JP2001235582A - Cask for dry transport and storage of spent fuel, etc. - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the capacity removing decay heat from stored spent fuel, improve the neutron shielding capacity, and improve the assemblage by simplifying the structure. SOLUTION: A plurality of shielding body fitting seats 11 are attached to the outer circumferential face of a bottomed cylinder cask 1 with some clearances and a neutron shielding material 4 is provided outside the shielding body fitting seats 11. The outside of the neutron shielding material 4 is covered with a shielding cover 5. A fluid cooling path 12 is formed between the outside of the cask and the shielding cover 5 of the neutron shielding material 4, and cooling fluid 13 flows inside the fluid cooling path 12 from the bottom to the top so as to cool the cask 1. The fluid cooling path 12 prevents the outside face of the cask 1 and the neutron shielding material 4 from directly touching with each other, and the natural convection removes heat from the neutron shielding material 4 so as to prevent it from getting high temperature and eliminate the weight decrease by the long-term heat action, thus preventing the lowering of the neutron shielding capacity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cask for dry transportation and storage of spent fuel and the like having an enhanced ability to remove decay heat from spent fuel assemblies and the like stored in a cask.

[0002]

2. Description of the Related Art A cask storage system, which is one type of dry storage of spent fuel in a nuclear power plant, is used outdoors or in a building with spent fuel stored in a container (cask) having a shielding ability. It is a method of removing heat using ventilation, and performing radiation shielding on heavy metal or concrete walls. In addition, since it takes time and effort to refill the storage cask, a method has been developed in which the transport cask is also used for storage.

[0003] A typical conventional cabin for dry transportation and storage will be described with reference to Figs. FIG. 5 is a longitudinal sectional view showing a cask for dry transportation and storage, and FIG.
It is a cross-sectional view cut in the direction of arrow A, and is shown slightly enlarged.

That is, a conventional cask for dry transport and storage is a steel bottomed cylindrical container 1 for confining spent fuel and shielding γ-rays, and a steel container for closing an upper end opening of the container 1. A cover plate 2, a seal 3 for sealing the container 1 and the cover plate 2, a bolt 18, a neutron shielding material 4 for neutron shielding which is installed without gaps around the outer surface and upper and lower surfaces of the container 1, A shielding cover 5 for covering the outside of the neutron shielding material 4, a plurality of heat-dissipating heat transfer plates 10 penetrating through the neutron shielding material 4, and a plurality of heat-transfer plates 10 for handling during transportation and holding during storage. The trunnion 6 includes a trunnion 6 attached to the outer peripheral surface of the container, and a basket 7 installed in the container 1 for holding the spent fuel assembly 8 and also having a function of preventing criticality.

[0005]

The conventional cask for dry transportation and storage is designed to prevent overheating of the spent fuel assembly itself, to limit creep and neutron shielding caused when aluminum or the like is used as the material of the basket 7 and the seal 3. It is necessary to appropriately remove the decay heat from the spent fuel assembly 8 in order to limit the temperature from the heat resistance of the organic composition material such as the material 4.

However, the neutron shielding material 4 surrounding the outer peripheral surface and the bottom surface of the container 1 is equivalent to a heat insulating material as compared with the metal material which is the material of the container 1, and hinders sufficient heat removal. Then, in order to directly promote heat conduction and heat removal from the container 1 to the outside of the neutron shielding material 4, for example, a copper heat transfer plate 10 installed through the neutron shielding material 4.
Are attached to the inner peripheral surface of the container 1 or the container 1
It is necessary to attach cooling fins (not shown) also to the outer surface of the fin.

When the heat transfer plate 10 and the cooling fins are attached, there is a problem that the structure becomes complicated and the assembling property is deteriorated. The neutron shielding material 4 is a heat transfer plate 10
The neutron shielding function is reduced due to the leakage of neutron flux from the neutron shielding material 4, and there are restrictions such as that the material of the neutron shielding material 4 is limited to, for example, a silicon rubber-based material having high heat resistance. There are problems such as weight reduction due to the action and the accompanying decrease in the neutron shielding function.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has an improved ability to remove decay heat from spent fuel and the like stored in a cask, thereby improving a neutron shielding ability and, furthermore, a structure. An object of the present invention is to provide a cask for dry transportation and storage of spent fuel and the like, which is simple and has a function of improving assemblability.

[0009]

The invention according to claim 1 is
A steel container for confining spent fuel and the like and having a γ-ray shielding portion, a steel cover plate for sealing the container, a seal and bolt for sealing the cover plate and the container, the container and the cover plate A neutron shielding material installed around the container, a trunnion attached to the side of the container, and a basket installed in the container and holding a spent fuel and the like and also having a function of preventing criticality. In a cask for dry transportation and storage of fuel or the like, a gap for a fluid cooling path for flowing fluid cooling is provided between the container and the neutron shielding material.

According to the present invention, a fluid cooling path is provided in a gap formed between a container and a neutron shielding material provided on the outer periphery of the container, and a portion serving as an inlet / outlet of a cooling fluid is tapered or has a gentle curvature. By having the flow path shape having the above, the flow of the cooling fluid can be made smooth and the heat removal can be promoted.

Further, by installing a shielding cover on the inner and outer surfaces of the neutron shielding material installed on the outer periphery of the container, that is, on the entire surface, the neutron shielding material which is softer and more easily damaged than metal is protected, and fixing and handling on the container are facilitated. It can prevent the spread of fire in the event of fire.

The invention according to claim 2 is characterized in that a plurality of shielding body mounting seats are provided with a predetermined gap between the outer peripheral surface of the container and the shielding material. According to the present invention, an appropriate gap can be provided between the outer surface of the shielding body mounting seat container and the neutron shielding material,
It is possible to prevent direct contact between the neutron shielding material and the high temperature container.

[0013] The invention according to claim 3 is that at least a part of the neutron shielding material is divided into a movable shielding body and a fixed shielding body at a plurality of locations so that the movable shielding body can be opened and closed by a movable mechanism. Features. According to the present invention, the natural convection of cooling air is promoted when the cask is lying down during transportation or storage,
Heat can be effectively removed even when lying down.

[0014] The invention according to claim 4 is characterized in that the connecting portion between the movable shield and the fixed shield has an offset structure for preventing radiation streaming, and has a structure capable of maintaining the offset even when opened. .

According to the present invention, the heat removal function can be exerted even in the side-down state without impairing the neutron shielding effect.
Also, the movable shield that can be opened and closed, and the offset structure of the connection portion of the fixed shield is a tapered, or a cooling air flow path having a structure with a gentle curvature, thereby allowing the cooling air flow even in a sideways state. It can smooth out and promote heat removal.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of a cask for dry transportation and storage of spent fuel and the like will be described with reference to FIGS. FIG. 1 is a longitudinal sectional view showing a first embodiment of a cask for dry transportation and storage according to the present embodiment, and FIG.
2 is a cross-sectional view cut along the direction of arrows BB in FIG. In the present embodiment, an example of a spent fuel assembly will be described as spent fuel or the like, but the present invention is not limited to this.

In this embodiment, a steel container 1 having a function for confining a spent fuel assembly 8 and shielding γ-rays is provided.
, A steel cover plate 2 covering the upper end opening of the container 1, a seal 3 and a bolt 18 for sealing the container 1 and the cover plate 2, and a neutron shield installed around the container 1 and the cover plate 2. Neutron shielding material 4 for use, a shielding cover 5 covering the entire circumference of the neutron shielding material 4 including a surface on the side of a cooling path 12 described later, and a container 1 for handling during transportation and holding during storage.
A trunnion 6 attached to an upper outer surface of the container 1 and a basket 7 installed in the container 1 and holding a spent fuel assembly 8 and also having a function of preventing criticality. Further, the container 1 and the neutron shielding material 4 are provided. A fluid cooling path through which the cooling fluid 13 can flow through the shield mounting seat 11
12 are provided.

This fluid cooling path 12 is most suitable when the container 1 is supported and stored vertically by a support structure (not shown), and the floor 9 is located below the upright cask as shown in FIG. The cooling effect can be efficiently exhibited, and the portion corresponding to the entrance / exit flow path has a structure having a taper or a gentle curvature.

Further, the neutron shielding material 4 and the shielding cover 5 are fixed to the container 1 and the cover plate 2 by bolts or the like (not shown), and no structure such as the heat transfer plate 10 is required inside. Further, as a material of the basket 7, a boron-containing aluminum or a boron-containing stainless steel having a high neutron absorption effect and a strength as a structural material is used to prevent criticality.

Next, the operation of the cask for dry transportation and storage of the spent fuel assembly and the like according to the present embodiment will be described. As shown in FIG. 1, in a state where the cask is supported and stored in a vertical shape, the decay heat from the spent fuel assembly 8 is first transmitted to the outside via the container 1 by heat conduction. As a result, the wall temperature of the outer surface of the container 1 rises, and the cooling fluid 13 flowing through the fluid cooling path 12 is also warmed, causing a density difference between the cooling fluid 13 and the outside atmosphere. Buoyancy occurs.

Due to the buoyancy, the cooling fluid 13 in the fluid cooling path 12 starts flowing, and dissipates this heat to the outside atmosphere at a flow rate according to the amount of heat from the inside. The cooling fluid 13 flows in from a taper at the lower end of the fluid cooling path 12 or an inlet having a gentle curvature, and flows out from an outlet having a taper at the upper end of the fluid cooling path 12 or a shape having a gentle curvature. As a result, the internal decay heat is almost completely removed without directly passing through the neutron shielding material 4, and the temperature of the neutron shielding material 4 does not increase.

Since the length of the flow path of the cooling path 12 is longer than the width thereof, an improvement in the heat removal effect by the chimney effect can be expected. Further, the neutron shielding material 4 and the shielding cover 5
Is fixed to the container 1 and the cover plate 2 by bolts or the like (not shown), and since no structure such as the heat transfer plate 10 is required inside, it can be manufactured integrally.

Further, between the container 1 and the neutron shielding material 4, a portion serving as an inlet / outlet of the cooling fluid 13 is formed as a flow path having a taper or a gentle curvature, so that the flow of the cooling fluid is smoothed and removed. Can promote heat. Further, by attaching the shielding cover 5 so as to cover the entire neutron shielding material 4, the internal decay heat is dissipated into the outside air without directly passing through the neutron shielding material 4, and the temperature of the neutron shielding material 4 does not increase. .

Therefore, the heat removal efficiency is improved, the weight of the neutron shielding material 4 is not reduced when the neutron shielding material 4 is subjected to a thermal action for a long time, and the neutron shielding function is not reduced. It is possible to use materials with low heat resistance,
The range of material selection can be expanded.

Further, since a structure such as the heat transfer plate 10 shown in FIG. 6 is not required, the structure of the neutron shield is simple, and the neutron shield can be manufactured integrally. 4 is superior in assemblability to the conventional structure in which 4 must be alternately constructed. Further, since the neutron shielding material 4 is entirely covered with the shielding cover 5, the neutron shielding material 4 which is softer and more easily damaged than metal is protected, and the neutron shielding material 4 can be easily fixed to the container 1 and handled easily. Can be prevented.

Next, FIGS. 3A and 3B and FIG.
A second embodiment of a cask for dry transportation and storage of a spent fuel assembly or the like according to the present invention will be described with reference to (a) and (b). This embodiment is an example in which the cask is used in a horizontal state during transportation or storage. FIG. 3A is a longitudinal sectional view of the cask according to the embodiment, and FIG.
FIG. 4A is an enlarged view of a portion C of FIG.
FIG. 4 (b) is an enlarged view of a portion E in FIG. 4 (a). In FIGS. 3 and 4, the same parts as those in FIGS. 1 and 2 are denoted by the same reference numerals, and the description of the overlapping parts will be omitted.

The basic structure of the cask according to this embodiment is almost the same as that of the first embodiment shown in FIGS. 1 and 2, and when the cask is supported and stored in a vertical type, the first structure is adopted. It has a heat removal function equivalent to that of the embodiment.

In the sideways state, the flow of the cooling fluid 13 due to natural convection is slightly lower in performance than in the case of a vertical type, so in the present embodiment, the neutron shielding material 4 which is in the upside-down position in the sideways state is used. A part of the shielding cover 5 is divided into a movable shielding body 14 and a fixed shielding body 15 at a plurality of locations and separated.

That is, as shown in FIGS. 3 (b) and 4 (b), the link mechanism 16 is attached to the container 1, the slider 17 is attached to the movable shield 14, and the movable shield is attached by the link mechanism 16 and the slider 17. The body 14 can be opened and closed by moving it up and down.

Next, the operation of the present embodiment will be described. In the present embodiment, since the flow of the cooling fluid as in the vertical type described in the first embodiment cannot be expected, it is necessary to create a fluid cooling path through which the cooling fluid 13 can flow. , Upper and lower movable shields
14 is moved to provide an inlet / outlet for the cooling fluid 13 at this position.

When the movable shield 14 is opened, the link mechanism 16 is lifted up, and the movable shield 14 and the link mechanism 16 are connected by a dovetail-shaped rail by a slider 17 whose joint can slide. Although a sufficient flow path can be maintained to allow the cooling fluid 13 to flow, neutron streaming is fixed at that position when an offset gap is opened enough to prevent it. In this state, first, the decay heat from the spent fuel assembly 8 is
Is transmitted to the outside through heat conduction.

As a result, the wall temperature on the outer surface of the container 1 rises, and the fluid inside the cooling path 12 is warmed accordingly,
This creates a density difference with the outside atmosphere, which results in upward buoyancy. This buoyancy causes the cooling fluid in the cooling path 12
13 starts to flow and dissipates this heat to the outside atmosphere at a flow rate according to the amount of heat from the inside.

The cooling fluid 13 flows in from the tapered opening having the opening of the lower movable shield 14 or an inlet having a gentle curvature, and from the taper which is the opening in the upper movable shielding 14 or the outlet having a gentle curvature. leak. As a result, the internal decay heat is removed almost without passing through the neutron shielding material 4, and the temperature of the neutron shielding material 4 does not increase.

The mechanism for opening and closing the movable shield 14 is not particularly limited to the structure of the present embodiment.
Various types such as a jack bolt type and a spacer type can be used. If a certain amount of traveling wind can be expected during transportation, cooling can be performed using a baffle plate or the like.

According to the second embodiment, the neutron shielding material 4 and a part of the shielding cover 5 attached to the outer periphery of the container 1 are divided into a plurality of blocks, which can be opened and closed by the link mechanism 16, and can be opened and closed. The connection between the movable shield 14 and the fixed shield 15 has an offset structure for preventing radiation streaming, so that the offset can be maintained even when it is opened, and the entrance and exit of the cooling fluid 13 of this offset structure are tapered or have a gentle curvature. It has a cooling air passage having a structure having.

As a result, even if the neutron shielding material 4 is laid sideways, the internal decay heat is radiated into the outside air without directly passing through the neutron shielding material 4, so that the temperature of the neutron shielding material 4 is not increased, so that the heat removal efficiency is good and the neutron shielding is good. When the material 4 is subjected to thermal action for a long period of time, the weight does not decrease and the neutron shielding function does not decrease.

Further, since it is possible to use a material having low heat resistance, such as polyethylene containing boron, as the neutron shielding material 4, the range of material selection can be widened, and the radiation structure can be provided even when the movable shielding body 14 is opened by the offset structure. And the flow path of the cooling fluid 13 can be secured.

[0038]

According to the present invention, the cooling fluid can flow between the container and the neutron shielding material even when the container is placed vertically or in a horizontal position, so that the collapse of the spent fuel or the like stored in the container can be achieved. It is possible to obtain a cask for dry transportation and storage in which the ability to remove heat is enhanced, the neutron shielding ability is improved, the structure is simplified, and the assemblability is improved.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a first embodiment of a cask for dry transportation and storage of spent fuel and the like according to the present invention.

FIG. 2 is a cross-sectional view cut along the direction of arrows BB in FIG.

FIG. 3 (a) is a longitudinal sectional view showing a second embodiment of a cask for dry transportation and storage of spent fuel and the like according to the present invention,
(B) is an enlarged view of a portion C in (a).

4A is a cross-sectional view cut along a direction indicated by an arrow D-D in FIG. 3, and FIG. 4B is an enlarged view of a portion E in FIG.

FIG. 5 is a longitudinal sectional view showing a conventional cask for dry transportation and storage of spent fuel and the like.

FIG. 6 is a cross-sectional view cut along the line AA of FIG. 5;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Container, 2 ... Lid plate, 3 ... Seal, 4 ... Neutron shielding material, 5 ... Shielding cover, 6 ... Trunnion, 7 ... Basket, 8 ... Spent fuel assembly, 9 ... Floor, 10 ... Heat transfer plate, 11 ... shield mounting seat, 12 ... fluid cooling path, 13 ... cooling fluid, 14 ... movable shield, 15 ... fixed shield, 16
... link mechanism, 17 ... slider, 18 ... bolt.

Claims (4)

[Claims] 1. A steel container for confining spent fuel and the like and having a γ-ray shielding portion, a steel cover plate for sealing the container, a seal and a bolt for sealing the cover plate and the container, and the container. And a neutron shielding material installed around the lid plate, a trunnion attached to the side of the container, and a basket installed in the container, which also holds a spent fuel and the like and also has a function of preventing criticality. A cask for dry transportation and storage of spent fuel, etc., characterized in that a fluid cooling path is provided between the container and the neutron shielding material to allow fluid cooling to flow. Cask. 2. The spent fuel or the like according to claim 1, wherein a plurality of shielding body mounting seats are provided with a predetermined gap between the outer peripheral surface of the container and the shielding material. Cask for dry transport and storage. 3. The method according to claim 1, wherein at least a part of the neutron shielding material is divided into a movable shielding body and a fixed shielding body at a plurality of locations, and the movable shielding body can be opened and closed by a movable mechanism. A cask for dry transportation and storage of the used spent fuel, etc. 4. The connection according to claim 3, wherein the connection between the movable shield and the fixed shield has an offset structure for preventing radiation streaming, and the offset can be maintained even when the shield is opened. Cask for dry transport and storage of spent fuel.