JP2000284094A - Radioactive material storage facility - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the temperature difference between the inner and the outer surfaces of a shield body. SOLUTION: A concrete module 10 is provided with a canister 12 and a shield body 14. Between the shield body 14 and the canister 12, a gap is formed and in the shield body 14, a first cooling air path 34 and a second cooling air path 42 are formed. Also, a closed cylindrical air layer 50 is formed in the shield body 14 and this air layer 50 reduces the temperature difference between the inner and the outer surfaces of the concrete body 26.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radioactive substance storage facility for shielding radiation emitted from a sealed body containing a radioactive substance.

[0002]

2. Description of the Related Art There is a plan to disassemble a spent fuel assembly generated from a nuclear power plant and to reprocess it to collect useful substances such as plutonium that can be reused as fuel. Conventionally, such spent fuel has been temporarily stored in a fuel assembly pool or the like of a nuclear reactor until the spent fuel is reprocessed. May reach its limit. Therefore, there is a need for a facility capable of storing spent fuel for a long time in a safe, inexpensive and removable state until reprocessing.

[0003] As such equipment, development of a dry method for performing natural cooling by air has been promoted, and attention has been paid to the fact that the operating cost is lower than that of a pool.

[0004] 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 system is further classified into a vault system in which many canisters are shielded by one storage facility, and a silo or concrete cask system in which one canister is shielded by one concrete structure. Although each method has advantages and disadvantages, the concrete cask method has recently attracted attention in the United States because of its low cost. FIG.
FIG. 11 shows a concrete module used in a conventional concrete cask system.

[0005] The concrete module 1 basically comprises a canister 2 and a concrete shield 3. The canister 2 has a welded and sealed structure in which a plurality of spent fuel assemblies are sealed, and has a structure in which a radioactive substance inside the sealed fuel does not leak to the outside, and is formed in a cylindrical shape.
The canister 2 is a cylindrical concrete shield 3.
Loaded inside. A fixed gap forming a cooling air flow path 4 is provided between the canister 2 and the shield 3. In order to introduce external air into the cooling air passage 4, a cooling air inlet 5 is provided on the bottom side of the shield 3,
A cooling air outlet 6 is provided on the upper side of the shield 3. A metal liner 7 is provided on the inner surface of the cooling air passage 4 of the shield 3.

[0006] Usually, the spent fuel is accompanied by heat generation and radiation due to decay heat. Therefore, in this concrete module 1, it is necessary to cool spent fuel, shield radiation, and seal radioactive materials. In the concrete cask system, cooling is performed by air flowing through the cooling air flow path 4 between the canister 2 and the shield 3, the shield is secured by the shield 3, and the seal is secured by the canister 2. The strength of the concrete module 1 is also ensured by the shield 3. Here, the radioactive material must not leak to the outside when sealed, the radiation dose inside and outside the storage facility must be lower than the legally stipulated reference value for shielding, and the surface of the canister during the storage period must be cooled for cooling. It is required that the temperature of the concrete shield 3 should not adversely affect the properties of the canister and concrete.

[0007]

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 becomes large. , Thermal stress (compressive stress inside, tensile stress outside) acts, the tensile stress at the outer periphery often becomes larger than the tensile strength of concrete, so if cracks occur outside, radiation shielding of the shield Performance decreases.

The present invention has been made in view of such a background, and provides a radioactive substance storage facility capable of reducing the occurrence of cracks in concrete and maintaining the radiation shielding ability of a concrete shield for a long period of time. The purpose is to do.

[0009]

SUMMARY OF THE INVENTION According to the present invention, a concrete shield is provided around the outside of a hermetically sealed body containing a radioactive substance.
An air inflow space is provided between the sealing body and the shield, and in a radioactive substance storage facility for removing heat generated by the radioactive substance due to air flowing inside the air inflow space, a hermetic seal is provided inside the shield. An air layer is provided.

Further, according to the present invention, the outside of a sealed body in which a radioactive substance is sealed is surrounded by a concrete shield, an air inflow space is provided between the seal and the shield, and the inside of the air inflow space is provided. In a radioactive substance storage facility for removing heat generated by a radioactive substance due to flowing air, a ventilation path through which air flows in and out is provided inside the shield.
In the present invention, it is preferable that the wall surface of the ventilation path and the inner surface of the shield be formed of a material having a low emissivity.

In the present invention, the air layer or the air passage is provided inside the shield, and the shield is divided into two layers, so that the temperature difference between the inner and outer surfaces of each of the divided shields is reduced. Thus, the shield can be prevented from cracking, and the radiation shielding performance can be maintained.

[0012]

1 and 2 show a concrete module 10 as a radioactive substance storage facility according to a first embodiment of the present invention. This concrete module 1
Reference numeral 0 denotes a canister 12 and a concrete shield 14. The canister 12 is cylindrical and has a radioactive substance sealed inside. Shield 14 is lower case 1
6 and an upper case 18. The upper case 18 includes a bottomed cylindrical main body 20 made of concrete, a circular heat insulating material 22 formed of a ceramic heat insulating material or the like affixed inside the upper wall 20A of the main body 20,
It is composed of a metal liner 24 made of lead, aluminum, or the like having a low emissivity and concentrically attached to the heat insulating material 22 on the heat insulating material 22. When the calorific value of the radioactive substance is small, the heat insulating material 22 and the metal liner 24 may not be provided.

The lower case 16 has a cylindrical main body 26 having a bottom and made of concrete, a circular heat insulating material 28 made of a ceramic heat insulating material or the like affixed inside a side wall 26A of the main body 26, and a heat insulating material 28. And a metal liner 30 formed of lead, aluminum, or the like having a low emissivity. The upper end 28A of the heat insulating material 28 is the main body 2
6, the upper end 30A of the metal liner 30 is located above the upper end 26B of the main body 26 and is located below the upper end 28A of the heat insulating material 28. When the lower case 16 and the upper case 18 are combined, The heat insulating material 28 of the lower case 16 is the heat insulating material 2 of the upper case 18.
2, the metal liner 30 of the lower case 16 is continuous with the metal liner 24 of the upper case 18.

A gap 32 is formed between the inner diameter of the shield 14 and the outer diameter of the canister 12.

On the lower side of the lower case 16, one or more first cooling air flow paths 34 for communicating the outside of the shield with the gap 32 are formed. This first cooling air passage 34
A first horizontal portion 34A formed horizontally on the outside, a vertical portion 34B extending upward from an inner end of the first horizontal portion 34A,
And a second horizontal portion 34C extending horizontally inward from the upper end of the vertical portion 34B. 1st horizontal part 34A
Is located on the same plane as the lower surface 38 of the second horizontal portion 34C or below the lower surface 38 of the second horizontal portion 34C, so that the radiation passing through the second horizontal portion 34C can be bent.
The light is reflected by the wall surface 40 of B and does not leak to the outside. Note that each horizontal portion may be inclined upward as it goes inside.

A plurality of projections (not shown) are formed inside the lower case 16 above the first cooling air flow path 34, and the projections support the canister 12 in the shield 14.

Further, a second cooling air flow path 42 is formed in an upper portion of the lower case 16 at a position facing the first cooling air flow path 34 formed below the lower case 16.
The second cooling air flow path 42 is formed from a first horizontal portion 42A formed horizontally inside, a vertical portion 42B extending upward from an outer end of the first horizontal portion 42A, and an outer side from an upper end of the vertical portion 42B. And a second horizontal portion 42C extending horizontally. The upper surface 44 of the first horizontal portion 42A is the second horizontal portion 42C.
Is located on the same plane as the lower surface 46 of the second horizontal portion 42C or below the lower surface 46 of the second horizontal portion 42C, whereby the radiation passing through the first horizontal portion 42A is reflected by the wall surface 48 of the bent portion 42B and does not leak to the outside. It has become. In addition, each horizontal part may incline upward as it becomes outside. Further, the heat insulating material 28 and the metal liner 30 are affixed inside the second cooling air passage 42, so that the exhaust heat passing through the air passage 42 is hardly absorbed inside.

The cooling air is introduced from the first cooling air flow path 34 to the lower side inside the shield, cools the canister 12 loaded in the shield, rises in the shield 14 due to a rise in temperature, and Air is exhausted from the cooling air passage 42.

A cylindrical hole is formed in the lower case 16 of the shielding body 14 concentrically with the internal space in the lower case 16, and air is sealed in this hole to form an air layer 50. ing.

The decay heat emitted from the radioactive substance in the canister 12 is cooled by the air flowing through the first cooling air flow path 34, the gap 32, and the second cooling air flow path 42. Further, the heat is transmitted to the main body 26 and radiated from the outer surface through the air layer 50. Since the shield 26 is divided into two layers by the air layer 50, the temperature difference between the inner and outer surfaces of each divided layer is reduced, and the shield 26 is
Of the shielding body 14 is maintained for a long period of time.

FIG. 3 shows a concrete module 60 as a radioactive substance storage facility according to a second embodiment of the present invention. In addition, the same code | symbol is attached | subjected about the structure same as the structure of the concrete module 10 of 1st Embodiment, and description is abbreviate | omitted.

The concrete module 60 includes the canister 12 and a shield 62 made of concrete. The shield 62 is a cylindrical third cooling air flow communicating with the first cooling air passage 34 and the second cooling air passage 42. Road 64,
The first cooling air passage 34, the second cooling air passage 42, and the third cooling air passage 64 form an air passage.

In the concrete module 60, the air in the air layer inside the shield 62 is replaced through the first cooling air passage 34 and the second cooling air passage 42, so that the cooling effect is higher than that of the concrete module 10. .

FIG. 4 shows a concrete module 70 as a radioactive substance storage facility according to a third embodiment of the present invention. In addition, the same code | symbol is attached | subjected about the structure same as the structure of the concrete module 10 of 1st Embodiment, and description is abbreviate | omitted.

The concrete module 70 includes the canister 12 and a shield 72 made of concrete. The shield 72 is a cylindrical third cooling air flow path 74 communicating with the second cooling air flow path 42, and a third cooling air flow Lower end of road 74 and gap 3
A fourth fourth cooling air flow path 76 communicating with the second cooling air flow path;
A fifth fifth cooling air flow path 78 is provided to communicate a substantially central portion of the cooling air flow path 74 with the gap 32, and the second cooling air flow path 42, the third cooling air flow path 74, and the fourth cooling air flow Channel 7
The sixth and fifth cooling air flow paths 78 form a ventilation path.

In the concrete module 70, the air in the air layer inside the shield 72 is replaced by the second cooling air flow path 42, the fourth cooling air flow path 76, and the fifth cooling air flow path 78. The cooling effect is higher than that of the module 10. The fourth cooling air passage 76,
The fifth cooling air passage 78 may be inclined so as to become higher as it goes outward.

FIGS. 5 to 7 show a concrete module 8 as a radioactive substance storage facility according to a fourth embodiment of the present invention.
Indicates 0. In addition, the same code | symbol is attached | subjected about the structure same as the structure of the concrete module 10 of 1st Embodiment, and description is abbreviate | omitted.

The concrete module 80 includes a canister 12 and a shield 82 made of concrete, and a first cooling air flow inclined at one or a plurality of locations below the shield 82 so as to be inwardly upward. A passage 84 is formed. As shown in FIG. 6, the first cooling air passage 84 is formed to be curved. Also, the shield 82
Above the second cooling air flow path 8, which is inclined so as to become higher toward the outside at a position facing the first cooling air flow path.
6 are formed. This second cooling air passage 86 is provided in FIG.
It is formed so as to be curved. Further, a cylindrical third cooling air passage 88 is formed inside the shield 82. The third cooling air passage 88 communicates with the first cooling air passage 84 at the air inlet 90 and communicates with the second cooling air passage 86 at the air outlet 92.

The cooling air is introduced from the first cooling air passage 84 into the shield 82, and a part of the cooling air passes through the gap 32 to the second cooling air passage 84.
The air is exhausted from the cooling air passage 86, and the rest is
Then, the air enters the third cooling air passage 88 from the air outlet 92, and enters the second cooling air passage 86 to be exhausted.

The radiation that has entered the first cooling air passage 84 or the second cooling air passage 86 does not leak to the outside because these air passages are curved.

In the concrete module 80, the air in the air layer inside the shield 82 is replaced through the first cooling air flow path 84 and the second cooling air flow path 86,
The cooling effect is higher than that of the concrete module 10.

The concrete module 80
In place of the third cooling air passage 88, the air layer 50 of the concrete module 10 of FIG. 2 and the third cooling air passage 74, the fourth cooling air passage 76, and the fifth cooling air passage of the concrete module 70 of FIG. A cooling air passage 78 may be provided.

FIGS. 8 and 9 show a concrete module 1 as a radioactive substance storage facility according to a fifth embodiment of the present invention.
00 is shown. The same components as those of the concrete module 80 according to the fourth embodiment are denoted by the same reference numerals, and description thereof is omitted.

The concrete module 100 includes a canister 12 and a shield 102 made of concrete. A second cooling air passage 104 is formed above the shield 102 at a position facing the first cooling air passage 84. I have. The second cooling air flow path 104 includes an inclined portion 104A that is inclined so as to become higher as it goes outward, and a vertical portion 104B that extends vertically upward outside the inclined portion 104A. The inclined portion 104A of the second cooling air passage 104 is formed to be curved as shown in FIG. In addition, the shield 10
A cylindrical third cooling air passage 88 is formed inside the second cooling air passage 88. The third cooling air passage 88 is provided with an air
The cooling air passage 84 communicates with the second cooling air passage 104 at an air outlet 106.

The cooling air is introduced into the shield 102 from the first cooling air flow path 84, a part of which is exhausted from the second cooling air flow path 104 through the gap 32, and the rest is discharged from the air inflow section 90 to the second cooling air flow path 104. 3 Entering the cooling air passage 88 and the air outlet 106
From the second cooling air passage 104 to be exhausted.

In this concrete module 100,
Since the air in the air layer inside the shield 102 is replaced via the first cooling air flow path 84 and the second cooling air flow path 104, the cooling effect is higher than that of the concrete module 10. In addition, the average position of the outlet opening is higher than that of the concrete module 80, and the difference between the height of the inlet opening and the height of the outlet opening can be increased, so that natural ventilation is more induced.

The concrete module 100
In place of the third cooling air passage 88, the air layer 50 of the concrete module 10 of FIG. 2 and the third cooling air passage 74, the fourth cooling air passage 76, and the fifth cooling air passage of the concrete module 70 of FIG. A cooling air passage 78 may be provided.

In order to change the air flow according to the calorific value of the stored radioactive material, in the second embodiment of the present invention, the first cooling air passage 34, the third cooling air passage 64, and the third embodiment are used. In the embodiment, the first cooling air passage 34 and the fourth and fifth cooling air passages 76 and 78, and in the fourth and fifth embodiments, the first cooling air passage 84 and the third cooling air passage 88 The cross section of each of the
It is desirable to change the ventilation resistance in consideration of the shapes of the branch and the inlet.

Further, the concrete modules 10 and 6
At 0, 70, 80, and 100, the surface of the shield facing the canister is desirably made of a material having a low emissivity, but the walls on both sides of the third cooling air flow paths 64, 74, and 88 are also made of lead or It is preferable to form a layer formed of a material having a low emissivity such as aluminum. However, the emissivity of the wall surface may be changed according to the calorific value and the amount of exhaust of the radioactive material.

[0040]

According to the present invention, since the inside of the shield is divided by the air layer, the temperature difference between the inner and outer surfaces of each of the divided shield layers can be reduced, thereby preventing the concrete shield from cracking. Radiation shielding performance can be maintained for a long time.

[Brief description of the drawings]

FIG. 1 is a plan view of a concrete module as a radioactive substance storage facility according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view when the concrete module of FIG. 1 is cut in a vertical direction.

FIG. 3 is a cross-sectional view when a concrete module as a radioactive substance storage facility according to a second embodiment of the present invention is cut in a vertical direction.

FIG. 4 is a cross-sectional view when a concrete module as a radioactive substance storage facility according to a third embodiment of the present invention is cut in a vertical direction.

FIG. 5 is a sectional view when a concrete module as a radioactive substance storage facility according to a fourth embodiment of the present invention is cut in a vertical direction.

FIG. 6 shows a bottom view of the concrete module of FIG.

FIG. 7 shows a plan view of the concrete module of FIG. 5;

FIG. 8 is a cross-sectional view when a concrete module as a radioactive substance storage facility according to a fifth embodiment of the present invention is cut in a vertical direction.

FIG. 9 shows a plan view of the concrete module of FIG. 8;

FIG. 10 shows a plan view of a conventional concrete module.

11 shows a cross-sectional view when the concrete module of FIG. 10 is cut in the vertical direction.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Concrete module 12 Canister 14 Shield 32 Gap (air inflow space) 34 1st cooling air channel 42 2nd cooling air channel 50 Air layer 60 Concrete module 62 Shield 64 Third cooling air channel 70 Concrete module 72 Shield Body 74 Third cooling air channel 76 Fourth cooling air channel 78 Fifth cooling air channel 80 Concrete module 82 Shield 84 84 First cooling air channel 86 Second cooling air channel 88 Third cooling air channel 100 Concrete module 102 Shield 104 Second cooling air flow path

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G21F 5/002 G21F 5/00 W 5/005 (72) Inventor Tetsuo Mochida 1-5 Otsuka, Inzai City, Chiba Prefecture No. 1 Inside Takenaka Corporation Technical Research Institute (72) Inventor Yoshiaki Higuchi 1-5-1, Otsuka, Inzai City, Chiba Prefecture Inside Takenaka Corporation Technical Research Institute (72) Inventor Yuichi Yamamoto Ginzahachi, Chuo-ku, Tokyo No. 21-1, Takenaka Corporation Tokyo Head Office

Claims (4)

[Claims] 1. An outside of a sealed body in which a radioactive substance is sealed is surrounded by a concrete shield, an air inflow space is provided between the seal and the shield, and radioactive air is supplied through the air in the air inflow space. A radioactive substance storage facility for removing heat generated by a substance, wherein a closed air layer is provided inside the shield. 2. The outside of a sealed body in which a radioactive substance is sealed is surrounded by a concrete shield, and an air inflow space is provided between the seal and the shield. A radioactive substance storage facility for removing heat generated by a substance, wherein a ventilation path through which air flows in and out of the shield is provided. 3. The radioactive substance storage facility according to claim 2, wherein a wall surface of the ventilation path is formed of a material having a low emissivity. 4. The radioactive substance storage facility according to claim 1, wherein an inner surface of the shield is formed of a material having a low emissivity.