JP4567839B2 - Radioactive material storage equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
TECHNICAL FIELD The present invention relates to a radioactive substance storage facility such as a radioactive object storage container and a radioactive shielding structure for shielding radiation emitted from a sealed body sealed with a radioactive substance, and in particular, suppresses deterioration of the shield due to heat and external atmospheric conditions. The present invention relates to a radioactive material storage facility having excellent durability.
[0002]
[Prior art]
There are plans to disassemble spent fuel assemblies generated from nuclear power plants and reprocess them to recover useful materials that can be used again as fuel, such as plutonium. Conventionally, such spent fuel has been primarily stored in the fuel assembly pool of the nuclear reactor until reprocessing, but the capacity of storage facilities such as the pool is increased by the spent fuel that increases year by year. May reach the limit. Therefore, there is a need for equipment that can store spent fuel for a long period of time in a safe, inexpensive, and removable state until reprocessing.
[0003]
Development of a dry method for natural cooling by air as such equipment has been promoted, and attention is paid to the fact that the operation cost is lower than that of a pool.
The dry method is roughly classified into two methods, a method using a welded sealed metal container (hereinafter referred to as a canister) and a metal cask method similar to a transport canister. The canister method can be further divided into a vault method in which a large number of canisters are shielded by one storage facility, and a silo or concrete cask method in which one canister is shielded by one concrete structure. Each method has advantages and disadvantages, but in recent years, the concrete cask method has attracted attention because of its low cost.
5 and 6 show schematic cross-sectional views in the horizontal and vertical directions of a concrete module used in a conventional concrete cask method.
[0004]
The concrete module 30 basically includes a canister 31 and a concrete shield 32. The canister 31 has a welded and sealed structure in which a plurality of spent fuel assemblies are enclosed. The canister 31 has a structure in which the enclosed radioactive material does not leak to the outside, and is formed in a cylindrical shape. The canister 31 is loaded in a cylindrical concrete shield 32. A constant gap that forms a cooling air flow path 33 is provided between the canister 31 and the shield 32. In order to introduce external air into the cooling air channel 33, a cooling air inlet 34 is provided on the bottom side of the shield 32, and a cooling air outlet 35 is provided on the upper side of the shield 32. Further, a metal liner 36 is provided on the inner surface of the cooling air passage 33 of the shield 32.
[0005]
Usually, spent fuel is accompanied by heat generation and radiation associated with decay heat. Therefore, the concrete module 30 needs to cool spent fuel, shield radiation, and seal radioactive materials. In the concrete cask method, the cooling is air flowing through the cooling air flow path 33 between the canister 31 and the shield 32, the shield is secured by the shield 32, and the sealing is secured by the canister 31. Further, the strength of the concrete module 30 is also secured by the shield 32. Here, the radioactive material does not leak to the outside when sealed, the radiation dose inside or outside the storage facility is below the standard value stipulated by the law for shielding, and the surface of the canister is stored during the storage period for cooling. It is required that the temperature and the temperature of the concrete shield 32 do not adversely affect the properties of the canister and concrete.
[0006]
By the way, in the conventional concrete shield, the outer surface is at room temperature, but the inner surface becomes high temperature due to decay heat from the spent fuel, and the temperature difference between the inner and outer surfaces increases, resulting in thermal stress (compression at the inner periphery). Stress, tensile stress at the outer peripheral portion), and the tensile stress at the outer peripheral portion is often larger than the tensile strength of the concrete, which causes cracks at the outer peripheral portion. If excessive temperature cracks occur in the concrete shield, if there is no sealing material covering the outer surface, moisture and salt can easily enter through the cracks. There is a concern that the durability and shielding performance of the shield body will be lowered. In addition, when temperature cracks occur excessively, there is a concern about the deterioration of the structural integrity of the concrete shield, and as a result, there is a problem that durability and radiation shielding performance are deteriorated and become unsuitable for use. there were.
[0007]
In order to prevent the influence of the cracks due to heat, for example, there is a method of canceling the tensile force due to thermal stress by introducing prestressed as a known technique. Japanese Patent Application Laid-Open Nos. 7-27897 and 8-43591 disclose a structure in which a heat shield plate or further a heat pipe is disposed between a canister or its metal liner and a shield. In such a structure, the prestress introduction method is technically possible, but it is expensive, and it is expected that the increase in the internal temperature of the concrete shield will be suppressed to some extent by providing a heat shield and heat pipe. However, it is difficult to prevent cracks that occur on the outer surface of the concrete shield due to the temperature difference between the inner and outer surfaces and drying shrinkage of the concrete, and the deterioration of the concrete that progresses from the surface (neutralization, infiltration of salt, etc.). Furthermore, there was a problem of high cost.
For this reason, a radiation material storage facility that is low in cost and does not deteriorate in durability and shielding performance over a long period of time has been desired.
[0008]
[Problems to be solved by the invention]
The present invention has been made in view of such a background, and is due to the temperature difference between the inner and outer surfaces of the concrete shield and the temperature rise of the inner metal liner or inner steel plate due to the radiant heat generated from the sealed body of radioactive material. An object of the present invention is to provide a radiation material storage facility capable of preventing the occurrence of temperature cracks due to thermal stress and maintaining the durability and radiation shielding ability of a concrete shield for a long period of time.
[0009]
[Means for Solving the Problems]
As a result of intensive studies, the present inventors have provided a slit having a specific shape, which will be described later, capable of absorbing deformation due to an increase in the inner surface temperature in a part of the concrete shield , and the slit is more rigid than concrete. small material for radiation shielding in Rukoto be filled with a, it found that can solve the above problems, and completed the present invention.
That is, the radioactive substance storage facility of the present invention surrounds the outside of the sealing body sealed with the radioactive substance with a cylindrical concrete shield, and provides an air inflow space between the sealing body and the shield. In a radioactive material storage facility for removing heat generated by a radioactive material by air flowing in an inflow space, the inner periphery of the cylindrical concrete shield is covered with a metal liner or an inner steel plate, and the metal liner or directed from the inner surface steel sheet on the outer peripheral surface from said cylindrical concrete shielding body circumferential surface, and a cylindrical name a concrete shield is provided a slit does not penetrate is, the forming the cylindrical-shaped concrete shield The slit is filled with a radiation shielding substance having a rigidity lower than that of concrete .
[0010]
The slit formed in such a cylindrical concrete shield is preferably filled with a radiation shielding material having a rigidity lower than that of concrete, and the radiation shielding material is liquid or gel-like. A material having fluidity is preferable from the viewpoint of handling properties. When such a liquid radiation shielding material is used, the heat of the concrete shield is prevented in order to prevent the material from leaking inside. It is preferable to form a recess for holding the liquid substance inside the slit during deformation.
[0011]
Usually, the inner surface temperature of the concrete shield rises due to the radiant heat generated from the sealed body of radioactive material, due to the temperature difference between the inner and outer surfaces of the shield and the temperature rise of the metal liner or inner steel plate attached to the inner surface of the shield, Tensile stress is generated in the concrete shield. This tensile stress often exceeds the tensile strength of concrete, and it is inevitable that temperature cracks due to thermal stress occur inside the concrete shield starting from the outer surface of the concrete shield.
According to the present invention, the inner peripheral portion of the cylindrical concrete shield of the radioactive substance storage facility is covered with a metal liner or an inner steel plate, and continuously from these covers to a part of the concrete shield. By forming a slit from the peripheral surface of the cylindrical concrete shield to the outer peripheral surface and not penetrating the cylindrical concrete shield, deformation due to a temperature difference of the outer surface of the concrete shield can be absorbed. It is possible to effectively prevent the occurrence of cracks starting from an undesired outer peripheral surface.
In the present invention, further, by filling the slit with a radiation shielding substance having a low rigidity, it is possible to ensure the radiation shielding performance at the slit forming portion without reducing the crack prevention effect against thermal deformation. it can.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is described in detail below.
In the radioactive substance storage facility of the present invention, the outside of the sealing body sealed with the radioactive substance is surrounded by a concrete shielding body, an air inflow space is provided between the sealing body and the shielding body, and the inside of the air inflow space is formed. A structure that removes the heat generated by radioactive material by flowing air, but has a thick cylindrical concrete shield that goes from the inner peripheral surface to the outer peripheral surface and does not penetrate the cylindrical concrete shield. In addition, a slit is also provided in a metal liner or an inner steel plate disposed on the inner surface of the concrete shield, and a mechanism for absorbing thermal deformation of the concrete shield when the canister is loaded is used. It is characterized by preventing temperature cracking.
[0013]
Such slits may be provided in one or more places in the circumferential direction, and are necessary in consideration of conditions such as the size of equipment, the material of the concrete shield, and the thickness of the cylindrical part. However, in the case where slits are provided at a plurality of locations, in principle, it is preferable to provide the circumference so as to be equally divided.
This slit is thermally deformed when the canister is loaded, that is, the thermal expansion of the shape and the material so that the slit is closed without gaps when the concrete shield is thermally expanded. The radiation shielding performance at the time of thermal deformation is also ensured by designing in consideration of the rate and temperature conditions.
For example, when the inner radius (r) of the concrete shield is about 1000 mm and the rise in inner surface temperature (ΔT) is about 60 ° C., the linear expansion coefficient α (1 × 10 ⁻⁵ / ° C.) is used to The change in the length of is obtained by the following equation.
Δl = 2π ・ R ・ αΔT
If the above numerical value is applied to this equation, Δl = 2 × 1000 × 10 ⁻⁵ × 60 × π = 3.8 (mm), which is a change (expansion) in length on the inner peripheral surface of the concrete shield. Therefore, the slit width on the inner peripheral surface necessary to absorb this expansion is about 3.8 mm.
[0014]
In the present invention, when the canister is loaded, an appropriate substance for radiation shielding having a rigidity lower than that of concrete is provided in the slit for the purpose of ensuring radiation shielding performance until the slit is completely closed by thermal deformation. you filling. Examples of such a substance include coal tar.
In addition, as a filling material for radiation shielding, for example, when filling a fluid material such as liquid or gel material such as coal tar, a concrete shielding body is provided by providing a recess in a part of the slit. It is desirable to provide a mechanism that guides and holds these substances inside the shield during heat deformation of the concrete so as not to leak into the inner surface of the concrete shield. For example, the aspect which provides the recessed part 17a in the intermediate part of a slit as shown in FIG. 1 is mentioned. As the temperature rises, the fluidity of the coal tar filled inside increases, and the slit narrows and coal tar is guided to the inside. When the slit is closed, the coal tar is held in the recess 17a.
[0015]
A metal liner or an inner steel plate is attached to the inner peripheral surface of the concrete shield. A general metal liner can be used. Moreover, as a material for the inner surface steel plate, generally, a structural rolled steel material defined in JIS G3101 and JIS G3106 can be suitably used. The thickness of the metal liner or the inner steel plate is not particularly limited and is appropriately selected depending on the required strength, but is generally about 5 to 20 mm, and more preferably about 10 mm. Moreover, it is preferable that the inner surface steel plate is subjected to a rust prevention treatment such as rust prevention coating for the purpose of improving durability.
[0016]
In order to ensure strength, the concrete shield is preferably constructed with a reinforced concrete structure or with a structure in which the concrete surface is covered with a steel plate. When the concrete shield is covered with a steel plate, it may be constructed of a steel plate concrete structure in which the steel plate is integrated with a steel plate by forming a stopper such as a headed stud. Such a steel-concrete concrete structure is described in detail in the specification of Japanese Patent Application No. 2000-36834 previously proposed by the present inventors.
[0017]
When constructing a concrete shield with a reinforced concrete structure, the slit length is shorter than the distance between the outer circumferential reinforcing bar and the inner wall of the thick cylindrical wall, and the outer circumferential reinforcing bar is continuously arranged in the circumferential direction. In addition, the inner circumferential reinforcing bar does not penetrate the slit portion and is fixed in the concrete shield body by bending or the like, thereby having a thermal deformation absorption mechanism while securing the structural integrity of the concrete shield body to the necessary degree. A concrete shield can be constructed.
[0018]
When constructing a concrete shield with a steel plate concrete structure, slits are provided in the inner steel plate, but the outer steel plate has a continuous structure in the circumferential direction to ensure the necessary structural integrity of the concrete shield. On the other hand, a concrete shield having a thermal deformation absorbing mechanism can be constructed.
[0019]
In addition, in order to suppress the temperature rise of the metal liner or inner steel plate and the concrete shield, and prevent deterioration due to the high temperature of the concrete shield near the inner surface, if necessary, for example, on the surface of the metal liner or inner steel plate A ceramic heat insulating material may be attached.
[0020]
Hereinafter, the present invention will be specifically described with reference to the drawings.
In FIG. 1, the radioactive substance storage facility 10 according to the first embodiment of the present invention, that is, an embodiment in which a concrete shield is constructed of reinforced concrete, and a slit for absorbing thermal deformation is provided in the cylindrical portion of the shield. The schematic plan view of is shown. FIG. 2 is a schematic elevational sectional view thereof.
The radioactive substance storage facility 10 includes a canister 11 and a concrete shield 12. The canister 11 has a cylindrical shape, and a radioactive substance is sealed inside.
[0021]
The concrete shield 12 includes a reinforced concrete cylindrical portion 12a having a metal liner 13 on the inner surface, a thick disc 12b that supports the cylindrical portion 12a, and an upper lid 12c of a canister loading / unloading port.
A gap between the inner diameter of the shield 12 and the outer diameter of the canister 11 functions as a cooling air flow path 14.
Under the shield 12, one or a plurality of cooling air passages 15 for communicating the outside of the shield with the cooling air passages 14 are formed. The inlet side cooling air flow path 15 includes a first horizontal portion formed horizontally on the outside, a vertical portion extending upward from an inner end portion of the first horizontal portion, and an inner side from an upper end portion of the vertical portion. It is comprised from the 2nd horizontal part extended to. The upper surface of the first horizontal portion is located on the same plane as the lower surface of the second horizontal portion or below the lower surface of the second horizontal portion, so that the radiation passing through the second horizontal portion is reflected by the wall surface of the bent portion. So that it does not leak outside. Each horizontal portion may be inclined upward as it goes inward.
A plurality of projections (not shown) are formed inside the cooling air channel 15 on the inlet side of the shield 12, and the canister 11 is supported by the shield 12 by these projections.
[0022]
Further, a cooling air flow path (outlet side) 16 is formed at a position facing the cooling air flow path (inlet side) 15 formed on the lower side of the shielding body at the upper part of the shielding body 12. The cooling air flow path (exit side) 16 has a first horizontal portion formed horizontally inside, a vertical portion extending upward from an outer end portion of the first horizontal portion, and horizontally extending from an upper end portion of the vertical portion to the outer side. It is comprised from the 2nd horizontal part extended to. The upper surface of the first horizontal portion is located on the same plane as the lower surface of the second horizontal portion or below the lower surface of the second horizontal portion, so that the radiation passing through the first horizontal portion is reflected by the wall surface of the bent portion. So that it does not leak outside. Each horizontal portion may be inclined upward as it goes outward.
A metal liner 13 is attached inside the cooling air flow path (inlet) 15 and the cooling air flow path (outlet side) 16.
[0023]
Cooling air is introduced from the cooling air flow path (inlet) 15 to the lower side of the shield, cools the canister 11 loaded in the shield 12 when passing through the cooling air flow path 14, and is shielded by natural convection. The body is raised and exhausted from the cooling air flow path (exit side) 16. In this process, decay heat emitted from the radioactive material in the canister 11 is discharged to the outside by natural convection of air passing through the cooling air flow path 14, and part of the decay heat is a metal liner of the concrete shield 12. 13 and through a metal liner to the concrete.
[0024]
The slit 17 of the concrete shield 12 is formed so as to narrow its width outward from the inside of the cylindrical portion 12a in order to absorb thermal deformation due to the temperature gradient generated in the shield cylindrical portion 12a due to the decay heat of such radioactive substances. In addition, it is necessary and sufficient to absorb the thermal deformation of the cylindrical part when using radioactive material storage equipment, such as widening upward from the bottom considering the temperature difference generated in the vertical direction of the cylindrical part due to natural convection of cooling air As a general rule, shape and dimensions.
[0025]
In the illustrated embodiment, an example is shown in which one slit 17 is provided in the cylindrical portion 12a. However, the present invention is not limited to this, and a plurality of slits 17 may be provided as necessary. It is desirable to arrange the slits 17 so that the circumference is roughly equally divided.
Further, a heat insulating material layer can be provided inside the metal liner 13 as desired.
[0026]
Further, in order to ensure the shielding performance immediately after the canister 11 is loaded and until the slit 17 is completely closed due to thermal deformation of the cylindrical portion 12a, the slit 17 portion is prefilled with a radiation shielding material such as fluid or gel. At the time of thermal deformation of the part, it is desirable to provide a mechanism for guiding this to a discharge groove provided in the slit or a holding recess (exemplified as the aforementioned 17a) and holding it inside or discharging it outside.
[0027]
In the case of constructing a shield of reinforced concrete structure as in this embodiment, in order to ensure the necessary integrity of the cylindrical portion 12a, the slit 17 is stopped inside the position of the reinforcing bar (outer reinforcing bar) 18 arranged outside, The reinforcing bar 18 is continuously arranged in the circumferential direction, but the inner peripheral reinforcing bar 19 is divided in the same direction at the slit portion, and the end portion is bent to fix the cylindrical portion concrete. It is preferable from the viewpoint of securing.
[0028]
As another embodiment, FIG. 3 shows an example (Example 2) in which a concrete shield is constructed of steel plate concrete and a cylindrical portion inner surface steel plate and a slit for absorbing thermal deformation are provided inside the concrete. FIG. 4 is a schematic vertical sectional view thereof. The cooling method for decay heat generated from the radioactive material in the canister 11 and the method for supporting the canister are the same as those in the first embodiment.
[0029]
The concrete shield 12 includes steel plates 20a and 20b attached to the outer peripheral surface of the inner peripheral surface of the cylindrical portion, a cylindrical inner concrete bowl 12a, a thick disc 12b that supports the cylindrical portion 12a, and a canister loading / unloading port. It is comprised from the upper cover 12c. The steel plates 20a and 20b and the concrete are integrated by a stopper 21 such as a headed stud provided on the steel plates 20a and 20b. The formation method and structure of the cooling air flow path on the inlet side and the outlet side are the same as in the first embodiment.
The cylindrical inner steel plate 20a is provided with a slit 17 for absorbing thermal deformation of the inner steel plate 20a, but the outer steel plate 20b is not provided with the slit 17. The method for forming the slit 17 and the method for securing the shielding performance until the slit 17 is closed due to thermal deformation of the concrete shield 12 are the same as in the first embodiment.
[0030]
As concrete which comprises the shielding body of this invention, a well-known thing can be used suitably, As the manufacturing method, for example, cement and a fine aggregate and coarse aggregate are thrown into a mixer sequentially, for several seconds. After empty kneading, if necessary, an additive such as a cement dispersant or a water reducing agent is added with water and kneaded, and the paste-like concrete composition thus obtained is placed in a mold and manufactured. Can be mentioned.
[0031]
Here, as usable cement, various mixed cements such as blast furnace cement, fly ash cement, and silica fume cement can be used in addition to various portland cements such as ordinary cement, early-strength cement, and moderately hot portland cement.
Further, if necessary, inorganic powders such as blast furnace slag fine powder, meteorite powder, limestone powder, and silica fume fine powder can be added to these cements within a range not impairing the effects of the present invention. .
[0032]
【The invention's effect】
According to the present invention, there is provided a radioactive material storage facility that prevents temperature cracks caused by the temperature difference between the inner and outer surfaces of a concrete shield and the temperature rise of a metal liner or inner steel plate, and has excellent durability and shielding performance. Can do.
[Brief description of the drawings]
FIG. 1 is a schematic plan view of a radioactive substance storage facility according to a first embodiment of the present invention.
FIG. 2 is a schematic cross-sectional view in the vertical direction of the radioactive substance storage facility of FIG.
FIG. 3 is a schematic plan view of a radioactive substance storage facility according to a second embodiment in which the shield is a steel-concrete structure.
FIG. 4 is a schematic sectional view in the vertical direction of the radioactive substance storage facility of FIG. 3;
FIG. 5 is a schematic sectional view in the horizontal direction of a conventional radioactive substance storage facility.
6 shows a schematic cross-sectional view in the vertical direction of the radioactive substance storage facility of FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Radioactive material storage equipment 11 Canister 12 Shielding body 12a Shielding body cylindrical part 12b Thick disk 12c which supports the shielding body cylindrical part Upper cover 13 of shielding body Metal liner 14 Gap (cooling air flow path)
15 Cooling air flow path 16 on the inlet side Cooling air flow path 17 on the outlet side Slit 17a Recess 18 formed in the slit Reinforcing bars arranged on the outside (peripheral reinforcing bars)
19 Inner Reinforcement Bar 20a Inner Steel Bar (Surface Steel Bar)
20b outer peripheral steel plate (surface steel plate)
21 Stud with head
20 Insulation layer

Claims (2)

The outside of the sealing body sealed with the radioactive material is surrounded by a cylindrical concrete shield, an air inflow space is provided between the sealing body and the shielding body, and the radioactive material is caused by the air flowing inside the air inflow space. in the radioactive substance storage facility for removing heat generated, the inner circumference of the cylindrical-shaped concrete shield covered with a metallic liner or inner surface steel sheet, said cylindrical concrete shielding body from the metallic liner or inner surface steel plate toward the outer peripheral surface than the peripheral surface, and, Ri Na with slits that do not pass through the cylindrical concrete shield, in said slit formed in said cylindrical in concrete shield, small rigidity as compared with concrete A radioactive substance storage facility filled with a radiation shielding substance. The radiation shielding material to be filled in the slit formed in the concrete shield is a liquid or gel-like material, and the radiation shielding material is applied to the heat of the concrete shield in a part of the slit. The radioactive substance storage facility according to claim 1 , wherein a concave portion is formed to be held inside during deformation.

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