JP2021162540A - Basket for storing spent nuclear fuel in a container - Google Patents

Abstract

To provide a basket for storing spent nuclear fuel in a container capable of maintaining structural soundness while reducing the dependence on material strength in the structural strength even when another aluminum alloy with lower strength than steel or conventional aluminum alloys is used.SOLUTION: The basket for storing spent nuclear fuel in a container has a structure of a basket 13 that is stored in a container 11. The basket 13 has a peripheral part 19 that is arranged along the inner peripheral surface 18 of container 11 and a central part 20 that is placed in the inner part along the diameter direction than the peripheral part 19. The peripheral part 19 is divided into multiple pieces 22 along the circumferential direction. Each piece 22 is fixed in surface contact with the inner peripheral surface 18 of the container 11. The basket is capable of getting a state where the inner surface of the peripheral part 19 and the outer face of the central part 20 keep a gap 37 therebetween, and a state in which the inner surface of the peripheral part 19 and the outer face of the central part 20 are in surface contact with each other due to the displacement of the central part 20 from the state where the gap 37 is kept.SELECTED DRAWING: Figure 8

Description

The present invention relates to a basket for storing spent nuclear fuel in a container.

In order to safely transport or store spent nuclear fuel generated in nuclear facilities such as nuclear power plants, containers called cask and canisters are used. In order to safely store the spent nuclear fuel in the cavities in these containers, a rack-shaped structure called a basket is used (Patent Document 1).

Of the four safety functions required for a container for storing spent nuclear fuel, the basket has a heat removal function, a sealing function, a shielding function, and a subcritical function. Structural strength is required to maintain these functions. In particular, it is required to maintain structural soundness without impairing the safety function even under the condition of dropping from a height of 9.0 m.

In Japan, it has been expected to use an aluminum alloy having excellent thermal conductivity and specific strength as a basket material. However, in recent years, from the viewpoint of safety, the standard for aluminum alloys for baskets has been abolished. For this reason, a basket using carbon steel or stainless steel for the structural strength member was considered, but a basket using an aluminum alloy having a higher thermal conductivity than steel is used for the purpose of lowering the temperature of the spent nuclear fuel. Development is still desired.

Japanese Unexamined Patent Publication No. 11-287894

Therefore, the present invention reduces the dependence of the structural strength of the basket on the material strength, and can maintain the structural soundness even if a steel material or another aluminum alloy having a lower strength than the conventional aluminum alloy is used. The purpose is to obtain.

In order to achieve this object, the basket for storing the spent nuclear fuel of the present invention in the container is
It presents the structure of a basket that is housed in a container,
The basket has a peripheral edge portion arranged along the inner peripheral surface of the container and a central portion arranged at an inner position along the radial direction from the peripheral edge portion.
The peripheral edge is divided into multiple pieces along the circumferential direction.
Each piece is fixed in surface contact with the inner peripheral surface of the container.
The peripheral portion and the central portion are a state in which an inner surface of the peripheral portion and an outer surface of the central portion maintain a gap with each other, and an inner surface and a central portion of the peripheral portion due to displacement of the central portion from the state in which the gap is maintained. It is characterized in that it can be formed by taking both a state in which the outer surfaces of the above are in surface contact with each other.

According to the basket for storing the spent nuclear fuel of the present invention in the container.
Has a fixture for fixing the peripheral edge to the inner peripheral surface of the container,
It is preferable that the fixture is configured so that the end portion of one piece adjacent to each other in the circumferential direction and the end portion of the other piece can be fastened together to the inner peripheral surface of the container.

According to the basket for storing the spent nuclear fuel of the present invention in the container.
Fixtures
As well as being configured to be fastened to the container
One pressing surface for pressing the end of one piece toward the inner surface of the container when fastened to the container, and one with the end of the other piece facing the inner surface of the container when fastened to the container. It is preferable to have the other pressing surface for pressing together with the piece.

The basket for storing the spent nuclear fuel of the present invention in the container has a structure in which a plurality of panels are stacked one above the other, and a first space for accommodating the spent nuclear fuel extends over the upper and lower panels. It is preferable that a second space for accommodating the neutron absorber is provided over the upper and lower panels.

The basket for storing the used nuclear fuel of the present invention in the container has a slit through which a neutron absorber composed of long bodies arranged in the vertical direction over a plurality of boards can pass through. The first board configured to hold a part along the length direction of the neutron absorber and the other part along the length direction of the neutron absorber without the slit are held. It is preferable to have a second board that is configured to pass through without passing through.

Since the known basket has a structure in which a structure smaller than the storage space of the container is only stored inside the container, stress concentration occurs especially in the thin portion of the outer peripheral portion when stress is applied. However, according to the present invention, the basket has a peripheral portion arranged along the inner peripheral surface of the container and a central portion arranged at an inner position along the radial direction from the peripheral portion. The peripheral edge is divided into a plurality of pieces along the circumferential direction, and each piece is fixed in surface contact with the inner peripheral surface of the container, so even if each piece has a thin portion. Since each piece is fixed in surface contact with the inner peripheral surface of the container, it is integrated with the container, and therefore the occurrence of stress concentration is mitigated even when stress is applied. be able to. Moreover, since the inner surface of the peripheral portion and the outer surface of the central portion are configured to be in surface contact with each other when the basket is in a laterally laid state, the structural member can be held in the elastic region. Therefore, according to the basket for storing the spent nuclear fuel of the present invention in the container, an aluminum alloy having good thermal conductivity can be used in a state where the structural strength is improved as compared with the conventional case.

According to the basket for storing the spent nuclear fuel of the present invention in the container, the structural strength can be improved as compared with the conventional case.

It is a top view of the main part of the basket for storing the spent nuclear fuel of embodiment of this invention in a container. It is a figure which shows the main part in FIG. 1 in an enlarged manner. It is a figure which shows the whole structure of the basket. It is a top view of a part of the board in the basket. It is sectional drawing of the main part in the basket. FIG. 5 is a cross-sectional view taken along the line VI-VI in FIG. FIG. 5 is a cross-sectional view taken along the line VII-VII in FIG. It is a figure which shows the state of the container including the basket. It is a figure which shows the state of the container including the basket for storing the spent nuclear fuel of another embodiment of this invention in a container. It is a figure which shows the state of the container including the basket for storing the spent nuclear fuel of still another Embodiment of this invention in a container.

In FIG. 1, reference numeral 11 denotes a container for transporting and storing spent nuclear fuel, and a storage space 12 is formed inside the container 11. In the illustrated example, the accommodation space 12 is formed in a columnar shape.

Reference numeral 13 denotes a basket according to an embodiment of the present invention for storing spent nuclear fuel inside the container 11. As shown in FIG. 3, the basket 13 has a configuration in which a plurality of block-shaped circular board 14s are stacked one above the other. The board 14 has a thin first board 15 and a second board 16 that is thicker than the first board 15. A third board 17 that is thicker than the second board is provided at the upper and lower ends of the basket 13. Although not shown, the plurality of board bodies 14 (15, 16, 17) are fastened to each other by a tie rod or the like in the vertical direction and integrated. Further, the vertically adjacent boards 14 (15, 16, 17) are aligned with each other by a reamer pin or the like.

Next, the detailed structure of the board 14 (15, 16, 17) will be described. FIG. 1 shows a structure when the upper end board 17 is viewed in a plan view. As shown in the figure, the board 17 has a peripheral edge portion 19 arranged along the inner peripheral surface 18 of the container 11 and a central portion 20 arranged at an inner position along the radial direction from the peripheral edge portion 19. ..

In the illustrated example, the peripheral edge 19 of the basket 13 is divided into four pieces 22 along the circumferential direction. Each piece 22 is formed in a bow shape in a plan view and has an outer curved surface 23 that can be in contact with the inner peripheral surface 18 of the container 11 and an inner flat surface 24. The plane 24 of the four pieces 22, 22, ... Along the circumferential direction forms a rectangular accommodation space 25 in a plan view on the inner portion along the radial direction from the peripheral edge portion 19.

The four pieces 22, 22 ... It is fixed to. As shown in detail in FIG. 2, the fixture 27 can fix each piece 22 to the inner peripheral surface 18 of the container 11 by fastening the fixing member 28 to the nut body 30 on the container 11 side by bolts 29. can. The fixing member 28 has one inclined surface 31 as one pressing surface and the other inclined surface 32 as the other pressing surface, and is formed at the end portion in the circumferential direction of one piece 22 adjacent to each other in the circumferential direction. One inclined surface 31 of the fixing member 28 is in contact with the pressed surface 33 of the above, and the other inclined surface 32 is in contact with the other pressed surface 34 formed at the end of the other piece 22 adjacent in the circumferential direction in the circumferential direction. .. As a result, the circumferential end of one piece 22 and the circumferential end of the other piece 22 can be fastened together by one fixture 27. The pressed surfaces 33 and 34 are formed in a direction parallel to the plane 24 of the pieces 22 and 22, whereby the piece 22 is placed by the fixture 27 in a direction perpendicular to the plane 24 with respect to the inner peripheral surface 18 of the container 11. It is configured so that it can be pressed. That is, the piece 22 is configured to be efficiently pressed and fixed to the inner surface of the storage space 12 along the radial direction of the storage space 12 of the container 11. On the fixing member 28, the space forming surfaces 35, 35 which are flush with the flat surface 24 of one and the other piece 22 when the pieces 22 and 22 are fixed to the inner peripheral surface 18 of the container accommodation space 25 by the fixture 27. Are formed respectively. By forming a pair of space forming surfaces 35, 35 on each fixing member 28, the accommodation space 25 can be formed in a strictly rectangular shape including its corners. The fixing member 28 may be individually provided for each of the plurality of stacked boards 15, 16 and 17, or may be formed of a long body continuous in the vertical direction over the plurality of boards 15, 16 and 17. can. The bolt 29 is configured to exert a fastening function in a state where the head 36 is subducted inside the fixing member 28 so that the head 36 does not protrude to the inner peripheral side in the radial direction from the space forming surface 35. Has been done.

The cross-sectional shape of the fixture 27 may be any shape other than those shown in the figure as long as the piece 22 can be properly fixed to the container 11. Further, the piece 22 can be fixed to the container 11 by using stud bolts or other fastening elements without using the fixing tool 27 as shown in the drawing.

By installing the four pieces 22, 22, ... As shown in the figure, the four pieces 22, 22, ... The shape of the accommodation space 25 is formed. The central portion 20 of the basket 13 is accommodated in the accommodation space 25. The central portion 20 is formed in a rectangular shape slightly smaller than the accommodation space 25 in a plan view, so that the central portion 20 is the plane of each piece 22 of the peripheral portion 19 when accommodated in the accommodation space 25. It is configured so that a gap 37 can be formed between the 25 and the 25.

As described above, the plurality of board bodies 14 (15, 16, 17) are fastened to each other by a tie rod or the like in the vertical direction to be integrated, and the board bodies 14 (15, 16, 17) adjacent to each other on the top and bottom are connected to each other. They are aligned with each other by a reamer pin or the like. Specifically, a plurality of peripheral edges 19 in the vertical direction, that is, a plurality of pieces 22 in the vertical direction and a plurality of central portions 20 in the vertical direction are fixed to each other and aligned with each other by the above configuration. Has been done. In some cases, it is possible to adopt a configuration in which the vertical dimension of each piece 22 and the vertical dimension of each central portion 20 are different from each other.

In the central portion 20 of each board 14 (15, 16, 17) and the piece 22 of the peripheral portion 19, a plurality of accommodating holes 38 for accommodating spent nuclear fuel are provided in the central portion 20 and the peripheral portion 19. It is formed in a state of penetrating the piece 22 in the vertical direction. Each accommodating hole 38 is formed in a rectangular shape in a plan view, and is provided for the spent nuclear fuel which is continuous in the vertical direction by the accommodating holes 38 provided in the upper and lower panels 14 (15, 16, 17), respectively. A containment space is formed as the first space.

FIG. 4 is a plan view of a portion of the second board 16. The main configuration of the second board 16 is the same as that of the third board 17, but in the second board 16, in addition to that, in the central portion 20 and the piece 22 of the peripheral portion 19, In addition to the accommodating holes 38, a large number of water storage holes 40 are formed so as to penetrate in the height direction. In the illustrated example, the water storage holes 40 are formed in a rectangular shape in a plan view, and as shown in FIG. 5, a second space continuous in the vertical direction by the water storage holes 40 provided in the upper and lower panels 16 respectively. Water storage space 41 is formed. By storing water in the water storage hole 40, the water storage space 41 functions as a water gap for the purpose of decelerating neutrons when the power plant pool is submerged.

A neutron absorber 42 is arranged in the water storage hole 40. Specifically, the neutron absorber 42 is formed of, for example, a boron-added aluminum alloy material, and is composed of a long strip material arranged over the upper and lower plates 16 and 16.

As shown in FIG. 5, the first board 15 is also formed with a water storage hole 43 for forming the water storage space 41. As shown in FIGS. 5 to 7, the neutron absorber 42 is arranged along the wall surface 44 for forming the water storage hole 40 in the second board 16. In the second board 16, no special means for holding the neutron absorber 42 on the wall surface 44 is provided. On the other hand, in the first board 15, the slit 45 through which the neutron absorber 42 having a rectangular cross section can be inserted in the vertical direction is formed thinner than the water storage hole 40 in the board 16 and is made of the board. It is provided in the vicinity of the water storage hole 43 communicated with the water storage hole 40 in 16.

With such a configuration, the neutron absorber 42 is held in the first board 15 by being passed through the slit 45 in the first board 15, and is held in the first board 16 in the second board 16. It is only arranged along the wall surface 44 and is not held by the second board 16 by any special means. As shown in the drawing, the second board 16 is provided with three bodies between the pair of the first board 15, 15 in the vertical direction. Therefore, in the end, the neutron absorber 42 has four boards. It will be held by only one slit 45 provided for each. Then, in order to hold the neutron absorber 42, it is sufficient to form a slit only in the first board 15, and it is not necessary to form a slit in the second board 16 for that purpose. The cost of the structure for holding the neutron absorber 42 can be reduced.

Since the basket for storing the spent nuclear fuel in the container according to the present invention has such a configuration, for example, the piece 22 of the peripheral edge portion 19 constituting each of the board 15, 16 and 17 is fixed to the fixture 27. After fixing to the inner peripheral surface 18 of the storage space 12 of the container 11 using the above, the central portion 20 is inserted into the storage space 25 formed thereby, and the upper and lower boards 15, 16 and 17 are not shown in the drawing. The basket 13 is constructed by aligning each other with a reamer pin and fastening with a tie rod (not shown). The constructed basket 13 can be accommodated in the accommodation space 25 of the container 11.

Then, according to the basket for storing the used nuclear fuel in the container according to the present invention, the piece 22 of the peripheral edge portion 19 is in a state where the curved surface 23 is in contact with the inner peripheral surface of the storage space 12 of the container 11. Since it is fixed to the container 11, even when a shocking external force is applied to the container 11, it is possible to effectively alleviate the occurrence of a situation in which stress concentration occurs particularly in the thin portion of the outer peripheral portion. ..

When the container 11 holding the basket 13 containing the spent nuclear fuel is in a sideways posture for some reason, the basket 13 inside the storage space 12 is changed from the state before the sideways orientation shown in FIG. 8A. That is, after the basket 13 is displaced from the state in which the gap 37 is formed over the entire circumference between the periphery of the central portion 20 and the inner circumference of the peripheral portion 19, and the basket 13 is turned sideways as shown in FIG. 8 (b). The state changes to a state in which the lower surface of the central portion 20 is in uniform surface contact with the inner surface formed by the flat surface 24 of the piece 22 at the peripheral portion 19. When the entire surface is in uniform surface contact, the container 11 holding the basket 13 containing the spent nuclear fuel falls (horizontal drop, inclined drop, corner drop, etc.) or falls, causing an impact on the container 11 sideways. Even when a load or the like is applied, it is possible to prevent local stress concentration from occurring in the basket 13, and it is possible to keep the constituent materials of the basket 13 in the elastic region. It should be noted that the case where the impact is received after the surface contact is uniform as described above, and in another case, for example, even if there is a gap before the impact, the surface contact is performed after the impact. It is also possible to suppress the occurrence of stress concentration by changing to the state of stress concentration.

Therefore, according to the present invention, sufficient strength can be imparted to the basket 13 even when the basket 13 is not made of a steel material or the like and an aluminum alloy having a lower strength than that of the basket 13 is used.

Also, if an aluminum alloy is used for the dry canister or cask basket used to store spent nuclear fuel, the aluminum alloy will be exposed to temperature conditions of 100 to 200 ° C for the 60-year design service period. Become. At this time, many aluminum alloys have aging properties, and if the over aging period is exceeded, the mechanical strength may decrease. Therefore, in post-storage transportation of canisters whose storage period has expired to reprocessing facilities, etc., the structural strength of the basket and the related safety functions must be evaluated by the mechanical strength in consideration of overaging.

According to the basket for storing the spent nuclear fuel in the container of the present invention, the dependence on the material strength is reduced by the optimum arrangement as described above, so that the mechanical strength exceeds the overaging. Even when the basket is made of an aluminum alloy with a reduced amount, the required structural strength can be achieved in the design.

In the above embodiment, the cross-sectional shape of the accommodation space 25 formed by the peripheral edge portion 19 of the basket 13 and the cross-sectional shape of the central portion 20 of the basket 13 are rectangular. However, these cross-sectional shapes are not limited to rectangular shapes, and are arbitrary as long as they have a structure in which stress concentration is unlikely to occur due to surface contact between the central portion 20 and the peripheral portion 19 of the basket 13 of the container 11. Can be in the form of.

For example, in another embodiment shown in FIG. 9, the outer peripheral surface 50 of the central portion 20 exhibits a complicated uneven structure. The inner surface of the accommodation space 25 also has a corresponding shape. However, the surfaces forming the unevenness are the surfaces 52, 52, ... Facing the first direction 51, and the second surface 54 facing the second direction 53 perpendicular to the first direction 51. , 54, ... Consists of only surfaces 52, 54 in two directions. Even with such a configuration, it is possible to change from the normal standing state shown in FIG. 9A to a state in which a part of the central portion 20 and a part of the peripheral portion 19 shown in FIG. 9B are in surface contact. Therefore, it is possible to prevent stress concentration from occurring in the basket 13. When the surface contact state shown in FIG. 9B is reached, the portion 56 in contact with the peripheral edge portion 19 is formed at a position and area as required among the surfaces 52 and 54 in the central portion 20. Can be done. By forming the portion 56 in contact with the peripheral edge portion 19 in this way, there is an advantage that the generated stress concentration can be relaxed.

FIG. 10 shows yet another embodiment of the present invention. Here, the central portion 20 is formed in an octagonal columnar shape. The inner surface of the accommodation space 25 also has a corresponding shape. Also in this case, when the normal standing state shown in FIG. 10 (a) is changed to the surface contact state shown in FIG. 10 (b), a part of the central portion 20 and a part of the peripheral portion 19 have an area as required. By surface contact, stress concentration can be prevented from occurring in the basket 13.

As described above, the cross-sectional shape of the accommodation space 25 formed by the peripheral edge portion 19 of the basket 13 and the cross-sectional shape of the central portion 20 of the basket 13 are not limited to those shown in the drawings, and are not limited to those shown in the drawings. In addition, for example, it may have a triangular cross section or any other shape.

11 Container 13 Basket 18 Inner peripheral surface 19 Peripheral part 20 Central part 22 Piece 25 Storage space 27 Fixture 31 One-sided inclined surface (one-sided pressing surface)
32 The other inclined surface (the other pressing surface)
38 Storage hole (first space)
41 Cooling water storage space (second space)

Claims (5)

It presents the structure of a basket that is housed in a container,
The basket has a peripheral edge portion arranged along the inner peripheral surface of the container and a central portion arranged at an inner position along the radial direction from the peripheral edge portion.
The peripheral edge is divided into multiple pieces along the circumferential direction.
Each piece is fixed in surface contact with the inner peripheral surface of the container.
The peripheral portion and the central portion are a state in which an inner surface of the peripheral portion and an outer surface of the central portion maintain a gap with each other, and an inner surface and a central portion of the peripheral portion due to displacement of the central portion from the state in which the gap is maintained. A basket for storing spent nuclear fuel in a container, which is configured to be in both a state in which the outer surfaces of the nuclear fuel are in surface contact with each other. Has a fixture for fixing the peripheral edge to the inner peripheral surface of the container,
The fixture according to claim 1, wherein the fixture is configured so that the end portion of one piece adjacent to each other in the circumferential direction and the end portion of the other piece can be fastened together with the inner peripheral surface of the container. A basket for storing spent nuclear fuel in a container. Fixtures
As well as being configured to be fastened to the container
One pressing surface for pressing the end of one piece toward the inner surface of the container when fastened to the container, and one with the end of the other piece facing the inner surface of the container when fastened to the container. The basket for storing the spent nuclear fuel according to claim 2, further comprising the other pressing surface for pressing together with the piece. The basket has a structure in which a plurality of boards are stacked one above the other, a first space for accommodating spent nuclear fuel is provided over the upper and lower panels, and a second for accommodating a neutron absorber. A basket for storing the spent nuclear fuel according to any one of claims 1 to 3, wherein the space is provided over the upper and lower panels. The basket has a slit through which a neutron absorber composed of long bodies arranged in the vertical direction over a plurality of boards can pass, and holds a part of the neutron absorber along the length direction. A first board configured to pass through the neutron absorber and a second board configured to pass the neutron absorber without holding other parts along the length direction of the neutron absorber without having the slit. A basket for storing the spent nuclear fuel according to claim 4, wherein the used nuclear fuel has and is stored in a container.

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