].

After recovering the gas generated from nuclear fuel removal and actinides such as uranium and plutonium using the PUREX method, including the cooling period, after a certain period of time, the soluble and poorly soluble nuclides are collected in the soluble and poorly soluble tanks. Calculate the change in nuclide weight separately. For calculations, the calculation function of Microsoft's spreadsheet software Excel worksheet was used. Hereinafter, unless otherwise specified, neutron irradiation refers to cold neutron irradiation, and neutron capture refers to cold neutron capture.

Table 1A shows an example of calculation for determining the change in nuclide weight when the nuclide is irradiated with neutrons. The nuclides are written in ascending order of atomic number for each mass number from column A, row 3 in the vertical direction, and the mass number z is written in ascending order as z1, z2, z3, ..., the atomic symbol and mass number are Az, Bz, Represented by Cz,... Note that atomic numbers are not shown in this table. In addition, nuclides with m added to their mass numbers represent nuclear isomers.
In the horizontal direction, row A is the nuclide, row B is the decay type, row C is the half-life τ, row D is the decay constant λ, and row E is the neutron capture probability σp (ratio of the neutron capture cross section σn and the nuclear cross section σ). Display. However, the half-life is not stated. The neutron energy of σp is 0.353 meV for solid nuclides in the soluble and refractory tanks, and 0.0253 eV for gas nuclides in the gas tank, but as shown in this table. Not showing actual numbers. Column F shows the nuclide weight after _t0 hours (days) of fuel removal, column G shows the status of nuclide transformation by the first neutron irradiation, +1n is written for nuclides with σp of 1 or more, and If the converted nuclide captures a neutron and the σp of the nuclide whose mass number increases by 1 is 1 or more, this nuclide is written as +1n, and the original converted nuclide whose mass number is reduced by 1 is written as +2n. Cells for nuclides for which σp is not listed are marked with ⇒, and nuclides that are not irradiated with neutrons (slightly soluble nuclides and gaseous nuclides generated by decay in the solubles tank, soluble nuclides and gaseous nuclides generated by decay in the poorly solubles tank) In the gas tank, ⇒ is also written for the cells for gaseous nuclides other than iodine from the second neutron irradiation and soluble nuclides generated by decay). Nuclides that have been converted by capturing neutrons are indicated by <>, and the nuclides (element symbol and mass number) before nuclide conversion are written as +1n, +2n, . . . in <>. Column H shows the cumulative weight after neutron irradiation, and nuclides converted by capturing neutrons during neutron irradiation are left blank at 0g. Enter the _t1 time expressed in seconds in the first row of column I. The weights ₁ hour after the first neutron irradiation are displayed in columns I to K, and the total is displayed in column L. In the following calculations, increase the mass number. The total values of the nuclide weights in the columns F, H, L, and N are displayed as ΣNt0, ΣNt0 ^* , ΣNt1, ΣNt1 ^* in the cells in the bottom row of the columns, and since these total values are equal, it follows the law of conservation of mass. holds, and the correctness of the calculation formula can be confirmed.
If the total weight of nuclides in column L and the cumulative weight of columns H and N are less than 1×10 ^-40 (hereinafter referred to as 1E-40) g, then in principle they are displayed as 0 g.
Column M shows the state of nuclide transformation due to the second neutron irradiation, and is the same as column G. However, in the soluble matter tank and the gas tank, iodine with σp>1 is +1n or +2n, unlike in the G column, and other iodine cells are written as ⇒. Column N shows the cumulative weight after the second neutron irradiation, and the columns are blank for nuclides that were converted by capturing neutrons during neutron irradiation.
Although not listed in Table 1A, the second storage time t 2 hours expressed in seconds is entered in the first row of column O, and the neutron irradiation time t ₂ hours is written in columns O to Q in the same way as columns I to K. Display the nuclide weight after ₂ hours, and display the total in column R. Further increase the mass number and calculate. The mass number and atomic number of the nuclide to be calculated will be explained using a specific example.
Here, we describe the case of calculating the nuclide weight change in the soluble substance tank and the gas tank, but when calculating the nuclide weight change in the hardly soluble substance tank, t ₁ is t ₁ ', t ₂ is t ₂ ' Replace with
Below, a method for determining the nuclide weights of these nuclides after _t1 hour has elapsed when the parent nuclide (decay type, decay constant) undergoes radioactive decay and decays into daughter nuclides after neutron irradiation will be explained. In addition, in the table, _t1 is displayed as t1 in half-width characters.

Assuming that the radionuclide Az1m with mass number z1 is the parent nuclide (m represents a nuclear isomer), Az1m (IT, λaz1m) → Az1 (β, λaz1) → Bz1 (β, λbz1) → Cz1m (IT, λcz1m) → Cz1 (stable), the weights of the nuclides Az1m, Az1, Bz1, Cz1m and Cz1 after ₁ hour of the first neutron irradiation t can be calculated by converting equations (6) to (10) shown in [Equation 2] below. Rewrite the initial weight _N0 as the cumulative weight Naz1m of the nuclide Az1m, and rewrite t as t1. However, * represents multiplication, and λcz1=0. Furthermore, the subscript (number) of N indicates the order of decay, and indicates that different decay reactions occur when the same nuclide appears in different decays. For example, Bz1 appears in equation (13) and equation (17).

The decay constant λ of each nuclide on the right side of equations (11) to (15) is set to the cell name of the corresponding row in column D (λ), the initial weight Naz1m is set to the cell name "H3", and t1 is set to the cell name "I". If you write these right-hand sides, rewritten as "$1" and rewritten to include an equal sign, in the cells of column I, rows 3 to 7, the calculation results of the weight of the corresponding nuclide after t ₁ hour will be displayed in these cells. . An example of the contents of cells in the written worksheet is shown in parentheses. Cell I3 contains the right side of formula (11) "=H3*exp(-$D3*I$1)", and cell I4 contains the formula The right side of (12) is written as "=H3*$D3*{exp(-$D3*I$1)-exp(-$D4*I$1)}/($D4-$D3)" in half-width characters. ing. However, $ indicates an absolute reference.

Similarly, when the radionuclide Az1 decays as Az1 (β, λaz1) → Bz1 (β, λbz1) → Cz1m (IT, λcz1m) → Cz (stable), the nuclide Az1, Bz1, Cz1m and Cz1 after ₁ hour t For the weight, equations (6) to (9) shown in [Equation 2] are rewritten as follows, the initial weight N ₀ is replaced with the cumulative weight Naz1 of the nuclide Az1, and t is replaced with t1.

The decay constant λ of each nuclide on the right side of equations (16) to (19) is set to the cell name of the corresponding row in column D (λ), the initial weight Naz1 is set to the cell name "H4", and t1 is set to the cell name "I". If you write these right-hand sides, rewritten as "$1" and rewritten to include an equal sign, into the cells of column J and rows 4 to 7, the calculation results of the weight of the corresponding nuclide after t ₁ hour will be displayed in these cells. . An example of the contents of cells in the written worksheet is shown in "", cell J4 has the right side of formula (16) "=H4*exp(-$D4*I$1)", and cell J7 has the formula The right side of (17) is written as "=H4*$D4*{exp(-$D4*I$1)-exp(-$D5*I$1)}/($D5-$D4)" in half-width characters. ing.
The radionuclide Bz1 (σp>1) captures neutrons by neutron irradiation and is converted to the nuclide Bz2, and the cumulative weight immediately after irradiation (H5 cell) becomes 0 g, but after t ₁ hour, the nuclide Az1m and the nuclide Az1 decay due to the Nuclide Bz1 is generated. These weights are the right-hand sides of N3bz1(t1) in equation (13) and N2bz1(t1) in equation (17), and the decay constant λ of each nuclide in the equation is expressed as the cell name of the corresponding row in column D (λ). Then, rewrite the initial weights as the cell names "H3" and "H4" for the cumulative weight of each nuclide, rewrite t as the cell name "I$1" written as t1, and rewrite both right-hand sides including the equal sign. By writing to cell I5 and cell J5, respectively, the calculation result of the weight of nuclide Bz1 after t ₁ hour will be displayed in these cells.

When the radionuclide Cz1m decays from Cz1m (IT, λcz1m) to Cz1 (stable), the weights of the nuclide Cz1m and Cz1 after t ₁ hour can be calculated using equations (6) and (7) shown in [Equation 2]. Rewrite as follows, rewriting the initial weight N ₀ as the cumulative weight Ncz1m of the nuclide Cz1m, and rewriting t as t1.

The decay constant λ of each nuclide on the right side of equations (20) to (21) is set to the cell name of the corresponding row in column D (λ), the initial weight Ncz1m is set to the cell name "H6", and t1 is set to the cell name "I". If you write the right sides of both equations, rewritten as "$1" and rewritten to include the equal sign, in the cells of column K and rows 6 and 7, the calculation results of the weight of the corresponding nuclide after t ₁ hour will be displayed in these cells. Ru.
The stable nuclide Cz1 (σp>1) captures neutrons during neutron irradiation and is converted to the nuclide Cz2, and the cumulative weight immediately after irradiation (H7 cell) becomes 0 g, but after t ₁ hour, the nuclide Az1m decays and the formula (15) The decay of nuclide Az1 produces N4cz1(t1) of equation (19), and the decay of nuclide Cz1m produces N2cz1(t1) of equation (21). The decay constant of each nuclide on the right side of these equations is the cell name of the corresponding row in column D (λ), the initial weight is the cell name of the cumulative weight of each nuclide "H3", "H4", "H6", If we rewrite t to the cell name of t1 "I$1" and write these rewritten right-hand sides including the equal sign into cells I7, J7, and K7, the calculation result of the weight of the nuclide Cz1m produced ₁ hour after t is displayed in that cell.
In the L column, the nuclide weights Naz1mt1, Naz1t1, Nbz1t1, Ncz1mt1, and Ncz1t1 of the nuclides Az1m, Az1, Bz1, Cz1m, and Cz1 after t ₁ hour are determined by the sum of cells in the same row of columns I to K.
Naz1mt1=N1az1m(t1),
Naz1t1=N2az1m(t1)+N1az1(t1),
Nbz1t1=N3bz1(t1)+N2bz1(t1),
Ncz1mt1=N4cz1m(t1)+N3cz1m(t1)+N1cz1m(t1),
Ncz1t1=N5cz1(t1)+N4cz1(t1)+N2cz1(t1).
An example of the content of a cell in a worksheet is shown in parentheses. Cell L4 contains "=I4+J4
" is written in half-width characters.

The weight of radionuclide Bz2 [σp=0.8], whose mass number has increased by 1, is converted by neutron capture from nuclide Bz1 [σp>1] and increases by Nbz1, but 20% of the weight of nuclide Bz1 is reduced by neutron irradiation. Since there is no nuclide conversion, the cumulative weight immediately after irradiation is Nbz2'=0.2×(Nbz1+Nbz2). When the nuclide Bz2 decays from Bz2 (β, λbz2) → Cz2 (β, λcz2) → Dz2 (stable), the weights of the nuclides Bz2, Cz2, and Dz2 after t ₁ hour are expressed by the formula shown in [Equation 2] ( 6)~Equations (8) are rewritten as follows, and the initial weight N ₀ is rewritten as the cumulative weight Nbz2' of the nuclide Bz2, and t is rewritten as t1. However, λdz2=0.

The decay constant λ of each nuclide on the right side of equations (22) to (24) is set to the cell name of the corresponding row in column D (λ), the initial weight Nbz2' is set to the cell name "H8", and t1 is set to the cell name " If you write these right-hand sides, which have been rewritten as "I$1" and included an equal sign, into the cells of column I, rows 8 to 10, the calculation results of the weight of the corresponding nuclide after _t1 hour will be displayed in these cells. Ru. An example of the contents of cells in the written worksheet is shown in parentheses. Cell I8 contains "=0.2*(F5+F8)*exp(-$D8*I$1)" and cell I9 contains "=0.2*(F5+F8)*F8*{(exp(-$D8*I$1)-exp(-$D9*I$1)}/($D9-$D8)" is written in half-width characters. ing.
The weight of the radionuclide Cz2 increases by Ncz1 due to nuclide conversion due to neutron capture of the nuclide Cz1 (σp>1) due to neutron irradiation, and the cumulative weight after irradiation becomes Ncz2'=Ncz1+Ncz2. When the nuclide Cz2 decays from Cz2 (β, λcz2) → Dz2 (stable), the weights of the nuclide Cz2 and Dz2 after t ₁ hour are calculated using equations (1) and (2) shown in [Equation 2] as follows: The initial weight _N0 is rewritten as the cumulative weight Ncz2' of the nuclide Cz2, and t is rewritten as t1.

On the right side of equations (25) and (26), the decay constant λ of each nuclide is set to the cell name of the corresponding row in column D (λ), the initial weight Ncz2' is set to the cell name "H9", and t1 is set to the cell name " If you rewrite both right-hand sides including the equal sign as "I$1" and write them in the cells of column J, rows 9 and 10, the calculation result of the weight of the corresponding nuclide after t ₁ hour will be in the cells of column J, rows 9 and 10. will be displayed.
The stable nuclide Dz2 (σp>1) is converted into Dz3 by neutron irradiation, and the cumulative weight (H10 cell) is 0 g, but after t ₁ hour, the nuclide Dz2 is generated by β decay of the nuclides Bz2 and Cz2. On the right side of N3dz1(t1) in Equation (24) and N2dz1(t1) in Equation (26), apply the decay constant λ of each nuclide to the cell name in column D (λ) of the corresponding row, and the initial weight of both equations. Rewrite t1 with the cell name "I$1" in the cell names "H8" and "H9" for the cumulative weight of nuclides to The calculation result of the weight of the nuclide Dz2 produced by decay after _one hour is displayed in the cell. Regarding the weight of nuclide Dz2 produced by ec decay of nuclide Ez2, on the right side of equation (28), the decay constant of each nuclide is assigned to each cell name in the corresponding row of column D (λ), and the initial weight _N0 is If you rewrite the cell name "H11" for the cumulative weight Nez2 of the nuclide Ez2, rewrite t1 to the cell name "I$1", and write the rewritten right side including the equal sign into the K10 cell, the corresponding nuclide after t ₁ hour will be calculated. The weight calculation result is displayed in the cell.
When the radionuclide Ez2 decays into a stable nuclide Dz2 whose atomic number is 1 less by EC decay, from Ez2 (ec, λez1) to Dz2 (stable), the weights of the nuclides Ez2 and Dz2 after t ₁ hour are [Equation 2] Equations (6) and (7) shown in are rewritten as follows, and the initial weight _N0 is rewritten as the cumulative weight Nez2 of the nuclide Ez2, and t is rewritten as t1.

On the right side of equations (27) to (28), the decay constant λ of each nuclide is set to the cell name of the corresponding row in column D (λ), the initial weight Nez2 is set to the cell name "H11", and t1 is set to the cell name "I". $1'' and both right-hand sides rewritten including the equal sign are written into the cells of column K and rows 11 to 10, respectively, and the calculation result of the weight of the corresponding nuclide after _t1 hour is displayed in the cell.
In column L, the weights Nbz2t1, Ncz2t1, Ndz2t1, and Nez2t1 of nuclides Bz2, Cz2, Dz2, and Ez2 after t ₁ hour are determined by the sum of cells in the same row of columns I to K.
Nbz2t1=N1bz2(t1),
Ncz2t1=N2cz2(t1)+N1cz2(t1),
Ndz2t1=N3dz2(t1)+N2dz2(t1)+N2ez2(t1),
Nez2t1=N1ez2(t1)+N2gz6(t1).
Note that N2gz6(t1) is generated by α decay of the nuclide Gz6, as described later.

The weight of the radionuclide Bz3 (σp is not stated) whose mass number has increased by 2 is due to the neutron capture of the isotopes Bz1 (σp>1) and Bz2 (σp=0.8) due to the first neutron irradiation. '=Nbz3+0.8×(Nbz1+Nbz2). When nuclide Bz3 decays from Bz3 (β, λbz3) → Cz3 (β, λcz3) → Dz3 (β, λdz3) → Ez3 (stable), the weights of nuclides Bz3, Cz3, Dz3 and Ez3 after t ₁ hour are: Equations (6) to (9) shown in [Equation 2] are rewritten as follows, and the initial weight N ₀ is rewritten as the cumulative weight Nbz3' of the nuclide Bz3, and t is rewritten as t1. However, λez3=0.

On the right side of formulas (29) to (32), the decay constant λ of each nuclide is assigned to the cell name in column D (λ) of the corresponding row, the initial weight Nbz3' is assigned to the cell name "H12", and t1 is assigned to the cell name " If you write these right-hand sides, which have been rewritten as "I$1" and rewritten to include an equal sign, into the cells of column I and rows 12 to 15, the calculation results of the weight of the corresponding nuclide after t ₁ hour will be displayed in these cells. Ru. An example of the content of a cell in the written worksheet is shown in "". In cell I12, "={F12+0.8*(F5+F8)}*exp(-$D12*I$1)" is written in half-width characters. It is.
The radionuclide Cz3 (σp>1) is converted into Cz4m by neutron capture and the cumulative weight (H13 cell) is 0, but after t ₁ hour Cz2 is generated by β decay of the nuclide Bz2. On the right side of Equation (30) N2cz3(t1), the decay constant λ of each nuclide is assigned to the cell name of the corresponding row in column D (λ), the initial weight Nbz3' is assigned to the cell name "H12", and t1 is assigned to the cell name "I". If the formula is written into cell I13, the calculation result of the weight of the nuclide Cz2 after _t1 hour will be displayed in that cell.

The weight of the radionuclide Dz3 increases by Ndz2 due to neutron capture of the isotopic nuclide Dz2 (σp>1), and the cumulative weight becomes Ndz3'=Ndz2+Ndz3. When the nuclide Dz3 decays from Dz3 (β, λdz3) → Ez3 (stable), the weights of the nuclide Dz3 and Ez3 after t ₁ hour can be calculated using equations (1) and (2) shown in [Equation 2] as follows: The initial weight _N0 is rewritten as the cumulative weight Ndz3' of the nuclide Dz3, and t is rewritten as t1.

On the right side of equations (33) to (34), the decay constant λ of each nuclide is set to the cell name of the corresponding row in column D (λ), the initial weight Ndz3' is set to the cell name "H14", and t1 is set to the cell name " If you write these right-hand sides, rewritten as "I$1" and rewritten to include the equal sign, into the cells of column J, rows 14 and 15, the calculation result of the weight of the corresponding nuclide after t ₁ hour will be displayed in the cells. .
Stable nuclide Ez3 (σp>1) is converted into Ez4 by neutron capture, and the cumulative weight (H15 cell) becomes 0 g, but after t ₁ hour, nuclide Ez3 is generated by decay of nuclides Bz3 and Dz3. On the right side of Equation (32) N4ez3 and Equation (34) N2ez3, the decay constant λ of each nuclide is written as the cell name of the corresponding row in column D (λ), and the initial weight is written as the cell name indicating the cumulative weight of each nuclide. H12" and "H14", rewrite t1 with the cell name "I$1", and write both the rewritten formulas including the equal sign into cells I15 and J15, respectively, to calculate the weight of the nuclide Ez2 after t ₁ hour. The calculation result is displayed in the cell.
In the L column, the nuclide weights Nbz3t1, Ncz3t1, Ndz3t1, and Nez3t1 of the nuclides Bz3, Cz3, Dz3, and Ez3 _one hour after t are determined by the sum of the cells in the same row of the I to K columns.
Nbz3t1=N1bz3(t1),
Ncz3t1=N2cz3(t1),
Ndz3t1=N3dz3(t1)+N1dz3(t1),
Nez3t1=N4ez3(t1)+N2ez3(t1).

The weight of the radionuclide Cz4m, whose mass number has increased by 3, increases by Ncz3 due to neutron capture of the nuclide Cz3 (σp>1), and the cumulative weight becomes Ncz4m'=Ncz3+Ncz4m. When the nuclide Cz4m decays from Cz4m (IT, λcz4m) → Cz4 (β, λcz4) → Dz4 (stable), the weights of the nuclides Cz4m, Cz4, and Dz4 after t ₁ hour are expressed by the formula (6 ) ~ Rewrite equation (8) as follows, rewrite the initial weight N ₀ as the cumulative weight Ncz4m' of the nuclide Cz4m, and rewrite t as t1. However, λdz4=0.

On the right side of equations (35) to (37), set the decay constant λ of each nuclide to the cell name of the corresponding row in column D (λ), set the initial weight Ncz4m' to the cell name "H16", and set t to the cell of t1. If you rewrite these right-hand sides with the name "I$1" and include the equal sign into the cells of column I, rows 16 to 18, the calculation result of the weight of the corresponding nuclide after t ₁ hour will be displayed in the cell. be done. An example of the contents of cells in the written worksheet is shown in parentheses. In cell I16, "=(F13+F16)*exp(-$D16*I$1)" is written in half-width characters.
The radionuclide Cz4 (σp>1) captures neutrons and is converted into Cz5, and the H17 cell (cumulative weight) becomes 0, but after _t1 hour, the IT decay of the radionuclide Cz4m produces the nuclide Cz4. On the right side of formula (36) N2cz4(t1) for the nuclide Cz4m, set the decay constant λ of each nuclide to the cell name of the corresponding row in column D (λ), set the initial weight Ncz4m' to the cell name "H16", and set t1 to the cell. By rewriting the formula with the name "I$1" and including the equal sign into cell I17, the calculation result of the weight of the corresponding nuclide after _t1 hour will be displayed in that cell.

The radionuclide Ez4, which has a higher nuclear energy level than the stable nuclide Dz4, decays into a stable nuclide Dz4 whose atomic number is 1 less by ε(β+) decay. The weight of the nuclide Ez4 increases by Nez3 due to neutron capture of the isotope Ez3 (σp>1), and the cumulative weight becomes Nez4'=Nez3+Nez4. When the nuclide Ez4 decays from Ez4 (ε, λez4) → Dz4 (stable), the weights of the nuclide Dz3 and Ez3 after t ₁ hour can be calculated using equations (1) and (2) shown in [Equation 2] as follows: The initial weight _N0 is rewritten as the cumulative weight Nez4' of the nuclide Ez4, and t is rewritten as t1.

On the right side of equations (38) and (39), the decay constant λ of each nuclide is set to the cell name of the corresponding row in column D (λ), the initial weight Nez4' is set to the cell name "H19", and t1 is set to the cell name " If both equations, rewritten to "I$1" and rewritten to include an equal sign, are written in the cells of column J, rows 19 and 18, respectively, the calculation result of the weight of the corresponding nuclide after _t1 hour will be displayed in the cells.
In the L column, the nuclide weights Ncz4mt1, Ncz4t1, Ndz4t1, and Nez4t1 after t ₁ hour of the nuclides Cz4m, Cz4, Dz4, and Ez4 are determined by the sum of cells in the same row of columns I to K.
Ncz4mt1=N1cz4m(t1),
Ncz4t1=N2cz4(t1),
Ndz4t1=N3dz4(t1)+N2dz4(t1),
Nez4t1=N1ez4(t1).

The weight of the radionuclide Cz5, whose mass number has increased by 4, increases by Ncz4 due to neutron capture of the isotope Cz4 (σp>1), and the cumulative weight becomes Ncz5'=Ncz4+Ncz5. When the nuclide Dz5 undergoes β decay, if the nuclear energy level of the nuclide Ez5m is higher than that of the nuclide Dz5, Dz5 does not decay to Ez5m but decays to Ez5. When decaying as Cz5 (β, λcz5) → Dz5 (β, λdz5) → Ez5 (stable), the weights of the nuclides Cz5, Dz5, and Ez5 after t ₁ hour are expressed by equations (6) to Ez5 shown in [Equation 2] Rewrite (8) as follows, rewrite the initial weight _N0 as the cumulative weight Ncz5' of the nuclide Cz5, and rewrite t as t1. However, λez5=0.

On the right side of equations (40) to (42), the decay constant λ of each nuclide is set to the cell name of the corresponding row in column D (λ), the initial weight Ncz5' is set to the cell name "H20", and t1 is set to the cell name " If we rewrite these right-hand sides, including the equal sign, into the cells of column I, rows 20-21 and 23, respectively, the calculation result of the weight of the corresponding nuclide after t ₁ hour will be written in the cells. Is displayed. An example of the contents of cells in the written worksheet is shown in parentheses. In cell I20, "=(F17+F20)*exp(-$D20*I$1)" is written in half-width characters.
Radionuclide Dz5 (σp>1) captures neutrons and is converted into Dz6, and the cumulative weight (H21 cell) becomes 0, but after _t1 hour, nuclide Dz5 is generated by β decay of radionuclide Cz5. On the right side of Equation (41) N2dz5, rewrite the decay constant λ of each nuclide to the cell name of the corresponding row in column D (λ), change the initial weight Ncz5' to the cell name "H20", and t1 to the cell name "I$1". If you write this right side together with an equal sign into cell I21, the calculation result of the weight of nuclide Dz5 after _t1 hour will be displayed in that cell.
When the radionuclide Ez5m disintegrates from Ez5m (IT, λez5m) → Ez5 (stable), the weight of the nuclide Ez5m and Ez5 after t ₁ hour is expressed by formula (6) and formula (7) shown in [Equation 2] as follows. Rewrite the initial weight _N0 as the cumulative weight Nez5m of the nuclide Ez5m, and rewrite t as t1.

On the right side of equations (43) and (44), the decay constant λ of each nuclide is set as the cell name of the corresponding row in column D (λ), the cumulative weight Nez5m is set as the cell name "H22", and t1 is set as the cell name "I$". 1" and write both right-hand sides, including the equal sign, in the cells of column J, rows 22 and 23, respectively, and the calculation result of the weight of the corresponding nuclide after t ₁ hour will be displayed in the cells of column J, rows 22 and 23. .
The stable nuclide Ez5 (σp>1) is converted into the isotope Ez6 and the cumulative weight (H23 cell) becomes 0 g, but after t ₁ hour, Ez5 is generated by decay using the nuclides Cz5 and Ez5m as parent nuclides. Rewrite the decay constant λ of each nuclide on the right side of Equation (42) N3ez5(t1) and the right side of Equation (44) N2ez5(t1) to the cell name of the corresponding row in column D (λ), and write the cumulative weight of each into the cell. By rewriting t1 as cell name "I$1" and writing both right-hand sides, including the equal sign, into cell I23 and cell J23, respectively, the weight of nuclide Ez5 after t is ₁ hour. The calculation result is displayed in the cell.
In the L column, the nuclide weights Ncz5t1, Ndz5t1, Nez5mt1, and Nez5t1 of the nuclides Cz5, Dz5, Ez5m, and Ez5 after t ₁ hour are determined by the sum of cells in the same row of columns I to K.
Ncz5t1=N1cz5(t1),
Ndz5t1=N2dz5(t1),
Nez5mt1=N1ez5m(t1),
Nez5t1=N3ez5(t1)+N2ez5(t1).

The weight of the radionuclide Dz6, whose mass number has increased by 5, increases by Ndz5 due to neutron capture of the isotope Dz5 (σp>1), and the cumulative weight immediately after neutron irradiation becomes Ndz6'=Ndz5+Ndz6. When the nuclide Dz6 decays from Dz6 (β, λdz6) → Ez6 (β, λez6) → Fz6 (stable), the weight of the nuclides Dz6, Ez6, and Fz6 after t ₁ hour is expressed by the formula (6 ) ~ Rewrite equation (8) as follows, rewriting the initial weight N ₀ as the cumulative weight Ndz6' of the nuclide Dz6, and rewriting t as t1. However, λfz6=0

On the right side of equations (45) to (47), the decay constant λ of each nuclide is set to the cell name of the corresponding row of column D (λ), the cumulative weight Ndz6' is set to the cell name "H24", and t1 is set to the cell name "I". $1'' and write these right-hand sides, including the equal sign, in the cells of column I, rows 24 to 26, respectively, and the calculation result of the weight of the corresponding nuclide after t ₁ hour will be displayed in the cells of column I, rows 24 to 26. be done. As an example of the contents of cells in the written worksheet, in cell I24, "=(F21+F24)*exp(-$D24*I$1)" is written in half-width characters.
The weight of the radionuclide Ez6 increases by Nez5 due to neutron capture of the isotope Ez5 (σp>1), and the cumulative weight becomes Nez6'=Nez5+Nez6. When the nuclide Ez6 decays from Ez6 (β, λez6) → Fz6 (stable), the weights of the nuclide Ez6 and Fz6 after t ₁ hour can be calculated using equations (6) and (7) shown in [Equation 2] as follows: Rewrite the initial weight _N0 as the cumulative weight Ndz6' of the nuclide Dz6, and rewrite t as t1. However, λfz6=0.

On the right side of equations (48) and (49), the decay constant λ of each nuclide is set to the cell name of the corresponding row in column D (λ), the cumulative weight Ndz6' is set to the cell name "H24", and t1 is set to the cell name "I$1" and write these right sides including the equal sign into the cells of column J, rows 25 and 26, respectively, and the calculation result of the weight of the corresponding nuclide after _t1 hour will be displayed in the cell.
The weight of the stable nuclide Fz6 after ₁ hour t is the initial value Nfz6 plus the weight generated by β decay of the radionuclides Dz6 and Ez6. Rewrite the decay constant λ of each nuclide on the right-hand sides of Equation (47) N3fz6(t1) and Equation (49) N2fz6(t1) to the cell name of the corresponding row in column D (λ), and write these right-hand sides including the equal sign. If these are written in cells I26 and J26, respectively, the calculation result of the weight of the nuclide Fz6 after _t1 hour will be displayed in the cells.
The radionuclide Gz6 decreases its atomic number by 2 and mass number by 4 due to alpha decay, and decays into the nuclide Ez1. Therefore, when the nuclide Gz6 decays from Gz6 (α) to Ez2 (stable), the nuclide Gz6 and Ez2 after ₁ hour t For the weight, Equations (6) and (7) shown in [Equation 2] are rewritten as follows, and the initial weight _N0 is rewritten as the cumulative weight Ngz6 of the nuclide Gz6, and t is rewritten as t1.

On the right side of equations (50) and (51), the decay constant λ of each nuclide is set as the cell name of the corresponding row in column D (λ), the cumulative weight Ngz6 is set as the cell name "H27", and the cell name of t1 is set as "I$". 1'' and write both right sides, including the equal sign, into cells 27 and 11 of column J, respectively, the calculation result of the weight of the corresponding nuclide after _t1 hour will be displayed in the cells.
In the L column, the weights Ndz6t1, Nez6t1, Nfz6t1, and Ngz6t1 of the nuclides Dz6, Ez6, Fz6, and Gz6 _one hour after t are determined by the sum of the cells in the same row of the I to K columns.
Ndz6t1=N1dz6(t1),
Nez6t1=N2ez6(t1)+N1ez6(t1),
Nfz6t1=Nfz6+N3fz6(t1)+N2fz6(t1),
Ngz6t1=N1gz6(t1).

To calculate the weight of the nuclide after ₂ -hour storage, t2 of the second neutron irradiation, write t2 expressed in seconds in the cell of column O, row 1, and compare it with the cumulative weight of the first neutron irradiation. t Copy the formulas in columns H to L (cells H3 to L27) that display the weight and total weight of nuclides after ₁ hour, and paste them as they are in columns N to R (cells N3 to R27). In the formula, t1 is rewritten as t2 (I1 is O1 in the formula), the cell in column D of the decay constant λ in the formula is set as a fixed address (absolute reference), and the cell related to weight is set as a relative reference address. In formulas (11) to (51), t1 is simply changed to t2, and the cumulative weight of column H, which corresponds to the initial weight, is changed to the cumulative weight of column N. The pasted and moved cells are automatically changed, for example, the formula "=H3*exp(-$D3*I$1)" in cell I3 becomes "=N3*exp(-$D3*O$1)"" is written in half-width characters. Note that $ means absolute reference. The calculation results of the nuclide weight after ₂ hours t are displayed in the corresponding cells in columns O to Q. In column R, the nuclide weight after ₂ hours t of all the nuclides listed in column A is determined by the sum of the cells in the same row of columns O to Q.

Table 1B shows a calculation example for determining the weight change of the nuclide after the Nith neutron irradiation and after being left for a certain period of time _ts after irradiation. This table shows an example of Ni times of neutron irradiation, and the column names (AA to AN) are tentative names and will differ in the actual table. Enter the t _i time expressed in seconds in the AF1 cell, and calculate the total weight of the nuclide immediately before the Nith neutron irradiation displayed in the AC column, taking into account the value of σp in the E column, and calculate the neutrons displayed in the AD column. Copy the irradiation conditions to each cell in the AE column. ⇒ indicates that the weight of the cell in the AC column is copied as is to the cell in the AE column in the same row. The cumulative weight of the AE array of nuclides with σp of 1 or more is 0 g, and when σp is 1 or less, the cumulative weight takes into account this neutron capture probability. In addition, for cells where σp is an unspecified nuclide and are displayed in <>, the weight increased by nuclide conversion due to neutron capture of the same element with a small mass number is added (for example, AE9, AE14 cells, etc.). To determine the nuclide weight after t _i hours of the Nith neutron irradiation, use formulas (11) to (51) after rewriting written in each cell in columns I to K for the first neutron irradiation in Table 1A. , copy it as it is to each cell in the AF column to AH column, and replace the initial weight N ₀ of the variable in the formula with the cell name corresponding to the cumulative weight in the AE column, and t with the cell name "AF$1", then t _i time The subsequent nuclide weight calculation results are displayed in the corresponding cells in columns AF to AH. For example, the difference between formulas (11) to (15) displayed in cells 3rd to 7th rows of column I and formulas (11) to (15) displayed in cells 3rd to 7th rows of AF column is that the variable t is to ti, the initial weight N ₀ is only changed from Naz1m to Naz1mti-1. In column AI, the weight of all nuclides after time t _i is determined by the sum of cells in the same row of columns AF to AH. However, for stable nuclides whose σp is not listed, the cumulative weight of the AE column is added. For example, for the stable nuclides Dz4 and Fz6 in rows 18 and 26, AE18 is added to the sum of AF18 and AG18 for the former, and AE26 is added to the sum of AF26 and AG26 for the latter. This table describes the case of determining the nuclide weight change in the soluble matter tank and the gas tank, but when determining the nuclide weight change in the hardly soluble matter tank, t _i is t _i ', t _s is t _s ', Ni Replace with Nj.

After time t _i of the Nith neutron irradiation, the stored material is left for t _s to reduce the temperature and radioactivity of the stored material due to the decay energy of the radionuclide. To calculate the weight of the nuclide after leaving it for t _s , write the t _s time expressed in seconds in cell AJ1, and then write the t s time in seconds after the rewrite written in each cell in columns I to K of the first neutron irradiation in Table 1A. Move the copied cells of formulas (11) to (51) to each cell in columns AJ to AL, change the initial weight _N0 in the formula to the corresponding cell name in the AI column (weight subtotal), and change t1 to the cell name "AJ If it is rewritten as "$1", the calculation result of the nuclide weight after _ts time will be displayed in the corresponding cell in columns AJ to AL. The difference between formulas (11) to (15) displayed in cells 3rd to 7th rows of column I and formulas (11) to (15) displayed in cells 3rd to 7th rows of column AJ is the column name and variable t1. The only difference is that the cumulative weight Naz1m has been changed to Naz1mti. The weight of the nuclide in column AN after time t _s is determined by the sum of the cells in the same row of columns AJ to AL. However, for stable nuclides, the cumulative weight of the AE row is also added, and Cz1, Dz2, Ez3, Dz4, Ez5, and Fz6 correspond. Furthermore, since neutrons are not irradiated, for a nuclide whose cumulative weight in the AE array is 0 g, the decay sequence into daughter nuclides using this nuclide as a parent nuclide is not described, so a sequential equation for this series is required.
When the nuclide Bz1 in the 5th row decays from Bz1 (β, λbz1) → Cz1m (IT, λcz1m) → Cz (stable), the weight of these nuclides after ts time is determined by the AM column and the cells in the 5th to 7th rows of the AM column. Rewrite equations (6) to (8) shown in [Equation 2] as follows, and replace the initial weight N ₀ with the weight subtotal Nbz1ti of the nuclide Bz1 and t with ts. However, λcz1=0.

On the right side of formulas (52) to (54), the decay constant λ of each nuclide is assigned to the cell name in column D (λ) of the corresponding row, the weight subtotal Nbz1ti is assigned the cell name "AI5", and ts is assigned the cell name "AJ". $1'' and write these right-hand sides, including the equal sign, in the cells of rows 5 to 7 of column AM, respectively, and the calculation result of the weight of the corresponding nuclide after t _s time will be displayed in the cells of column 5 to row 7 of AM. be done.
When the radionuclide Cz3 in the 13th row decays from Cz3 (β, λcz3) → Dz3 (β, λdz3) → Ez3 (stable), to find the weight of these nuclides after t _s time, use AM columns 13 to 15. Rewrite equations (6) to (8) shown in [Equation 2] in the row cells as follows, and rewrite the initial weight N ₀ as the weight subtotal Ncz3ti of the nuclide Cz3, and t as ts. However, λez3=0

On the right side of formulas (55) to (57), put the decay constant λ of each nuclide in the cell name of column D λ of the corresponding row, put ts in the cell name "AI13" of the weight subtotal Ncz3ti, and put ts in the cell name "AJ$". 1" and write these formulas including the equal sign in the cells of columns 13 to 15 of column AM, the calculation results of the weight of the corresponding nuclide after t _s time will be displayed in the cells of columns 13 to 15 of column AM. Ru.
Similarly, when the radionuclide in the 17th row decays from Cz4 (β, λdz4) to Ez4 (stable), to find the weight of these nuclides after t _s time, enter [Equation 2] in the AM column 17th to 18th row cells. Rewrite equations (6) and (7) as shown below, and rewrite the initial weight N ₀ as the weight subtotal Ncz4ti of the nuclide Cz4, and t as ts. However, λdz4=0.

On the right side of formula (58) and formula (59), put the decay constant λ of each nuclide in the cell name of column D (λ) of the corresponding row, put the cell name "AI17" of the weight subtotal Ncz4ti, and put ts in the cell name "AJ$1" and write both formulas, including the equal sign, in the cells of the 17th and 18th rows of the AM column, respectively, and the calculation result of the weight of the corresponding nuclide after t _s time will be displayed in the cells of the 17th and 18th rows of the AM column. be done.
Similarly, for the radionuclide Dz5 (β, λdz5) → Ez5 (stable) in the 21st row, to find the weight of these nuclides after t _s , use the formula shown in [Equation 2] in the AM column 21 and 23 row cells. Equations (6) and (7) are rewritten as follows, and the initial weight N ₀ is rewritten as the weight subtotal Ndz5ti of the nuclide Dz5, and t is rewritten as ts. However, λez5=0

On the right side of equations (60) and (61), put the decay constant λ of each nuclide in the cell name of column D (λ) of the corresponding row, put the cell name "AI21" in the weight subtotal Ndz5ti, and put t in the cell name of ts. If you rewrite it as "AJ$1" and write both formulas including the equal sign into cells AM21 and 23, respectively, the calculation result of the weight of the corresponding nuclide after t _s time will be displayed in the cells of column AM 21 and row 23. .
The cells in the bottom row of columns AC, AE, AI, and AN in Table 1B display the sum of the nuclide weights in these columns as ΣNti-1, ΣNti ^* , ΣNti, ΣNts, whereas ΣNt0, ΣNt0 ^* in Table 1A , ΣNt1, ΣNt1 ^* , and confirming that all these values are equal reflects the correctness of the calculation formula based on the law of conservation of mass.

As an example according to the present invention, data on weight changes of 879 types of FP generated from spent nuclear fuel in reactor No. 2 of Tokyo Electric Power Company's Fukushima Daiichi Nuclear Power Plant was used. [Data source 3; listed at the end] In addition, 14 nuclides not listed in the above data and 18 nuclides newly generated by neutron irradiation are added to the calculation targets. The fixed period of time t ₀ from the removal of spent nuclear fuel is from several tens of days to several decades, and in this embodiment is set to 180 days. In the solubles tank, hardly solubles tank, and gas tank, nuclides with a weight of 1E-40g or more 180 days after removal of the spent nuclear fuel are stored in the same mass number order, decay type, half-life τ, decay constant. The present invention was applied by writing λ, neutron capture probability σp, and weight after 180 days in the corresponding cell, and writing the storage period shown below in the corresponding cell, increasing the column to display the nuclide weight by the number of times of neutron irradiation. An Excel worksheet was created based on Tables 1A and 1B to show the changes in nuclide weight over time. Since the worksheet would take more than 120 sheets to be printed on A4 paper, it will be omitted and the results calculated for the nuclides for each tank will be shown. The units of half-life are seconds: s, minutes: m, hours: h, days: d, and years: y.
The neutron capture probability σp is expressed as the ratio of the neutron capture cross section σn and the nuclear cross section σ, and the neutron capture cross section σn (0.353 meV) is calculated from the JENDL-5 σn (0 .0253eV). Note that nuclides whose σn is not inversely proportional to the neutron speed are defined as having a thermal neutron value or higher. If σp of the nuclide is 1 or more, the nuclide is converted by capturing neutrons, and its weight becomes 0 g, and the nuclide whose mass number has increased becomes the weight of the nuclide that captured the neutron. Furthermore, if σp of the captured nuclide is 1 or more, it is converted to a nuclide whose mass number has increased by 2, and if σp of the converted nuclide is 1 or more, it is further captured and converted into a nuclide, and its mass number is 3. increase. For example, the σp of barium isotopes at 0.353 meV is 53.7 for Ba132, 18.1 for Ba133m, 18.1 for Ba133, 9.89 for Ba134, and 38 for Ba135, which are 4 to 1, respectively. neutrons are captured and converted into 56Ba136m.
In the present invention, generated high-level radioactive waste is separated and stored into nitric acid-soluble soluble materials and poorly soluble/insoluble materials, and in the former case, neutrons are applied to the stable poorly soluble materials generated by decay. In the latter case, stable soluble materials generated by decay are not irradiated with neutrons, so the amount of stable nuclides recovered is significantly greater than in the case without tank separation. In addition, in order to minimize the weight of high-level radioactive waste to be vitrified, we calculated the number of neutron irradiations from 3 to 16 times and the subsequent storage period from 3 days to 1 year. It was set as 30 days. The number of irradiations varies depending on the tank.

(Nuclide in the solubles tank)
When applying Tables 1A and 1B to the nuclides in the solubles tank, the weights of poorly soluble nuclides and gas nuclides after t0 day (F column) are 0 g, and the Soluble nuclides and gas nuclides are not irradiated with neutrons, so G, M, ... AD, in the rows corresponding to these nuclides
...A ⇒ is displayed in the cell of the column, and the cumulative weight after neutron irradiation is the total weight before irradiation. However, iodine with σp of 1 or more is excluded only in the second neutron irradiation. In the case of a decay series with the same mass number and no soluble nuclides, the initial weight is 0 g, so nuclides with this mass number are excluded from the table (for example, 32Ge73m to 32Ge75, 40Zr93 to 46Pd107 and 50Sn118 to 51Sb122). The calculation targets are from 2He4 to 72Hf178, and the first nuclide is neutron irradiation, and the soluble nuclide 3Li6 is neutron captured, resulting in 3Li8 (β, 0.84 s) → 4Be8 (α, 8.2×10 ^-17 s) → 2He4 (stable) The nuclide at the end is a soluble stable nuclide 70Yb172 described in the JAEA data, but the undescribed isotope 70Yb173-176 has a nuclide conversion of 70Yb173 to 176 because σp is 1 or more, so the first neutron irradiation causes nuclide conversion. The resulting radionuclide 70Yb177 (β, 1.91h) undergoes β decay to produce a soluble nuclide 71Lu177 (β/IT, 160.4d) with σp of 1 or more, which is converted by the second irradiation. This is because the β decay of the generated 71Lu178m (β, 23.1m) generates a poorly soluble nuclide 72Hf178m (IT, 23.1m) → 72Hf178 (stable). A nuclide with a mass number of 172 or more is a nuclide newly generated by neutron irradiation. The weights of gaseous nuclides and poorly soluble nuclides generated in the solubles tank are listed in the table for the solubles tank.

Only the soluble nuclides in the soluble tank are irradiated with neutrons Ni times, and after storage for t _i hours, the generated gas nuclides are collected in the gas tank, and the generated poorly soluble nuclides are transferred to the poorly soluble tank A using a solid-liquid separator, etc. This process is repeated Ni times, and neutrons are not irradiated to anything other than soluble nuclides. In this example, the number of irradiations Ni is set to 9 times to minimize the vitrification weight of the solubles tank, and the storage period t _i is 30 days for t ₁ to t ₈ and 310 days for t ₉ (total from nuclear fuel removal). (equivalent to 2 years), and _ts is 4 years.
Even if the soluble nuclide contained in the nitric acid solution after reprocessing such as the PUREX method is used as a solution in the solubles tank, once denitrified, about 300 L of a new nitric acid solution with a concentration of 4 mol/L is added, The nuclide soluble in nitric acid may be a nitrate or oxide, and the nitric acid solution containing the nuclide soluble in nitric acid is collected in a solubles tank. Note that the solution temperature rises due to heat generation due to radioactive decay, but the nitric acid solution evaporates due to heating if necessary to change the iodine from the liquid phase to the gas phase, so a nitric acid solution with a concentration of 4 mol/L will have a It is necessary to keep it at 300L.
Based on Tables 1A and 1B, when only the soluble nuclides in the soluble tank were irradiated with neutrons under the conditions described above, the change in the weight of the nuclides due to decay was calculated using an Excel worksheet. There are 241 types of soluble nuclides in the solubles tank (164 types of radionuclides, 77 types of stable nuclides), and the weight 180 days after nuclear fuel removal is 1097.3 kg of soluble nuclides (397.0 kg of radionuclides, 700.0 kg of stable nuclides). 3 kg). All of these weights are the weights of individual nuclides.

Regarding the radionuclides in the solubles tank, the weight after 180 days after removing the spent nuclear fuel, the case where it was left untreated for 6 years, and the case where the present invention was applied (irradiating only soluble nuclides with neutrons under the above conditions) Table 2A-1 shows the results of calculations regarding the weight [unit: g] and radioactivity [unit: Bq] after 2000 years. The weight of 164 types of radioactive solid nuclides after 6 years without countermeasures is 371.5 kg, but with countermeasures, the weight of 16 types of nuclides and 24.6 kg (24.6 kg with 14 types of soluble nuclides, and 9.5 kg with 2 types of poorly soluble nuclides). 6 μg, no gaseous nuclides). All of these weights are the weights of individual nuclides, not the weights of compounds such as oxides and nitrates. As a result of the countermeasures, the radioactivity of soluble nuclides will be reduced to 278.8PBq (P is peta) and that of poorly soluble nuclides will increase to 20.8PBq.
Of the 150 unlisted radioactive soluble nuclides, 105 have a short half-life of 10 days or less, and will be 0 g after 6 years of countermeasures, and 45 soluble nuclides with a long half-life of 50 days or more have a σp of 1 or more, and are neutron The nuclide is converted by irradiation and its weight becomes 3.56E-73g. This is because the nuclide 64Gd161 produced by the nuclide transmutation of 64Gd158 (stable) weighing 76.25 kg in the ninth neutron irradiation is Gd161 (β, 3.7m) → 65Tb161 (β, 6.9d) → 66Dy161 (stable). ) 3.56E-73g of radionuclide 65Tb161 generated during the decay process remains after 6 years. The weight of 397.0 kg of soluble radionuclides that existed 180 days after nuclear fuel removal will be reduced to 24.6 kg six years later due to countermeasures.

For radionuclides in the solubles tank that weigh more than 1E-40g after countermeasures, the results of calculations regarding changes in weight and radioactivity when left for 6 years without countermeasures and when the present invention is applied are shown in Table 2A- Shown in 2. The table shows the decay type and half-life of the radionuclide generated in the solubles tank, the probability of neutron capture σp (0.353 meV), the weight of the nuclide [unit: g], and the radioactivity [unit: Bq]. Note that the weight is the weight of a single nuclide, not the weight of compounds such as oxides and nitrates.

Among the radioactive soluble nuclides generated in the solubles tank, six types have radioactivity of 0.1 Bq or less: 48Cd116, 55Cs134/135, 58Ce141/142, and 60Nd144, and the nuclides whose radioactivity has decreased due to countermeasures are 38Sr90. The nuclides with increased radioactivity are 39Y91, 63Eu155, and 71Lu177m/177.
Among the 10 nuclides whose radioactivity (weight) has decreased due to countermeasures, 38Sr90 and 48Cd116 have σp of 0.09 and 0.54, respectively, and have no parent nuclides, and both have long half-lives and some are not converted by neutron irradiation. remains, but the weight decreases with the number of irradiations, and it decreases more than after 6 years if left untreated. The remaining 39Y90, 55Cs134/135, 58Ce141/142, 60Nd144, 62Sm151, and 63Eu154 have σp greater than 1 and are converted into nuclides after 8 neutron irradiations, and their weight becomes 0 g, but these nuclides are converted into nuclides by the 9th neutron irradiation. Converted radioactive parent nuclides 38Sr90 (β), 55Cs134m (IT)/Cs135m (IT), 56Ba141 (β), 57La142 (β), 59Pr144m (IT) → Pr144 (β), 60Nd151 (β) → 61Pm151 ( β), 63Eu154m (IT) produced by IT and β decay, each weighing less than 6 years after being left untreated. Note that 39Y90 remains until β decay of the parent nuclide 38Sr90, which has a long half-life, disappears.
The four nuclides whose radioactivity (weight) increased as a result of the countermeasures, 39Y91, 63Eu155, and 71Lu177m/177, have σp greater than 1 and undergo nuclide conversion at the 8th neutron irradiation, and their weight becomes 0 g. Produced by IT and β decay of radioactive parent nuclides 38Sr91(β)/39Y91m(IT), 62Sm155(β), 70Yb177m(IT) → Yb177(β) converted by irradiation, after 6 years of leaving untreated, respectively. More than the weight. In addition, in 71Lu177m/177, the parent nuclide 71Yb177 generated by neutron capture of 70Yb172/173 is ) is a new nuclide generated by decay.
The radioactive poorly soluble nuclides produced in the solubles tank are 50Sn117m and 72Hf177m, and the parent nuclides of both have σp of 0, the former is 48Cd117m (β), the latter is 70Yb177m (IT), and the weight of the daughter nuclide produced by decay is Although both are increasing, the time taken to reach 0.1 Bq is 3.4 years and 6 years. 72Hf177m is a parent nuclide, 71Lu177m/177, which was separated as a soluble nuclide after 6 years, and has a short half-life of 1.09 seconds, so after about 1.2 minutes, its radioactivity will be less than 0.1 Bq and Hf177 (stable) decays into Incidentally, neither 50Sn117m nor 72Hf177m is generated in the refractory tank.
Six types of radioactive gas nuclides are generated in the solubles tank: 35Br83, 36Kr83m, 53I132/133, and 54Xe133m/133. These nuclides are generated by the following three types of decay: 34Se83m (β, 70s) → 35Br83 (β, 2.37h) → 36Kr83m (IT, 1.83h) → Kr83 (stable), 52Te132 (β, 3.2d) ) → 53I132 (β, 2.3h) → 54Xe132 (stable), 52Te133m (β/IT, 55.4m) → Te133 (β, 12.5m) → 53I133 (β, 20.8h) → 54Xe133m (IT, 2 .19d) -> It can be ignored if it is less than 0.1 Bq.

Table 2B-1 shows the results of calculating the weight of stable nuclides in the solubles tank after 180 days, and the weight changes after 6 years of being left untreated and when the present invention is applied. 138 stable nuclides; weight 817.9 kg (77 soluble nuclides; 715.6 kg; 44 poorly soluble nuclides; 102.3 kg; 17 gaseous nuclides; 0 g) after 6 years without countermeasures. The number of nuclides decreased to 42 (24 soluble nuclides, 11 poorly soluble nuclides, 7 gaseous nuclides), and the weight was 1072.7 kg (432.5 kg soluble nuclides, 634.2 kg low soluble nuclides, gaseous nuclide increases to 6.1 kg). However, all the weights of these nuclides are the weights of individual nuclides. In addition, the 11 types of poorly soluble nuclides generated in the solubles tank do not occur in the solubles tank, so the weight after 6 years of being left untreated is recorded, and the weight of 7 nuclides after 6 years of leaving the gas in the gas tank is Described.
All 53 soluble and stable nuclides not listed have a σp of 1 or more, and the weight of the nuclides becomes 7.7E-50g by neutron irradiation. This is because the σp of the parent nuclide 66Dy166 (β, 3.4d) of 68Er166, which becomes 0g at the 8th neutron irradiation, is 0.91, and the remaining weight of 68Er166 without capturing neutrons due to neutron irradiation becomes 0g at the 9th neutron irradiation. 7.7E-50g of Dy166 (β, 3.4d) produced by adding the weight generated by nuclide conversion decays as 67Ho166 (β, 26.8h) → 68Er166 (stable), and after 6 years, Er166 becomes 7.7E-50g remains. Even if a stable nuclide is transmuted by neutron irradiation and a radionuclide is generated, even if there is a daughter nuclide produced in the decay process that has a long half-life, the σp of the nuclide is greater than 1, and the next neutron It is converted into a stable nuclide by irradiation.

Of the stable nuclides in the solubles tank, 24 soluble nuclides with a weight of 1E-40g or more after countermeasures, 11 poorly soluble nuclides and 7 gaseous nuclides generated by neutron irradiation, neutron capture probability σp, nuclear fuel removal 180 Table 2B-2 shows the nuclide weight [unit: g] after 1 day and 6 years after being left untreated and after taking measures. Weight indicates the value of a single nuclide.
There are three soluble stable nuclides with σp (values shown in brackets) of 1 or less, and 30Zn70 [0.93] and 34Se82 [0.4] are partially converted by neutron irradiation without undergoing nuclide conversion. The former does not generate a parent nuclide after the second irradiation, and the latter does not have a parent nuclide, so in both cases, after nine neutron irradiations, part of the nuclide is converted by neutron capture, and its weight gradually decreases and the remaining nuclide remains. It will decrease from 6 years after no countermeasures are taken. 38Sr88[0.05] has a large weight that remains without being converted by neutron irradiation, and in the first and second irradiation, it is due to the β decay of the parent nuclide 37Rb88 (β, 17.8m) generated by the nuclide conversion of 37Rb86/87. The resulting weight is added, and the nuclide remains untransformed by neutron irradiation, and the weight gradually decreases, but it becomes larger than it would be after 6 years if no countermeasures were taken.
The remaining 21 types of soluble stable nuclides all have σp of 1 or more and are converted into nuclide by the 8th neutron irradiation and weigh 0g, and by the 9th irradiation are converted into radioactive parent nuclides with σp of 0 or 1 or less, and then The weight of stable soluble nuclides produced by decay will be larger or smaller than that after 6 years without countermeasures. There are 13 types whose weight will decrease as a result of countermeasures: 31Ga71, 56Ba134-138, 59Pr141, 60Nd142/145, 62Sm152/154, 63Eu151, and 64Gd154, and weight will increase in 13 types: 64Gd155/158, 66Dy161/162, 67Ho165, and 68E. r167, There are eight types of 70Yb172/173, and 70Yb173 is a new nuclide that has increased due to neutron irradiation. The weight of stable nuclides with a mass number of 155 or more increases significantly due to countermeasures.
Since the hardly soluble nuclides generated in the soluble matter tank are not irradiated with neutrons, the value of σp of the soluble radionuclide that serves as the parent nuclide is affected. The parent nuclide of 32Ge72 is 30Zn72(β) [0.095
], the parent nuclide converted by the third neutron irradiation becomes 0g, which is less than the weight after 6 years of neglect. The parent nuclides of 40Zr90 are 38Sr90[0.09] and 39Y90m[0], which remain without undergoing nuclide conversion after each neutron irradiation, and the weight generated by the decay of 38Sr90(β) → 39Y90(β) → 40Zr90 (stable) In addition, the weight generated by the decay of 39Y90m (IT/β) → Y90 (β) → 40Zr90, which occurred due to the nuclide transformation of Y89[11.1] by neutron irradiation up to two times, is added, and the weight increases from 6 years after being left untreated. do. For the other nine stable poorly soluble nuclides, the radioactive parent nuclide σp is 0, and for the three types whose parent nuclide is 0 g after the second neutron irradiation, the weight of 32Ge70 with 31Ga70 as the parent nuclide is left untreated6 The weight of 46Pd108/110, whose parent nuclide is 47Ag108/110, will be lower than that after 6 years of being left without countermeasures. Of the remaining six species, 32Ge73 and 40Zr91/92, whose parent nuclides are generated after nine neutron irradiations, decreased in weight after 6 years of being left untreated, and 50Sn117 increased in weight after 6 years of being left untreated, and 72Hf177/178 is a new nuclide generated by neutron irradiation.
Seven types of stable gases are generated in the solubles tank, and 2He4 is a nuclide newly generated by neutron irradiation and is not generated in the gas tank but only in the solubles tank. This is because 2He4 (stable) is generated by α decay of 4Be8 (α, <1 fs) using 3Li8 (β, 0.84s), which has been converted by neutron capture of 3Li6/7, as the parent nuclide. The parent nuclide of 54Xe132, 52Te132(β) [0.93], undergoes nuclide conversion by neutron irradiation and its weight decreases, and the weight generated by β decay of 53I132(β, 2.3h) → 54Xe132 (stable) is added, but it is left unaddressed. The weight will be lower than after 6 years. The remaining five species, 35Br79/81, 36Kr83/86, and 54Xe134, have parent nuclides σp of 0, and parent nuclides 34Se79m (IT/β) and Se81m (IT/β), respectively.
), Se83m (β), 37Rb86m (IT)→Rb86 (β/ec), and 55Cs134m (IT), and the weight of the four nuclides except 35Br81 decreases compared to the weight after 6 years if left untreated.

There are some stable nuclides whose weight increases after 6 years, and this is due to the decay of the radioactive parent nuclide with a long half-life shown in [ ]. Among the soluble nuclides, there are 62Sm154, 64Gd154 [63Eu154m/154], and Gd155 [Eu155]. , and poorly soluble nuclides include 40Zr90 [38Sr90], 40Zr91 [39Y91], 50Sn117 [Sn117m], and 72Hf177 [71Lu177m/177]. The soluble radionuclides of these parent nuclides are vitrified, but the radioactive soluble nuclides strontium 38Sr90 and lutetium 71Lu177, which are the parent nuclides of poorly soluble and stable nuclides, are recovered as reusable radionuclides. (described later)

(Nuclide in the refractory tank)
When applying Tables 1A and 1B to the nuclides in the sparingly soluble substance tank, the weight of soluble nuclides and gaseous nuclides after t day ₀ (column F) is 0 g, which is generated by radioactive decay of the sparingly soluble nuclides after neutron irradiation. Since neutrons are not irradiated to soluble nuclides and gaseous nuclides, G, M, ・ in the rows corresponding to these nuclides are
⇒ is displayed in the cells of ・, AD, . . . , and the cumulative weight after neutron irradiation is the total weight immediately before irradiation. The storage times _tj are assumed to be _t1 ', _t2 ', . In the case of a decay series with only soluble nuclides and gas nuclides with the same mass number, the initial weight is 0 g, so nuclides with this mass number are excluded from the table (
34Se78 to 39Y90 and 54Xe127 and later). The nuclides to be calculated are from 4Be9 to 54Xe128, and the soluble nuclide 52Te128 generated by β decay of the hardly soluble nuclide 51Sb128 produces a stable gas nuclide 54Xe128 by 2β decay. The weights of gaseous nuclides and soluble nuclides generated in the refractory tank are shown in the table for the refractory tank.

Only the refractory nuclides in the refractory tank are irradiated with Nj neutrons, and after neutron irradiation, a nitric acid solution of a specified concentration (4 mol/L in this example) is added to the refractory tank and stored for _tj hours. The generated soluble nuclides are collected into the soluble tank B using a filter or the like, and after the next neutron irradiation, the soluble nuclides and nitric acid solution in the soluble tank B are returned to the refractory tank, which is repeated Nj times.
In this example, the number of irradiations Nj is set to 13 to minimize the vitrified weight of the refractory tank, and the storage period _tj is 30 days from _t1 to _t12 , and 190 days at _t13 (total from nuclear fuel removal). (equivalent to 2 years), and t _s ' is 4 years. Note that the nitric acid solution with a concentration of 4 mol/L required to dissolve the generated soluble nuclides increases to 5 L, 30 L, 70 L, 75 L, . . . for each neutron irradiation, and reaches a maximum of about 100 L.
Based on Tables 1A and 1B, when only the poorly soluble nuclides in the poorly soluble tank were irradiated with neutrons under the conditions described above, the change in the weight of the nuclides due to decay was calculated using an Excel worksheet. There are 133 types of poorly soluble solids in the poorly soluble solids tank (86 types of radionuclides, 47 types of stable nuclides), and the weight 180 days after nuclear fuel removal is 763.4 kg of poorly soluble nuclides (235.9 kg of radionuclides, 47 types of stable nuclides). 527.4 kg). All of these weights are the weights of individual nuclides.

Regarding the hardly soluble nuclides in the hardly soluble matter tank, the weight after 180 days after removal of the spent nuclear fuel, when left untreated for 6 years, and when the present invention is applied (neutrons are irradiated only to soluble nuclides under the above conditions). Table 3A-1 shows the calculation results of weight [unit: g] and radioactivity [unit: Bq] after 6 years.
The weight of 90 types of poorly soluble radioactive solid nuclides after 6 years of unmeasured storage is 234.0 kg (including the weight of 6.16 kg of 4 soluble radionuclides that are not generated in the solubles tank after 6 years of unmeasured storage). As a result of countermeasures, the weight is reduced to 31.3 kg for 12 nuclides (58.3 g for 4 soluble nuclides, 31.2 kg for 8 poorly soluble nuclides, and no gas nuclides). All of these weights are the weights of individual nuclides, not the weights of compounds such as oxides and nitrates. As a result of the measures taken, radioactivity will be reduced to 2.36 TBq (T is T) for available nuclides and 0.15 TBq for poorly soluble nuclides.
There are 78 undescribed radioactive poorly soluble nuclides, of which 15 poorly soluble nuclides with long half-lives of 50 days or more all have σp of 1 or more, including 40Zr93/95, 41Nb92, 42Mo100, 43Tc98, 44Ru106, 45Rh102, 50Sn119m. 10 types of /121m/123 have no parent nuclide, and the parent nuclide of 41Nb93m/95 is a poorly soluble radionuclide 40Zr93/Zr95 with σp greater than 1, so these 12 nuclides undergo nuclide conversion in the first neutron irradiation and 0g becomes. For three types of daughter nuclides, 41Nb94, 43Tc99, and 49In115, whose parent nuclide has a σp of 0 but has a long half-life, the parent nuclide is not generated through nuclide conversion by the second neutron irradiation, and the weight of the daughter nuclide becomes 0 g.
The parent nuclides of 45Rh106 and 50Sn121, which have short half-lives, are 44Ru106 (β, 371.8d) and 50Sn121m (IT/β, 43.9y), which have long half-lives, but each has a σp of 1.12. At 8.52, the parent nuclide undergoes nuclide conversion and becomes 0 g with the first neutron irradiation, and the weight of its daughter nuclide becomes 0 g.
The remaining 61 species have short half-lives and will weigh 0g after 6 years, and 168.8kg of poorly soluble radionuclides that were present 180 days after the nuclear fuel was removed will weigh 0g due to countermeasures.
The gas generated in the poorly soluble substance tank using radioactive hardly soluble substances as parent nuclide is only stable 53I127, and no radioactive gas is generated. Daughter nuclides produced by the decay of poorly soluble nuclides in the decay series of the same mass number Z are only soluble nuclides, and gaseous nuclides are not directly generated. There are two types of decay sequences in which the parent nuclide is a poorly soluble nuclide and gaseous nuclides are generated: 32Ge → 33As → 34Se → 35Br → 36Kr and 49In → 50Sn → 51Sb → 52Te → 53I → 54Xe, and the radionuclides have nuclear isomers. The former has a mass number of 79 to 88, and the latter has a mass number of 127 to 134. The former has a half-life of Ge79-88 of less than 30 seconds and will not exist 180 days after the nuclear fuel is removed, and gaseous bromine and krypton will not be generated. In the latter, 51Sn127m and 52Sb128 are generated by neutron irradiation, but in the 127 series, decay ends at 53I127 (stable), and in the 128 series, decay ends at 52Te128 (2β, 7.7E + 24y) → 54Xe128 (stable), and no radioactive gas is generated. . Further, when the mass number is 129 or more, hardly soluble nuclides are not generated, and gaseous nuclides are generated only when the mass numbers are 127 and 128 in this decay series.

Table 3A shows the results of calculating the changes in weight and radioactivity for radionuclides in the refractory tank weighing 1E-40g or more after countermeasures, when they are left for 6 years without countermeasures, and when the present invention is applied. Shown in 2. The table shows the decay type and half-life of the radionuclide generated in the refractory tank, the probability of neutron capture σp (0.353 meV), the weight of the nuclide [unit: g], and the radioactivity [unit: Bq]. Note that the weight is the weight of a single nuclide, not the weight of compounds such as oxides and nitrates.

Among the radioactive and poorly soluble nuclides generated in the poorly soluble substance tank, there are two types, 40Zr96 and 50Sn126, whose radioactivity will be 0.1Bq or less after 6 years of countermeasures, and 4Be10 and 46Pd107 whose radioactivity will be 0.1Bq or more. , 51Sb124/125/126m/126. The nuclides whose radioactivity decreased as a result of the measures were 40Zr96, 46Pd107, 50Sn126, and 51Sb124/125/126m/126, and the nuclide whose radioactivity increased was 4Be10.
Among the seven nuclides whose radioactivity (weight) has been reduced by countermeasures, 40Zr96 and 50Sn126 have σp of 0.183 and 0.62, and have no parent nuclide, and both have long half-lives, and some of them are not converted by neutron irradiation. The remaining weight decreases with the number of irradiations. 46Pd107, 51Sb124 and Sb125 have σp greater than 1 and undergo nuclide conversion after 13 neutron irradiations, resulting in a weight of 0g. This occurs due to the decay of 50Sn125m(β), but each weight is smaller than the weight after 6 years of storage. In addition, 51Sb126m/126 has a long half-life with the parent nuclide 51Sn126(β) having a σp of 0.62, so it remains unconverted after 13 neutron irradiations and remains until β decay of the parent nuclide disappears. However, each weight is less than the weight after 6 years of neglect.
There was only one type of nuclide whose weight increased as a result of the countermeasures, and there was no parent nuclide of 4Be10 with an extremely small σp, but a radioactive nuclide, 4Be10 ( The weight of β) increases slightly from the weight after 6 years of storage.
The only radioactive soluble nuclide that remains after 6 years in the refractory tank is tellurium, and there are four types: 52Te125m, Te128, and Te127m/127. ), which is produced by β-decay of the parent nuclide that has undergone nuclide conversion after 13 neutron irradiations, and its weight gradually decreases with the number of irradiations. After 6 years, it will be separated from the parent nuclide in the refractory tank, so the time it takes for 52Te125m to reach 0.1Bq is 3.1 years, and it decays into stable Te125. In addition, 52Te128 is a long-lived nuclide, and if measures are taken, the weight will be reduced compared to 6 years after being left untreated. The parent nuclide of the latter two is 50Sn127m with a σp of 0, and 50Sn127m (β, 4.13m) produced by nuclide conversion of 50Sn126, which has a long-lived 50Sn126 with a σp of 0.62 after 13 neutron irradiations, becomes 51Sb127 (β, 3 .85d) → 52Te127m (IT/β, 106.1d) → Te127 (β, 9.35h) → 53I127 (stable) and changes into stable gas I127 after about 19 years. Note that tellurium is not generated in the solubles tank.
There are no radioactive gas nuclides generated in the refractory tank.

Table 3B-1 shows the weight of stable nuclides in the refractory tank after 180 days, and the calculated weight changes when left untreated for 6 years and when the present invention is applied. 141 stable solid nuclides; weight 450.9 kg (77 soluble nuclides; 7.57 kg; 47 poorly soluble nuclides; 443.4 kg; 17 gaseous nuclides; 0 g) after being left untreated for 6 years. The number of nuclides was reduced to 24 (12 soluble nuclides, 11 poorly soluble nuclides, and 1 gas nuclide), and the weight was 732.1 kg (718.1 kg soluble nuclides, 12.6 kg poorly soluble nuclides). , gaseous nuclide increases to 1.41 kg). However, all the weights of these nuclides are the weights of individual nuclides.
All 36 undescribed poorly soluble stable nuclides have σp of 1 or more, and their weight becomes 0 g after nuclide conversion by neutron irradiation. Even if the converted parent nuclide radionuclide has a long life, it is poorly soluble with σp of more than 1. It becomes a nuclide and undergoes nuclide conversion by neutron irradiation to become 0g. For example, stable 49In113 undergoes nuclide transmutation by the first neutron irradiation and decays as 49In115m (IT/β, 4.5h) → In115 (β, 4.4E+14y) → 50Sn115 (stable), and σp is 1. The larger In115 is converted into In116m by the second neutron irradiation and becomes 0g, and decays as 49In116m (β, 54.3m) → 50Sn116 (stable), and In113 becomes 0g, and the weight of stable 50Sn116 increases, but the nuclide Also, when σp is 0.9, the weight decreases with the number of neutron irradiations. In addition, stable 46Pd108 undergoes nuclide transmutation by neutron irradiation and decays as 46Pd108+1n → Pd109m (IT) → Pd109 (β, 13.6h) → 47Ag109m (IT, 39.8s) → Ag109 (stable), and Pd108 becomes 0g and is stable. 47Ag109, a soluble nuclide, increases.

Neutron capture probability σp (0.353 meV) for 11 stable poorly soluble nuclides with a weight of 1E-40 g or more after countermeasures, 12 stable soluble nuclides generated by neutron irradiation, and 1 gas nuclide, 180 days after nuclear fuel removal Table 3B-2 shows the nuclide weight (in g) after 6 years without countermeasures and after countermeasures.
The weight of all 11 poorly soluble stable nuclides after 6 years of countermeasures was lower than the weight after 6 years of no countermeasures. There are seven types of nuclides with σp of 1 or less (the value of σp is shown in brackets), and four of them are 4Be9[0.34], 40Zr90[0.09], Zr94[0.42], and 50Sn124[ 0.94] has no parent nuclide, so its weight gradually decreases with the number of neutron irradiations. The other three types of 50Sn114[0.92]/Sn116[0.91]/Sn122[0.98] partially remain without being converted by neutron irradiation, and after the second neutron irradiation, their respective parent nuclides 49In114 (β/ε), 49In116m (β), 51Sb122m (IT) → Sb122 (β/ε) are not generated, so the weight of the daughter nuclide is 0 g, and in the 13th neutron irradiation, some of it is converted by neutron capture. , the weight of the remaining daughter nuclides has decreased and is less than after 6 years without countermeasures. The remaining four types, 42Mo97/98, 44Ru101, and 51Sb123, have σp of 1 or more and undergo nuclide conversion to 0g after 13 neutron irradiations, but the parent nuclides 40Zr97(β)/98(β), 42Mo101(β), and 50Sn123m(β ) The weight of daughter nuclides generated by β-decay will be less than after 6 years if no countermeasures are taken.
The 12 types of soluble nuclides generated in the refractory tank are not irradiated with neutrons. Four of these, 31Ga71, 33As75, 34Se77, and 48Cd114, have parent nuclides of 32Ge71m (IT) → Ge71 (ec), 32Ge75m (IT), 32Ge77m (β/IT), and 49In114m (IT/ε) whose σp is 0. In this case, the parent nuclide is generated up to three times due to neutron irradiation, and the weight of the daughter nuclide generated is less than after 6 years of no countermeasures. 52Te125 is generated by the decay of the parent nuclide 50Sn125m (β) generated by nuclide transmutation each time after 13 neutron irradiations, but its weight gradually decreases with the number of irradiations, and is less than after 6 years of no countermeasures. The remaining seven species, 5B10, 47Ag107/109, 48Cd111, 52Te122/124/126, have their respective parent nuclides 4Be10 (β), 44Ru107 (β), 46Pd109m (IT), 46Pd111m (IT/β), and 51Sb122m (IT). /124m(IT/β)/126m(β/IT) σp is 0, β of the parent nuclide generated by 13 neutron irradiations, produced by IT decay, and the weight of these daughter nuclides has been left untreated for 6 years. The weight will be more than the latter.
The stable gas nuclide generated in the refractory tank is only 1.41 kg of 53I127, and 51Sb127 (β, 3.85d) → 52Te127m (IT/β, 106.1d) → 52Te127 (β, 9.35h) → 53I127 (stable). It can be released after confirming safety with a radiation dose monitor. In addition, after the 6th year of countermeasures, the radioactive tellurium remaining in the soluble tank B attached to the refractory tank and turned into a vitrified substance is 52Te127m (IT/β, 106.1d) → Te127 (β, 9.35h) → 53I127 (stable) and 0.63 mL (3.35 mg) of I127 is generated at 20°C, so when tellurium is vitrified, silver is added and solidified as silver iodide.
Countermeasures There are stable nuclides whose weight increases after 6 years, but this is due to the decay of the radioactive parent nuclides with long half-lives shown in [ ], and they are not sparingly soluble nuclides, but soluble nuclides such as 5B10 [4Be10] and 47Ag107. [46Pd107], 52Te124 [51Sb124m], and 52Te125 [51Sb125] are applicable. The poorly soluble radionuclides of these parent nuclides are vitrified. However, 7.758 kg of 46Pd107, which has a large σp even for thermal neutrons, exists alone after 6 years of nuclide separation, so it undergoes nuclide conversion by thermal neutron irradiation, and 46Pd107+2n → 46Pd109m (IT, 3.1s) → Pd109 (β, 13.6h) → 47Ag109m (IT, 39.8s) → Ag109 (stable) disintegrates and can be converted to stable Ag109 and recovered after 41.2 days.

(Nuclide in gas tank)
When applying Tables 1A and 1B to nuclides in a gas tank, the weight of soluble nuclides and poorly soluble nuclides after t day ₀ (column F) is 0 g, and the solid nuclides generated by radioactive decay of gas nuclides and Since gaseous nuclides are not irradiated with neutrons, ⇒ is displayed in the cells in columns G and M of the row corresponding to these nuclides, and the cumulative weight after neutron irradiation is the weight immediately before irradiation. In the gas tank, the gaseous nuclides generated in the solubles tank are recovered immediately before the neutron irradiation of the solubles tank. Since neutrons are irradiated only once to the iodine recovered just before the second time, +n is displayed in the M column cells corresponding to iodine nuclides with σp of 1 or more, and σp whose mass number has increased due to nuclide conversion is not listed. In the M column cell corresponding to the iodine nuclide, the nuclide with the mass number before nuclide conversion and the number of captured neutrons are displayed in <>. Note that since iodine is irradiated with thermal neutrons, a value of neutron energy of 0.0253 eV is used as σp of the gas nuclide.
Iodine 53I127 (stable), I128 (β/IT, 25m), and I129 (β, 1.57E+7y) with σp of 1 or more are irradiated with neutrons and capture 3 to 1 neutron each to become I130m (IT/β, 8 .84m), and I130 (β, 12.4h) and I131 (β, 8.03d) capture two and one neutrons, respectively, and are converted into I132 (β, 2.30h). If there are only soluble nuclides and poorly soluble nuclides with the same mass number, the initial weight is 0 g, so nuclides with this mass number are excluded from the table (29Cu66-34Se78, 37Rb87-52Te126 and 54Xe137 onwards). The nuclides to be calculated are from 1H3 to 54Xe137.

In the gas tank, the gaseous nuclides generated after being left for a certain period of time (t ₀ hours) after spent nuclear fuel removal are collected in the solubles tank after the first cold neutron irradiation t ₁ hour and just before the second cold neutron irradiation. The gas tank is heated to sublimate and vaporize bromine and iodine, including the gaseous nuclides recovered from the tank, and the iodine tray at the top of the gas tank is cooled to a temperature above the boiling point of bromine using a cooling device to liquefy and extract only the iodine. Then, the iodine is transferred to an iodide tank and only iodine is irradiated with thermal neutrons to convert the nuclide. Note that in this example, t ₀ is 180 days.
Since thermal neutron irradiation is performed only on iodine in synchronization with the second solubles bath, _t1 is 30 days in this example. The gaseous nuclides generated in the solubles tank are collected into the gas tank in synchronization with the neutron irradiation in the solubles tank.
Based on Tables 1A and 1B, when only iodine in the gas tank was irradiated with neutrons under the conditions described above, the change in nuclide weight due to decay was calculated using an Excel worksheet. The weight of gaseous nuclides generated in the soluble matter tank and the hardly soluble matter tank is not included in the gas tank.
The gas tank contains 47 nuclides (30 radionuclides, 17 stable nuclides), and the weight 180 days after nuclear fuel removal is 385.4 kg (158.1 kg of radionuclides, 227.3 kg of stable nuclides). All these weights are the weights of gaseous nuclides only.

Regarding the radionuclides in the gas tank, the weight after 180 days after removing the spent nuclear fuel, the weight after 6 years when left untreated for 6 years, and when the present invention is applied (only iodine is irradiated with neutrons under the above conditions) Table 4A-1 shows the results of calculating changes in [unit g] and radioactivity [unit Bq]. The weight of 30 types of radioactive gas nuclides and 157.5 kg after 6 years of unaddressed use will decrease to 146.0 kg with 6 types of nuclides after countermeasures are taken. All of these weights are the weights of individual nuclides. Due to the measures taken, radioactivity remains unchanged at 22.1PBq (P is peta).
There are 24 types of radioactive gas nuclides that are not listed, and they weigh 114.8 kg after 6 years without countermeasures, but with countermeasures, the weight of the nuclides will be 6.56 x 10 ^-55 g. This is because 0.695 mg of 54Xe131m decays as Xe131m (IT, 11.8d) → Xe131 (stable), and 6.56E-55 g of 54Xe131m remains after 6 years.
Of the eight types of radioactive iodine, the three nuclides that weigh more than 1E-40g 180 days after removal of spent nuclear fuel are 53I129/131/132, and 11.48kg of 53I129 (β, 15.7 million years) [σp24.2] 210 days after removal, the nuclide is converted by the first thermal neutron irradiation and its weight becomes 0g, and 53I130m (IT/β, 8.84m) generated by nuclide conversion becomes I130 (β, 12.4h) after 37.4 days. → It decays to 54Xe130 (stable) and undergoes nuclide conversion to 11.48 kg of stable 54Xe130. 93μg of I131 (β, 8.03d) [σp63.2] was converted into nuclide by neutron irradiation and its weight became 0g, and 53I132 (β, 2.3h) generated by nuclide conversion was converted to 54Xe132 ( stable). 0.1 fg of 53I132[σp0] becomes 54Xe132 (stable) after about one day. The other five species, 53I128/130/130m/133/134, have short half-lives and disappear within 180 days.
The remaining 16 radioactive gases other than those mentioned above are nuclides with short half-lives of 10 days or less, and because they are not irradiated with neutrons, they disintegrate into stable nuclides through radioactive decay, and the weight of all 16 nuclides becomes 0 g.
The reason why gaseous nuclides other than iodine are not irradiated with neutrons is that when 54Xe136 (2β, 2.2E + 21y) [σp0.1], which exists in large quantities, is irradiated with thermal neutrons, 10% is converted into a nuclide, and 54Xe137 (β, 3.8m ) → 55Cs137 (β, 30.1y) → 56Ba137m (IT, 2.6m) → 56Ba137 (stable) decay occurs, and a large amount of long-lived radionuclide 55Cs137 is generated during this decay process.
The radioactive gas nuclides recovered from the solubles tank were 35Br83, 36Kr83m, 53I132/133, and 54Xe133m/133. generated, 34Se83m (β) → 35Br83 (β) → 36Kr83m (IT) → 36Kr83 (stable), 52Te132 (β) → 53I132 (β) → 54Xe132 (stable), 52Te133m (IT/β) → 52Te133 (β) → 53I133 (β) → 54Xe133m (IT) → 54Xe133 (β) → 55Cs133 (stable), and the weight of the generated radioactive gas nuclide gradually decreases with the number of neutron irradiation, reaching 1E-40g or less after 6 years of countermeasures.
Radioactive gas nuclides are not generated in the refractory tank.
Although there are no radioactive gas nuclides recovered from the refractory tank, radioactive gas is generated when the FP generation status of spent nuclear fuel changes due to nuclear power generation operating conditions, irradiation time, etc., or when MOX fuel, etc. is used. When this happens, collect it in a gas tank and take the measures shown in the examples.

Table 4A-2 shows the results of calculating the changes in weight and radioactivity for radionuclides in gas tanks weighing 1E-40g or more after countermeasures, when left for 6 years without countermeasures, and when the present invention is applied. show. The table shows the decay type and half-life of the radionuclide generated in the refractory tank, the probability of neutron capture σp (0.0253 eV), the weight of the nuclide [unit: g], and the radioactivity [unit: Bq]. Note that the weight is the weight of a single nuclide.

The weight and radioactivity of the six radioactive gas nuclides produced in the gas tank after 6 years of countermeasures are almost the same as after 6 years of no countermeasures. After six years of countermeasures, there are two nuclides with radioactivity of 0.1 Bq or less, 54Xe127/136, and four nuclides with radioactivity of 0.1 Bq or more: 1H3, 6C14, and 36Kr81/85. Note that 6C14 exists as an oxide gas. Countermeasures are not effective for 54Xe136 (2β, 2.165E+21y), which has a small σp, but its radioactivity is as small as 6.5 mBq, and it is a nuclide with a natural abundance ratio of 8.86%.
There are no radioactive solid nuclides generated in the gas tank.

Table 4B-1 shows the results of calculating the weight of stable nuclides in the gas tank after 180 days and the change in weight when left untreated for 6 years and when the present invention is applied. 17 types of stable gas nuclides; weight 227.3 kg after 6 years without countermeasures; 18 types of nuclides have been added due to countermeasures; weight 239.4 kg (2 types of soluble nuclides; 623 g, no hardly soluble nuclides, gaseous nuclides 16 types; 238.8 kg). The weight of stable gaseous nuclides has increased slightly. However, all the weights of these nuclides are the weights of individual nuclides.
One stable gas nuclide that is not described is 2He4, which is not generated in the gas tank but only generated in the solubles tank during the first neutron irradiation, so it will not be described here.

For 16 stable gas nuclides with a weight of 1E-40 g or more after countermeasures and 2 soluble stable nuclides generated by neutron irradiation, the neutron capture probability σp (0.0253 eV for gas, 0.353 meV for solid), nuclear fuel removal 180 Table 4B-2 shows the weight of the nuclide (in g) after 6 years without countermeasures and after countermeasures.

By irradiating only iodine with neutrons, which are stable gas nuclides, the weight of 54Xe130 has increased compared to the weight after 6 years without countermeasures, and 53I127 (stable) with large σp (stable) 2.6 kg and 53129 (β, 1.57E + 7y) 11. This is due to an increase of 14.1 kg due to the decay of 53I130m (IT/β, 8.84m) → I130 (β, 12.36h) → 54Xe130 (stable), which was generated by nuclide conversion of 5kg. 2He3 increases slightly due to the decay of radionuclide 1H3.
The 11 stable gas nuclides 7N14, 35Br81, 36Kr80/82/83/84/86, and 54Xe128/131/132/134 do not irradiate thermal neutrons, so the total amount remains unchanged until 6 years after each spent fuel is removed. The weight remains unchanged at 224.3 kg.
For the remaining three types, 35Br79, 53I127, and 54Xe129, the weight after 6 years of countermeasures is lower than the weight after 6 years of no countermeasures.
There are gaseous nuclides that are stable nuclides and increase in weight after 6 years, but this is due to the decay of radioactive gas parent nuclides with long half-lives shown in [ ], such as 2He3 [1H3], 7N14 [6C14], 35Br81 [36Kr81] is applicable.
The weight of stable soluble nuclides generated in the gas tank is 623.3 g of 37Rb85 and 38.6 ng of 55Cs133, which are generated by β decay of radioactive gas, and the parent nuclide is 36Kr85 (β, 10.74 y ), and the latter is 54Xe133 (β, 5.25d), which are recovered in a solid tank attached to the gas tank, and the former increases in weight even after 6 years. Furthermore, stable, poorly soluble nuclides are not generated in the gas tank.
The seven stable gaseous nuclides transferred from the solubles tank are 2He4, 35Br79/81, 36Kr83/86, and 54Xe132/134, and their weight is 6.06 kg. The weight will not increase after 6 years of countermeasures.
The stable gas 53I127 generated by the decay of 52Te127m/127 remaining in the solubles tank B attached to the refractory tank increases even after 6 years, but this is the same as the treatment in the refractory tank.

180 days after spent nuclear fuel is removed, the soluble nuclides in the solubles tank are repeatedly irradiated with cold neutrons nine times at 30-day intervals, and the poorly soluble nuclides and gaseous nuclides generated are not irradiated with cold neutrons. Similarly, cold neutron irradiation is repeated 13 times to the poorly soluble nuclides in the poorly soluble tank at 30-day intervals, and the generated soluble and gas nuclides are not irradiated with cold neutrons.In the gas tank, only iodine is heated after 210 days after fuel removal. If measures are taken to irradiate with neutrons only once, the time required to reach 0.1Bq of radionuclides remaining after 6 years after spent nuclear fuel is removed from each tank (the numbers in brackets indicate unmeasured → after measures) will be more than 10 years. The following is a summary of nuclides and long-lived nuclides with radioactivity of 0.1 Bq or less.
The soluble nuclides in the soluble tank are 38Sr90 [1748 → 1736], 39Y90 [1748 → 1736] / 91 [10 → 12], 62Sm151 [4766 → 3753], 63Eu154 [486 → 396 years] / 155 [202 → 274 years], 71Lu177m [* → 31 years] / 177 [* → 20 years], long-lived 48Cd116 (1.1 years → 49 μBq), 58Ce142 (52 .3 quadrillion years → 5.0 pBq) and 60Nd144 (3.36 quadrillion years → 21.3 fBq), and the two poorly soluble nuclides 50Sn117m and 72Hf177m reach 0.1Bq in 3.4 years and 6 years. It is.
The poorly soluble nuclides in the poorly soluble tank are 4Be10 [39.5 million years → 39.8 million years], 46Pd107 [270 million years → 260 million years], 50Sn126 [9.79 million years → 5.61 million years], 51Sb125 [158 25 years] / 126 m [9.79 million years → 5.61 million years] / 126 [9.79 million years → 5.61 million years], and the long-lived 40Zr96 [3,567 quintillion years → 82.9 mBq], which are soluble nuclides. There are two types of 52Te127m [17 years → 19 years]/127 [17 years → 19 years] and the long-life 52Te128 (83 nBq → 0.78 nBq).
The gas nuclides in the gas tank are 1H3 [659 → 658], 6C14 [180,000 years → same year], 36Kr81 [4.71 million years → same year] / 85 [624 → same year], and the long-lived 54Xe136. (6.5 mBq→same Bq), and no radioactive soluble or poorly soluble nuclides are generated. The effect of the present invention is limited on these 8 soluble nuclides, 6 poorly soluble nuclides, and 5 gaseous nuclides, but 3 long-lived soluble nuclides and 1 poorly soluble nuclide have been left untreated for 6 years. The weight has significantly decreased compared to the previous weight, and the effects of the countermeasures are remarkable.

In the present invention, generated high-level radioactive waste is separated and stored into nitric acid-soluble soluble materials and poorly soluble/insoluble materials, and in the former case, neutrons are applied to the stable poorly soluble materials generated by decay. In the latter case, stable soluble materials generated by decay are not irradiated with neutrons, so the amount of stable nuclides recovered is significantly greater than in the case without tank separation. In addition, in order to minimize the weight of high-level radioactive waste that is made into a vitrified material, we reduce the daughter nuclides generated by the radioactive decay of the parent nuclide that has undergone nuclide conversion, using the number of neutron irradiations and the subsequent storage period as parameters, and stabilize the waste. In order to increase the weight of the nuclide, the neutron irradiation interval was calculated to vary from 3 days to 1 year, and was set at 30 days. When the number of neutron irradiations is increased in the solubles tank, the radioactivity of the radionuclide 55Cs134/135 decreases to 0.16 mBq/23.3 μBq after 8 irradiations and 71.4 nBq/2.73 nBq after 9 irradiations. However, the radioactivity of the radionuclide 71Lu177m/177 increases to 18.3PBq/4.08PBq after 8 irradiations and to 20.0PBq/4.46PBq after 9 irradiations, but the latter is a reusable nuclide, so this example So I set it to 9 times.
In the refractory tank, 40Zr96 (2β, 3.9E + 19y) with a σp of 0.18 weighs 53.4 kg after 6 years without countermeasures, and after 12 neutron irradiations it weighs 28.5 kg, and its radioactivity is also over 0.1 Bq. However, after 13 irradiations, the weight of the nuclide was reduced to 23.5 kg and the radioactivity was reduced to 83 mBq, and in this example, the number of irradiations was 13 times.
Up to now, we have described nuclides whose nuclide weight remains 1E-40g or more after 6 years in each tank due to countermeasures, but in order to evaluate the effect of implementing the present invention on nuclides that remain after 6 years without countermeasures. Radionuclides whose arrival time of 0.1Bq is 10 years or more and radionuclides whose radioactivity is 0.1Bq or less but have a long life are summarized in Tables 5-1 and 5-2 for each tank.
The table shows the radionuclide, decay type, half-life, neutron capture probability, the weight (in grams) generated in each tank after 6 years of unmeasured neglect and after 6 years of countermeasures, and the weight (unit: g) of radionuclides, decay type, half-life, neutron capture probability, after 6 years of unmeasured neglect and after 6 years of countermeasures, and after 6 years of unmeasured neglect and after 6 years of countermeasures. It shows the radioactivity [in Bq] after 20 years and the time to reach 0.1 Bq.

[Table 5.1] - [Table 5.2]

46 nuclides with long half-lives of 50 days or more with a time to reach 0.1Bq of 10 years or more without countermeasures, and 10 daughter nuclides with short half-lives but with long half-lives of their parent nuclides, can be reduced by countermeasures using neutron irradiation. After a year, the radioactivity of 53 nuclides except 53Te125m [9.1 years] will be 0Bq.
Radioactive soluble nuclides with long half-lives are 34Se79, 37Rb87, 47Ag108m/110m, 48Cd109/113m/113, 52Te123m/125, 55Cs134/135/137, 56Ba133, 57La138, 58Ce139/144, 60Nd1 50, 61Pm146/147, 62Sm146/147 There are 30 types: /148, 63Eu150/152, 64Gd152/153, 65Tb160, 67Ho166m, and 69Tm170/171, and the daughter nuclides with short half-lives and long half-lives of the parent nuclide are 47Ag108/109m/110, 56Ba137m, and 59Pr144m/144. The three long-lived radionuclides Te123/128/130, which are 0.1Bq or less, have a concentration of almost 0g 180 days after removal of spent nuclear fuel, and their radioactivity can be ignored.
There are 16 radioactive poorly soluble nuclides with long half-lives: 40Zr93/95, 41Nb92/93m/94/95, 42Mo100, 43Tc98/99, 44Ru106, 45Rh102, 49In115, 50Sn119m/121m/123/126, which have short half-lives. There are four daughter nuclides with long half-lives of the parent nuclide: 45Rh106, 50Sn121, and 51Sb126m/126. 50Sn126, which has a long half-life and a σp of 0.62, is unmeasured, and 51Sb126m/126, which uses this as its parent nuclide and has a short half-life, is the parent nuclide. It decreased to 4.87 mg, and the time to reach 0.1 Bq was reduced from 9.79 million years, but it was still long at 5.61 million years.

180 days after spent nuclear fuel was removed, the soluble material tank was irradiated with cold neutrons nine times at 30-day intervals, and the refractory material tank was irradiated 13 times. Collected in the soluble tank (including the poorly soluble nuclides in the poorly soluble tank A and the soluble nuclides generated in the solid tank attached to the gas tank) and the hardly soluble tank (including the soluble nuclides in the soluble tank B), The former recovered nuclides and nitric acid solution are transferred to a chloride tank 1, and the latter recovered nuclides and nitric acid solution are transferred to a chloride tank 2, where they are heated separately to drive out nitric acid and turn the nuclides into oxides.
The elements of these generated oxide nuclides are separated using differences in their boiling points, but since the boiling points of these oxides are extremely high, they are converted to chlorides with a lower boiling point from the viewpoint of energy conservation. In this example, the oxides transferred to chloride tanks 1 and 2 after 6 years are calculated by the nuclide weight (not the oxide weight but the nuclide weight) generated in the solid tank and refractory tank attached to the soluble tank and gas tank. The weights of germanium, zirconium, palladium, and hafnium, which are not chlorinated with hydrochloric acid, are 1091.3 kg, 623 g, and 762.0 kg, respectively, in chloride tank 1. In the chloride tank 2, 50 L and 40 L of hydrochloric acid solution with a concentration of 6 mol/L were added to 723.4 kg excluding the weight of 38.6 kg of boron, zirconium, ruthenium, and palladium nuclides that are not chlorinated with hydrochloric acid in the chloride tank 2. Chlorine gas (1 atm, 20°C conversion) was added to 597.1 kg of nuclides in chloride tank 1 and 46.81 kg of nuclides in chloride tank 2, each with 180 m ^{3 of} nuclides that are not chlorinated with hydrochloric acid. , 15 m ³ is injected and converted to chloride. When using chlorine gas, add an appropriate amount of carbon.
As a result of the measures, there are 48 kinds of solid nuclides weighing 1E-40g or more in the soluble matter tank, 35 kinds in the hardly soluble matter tank, and 2 kinds in the gas tank. These nuclides are listed in ascending order of the boiling point of chloride for each tank: nuclide, decay type, half-life, neutron capture probability σp, boiling point of chloride [unit: °C], untreated after 6 years, and tank after taking measures. Tables 6.1 to 6.3 summarize the weight [unit: g], radioactivity (unit: Bq) between unmeasured and after countermeasures, and time to reach 0.1 Bq between unmeasured and after countermeasures. Note that the nuclide weight is the weight of the nuclide itself, not the chloride.

[Table 6.1] ~ [Table 6.3]

(Solid nuclide in chloride tank 1)
Chlorides (60 nuclides in the example) generated in the soluble matter tank and gas tank existing in chloride tank 1 are put into the vaporization tank, heated in ascending order of chloride boiling point, and vaporized in a rectification column for each boiling point. Stable nuclides or stable isotopes are transferred to a nuclide recovery tank via a cooling device, and radionuclides or radioisotopes and isotopes containing a mixture of radionuclides and stable nuclides are collected as vitrified nuclides. Collect in the collection tank. Furthermore, the only two types of isotopes that can be reused as resources, radionuclides and stable nuclides, are separated using a gas centrifugal separator that takes advantage of the mass difference used in the production of uranium fuel. It is separated into nuclides and radioactive heavy nuclides with a large mass number, and collected into a light nuclide recovery tank and a heavy nuclide recovery tank, respectively. Describing the recovery steps in ascending order of boiling point would be redundant, so each recovery method will be described.

(Recovery of stable nuclides in chloride tank 1, including solid tank attached to gas tank)
The chloride tank 1 was heated to 87°C, germanium chloride (stable isotope 32Ge70/72; 76.7mg) was heated to 196°C, and selenium chloride (34Se82; 22.7g) was heated to 331°C. Zirconium chloride (stable isotope 40Zr90-92; 62.8 kg) is heated to 432°C to form hafnium chloride (radioactive nuclide 72Hf177m is separated from the soluble parent nuclide and decays into stable Hf177 in a short time, stable isotope Hf177- 178; 561.7 kg) was heated to 623°C and tin chloride (radioactive nuclide 50Sn117m; 3E-37g is negligible, stable nuclide Sn117; 9.75kg) was heated to 1388°C and rubidium chloride (gas bath 37Rb85; 623g), heated to 1453°C to produce ytterbium chloride (stable isotope 70Yb172/173; 172.4kg), and heated to 1500°C to produce holmium chloride (67Ho165; 14.5kg) and erbium chloride (68Er167; 108. 3kg) is heated to 1530°C to vaporize and fractionate dysprosium chloride (66Dy161/162; 77.1kg), heated to 1580°C to vaporize and fractionate gadolinium chloride (64Gd154/155/158; 27.5kg), and then cooled. Collected into a nuclide recovery tank via a device. If separate recovery tanks are used, the chlorides of these stable nuclides can be recovered.
In chloride tank 1, the weight of gallium whose chloride boiling point is 201°C, palladium at 675°C, zinc at 732°C, barium at 1560°C, and promethium whose boiling point is 1600°C or higher is less than 1 μg, making it difficult to recover. . Note that erbium chloride and holmium chloride, which have the same boiling point of 1500° C., can be separated based on the difference in their melting points.

(Recovery of vitrified nuclides in chloride tank 1)
The chloride tank 1 is heated to 632°C and europium chloride (radioactive isotope 63Eu154/155; 552g and stable nuclide Eu151; 11.9mg are mixed) is heated to 682°C and samarium chloride (radioactive nuclide 62Sm151; 0. Cadmium chloride (radioactive nuclide 46Cd116; 14.2g) was heated to 960°C, and lutetium chloride (radioactive isotope 71Lu177m/177) was heated to 1480°C. 119 g) is heated to 1507° C. to vaporize and fractionate yttrium chloride (radioactive isotope 39Y90/91; 6.1 g), which is recovered into a vitrified nuclide recovery tank via a cooling device. The radioactive nuclides, neodymium chloride (0.53 pg) and cerium chloride (2.7 ng), which have a boiling point of 1600°C or higher, are trace amounts and their radioactivity is 0.2 pBq or less and can be ignored.
The radioactivity of the radionuclide Cd116 is 49.2 μBq, and the probability of its existence on Earth is 7.5%, so it is considered that there is no need for vitrification. Lutetium chloride will also be recovered as it can be used as a radiopharmaceutical.

(Nuclide that can be separated into stable nuclides and radionuclides in chloride tank 1 and recovered as resources)
After heating the chloride tank 1 to 1250° C. to vaporize and fractionally distill strontium chloride (radioactive nuclide 38Sr90; 23.9 kg and stable nuclide Sr88; 32.7 kg), fractional distillation is performed via a cooling device. Nuclide separation is performed using a gas centrifugal separator that utilizes mass differences, separating stable nuclides with a small mass number and radionuclides with a large mass number. The stable nuclides are sent to a light nuclide recovery tank, and the radionuclides are sent to a heavy nuclide recovery tank. It can be recovered.

(Solid nuclides present in chloride tank 2)
Next, the chlorides present in the chloride tank 2 (36 nuclides in the example) are charged into the vaporization tank, and heated in the ascending order of the boiling point of the chloride in the same manner as above. The substance is taken out as chloride gas in a condenser, and if it is a stable nuclide or stable isotope, it is collected in a nuclide recovery tank via a cooling device, and it is collected as a radionuclide or radioisotope and an isotope containing a mixture of radionuclides and stable nuclides. is collected in the vitrified nuclide recovery tank. Since the nuclides generated in the soluble matter tank and the nuclides generated in the refractory tank are treated separately, the weight of waste nuclides to be vitrified can be reduced.

(Recovery of stable nuclides in chloride tank 2)
Chloride tank 2 was heated to 131°C to collect arsenic chloride (33As75; 5.5g), heated to 196°C to collect selenium chloride (34Se77; 32.4g), and heated to 268°C to collect molybdenum chloride (stable isotope). Ruthenium chloride (stable nuclide 44Ru101; 6.39 kg) was heated to 500°C, and cadmium chloride (stable isotope 48Cd111/114; 2.38 kg) was heated to 960°C. is heated to 1550° C. to vaporize and fractionate silver chloride (stable isotope 47Ag107/109; 712.5 kg), which is recovered into a nuclide recovery tank via a cooling device. Ruthenium chloride decomposes thermally at its boiling point, so it can be recovered as metal. Note that boron chloride, which has a boiling point of 12.6°C, and gallium chloride, which has a boiling point of 201°C, are difficult to recover because they are in trace amounts of 1 μg or less.

(Recovery of vitrified nuclides in chloride tank 2)
In chloride tank 2, tellurium chloride (radioactive isotope 52Te125m/127m/127/128; 58.3g and stable isotope Te122/124/125/126; 3.15kg are mixed) is heated to 380°C. By heating to 623°C, beryllium chloride (a mixture of radionuclide 4Be10; 9.8 mg and stable nuclide Be9; 6 μg) was heated to 623°C to form tin chloride (radioactive nuclide 50Sn126; 4.9mg and stable isotope Sn114/116/ 122; 71 pg) is heated to 675° C. to vaporize and fractionate palladium chloride (radioactive nuclide 46Pd107; 7.76 kg), and collect it in a glass solidification nuclide recovery tank via a cooling device.
In addition, antimony chloride at 224°C (radioactive isotope 51Sb124-126/126m; 0.25ng and stable isotope Sb123; 0.7ng mixed) is a trace amount and cannot be recovered, and zirconium, whose sublimation point is 331°C, is radionuclide 40Zr96. (Natural abundance ratio: 2.8%) 23.5 kg and 931 g of stable isotope Zr90/94 are mixed, but its radioactivity is 82.9 mBq, and it can be treated as radioactive waste without vitrification. Further, as will be described later, since σp of 46Pd107 is large even with respect to thermal neutrons, the nuclide can be converted to Pd109m (IT, 4.7m) by thermal neutron irradiation and recovered as stable 47Ag109.

(Gas nuclides generated in the gas tank, soluble material tank, and hardly soluble material tank)
180 days after fuel removal, the generated gas nuclides are listed in order of boiling point of the element, decay type, half-life, boiling point of the element, σp (value of thermal neutron energy 0.0253 eV), and weight if left untreated after 6 years. Table 7 shows the weight of each tank and the total weight of each tank [unit: g], the radioactivity after 6 years without countermeasures and after countermeasures [unit: Bq], and the time to reach 0.1 Bq after countermeasures and when no countermeasures were taken. Note that the boiling point of carbon is the boiling point of CO ₂ since it exists as an oxide.

Weight and volume of gaseous nuclides 180 days after spent nuclear fuel removal (value at 1 atm/20°C [
]) contains 158.1 kg [27.3 m ³ ] of radionuclides and 227.3 kg [43.5 m ³ ] of stable nuclides. [27.1 m ³ ] to 146.0 kg [26.0 m ³ ], and stable nuclides increase from 227.3 kg [43.5 m ³ ] to 238.8 kg [47.3 m ³ ]. The weight [volume] of the radionuclide 54Xe136 is 144.5 kg [25.6 m ³ ] after 6 years without countermeasures, accounting for 91.7% [volume ratio 94.5%] of the total radionuclide, but the weight after countermeasures is Although they are the same, they account for 99.0% [98.5%] of radionuclides, and the weight of the second largest I129 is 11.5 kg [1.1 m ³ ], which accounts for 7.3% [4.1%]. However, after the measures are taken, it will become 0%.
In this example, 3.0 kg of generated stable bromine (including 35Br79/81 generated in the solubles tank) and 1.4 kg of iodine (including 53I127 generated in the hardly solubles tank) were converted into liquids at room temperature. 11.5 kg of long-lived radioactive iodine (53I129), which can be recovered as a solid, can be transmuted into stable xenon (54Xe130). If the gas tank is cooled from room temperature in descending order of boiling point, it is possible to separate gases by element, but isotope separation is difficult because radioactive gases and stable gases coexist, and there is also an issue with the recovery cost due to the use of cooling energy. Gaseous nuclides at temperatures below room temperature will be disposed of in the conventional manner.
Among the unlisted radioactive gas nuclides, there are eight types whose 0.1Bq arrival time becomes longer due to countermeasures: 427 days for 35Br83 (β, 2.4h), 425 days for 36Kr83m (IT, 1.8h), and 425 days for 53I130 ( β, 12.4h) 247 days, 53I130m (IT/β, 8.84m) 211 days, 53I132 (β, 2.3h) 331 days, 53I133 (β, 20.8h) 281 days, 54Xe133 ( This corresponds to 372 days for β, 5.3d) and 357 days for 54Xe133m (IT, 2.2d), and the countermeasure shortens the 0.1Bq arrival time of 53I131 (β, 8.03d) to 210 days. Twelve species with short half-lives, 35Br80 (β/ec, 17.7m)/Br80m (IT, 4.42h)/Br82m (IT/β, 6.1m)/Br82 (β, 35.3h), 36Kr79 (ε , 35h)/Kr81m (IT/β, 13s)/Kr85m (β/IT, 4.5h), 53I128 (β/ec, 25m)/I134 (β, 52.5m), 54Xe135 (β, 9.1h) /Xe135m (IT, 15.3m) /Xe137 (β, 3.8m) has a nuclide weight of 0g and radioactivity of 0Bq 180 days after the spent nuclear fuel is removed.

The weight of high-level radioactive solid nuclides and the weight of radioactive and stable solid nuclides generated in the soluble material tank, hardly soluble material tank, and gas tank after countermeasures by neutron irradiation shown in Tables 6.1 to 6.3. The nuclide generated in each tank is treated as chloride, and the elements are separated according to their boiling point. Stable nuclides or isotopes are recovered, and reusable radionuclides are also recovered. Alternatively, in the case of isotopes or when radioactive nuclides or isotopes and stable nuclides or isotopes are mixed, if the total radioactivity is 0.1Bq or less, it is treated as radioactive waste, and if it is 0.1Bq or more, it is treated as radioactive waste. It is stored in a canister (inner capacity 150 L, allowable weight 550 kg or less) and processed as a vitrified material. Table 8.1 shows the results of evaluating the stable solids that can be recovered through countermeasures, radioactive solids, solids to be disposed of, weights of solids to be vitrified and disposed of, and radioactivity in terms of recovery rate and waste vitrification rate.
Note that this weight is the value of a single nuclide, not the value of chloride.

The FP after 180 days of spent nuclear fuel removal contains 1861 kg of solid nuclides (1228 kg of stable nuclides, 633 kg of radionuclides) and 385.4 kg of gas nuclides (227.3 kg of stable nuclides, 158.1 kg of radionuclides). If left untreated for 6 years, solid nuclides will be 1861 kg (stable nuclides; 1254 kg, radionuclides; 607 kg) and gaseous nuclides will be 384.8 kg (stable nuclides; 227.3 kg, radionuclides; 157.5 kg). After six years, the solid nuclides were 1853.5 kg (stable nuclides; 1797.6 kg, radionuclides; 55.9 kg), and the gaseous nuclides were 392.6 kg (stable nuclides; 246.2 kg, radionuclides; 146.4 kg). , the solid weight decreases to 99.6% and the gas weight increases to 102%. Solid stable nuclides increased to 143.3%, radionuclides decreased to 9.2%, gaseous stable nuclides increased to 108.3%, and radionuclides decreased to 93%. If spent nuclear fuel is removed without countermeasures and left unused for 6 years, 1,861 kg of nuclides are separated by element using the difference in boiling point.The weight of the vitrified nuclides to be disposed of is 1,504 kg, including the unspecified weight, and the disposal rate is 80. However, due to countermeasures, the single weight of solid nuclides present in the soluble matter tank (including gas tank) and the hardly soluble matter tank is 1092 kg, and the total weight of 762 kg is 1854 kg, and the single weight of the nuclide to be vitrified is The total weight is 11.52 kg (559 g and 10.97 kg, respectively), and the weight to be discarded by vitrification can be reduced to 0.62%. If this is converted into chloride, the weight of the solids present in the soluble matter tank (including the gas tank) and the hardly soluble matter tank is 1920 kg and 1027 kg, which is an increase of 76.0% and 34.8%, respectively, and becomes vitrified. The weight of chloride of the waste nuclide is 945 g and 19.8 kg, which is an increase of 1.7 times and 1.8 times, respectively, but the total is 20.7 kg, and the number of canisters to be disposed of as vitrified material is less than one. It is.
In addition, the radioactivity of 14.2 g of cadmium radionuclide 46Cd116 (2β, 3.3E + 19y) generated in the solubles tank is 49.2 μBq, and the natural abundance ratio is 7.49%, so it will not be included in the waste vitrified material and will be discarded. Included in treated solids. Similarly, the radioactivity of 24.4 kg of radionuclide Zr96 (2β, 3.9E + 19y) of zirconium (23.5 kg of radionuclide 40Zr96 and 0.9 kg of stable isotope 40Zr90/94) generated in the refractory tank is Since it is 82.9 mBq and the natural abundance ratio is 2.80%, it is not included in the waste vitrified material but is included in the waste treatment solid.
The radioactivity of discarded radioactive gas nuclides of FP generated from spent nuclear fuel after 6 years of uncountermeasures is 22.1 PBq, and there is no increase or decrease due to countermeasures, but the radioactivity of radioactive solid nuclides of 957.3 PBq has increased due to countermeasures. The radioactivity of the used radionuclide is 146.5PBq, and the radioactivity of the waste vitrified radionuclide is 153.2PBq.The radioactivity of the waste radionuclide is 153.2PBq, and the radioactivity to be treated as radioactive waste is zirconium (radionuclide 40Zr96; 23.5kg and stable isotope Zr90/94; 931g). The radioactivity of 24.4 kg (mixed with 46Cd116) is 83 mBq, and the radioactivity of 14.2 g of cadmium radionuclide (46Cd116) is 49.2 μBq.

(Recovered nuclides that can be reused in the solubles tank and nuclides that can be vitrified)
The stable chlorides of soluble nuclides that can be recovered in the solubles tank and their weight (nuclide alone) are 22.7g for selenium (34Se82), 623.3g for rubidium (gas tank 37Rb85), and 32.7kg for strontium (38Sr88). , gadolinium (64Gd154/155/158) is 27.5kg, dysprosium (66Dy161/162) is 77.1kg, holmium (67Ho165) is 14.5kg, erbium (68Er167) is 108.3kg, ytterbium (70Yb172/173) is 172.4 kg, stable chlorides of poorly soluble nuclides and their weights (nuclide alone) are 76.7 mg for germanium (32Ge70/72/73), 62.8 kg for zirconium (40Zr90/91/92), and 62.8 kg for tin (50Sn117). 9.75 kg, hafnium (72Hf177/178) is 561.6 kg, and the total weight in the solubles tank (including the gas tank) is 1067 kg, and these chlorides can be reduced and reused as metal.
The radionuclides that can be recovered and their weight (nuclide alone) are 23.9 kg of strontium (38Sr90) and 118.6 g of lutetium (71Lu177m/177), a total of 24.0 kg, and 38Sr90 (β, 28.8y) is It can be used in nuclear batteries as an energy source for powering unmanned machines, and 71Lu177 (β, 6.65d) can be used in radionuclide therapy for neuroendocrine tumors, and is used in the radiopharmaceutical "generic name: lutetium oxodotreotide (177Lu)". be done. (Source: Japanese Society of Nuclear Medicine)
The nuclides to be vitrified and their weights are 6.08 g for yttrium (radioactive isotope 39Y90/91), 0.3 g for samarium (radioactive nuclide 62Sm151; 0.3 g and stable isotope 62Sm152/154; 65 μg), and europium ( The radioactive isotope 63Eu154/155; 552.1g and the stable nuclide Eu151; 12mg) were 552.1g, for a total of 558.5g.
What is disposed of as radioactive waste without being vitrified is 14.2 g of cadmium (48Cd116) with a radioactivity of 49.2 μBq.

(Recovered isotopes that can be reused in the refractory tank and nuclides for vitrification)
The chlorides of soluble stable nuclides that can be recovered in the refractory tank and their weight (nuclide alone) are 5.5 g for arsenic (33As75), 32.4 g for selenium (34Se77), and 712 g for silver (47Ag107/109). 5kg, cadmium (48Cd111/114) is 2.38kg, poorly soluble stable chloride and its weight (nuclide alone) is molybdenum (42Mo97/98) 5.26kg, ruthenium (44Ru101) 6.39kg, total. It weighs 726.6 kg, and these chlorides can be reduced and reused as metal.
There are no radionuclides that can be recovered.
The nuclides to be vitrified and their weight (nuclide alone) are palladium (radionuclide 46Pd107) of 7.76 kg, tin (radionuclide 50Sn126; 4.9 mg and stable isotope Sn114/116/122/124; 71 pg). 4.9mg, antimony (radioisotope 51Sb124/125/126m/126; 0.25ng and stable nuclide Sb123; 0.7ng) 0.95ng, tellurium (radioisotope 52Te125m/127/127m/128; 58.3g and the stable isotope 52Te122/124/125/126; 3.15kg) are 3.21kg, for a total of 10.97kg.
Furthermore, as mentioned above, 24.4 kg of zirconium (48Cd116) with a radioactivity of 83 mBq is disposed of as radioactive waste without being vitrified.
Note that the σp of 46Pd107 to be vitrified is as large as 9.9 with respect to thermal neutrons (0.0253eV), so if the nuclide is converted to 46Pd109m by thermal neutron irradiation, Pd109m (IT, 3.1s) → Pd109(β , 13.6h) → 47Ag109m (IT, 39.8s) → Ag109 (stable), and after 41.2 days of irradiation, the radioactivity of the radionuclide decreased to 0.1Bq or less, and it was recovered as 7.76kg of stable 47Ag109. After the measures were taken, the stable solid recovery rate improved from 98.1% to 98.5%, and the waste vitrification ratio improved from 0.62% to 0.20%.

Approximately 1.25 bottles of vitrified material (high-level radioactive waste) are produced from 1 ton of spent nuclear fuel. (Chugoku Electric Power Home Page https://www.enerugia.co.jp) Generally speaking, if the concentration of uranium-235 from 1 million kW of nuclear power generation is 3.7% (5%), it will be approximately 31.5 tons (22.5 tons) per year. It is said that 6 tons) of spent nuclear fuel will be discharged, from which approximately 15.8 m ³ (11.3 m ³ ) of high-level radioactive waste liquid will be produced, and approximately 32 (23 bottles) of vitrified waste will be produced. (Japan Atomic Energy Agency Atomic Energy Encyclopedia ATOMICA)
The nuclear fuel from Unit 2 of the Fukushima Daiichi Nuclear Power Plant (electrical output: 784,000 kW) has a U235 concentration of 3.7%, and the nuclear fuel required to generate electricity for one year is 24.7 tons, so we will seek vitrified material. 31 from the former and 25 from the latter. In the FP after 180 days of nuclear fuel removal, the weight of the solid nuclide alone is 1.86t (3.4t in terms of nitrate, 2.3t in terms of oxide, which is generally said to be 1.6 times that of the nuclide alone, so it is solid.) By implementing the present invention, the weight of the nuclide alone to be vitrified can be reduced to 11.52 kg (20.7 kg in terms of chloride), and the canister for vitrifying the former The calculation results in 0.21 lines, and the latter calculation results in 0.17 lines.
Furthermore, considering the case where the nuclear fuel is left unused for several years or more after removal, the method of the present invention is applied to the nuclides 10 years after the removal of the nuclear fuel, and the method of the present invention is applied in the same way. The calculated results after 16 years of countermeasures are shown in Table 8.2.

Comparing the weight of nuclides after 16 years of being left without countermeasures and after 6 years of being left untreated, in solids, radionuclides decreased to 96.4%, stable nuclides increased to 101.8%, and the weight changed from radionuclides to stable nuclides. As the decay progresses, the radioactive nuclides in the gas decrease to 99.6%, but the stable nuclides remain at 100%. It is thought that gaseous radionuclides do not decay into stable gases, but instead decay into solids. As a result of the measures, the weight of stable solids recovered from spent nuclear fuel after being left unused for 10 years remains almost unchanged at 1,794 kg, the weight of recovered radioactive solids decreases by about 13% to 20.96 kg, and the weight of waste vitrified solids decreases to 11.9 kg. There is almost no change, only a decrease of 30g to 49kg, and the weight of the solid waste to be disposed of is 28.28kg, an increase of 15.8%. Even when spent nuclear fuel is left for 10 years, the waste vitrification rate is the same as the value after taking measures 180 days after the spent nuclear fuel was removed, and it is considered that the present invention is effective.

[References] and [Data source]
[Reference 1] Tsutomu Sakurai, Akira Takahashi “Behavior of iodine during reprocessing” JAERI-Review 97-002 Japan Atomic Energy Research Institute,
https://doi. org/10.11484/jaeri-review-97-002
[Reference 2] Japanese Patent Application Laid-open No. 05-072390 14 CO2 treatment method Industrial Creation Research Institute [Reference 3] Hiroaki Tagawa, "Pyrolysis of nitrates" Bulletin of the Institute of Environmental Studies, Yokohama National University 14: p. 41-57 (1987) )
https://ynu. repo. niii. ac. jp/
[Reference 4] Kensuke Kinoshita, Masaki Kurata “Separation technology for transuranium elements from high-level waste liquid” Central Research Institute of Electric Power Industry Review No. 37, p49-58
https://criepi. denken. or. jp/koho/review/No37/chap-6. pdf
[Data source 1] IAEA Nuclear Structure and Decay Data; IAEA Nuclear Data Section, Vienna International Center, PO Box100 A-1400 Vi Enna, Austria
https://www-nds. iaea. org/relnsd/vcharthml/VChartHTML. html
[Data source 2] Japan Atomic Energy Agency, Nuclear Data Research Group, JENDL-5
https://wwwndc. jaea. go. jp/jendl
[Data source 3] Kenji Nishihara, Daiki Iwamoto, Kenya Suyama “Evaluation of fuel composition for Fukushima Daiichi Nuclear Power Plant” JAEA-Data/Code 2012-018, Japan Atomic Energy Agency https://jopss. jaea. go. jp/pdfdata/JAEA-Data-Code-2012-018. pdf

In this example, we calculated the weight of solid nuclides that will become vitrified in the FP 180 days after the removal of spent nuclear fuel from Unit 2 of TEPCO's Fukushima Daiichi Nuclear Power Station and 10 years later. If the weight of FP generated from spent nuclear fuel is given, the worksheet of this example can be applied to determine the weight of the nuclide that will be vitrified. Furthermore, by implementing the present invention, the proportion of vitrified high-level radioactive waste from spent nuclear fuel generated in nuclear power generation can be reduced to 1% or less, reducing the area required for high-level radioactive waste storage sites and storage. We believe that it will be easier to manage, expand the options for waste storage locations, and serve as a stepping stone to increasing the proportion of nuclear power generation in the electricity supply, contributing to the prevention of global warming.

1 Gas tank 2 Solid tank 3 Soluble substance tank 4 Hardly soluble substance tank A
5 Refractory tank 6 Soluble tank B
7 Thermal neutron source device 8 Cold neutron source device 9 Neutron irradiation shutter 10 Solid-liquid separation device 11 Filtration device 12 Liquid iodine receiver 13 Cooling device 14 Iodide tank 15 Chloride tank 1 (with solidification device)
16 Chloride tank 2 (with solidification device)
17 Vaporizer 18 Rectification column 19 Condenser 20 Heating device 21 Nitric acid solution inlet 22 Hydrochloric acid solution inlet 23 Chlorine gas inlet 24 Valve (for liquid)
25 Valve with backflow prevention (for liquid)
26 Valve with backflow prevention (for gas)
27 Vacuum pump 28 Liquid reflux pump 29 Radiation dose monitor 30 Gas release valve 31 Flow path switching valve 32 Heating device with temperature control 33 Nitric acid recovery device 34 Cooling device 35 Stable nuclide recovery tank 36 Vitrified nuclide recovery tank 37 Liquefied iodine extraction tube 38 Gas centrifugal separator 39 Heavy nuclide recovery tank 40 Light nuclide recovery tank

Table 3B-1 shows the weight of stable nuclides in the refractory tank after 180 days, and the calculated weight changes when left untreated for 6 years and when the present invention is applied. 141 stable solid nuclides; weight 450.9 kg (77 soluble nuclides; 7.57 kg; 47 poorly soluble nuclides; 443.4 kg; 17 gaseous nuclides; 0 g) after being left untreated for 6 years. The number of nuclides was reduced to 24 (12 soluble nuclides, 11 poorly soluble nuclides, 1 gas nuclide), and the weight was 732.1 kg (718.1 kg soluble nuclides, 12.6 kg poorly soluble nuclides). , gaseous nuclide increases to 1.41 kg). However, all the weights of these nuclides are the weights of individual nuclides.
Unlisted poorly soluble stable nuclides All 36 nuclides have a σp of 1 or more, and their weight becomes 0 g after nuclide conversion by neutron irradiation.Even if the converted parent nuclide radionuclide has a long life, it is a poorly soluble one with σp greater than 1. It becomes a nuclide and undergoes nuclide conversion by neutron irradiation to become 0g. For example, stable 49In113 undergoes nuclide transmutation by the first neutron irradiation and decays as 49In115m (IT/β, 4.5h) → In115 (β, 4.4E+14y) → 50Sn115 (stable), and σp is 1. The larger In115 is converted into In116m by the second neutron irradiation and becomes 0g, and decays as 49In116m (β, 54.3m) → 50Sn116 (stable), and In113 becomes 0g, and the weight of stable 50Sn116 increases, but the nuclide Also, when σp is 0.9, the weight decreases with the number of neutron irradiations. In addition, stable 46Pd108 is converted into 46Pd109m by neutron irradiation and decays as 46Pd109m (IT, 4.7m) → Pd109 (β, 13.6h) → 47Ag109m (IT, 39.8s) → Ag109 (stable), and Pd107 becomes 0g, and stable soluble nuclide 47Ag109 increases.

Neutron capture probability σp (0.353 meV) for 11 stable poorly soluble nuclides with a weight of 1E-40 g or more after countermeasures, 12 stable soluble nuclides generated by neutron irradiation, and 1 gas nuclide, 180 days after fuel removal Table 3B-2 shows the nuclide weight (in g) after 6 years without countermeasures and after countermeasures.
The weight of all 11 poorly soluble stable nuclides after 6 years of countermeasures was lower than the weight after 6 years of no countermeasures. There are seven types of nuclides with σp of 1 or less (the value of σp is shown in brackets), and four of them are 4Be9[0.34], 40Zr90[0.09], Zr94[0.42], and 50Sn124[ 0.94] has no parent nuclide, so its weight gradually decreases with the number of neutron irradiations. The other three types of 50Sn114[0.92]/Sn116[0.91]/Sn122[0.98] partially remain without being converted by neutron irradiation, and after the second neutron irradiation, their respective parent nuclides 49In114 (β/ε), 49In116m (β), 51Sb122m (IT) → Sb122 (β/ε) are not generated, so the weight of the daughter nuclide is 0 g, and in the 13th neutron irradiation, some of it is converted by neutron capture. , the weight of the remaining daughter nuclides has decreased and is less than after 6 years without countermeasures. The remaining four types, 42Mo97/98, 44Ru101, and 51Sb123, have σp of 1 or more and undergo nuclide conversion to 0g after 13 neutron irradiations, but the parent nuclides 40Zr97(β)/98(β), 42Mo101(β), and 50Sn123m(β ) The weight of daughter nuclides generated by β-decay will be less than after 6 years if no countermeasures are taken.
The 12 types of soluble nuclides generated in the refractory tank are not irradiated with neutrons. Four of these, 31Ga71, 33As75, 34Se77, and 48Cd114, have parent nuclides of 32Ge71m (IT) → Ge71 (ec), 32Ge75m (IT), 32Ge77m (β/IT), and 49In114m (IT/ε) whose σp is 0. In this case, the parent nuclide is generated up to three times due to neutron irradiation, and the weight of the daughter nuclide generated is less than after 6 years of no countermeasures. 52Te125 is generated by the decay of the parent nuclide 50Sn125m (β) generated by nuclide transmutation each time after 13 neutron irradiations, but its weight gradually decreases with the number of irradiations, and is less than after 6 years of no countermeasures. The remaining seven species, 5B10, 47Ag107/109, 48Cd111, 52Te122/124/126, have their respective parent nuclides 4Be10 (β), 44Ru107 (β), 46Pd109m (IT), 46Pd111m (IT/β), and 51Sb122m (IT). /124m(IT/β)/126m(β/IT) σp is 0, β of the parent nuclide generated by 13 neutron irradiations, produced by IT decay, and the weight of these daughter nuclides has been left untreated for 6 years. The weight will be more than the latter.
The stable gas nuclide generated in the refractory tank is only 1.41 kg of 53I127, and 51Sb127 (β, 3.85d) → 52Te127m (IT/β, 106 .1d) → 52Te127 (β, 9.35h) → 53I127 (stable). It can be released after confirming safety with a radiation dose monitor. In addition, after the 6th year of countermeasures, the radioactive tellurium generated in the soluble tank B attached to the refractory tank decayed as 52Te127m (IT/β, 106.1d) → Te127 (β, 9.35h) → 53I127 (stable). Since 0.63 mL (3.35 mg) of I127 is generated at 20°C, when tellurium is vitrified, silver is added and solidified as silver iodide.
Countermeasures There are stable nuclides whose weight increases after 6 years, but this is due to the decay of the radioactive parent nuclides with long half-lives shown in [ ], and they are not sparingly soluble nuclides, but soluble nuclides such as 5B10 [4Be10] and 47Ag107. [46Pd107], 52Te124 [51Sb124m], and 52Te125 [51Sb125] are applicable. The poorly soluble radionuclides of these parent nuclides are vitrified. However, as will be described later, 46Pd107 with a large σp exists alone after 6 years of nuclide separation, so the nuclide is converted by thermal neutron irradiation, and 46Pd109m (IT, 3.1s) → Pd109 (β, 13.59h) → 47Ag109m (IT, 39.8s) → Ag109 (stable) decays and can be converted to stable Ag109 and recovered after 41.2 days.

Claims (5)

Among the fission products generated from spent nuclear fuel, there is a gas tank that collects the gaseous nuclides generated immediately after the fuel is removed, and a gas tank that collects the fission products that remain after recovering uranium, plutonium, etc. from the spent nuclear fuel over a specified period of time. After that, it is equipped with a soluble tank that stores nuclides that are soluble in nitric acid, and a refractory tank that separates and stores nuclides that are poorly soluble or insoluble in nitric acid, and irradiates these nuclides with cold or thermal neutrons. A method for disposing of radioactive waste, comprising performing nuclide conversion using the method described in claims 2 to 4, irradiating with neutrons a prescribed number of times, and storing for a prescribed period of time. In the method for disposing of radioactive waste according to claim 1, after a predetermined period of time has elapsed, nuclides that are soluble in nitric acid in the solubles tank among the fission products are irradiated with cold neutrons for the first time, and After storage, the gaseous nuclides generated by radioactive decay are collected in a gas tank, and the generated nuclides that are poorly soluble or insoluble in nitric acid are separated and collected in another storage tank. is not irradiated with neutrons, only the nuclides that are soluble in nitric acid in the solubles tank are irradiated with cold neutrons for the second time.After that, cold neutron irradiation and storage for a specified time are repeated multiple times, and the storage period after cold neutron irradiation is The gaseous nuclides generated by radioactive decay are collected in a gas tank, and the nuclides that are poorly soluble or insoluble in nitric acid are collected in a separate storage tank, and these nuclides are not irradiated with neutrons. Processing method. In the radioactive waste disposal method according to claim 1, after a predetermined period of time has elapsed, after irradiating the nuclear fission products that are poorly soluble or insoluble in nitric acid in the refractory tank with cold neutrons for the first time, A concentrated nitric acid solution is poured into a refractory tank, and after storage for a specified period of time, stable gaseous nuclides produced by radioactive decay are exhausted, and if there are radioactive gaseous nuclides, they are collected in the gas tank and soluble in the produced nitric acid. The nuclides are filtered together with the nitric acid solution and collected in another storage tank, and after the nuclides in the refractory tank are irradiated with cold neutrons for the second time, the filtered nitric acid solution is refluxed to the refractory tank and stored for a specified time. Thereafter, cold neutron irradiation and storage for a specified period of time are repeated multiple times, and stable gas nuclides generated by radioactive decay during the storage period after cold neutron irradiation are exhausted, and if there are radioactive gas nuclides, they are collected in a gas tank, and the resulting nitric acid is collected. A method for disposing of radioactive waste, characterized in that nuclides soluble in water are filtered together with a nitric acid solution and collected in a separate storage tank, and radioactive gases and soluble nuclides are not irradiated with neutrons. In the radioactive waste disposal method according to claim 1, after a predetermined period of time has elapsed, the nuclides in the gas tank among the fission products are the same as the gas nuclides generated in the solubles tank according to claim 2. This includes radioactive gas nuclides generated in the refractory tank described in Section 3, but iodine, bromine, and gases recovered from the soluble tank immediately before the second cold neutron irradiation to the soluble tank The iodine and bromine present in the tank are vaporized or sublimated, only the iodine is liquefied and separated, and the iodine is irradiated with thermal neutrons only once.The gaseous nuclides are not irradiated with neutrons after that, and the iodine generated during this storage period is A radioactive waste disposal method characterized by recovering solid nuclides in a separate storage tank and not irradiating the solid nuclides with neutrons. After carrying out the treatment of radioactive waste according to claims 2 to 4, the solid nuclides recovered in claims 2 and 4 and the solid nuclides recovered in claim 3 are separately denitrified, and then chloride is removed. elemental separation using a fractional distillation method that takes advantage of the difference in boiling point of chloride, and if necessary perform isotopic separation using gas centrifugation to recover useful radionuclides and stable nuclides that can be reused as resources. A method for disposing of radioactive waste characterized by minimizing the amount of waste of nuclides that vitrify. For elemental separation, general elemental separation methods such as elemental separation methods that utilize differences in melting points, precipitation methods, centrifugal separation methods, electrolytic methods, adsorption methods, solvent extraction methods, ion exchange methods, or combinations thereof can be used. may also be used.

Images