JP2001133584A - Concrete storage container and storage system having it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a concrete storage container capable of easily monitoring temperature, distortion and the like exerting an influence on the integrity of the concrete storage container and a storage system having the container. SOLUTION: A substantially cylindrical container main body 12 formed of concrete has a column-like storing part 22, and a canister 14 where radioactive material is sealed is stored in the storing part. The optical fiber 34 of a monitoring device 32 is wound a round the outer surface of the container main body. The monitor device is so constructed that pulse-like laser beam enters an optical fiber from a laser beam source 6, scattered beam of laser beam emitted from the optical fiber is measured by a wavelength analyzer 38, distortion and temperature are detected from the measured intensity of scattered beam and wavelength shift amount by a data processor 39, and the measurement position of the above distortion and temperature is detected from the time expansion of the measured scattered beam.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a concrete storage container for storing and managing a radioactive substance which generates heat, a so-called concrete cask, and more particularly to a concrete storage container provided with a monitoring device for monitoring soundness, and a concrete storage container. And a storage system comprising:

[0002]

2. Description of the Related Art Highly radioactive materials typified by spent fuel of a nuclear reactor are dismantled and reprocessed in order to collect useful materials such as plutonium which can be used again as fuel. These spent fuels are stored in a sealed state until reprocessing. As a method for storing such a highly radioactive substance, a wet method using a storage pool or the like, or a dry method using a cask or the like is known.

[0003] The dry method is a storage method in which air is naturally cooled instead of water, and has attracted attention because its operating cost is lower than that of the wet method, and is being developed. There are various types of casks used for the dry process, and concrete casks that shield spent fuel with a concrete structure have attracted special attention because of their low cost. Concrete is excellent as a neutron shielding material, is less expensive than other shielding materials, and has advantages such as obtaining necessary strength as a structure.

[0004] Generally, such a concrete cask is provided with a cylindrical concrete container whose top and bottom are closed, and a cylindrical metal hermetically sealed container filled with spent fuel, a so-called canister, is stored in the concrete container. The arrangement shields radioactive materials from spent fuel. In addition, since concrete itself has low heat transfer characteristics, the concrete cask is provided with a heat removal structure for removing decay heat generated from spent fuel. That is, a gap that functions as a cooling air passage is formed between the inner peripheral surface of the concrete container and the outer surface of the canister, and an intake port is provided at the bottom of the concrete container, and an exhaust port is provided at the top of the container. Each is provided.
Then, the outside air as cooling air introduced into the concrete container from the intake port flows through the cooling air flow path, is naturally convected, and is discharged from the exhaust port, thereby removing heat from the canister and cooling it.

[0005] In the concrete cask constructed as described above, cooling of the spent fuel and the concrete container is ensured by the above-mentioned heat removal structure, radiation shielding by the concrete container, and sealing of the spent fuel by the canister. The concrete cask is required to store highly radioactive substances safely and stably over a long period of time, and is required to have a high radiation shielding performance over a long period of time.

On the other hand, during the storage period, it is necessary to keep the surface temperature of the fuel cladding tube of the spent fuel and the temperature of the concrete container from exceeding a control temperature determined by a predetermined standard. That is, the spent fuel stored in the concrete cask is at a high temperature, and when the concrete is locally heated and exceeds the limit temperature, the strength of the concrete is locally reduced, causing distortion, cracks, and the like. Further, distortion, cracks, and the like may occur in the internal canister and the concrete container due to vibrations caused by an earthquake, collision of falling objects, and the like. If a crack or the like occurs in the concrete container, radiation leaks from that portion, making it difficult to ensure soundness.

[0007]

Therefore, during the storage period,
It is possible to monitor concrete container temperature and distortion, etc., and to detect the temperature rise of concrete container exceeding the control temperature or the distortion of concrete container leading to the occurrence of cracks at an early stage to prevent radiation leakage etc. in advance. Desirable for safety evaluation and security.

As a method of monitoring the temperature, strain, and the like of the concrete container, for example, a method of providing a strain gauge or a thermocouple at a plurality of locations of the concrete container and measuring at a plurality of locations can be considered. However, in this case, only point measurement can be performed at each installation position of the strain gauge and the thermocouple, and in order to perform measurement over a wide range of the concrete container, it is necessary to provide a large number of strain gauges and thermocouples. Therefore, installation and wiring of a strain gauge and a thermocouple are troublesome, and are not desirable in terms of cost.

The present invention has been made in view of the above points, and an object of the present invention is to provide a concrete storage container capable of easily monitoring the temperature, strain, and the like that affect the soundness of the concrete storage container, and to provide the same. Storage system is provided.

[0010]

In order to achieve the above-mentioned object, a concrete storage container according to the present invention is a concrete storage container storing a sealed container in which a radioactive substance is sealed, wherein the storage container stores the closed container. Having a portion inside, a substantially cylindrical container body formed of concrete, and a monitoring device that measures at least one of temperature and strain of the container body, wherein the monitoring device includes:
An optical fiber extending in contact with the concrete wall of the container body, a laser light source for injecting laser light into the optical fiber, and measuring the scattered light generated in the optical fiber, and the container body in contact with the optical fiber And a detector for detecting at least one of strain and temperature in the above.

According to the concrete storage container of the present invention, the detector measures the intensity and the wavelength shift amount of the scattered light generated in the optical fiber and emitted from the emission end of the optical fiber. An analyzer and a data processing device that detects the strain and the temperature from the measured intensity and wavelength shift amount of the scattered light, and detects the measurement position of the strain and the temperature from the time evolution of the measured scattered light,
It has.

Further, according to another concrete storage container according to the present invention, the optical fiber has a diffraction grating provided at an arbitrary position, and the detector detects the laser light reflected by the diffraction grating. A wavelength analyzer that detects reflected light and measures the wavelength shift amount of the reflected light, and a data processing device that detects distortion and temperature of the container body at the position of the diffraction grating from the measured wavelength shift amount. It is characterized by having.

According to another concrete storage container according to the present invention, the optical fiber is provided in contact with the outer surface of the container main body or is embedded in the concrete wall of the container main body.

According to the concrete storage container configured as described above, the monitoring device monitors the distortion and temperature of the container main body during the storage period, thereby controlling the control temperature of the container main body which leads to the generation and damage of cracks. Exceeded temperature rise and strain can be found early. If such a rise in temperature or distortion is found, appropriate repair and inspection of the container body can be performed to prevent damage or cracking of the container body,
It is possible to maintain the safety and soundness of the concrete storage container. Further, the monitoring device can easily measure the strain and the temperature over a wide area of the container body by using one optical fiber. Therefore, the number of wirings can be significantly reduced as compared with the case where a strain gauge or a thermocouple is used, so that the installation is easy and the cost can be reduced.

Further, the storage system according to the present invention has a storage portion for storing the above-mentioned closed container therein, a plurality of substantially cylindrical container bodies formed of concrete, and the temperature and temperature of each container body. And a monitoring device that measures at least one of the distortions,
1 extending in contact with the concrete wall of the plurality of container bodies
This optical fiber, a laser light source that emits laser light from the input end of the optical fiber, and scattered light or reflected light generated in the optical fiber are measured, and distortion and distortion in each container body contacting the optical fiber are measured. And a detector for detecting at least one of the temperatures.

According to the storage system configured as described above, by providing one optical fiber in contact with a plurality of container bodies, at least one of the distortion and the temperature of the plurality of container bodies can be reduced by a single monitoring device. Can be monitored. For this reason, it is possible to easily monitor the occurrence of distortion and excessive temperature rise in each container body, and to reduce the number of monitoring devices to reduce costs.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A concrete cask according to a first embodiment of the present invention will be described below in detail with reference to the drawings.

As shown in FIG. 1, a concrete cask 10 as a storage container made of concrete includes a container body 12 made of concrete and functioning as a shielding structure.
The canister 14 is housed in the container body. The canister 14 has a cylindrical metal sealed container 15 having both ends closed, and inside the metal sealed container,
A plurality of spent fuel assemblies 18 are sealed while being supported by the basket 16. These spent fuel assemblies 18 are, for example, spent fuel of a nuclear reactor, and include radioactive materials that generate heat due to decay heat and generate radiation. The metal sealed container 15 has a welded sealed structure so that the enclosed radioactive substance does not leak outside.

The container body 12 of the concrete cask 10
Has a closed cylindrical shape at the bottom as shown in FIG. 1 and FIG. 2, and is formed, for example, to a height of about 6 m and a diameter of about 4 m, and a concrete wall thickness of about 0.9 m It is formed to the extent. The upper end opening of the container body 12 is closed by a concrete lid 20 whose outer surface is covered with a carbon steel plate. The lid 20 is provided with a plurality of bolts 21
Is bolted to the upper end of the container body 12. In addition, the inside of the concrete wall of the container main body 12 is provided with reinforcing bars (not shown).

In the container main body 12, a cylindrical storage portion 22 is defined by the inner peripheral surface of the container main body and the lid 20. The canister 14 is housed in the housing 22. That is, the canister 14 is
It is placed on a plurality of ribs 31 formed on the bottom surface of the container 2 and is coaxially arranged with the container body 12.
The canister 14 is housed in the housing 22 with a predetermined gap, for example, about 10 cm, between the outer peripheral surface and the inner peripheral surface of the container body 12.

A cooling air passage 24 through which cooling air flows is formed by the gap between the outer peripheral surface of the canister 14 and the inner peripheral surface of the container body 12. The cooling air flow path 24 extends over the entire outer peripheral surface of the
Further, it is formed over the entire axial length of the outer peripheral surface.

A plurality of, for example, four intake ports 26 are formed at the bottom of the container body 12, and four exhaust ports 28 are formed at the upper end of the container body 12, each of which communicates with the cooling air flow path 24. are doing. The four air inlets 26 are provided at equal intervals along the circumferential direction of the container main body 12, and open at the bottom outer peripheral surface of the container main body 12. Also,
The exhaust ports 28 are provided at equal intervals along the circumferential direction of the container body 12 and open to the outer peripheral surface of the upper end of the container body 12. In addition, these exhaust ports 28 are defined by the upper end edge of the container body 12 and the lid 20.

The intake port 26, the exhaust port 28, and the cooling air flow path 24 constitute a heat removal section of the concrete cask 10. That is, the outside air as the cooling air introduced into the container body 12 from the intake port 26 flows around the canister 14 through the cooling air flow path 24, and during that time, removes heat and cools the canister 14 and the container body 12. Then, the cooling air heated and heated by the heat from the canister 14 is discharged from the exhaust port 28 to the outside of the container body 12.

A cylindrical liner 30 made of a metal such as carbon steel is provided on the inner peripheral surface of the container body 12. The liner 30 made of metal has a higher heat conductivity than concrete, promotes the transfer of heat generated from the spent fuel assembly 18, and emits radiation, mainly γ-rays, from the spent fuel assembly 18. It has the function of shielding.

On the other hand, the concrete cask 10 has a monitoring device 32 for detecting and monitoring the strain and the temperature of the concrete wall constituting the container body 10. As shown in FIGS. 1 and 2, the monitoring device 32 is
An optical fiber 34 provided in contact with a concrete wall of the optical fiber, a laser light source 36 connected to the input end of the optical fiber.
And a wavelength analyzer (SCA) 38 connected to the optical directional coupler 37 for inputting the pulsed laser light emitted from the optical fiber to the optical fiber. The wavelength analyzer 38 receives the backscattered light generated in the optical fiber and emitted from the input end of the optical fiber via the optical directional coupler 37, and detects and analyzes the backscattered light. The wavelength analyzer 38 is connected to a data processing device 39 and a monitor 40 for displaying a detection result. Note that the wavelength analyzer 38 and the data processing device 39 constitute a detector according to the present invention.

As the optical fiber 34, a pure silica core fiber, a fluorine-doped silica core fiber or the like having excellent radiation resistance is used. According to the present embodiment, the optical fiber 34 is spirally wound around the outer peripheral surface of the peripheral wall of the container body 12 at a predetermined pitch. In this case, a spiral groove may be formed on the outer peripheral surface of the container body 12, and the optical fiber 34 may be wound in the groove.

According to the concrete cask 10 configured as described above, the strain and temperature of the container body 12 are constantly monitored by the monitoring device 32 during the storage period of the canister 14. That is, the monitoring device 32 transmits the pulsed laser light from the laser light source 36 through the optical directional coupler 37 to the optical fiber 34.
And the laser light incident on the optical fiber propagates through the optical fiber along the outer peripheral surface of the container body 12. At this time, the backscattered light generated in the optical fiber 34 exits from the input end of the optical fiber and is sent to the wavelength analyzer 38 via the optical directional coupler 37.

The wavelength analyzer 38 detects and analyzes the input backscattered light and monitors the occurrence of distortion in the container body 12 and the occurrence of a high-temperature portion exceeding the control temperature.
That is, when a strain or a high-temperature portion occurs in a certain portion of the container main body 12, backscattering light specific to laser light passing through the optical fiber 34 close to this portion is generated, and the wavelength analyzer 38 generates the backscattering light. The intensity and the wavelength shift amount are measured. Then, the data processing device 39 includes a wavelength analyzer 38.
The magnitude of the distortion and the temperature are detected from the intensity of the backscattered light and the wavelength shift amount measured in step (1). At the same time, from the time evolution of the backscattered light, the position where the distortion has occurred and the position of the high-temperature portion can be specified.

The measurement accuracy of the monitoring device 32 is as follows: strain ± 0.1 mm, temperature ± 0.1 ° C., position accuracy 10-30.
cm.

According to the concrete cask 10 configured as described above, the monitoring device 32 monitors the strain and the temperature of the container body 12 during the storage period,
A temperature rise exceeding the control temperature of the container body 12 and a strain leading to crack generation and damage can be found at an early stage. When such a rise in temperature or distortion is found, the container body 12 is properly repaired and inspected to prevent damage to the container body or cracks, and to prevent radiation leakage in advance. can do. Therefore, a concrete storage container excellent in safety and soundness can be obtained.

Further, according to the monitoring device 32, the strain and the temperature can be measured over a wide area of the container body 12 with one optical fiber 34, and compared with the case where a strain gauge or a thermocouple is used. Wiring can be greatly reduced, installation is easy, and cost can be reduced. Further, the continuous distribution of strain and temperature along the optical fiber 34 can be easily measured.

Next, a concrete cask according to another embodiment of the present invention will be described. In the other embodiments described below, the same parts as those in the first embodiment are denoted by the same reference numerals, detailed description thereof will be omitted, and different parts will be described in detail. .

According to the second embodiment shown in FIG. 3, as the monitoring device 32 of the concrete cask 10, a monitoring device based on the fiber Bragg grating (FBG) method is used. According to this monitoring device 32,
The optical fiber 34 has a plurality of diffraction gratings 33 provided at predetermined intervals. Of the pulsed laser light that has entered the optical fiber 34 from the laser light source 36 via the optical directional coupler 37, only light having a wavelength that meets the Bragg reflection conditions is reflected by the diffraction grating 33, and the wavelength of the reflected light The shift amount is measured by the wavelength analyzer 38. The measured wavelength shift amount is subjected to arithmetic processing by the data processing device 39, whereby the magnitude of the distortion generated in the container body 12 and the temperature can be detected. The measurement accuracy of the monitoring device 32 is as follows: strain ± 0.1 mm, temperature ± 0.1 ° C., and position accuracy of about 10 to 30 cm.
In the concrete cask 10 including the monitoring device 32 as described above, the same operation and effect as those of the first embodiment can be obtained.

In the above embodiment, the monitoring device 3
Although the second optical fiber 34 is provided on the outer peripheral surface of the container body 12, the optical fiber 34 is embedded in the concrete wall of the container body 12 as in the third embodiment shown in FIG. Thus, it may be spirally arranged outside the canister 14. In the concrete cask 10 configured as described above, the same operation and effect as those of the above-described first embodiment can be obtained. In addition, the optical fiber 3
By embedding 4 in a concrete wall, the distortion and temperature of the container body 12 can be measured more accurately.

The optical fiber 24 of the monitoring device 32
The present invention is not limited to the spiral shape, and may be provided so as to extend along the axial direction of the container body 12 as in the fourth embodiment shown in FIG.

The measuring range of the optical fiber 34 is several km.
And can be set very long. Therefore, as shown in FIG. 6, a single optical fiber 34 is wound around the container main bodies 12 of the plurality of concrete casks 10, and the plurality of container main bodies 12 is monitored by the single monitoring device 32. Can be configured. According to such a storage system, similarly to the first embodiment described above, it is possible to easily monitor the occurrence of distortion and excessive temperature rise in each container main body 12, and in addition, a plurality of container main bodies 12 Twelve strains and temperatures can be monitored by a single monitoring device 32, and the number of monitoring devices can be reduced to reduce costs.

In addition, the present invention is not limited to the above-described embodiment, but can be variously modified within the scope of the present invention. For example, in the above-described embodiment, one monitoring device is provided for one container body 12, but a plurality of optical fibers 34 are installed in one container body, and It may be configured to monitor the strain and the temperature of the laser beam. The wall thickness of the concrete wall constituting the container body 12, the plate thickness of the liner, and the material and shape of each component can be variously modified as necessary.

[0038]

As described above in detail, according to the present invention, the strain and temperature of the container main body can be easily monitored by the monitoring device having the optical fiber provided in contact with the concrete container main body. It is possible to provide a concrete storage container capable of maintaining its integrity and soundness over a long period of time, and a storage system including the same.

[Brief description of the drawings]

FIG. 1 is a partially cutaway perspective view showing a concrete cask according to a first embodiment of the present invention.

FIG. 2 is a longitudinal sectional view of the concrete cask.

FIG. 3 is a perspective view showing a concrete cask according to a second embodiment of the present invention.

FIG. 4 is a sectional view showing a concrete cask according to a third embodiment of the present invention.

FIG. 5 is a perspective view showing a concrete cask according to a fourth embodiment of the present invention.

FIG. 6 is a perspective view showing a storage system according to the embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Concrete cax 12 ... Container main body 14 ... Canister 18 ... Spent fuel assembly 20 ... Lid 22 ... Storage part 24 ... Cooling air flow path 26 ... Intake port 28 ... Exhaust port 30 ... Liner 32 ... Monitoring device 34 ... Light Fiber 36 ... Laser light source 38 ... Wavelength analyzer

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Kenichi Matsunaga 1-1-1 Wadazakicho, Hyogo-ku, Hyogo-ku, Kobe-shi, Hyogo Mitsubishi Heavy Industries, Ltd. 1-1-1 Tazakicho Mitsubishi Heavy Industries, Ltd., Kobe Shipyard

Claims (10)

[Claims] 1. A concrete storage container containing a closed container in which a radioactive substance is sealed, the container having a storage portion for storing the closed container therein, and a substantially cylindrical container body formed of concrete; A monitoring device for measuring at least one of temperature and strain of the container body, wherein the monitoring device includes: an optical fiber extending in contact with a concrete wall of the container body; and a laser light source for injecting laser light into the optical fiber. And a detector that measures scattered light generated in the optical fiber and detects at least one of strain and temperature in the container body that is in contact with the optical fiber. . 2. A wavelength analyzer for measuring the intensity and wavelength shift of scattered light generated in the optical fiber and emitted from the optical fiber, and a detector for measuring the intensity and wavelength shift of the measured scattered light. 2. A concrete storage device according to claim 1, further comprising: a data processing device that detects strain and temperature from the data and detects the measurement position of the strain and temperature from the time evolution of the measured scattered light. container. 3. The optical fiber has a diffraction grating provided at an arbitrary position. The detector detects reflected light of the laser light reflected by the diffraction grating, and shifts the wavelength of the reflected light. 2. A wavelength analyzer for measuring the wavelength shift amount, and a data processing device for detecting distortion and temperature of the container main body at the position of the diffraction grating from the measured wavelength shift amount. Concrete storage container. 4. The concrete storage container according to claim 1, wherein the optical fiber is provided in contact with an outer surface of the container main body. 5. The concrete storage container according to claim 1, wherein the optical fiber is embedded in a concrete wall of the container body. 6. The concrete storage container according to claim 4, wherein the optical fiber is spirally wound. 7. The concrete storage container according to claim 4, wherein the optical fiber extends substantially linearly along the axial direction of the container main body. 8. A storage system for storing a plurality of hermetically sealed containers in which radioactive substances are sealed, the storage system having a storage portion for storing each of the hermetically sealed containers therein,
A plurality of substantially cylindrical container bodies formed of concrete, and a monitoring device for measuring at least one of the temperature and the strain of each of the container bodies, the monitoring device is provided on a concrete wall of the plurality of container bodies. A single optical fiber extending in contact therewith, a laser light source for emitting laser light from the incident end of the optical fiber, and scattered or reflected light generated in the optical fiber, and A detector for detecting at least one of strain and temperature in the container body. 9. The storage system according to claim 8, wherein the optical fiber is provided in contact with an outer surface of each of the container bodies. 10. The storage system according to claim 8, wherein said optical fiber is embedded in a concrete wall of each of said container bodies.