JPS5879196A - Radioactive ion adhesion suppression method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for suppressing the adhesion of radioactive ions, and more particularly, to a method for suppressing adhesion of radioactive ions suitable for suppressing the adhesion of 60CO ions to the structural material surface of a boiling water reactor. It is something.

When structural materials such as piping, pumps, valves, and equipment used in the primary cooling water system of a nuclear power plant, such as a boiling water nuclear power plant, are used for a long period of time, metal impurities may be leached from these structural materials. do. The metal impurities are eventually carried into the nuclear reactor, where they are activated by neutron irradiation and generate radioactive corrosion products. Radioactive corrosion products include components dissolved in cooling water (hereinafter referred to as ions) and insoluble solid components (hereinafter referred to as cladding).

In this way, 60 CO and 54M produced
Radioactive corrosion products having a long half-life such as 0 adhere to the surface of structural materials while circulating in the primary cooling water system of a nuclear reactor. This causes an increase in the radiation dose rate on the surface of the structural material. Therefore, it becomes difficult to carry out maintenance and inspection of the nuclear reactor in a short period of time in order to prevent radiation exposure of workers.

An object of the present invention is to overcome the drawbacks of the prior art described above and to suppress the adhesion of radioactive ions to structural materials.

The features of the present invention are Mg, Cr, V, Ti+ CIIN
The present invention is characterized in that metal ions of at least one substance selected from the group consisting of ', Z', and CD are added to the coolant.

In order to prevent an increase in the surface dose rate of the structural materials of the primary cooling system,
Mechanical removal of radioactive corrosion products adhering to structural materials has been implemented. Mechanical cleaning methods make it possible to temporarily reduce the surface dose rate of structural materials. However, some of the radioactive corrosion products deposited are very difficult to remove using mechanical cleaning methods. As such deposits gradually accumulate over many years, the surface dose rate of structural materials tends to gradually increase year by year.

The present invention provides that radioactive corrosion products that adhere firmly to the surface of structural materials and are difficult to remove by mechanical cleaning methods are based on radioactive ions in the primary cooling water, and that these radioactive ions are replaced by non-radioactive corrosion products. When forming a ferrite layer on the surface of a structural material together with ions, radioactive ions are incorporated into the ferrite layer in a solid solution state, and the rate of attachment of radioactive ions in the ferrite layer is inversely proportional to the a degree of metal ions in the coolant. This was done by focusing on the points. That is, by increasing the metal ion concentration in the cooling moon where radioactive ions are present, the rate at which radioactive ions adhere to the ferrite layer of the structural material is reduced.

Various experiments were conducted to elucidate the mechanism by which radioactive corrosion products adhere to piping, pumps, valves, etc. in the recirculation system of boiling water nuclear power plants. These experiments revealed that corrosion products adhere to each other as shown in the model schematically shown in Figure 1.

In FIG. 1, l indicates the structural side of the primary cooling system, 2 indicates the ferrite layer, 3 indicates the cladding, and 4 indicates the radioactive ions. The ferrite layer 2 formed on the surface of the structural material 1 that comes into contact with the cooling water is made of α-type diiron trioxide (a-Fe20al as the main component, with Ni, Co and Cr dissolved therein). Radioactive ions dissolved in cooling water4
For example, when this ferrite layer 2 is formed on the surface of the structural material 1, some are taken into the ferrite layer 2, and others are diffused into the ferrite layer 2 that has already been formed, and the ferrite layer is formed by an isotope exchange reaction, etc. Nl in 2.

There are some that replace Co, Mn, Cr, etc. and are firmly fixed. When forming the ferrite layer 2, radioactive ions diffuse into the oxide film formed on the surface of the structural material 1, and as the oxidation film progresses and ferrous oxide (Fed) oxidizes, the spinel incorporated into the structure. The cladding 3 is attached to the surface of the ferrite layer 20 in a relatively loose manner.

As mentioned above, radioactive corrosion products in the cooling water in the reactor pressure vessel can be broadly classified into radioactive ions and crud. In boiling water nuclear power plants where measures are taken to suppress corrosion of structural materials, such as by injecting oxygen into the water condensation system, the weight concentration of radioactive corrosion products in the cooling water in the reactor pressure vessel is below several ppb. ing. In such plants, the radioactivity concentration of ions in the cooling water within the reactor pressure vessel is much greater than the radioactivity concentration in the cladding. That is, the radioactivity concentration of the former is about 10 times or more that of the latter.

According to pipe adhesion experiments using tracers such as 58 Co, experiments have shown that when the radioactivity concentrations of two ion traps in cooling water are equal, the contribution of ions to pipe adhesion is more than 15 times that of the cladding. confirmed. Therefore, it is clear that prevention of ion adhesion is important in order to reduce the dose on the pipe surface.

The inventors investigated the state of adhesion of radioactive ions to the inner surface of the pipe using the experimental apparatus shown in FIG.

The structure of this experimental device will be briefly explained. The temperature rising section 11 is
A heater IIB is placed outside the container 11A. Temperature rising section 11. The piping test section 12 and the pump 17 are connected by a piping 18 which is a closed loop. Piping 19A and 19B connected to tracer tank 13 and metal ion tank 14, respectively, are attached to piping 18.

Pumps 15 and 16 are provided in piping 19A and 19B. 58CO ions in the tracer tank 13,
Ni ions are contained in the metal ion tank 14.

The experiment was conducted as follows. The pump 17 is driven to circulate cooling water (pure water was used in this experiment) within the temperature raising section 11, piping test section 12, and piping 18. The cooling water is heated in the temperature raising unit 11 to 285° C., which is the temperature condition for cooling water in a boiling water reactor. Open the valve and drive the pump 16, and inject the Ni ions in the metal ion tank J4 into the cooling water (F-) in the pipe J8 to reduce the metal ion concentration in the cooling water flowing in the pipe 18 to about 11) I) l
).

When the specified concentration is reached, close the valve. This metal ion concentration is detected by an ion concentration meter attached to the pipe 18. Next, open the valve and drive the pump 15 to transfer the 58CO ions in the tonzer tank 13 to the pipe 18.
Inject inside. This reduces the 58 co ion concentration in the cooling water flowing through the pipe 18 to approximately 1X10"0μC1/
Make it mt. Even when 58 CO ions are added in this way, the metal ion concentration in the cooling water flowing through the pipe 18 is about 1 ppb. While circulating the cooling water 5
A C□ ions adhere to the inner surface of the pipe of the pipe test section 12.

After a predetermined period of time, 58CO attached to the piping test section 12
Radioactivity was measured using a NaI ('14) scintillation detector. Next, Ni ions are further injected into the cooling water to increase the metal ion concentration of the cooling water flowing through the pipe 18 to about 15%.
A similar experiment was conducted with the concentration increased to ppb. The 58CO ion concentration in the cooling water at this time is approximately IXI O-6μCI
/mt. Piping test section 1 for each condition
From the measurement results of 58CO radioactivity in 2, the piping attachment coefficient of 58Co was determined.

The pipe adhesion coefficient δ (tyn/h) of 58CO can be determined by the following formula.

d7'/dt-δR・・・・・・・・・・・・Mark・・・・・・
(]) Here, P is the amount of 58CO deposited per unit area, (μC+/J), ' is the time (hi,, rl is the concentration of 68CO in the circulating cooling water (μCi/mt
).

The adhesion coefficient of 58CO to the piping in the latter case (metal ion concentration 15 pI) was approximately 1/10 of the former (metal ion concentration 1 ppb). As a result, it was found that increasing the N1 ion concentration in cooling water can reduce the adhesion of radioactive ions.

Instead of NI, Mg+ Cr, V, Ti + Cu+
A similar experiment was conducted by adding 7, n and cd ions to the cooling water, but as the concentration of these ions increased, the attachment coefficient of radioactive ions decreased. These metals are
It is a divalent or trivalent metal that is easily incorporated into the spinel structure of the ferrite layer.

Even if the ion concentration of C0lMn and Fe in the cooling water is increased, the adhesion coefficient of radioactive ions can be reduced. However, since CO and Mn are activated in a nuclear reactor to produce long half-life radionuclides of 60CO and Mn, it is not desirable to add them to the coolant.

Further, it is not preferable to add to the cooling water a substance such as Fe, which becomes a particulate oxide and adheres to the surface of the fuel rod, becomes a getter for CO ions, and becomes a factor in the production of 60CO. M g HCrg V +Ti, Cu, Ni, Z
Although n and cd produce radionuclides as shown in Table 1 through nuclear reactions, their half-lives are significantly shorter than that of 60 CO.

(9) Furthermore, even if these radioactive ions adhere to piping, their radioactivity will decrease within a short period of time because their half-life is extremely short. Therefore, when applied to a nuclear power plant, the surface dose rate of the piping drops rapidly after the nuclear power plant is shut down, so maintenance and inspection of the piping becomes easy if the system is on standby for a predetermined period of time after the nuclear power plant is shut down.

Table 1 (10) A preferred embodiment of the present invention applied to a boiling water nuclear power plant will be described below with reference to FIG.

As the cooling water passes through the reactor core 32 in the reactor pressure vessel 21, the fuel rods in the reactor core 32 are cooled. Cooling water, on the other hand, is heated and turns into steam. The generated steam is sent from the reactor pressure vessel 21 to the turbine 22 through the main steam pipe 28 and condensed in the condenser 23. Condenser 23
The condensed water inside the reactor pressure vessel 21 is purified by the demineralizer 24 and further heated to a predetermined temperature by the feed water heater 25, and is then used as cooling water to cool the reactor core 32 through the feed water pipe 29. will be returned to. Cooling water within the reactor pressure vessel 21 flows through the recirculation piping 30 and is supplied into the reactor core 32 by driving the recirculation pump 33 .

A portion of the cooling water flowing through recirculation piping 30 flows into piping 34 of the furnace purification system. This cooling water is supplied to one of the pumps 36.
By driving, the regenerative heat exchanger 35 and the non-regenerative heat exchanger 2
After passing through the filter 7 and being cooled, it is introduced into a desalination (11) filter 26 and purified. Radioactive cladding and ions contained in the cooling water are removed from the desalination filter 26.
will be removed. The purified cooling water is transferred to a regenerative heat exchanger 35.
The water is then heated and returned to the reactor pressure vessel 21 via the water supply pipe 29. The tank 31 is filled with Cr ions. The conductivity gauge 37 measures the metal ion concentration in the cooling water flowing inside the pipe 34. This measured value of metal ion concentration is sent to the controller 39. The measured metal ion concentration is the set value (1 diopI in this example)! When the temperature is below, the valve 38 is opened based on a signal from the controller 39, and Cr ions are injected into the pipe 34 from the tank 31. The metal ion concentration in the cooling water present in the reactor pressure vessel 21, pipes 30 and 34, etc. is adjusted to 10 pI)b. The metal ion concentration in the cooling water in the reactor pressure vessels and piping of conventional boiling water nuclear power plants is approximately 1
pI)b, the metal ion concentration in the cooling water of this example was increased about 10 times. therefore,
In this example, radioactive ions, especially 60 CO
Ion adhesion can be suppressed. It becomes easier to handle radioactive solid waste such as used pipes generated by replacing pipes during repairs, parts replaced during maintenance of equipment such as pumps, and the processing of the waste becomes easier. Furthermore, as described above, maintenance and inspection of piping and the like becomes easier.

When metal ions are injected into the cooling water in the piping 34 of the furnace purification system, it is necessary to do so on the downstream side of the desalination filter 26. Since the desalination filter 26il''lt handles crud and ions in the cooling water, when metal ions are injected into the piping 34 upstream of the desalination filter 26, the desalination filter 2
6, which significantly reduces the effectiveness of metal ion implantation. Even if metal ions are injected into the pipe 34 on the downstream side of the desalination filter 26, the metal ions are gradually removed by the desalination filter 26 because the cooling water is circulated. However, the removed metal ions are replenished from the tank 31. On the other hand, there is a concern that the lifespan (13) of the desalination filter 26 will be significantly shortened, but since the amount of metal ions injected from the tank 31 is small,
6's lifespan will not be shortened much.

The present invention can also be applied to the primary system of a pressurized water reactor.

According to the present invention, it is possible to significantly suppress the adhesion of radioactive ions to the surface of the structural material of the atomic couplant that comes into contact with the coolant.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram showing the adhesion mechanism of radioactive ions and cladding to the surface of structural materials. Figure 2 is a system diagram of the experimental equipment that confirmed the functionality of the present invention. Figure 3 is a diagram showing the mechanism of adhesion of radioactive ions and cladding to the surface of structural materials. FIG. 2 is a system diagram of a preferred embodiment of the present invention. 21... Reactor pressure vessel, 26... Desalination filter,
30.34...Piping, 31...Tank, 37...
Electrical conductivity (14) 2nd e3rd g Continued from page 1 Q > Inventor Yoshihiro Ozawa 1168 Moriyama-cho, Hitachi City Energy Research Laboratory, Hitachi, Ltd. Inventor Masao Endo 1168 Moriyama-cho, Hitachi City Address Hitachi, Ltd., Energy Research Laboratories Q > Inventor Naoto Uetake 1168 Moriyama-cho, Hitachi City Hitachi, Ltd. Energy Research Laboratories ■Applicant Tohoku Electric Power Co., Ltd. Sendai Type 1-cho 3-7-1 +7F) Applicant Chubu Electric Power Co., Ltd., Higashishinmachi Ichiban, Higashi-ku, Nagoya (7g) Applicant Hokuriku Electric Power Co., Ltd. 3-1 Sakurabashi-dori, Toyama-shi, 7p Applicant Chugoku Electric Power Co., Ltd. 4-33 Komachi, Naka-ku, Hiroshima City/? [Applicant: Japan Atomic Power Co., Ltd., Otemachi-6-chome, Chiyoda-ku, Tokyo, Japan CD Applicant: Hitachi, Ltd., 5-1 Shimome, Marunouchi, Chiyoda-ku, Tokyo

Claims (1)

[Claims] 1. In a method for suppressing the adhesion of radioactive ions to the structural material of an atomic couplant that comes into contact with a coolant containing radioactive ions, the amount of metal ions in the coolant is measured,
Based on this measured value, Mg, cr, v, T'+ cu, N
A method for suppressing adhesion of radioactive ions, comprising injecting metal ions of at least one substance selected from the group consisting of Zn and CD into the coolant.