JP4280255B2 - How to handle casks and casks - Google Patents

Description

  The present invention relates to a cask containing spent fuel generated from a reactor core and a method for handling the cask.

  After being used for a certain period in the nuclear reactor nuclear reactor core, spent fuel taken out of the core is temporarily stored in a spent fuel storage pool in the power plant and cooled. Spent fuel whose specified cooling period has expired is stored in a cask with radiation shielding capability to recover reusable nuclear fuel materials such as uranium and plutonium, and transported to a reprocessing facility by trailer or ship. Is done. The spent fuel may be stored in a cask in an intermediate storage facility inside or outside the nuclear power plant before being transported to the reprocessing facility.

In general, a cask is composed of a trunk portion in which a housing portion for containing spent fuel is formed, and a primary lid and a secondary lid that are attached to an upper opening of the trunk portion. And the sealing state of a cask is maintained by sealing a secondary cover.
In addition, in order to reduce the shielding burden of the ceiling part of a storage facility, what a tertiary lid is attached on a secondary lid during a storage period is proposed (for example, refer to patent documents 1).
JP-A-11-287893

By the way, the radionuclide contained in the spent fuel decays with the passage of time according to each half-life, and the number of generated gamma rays decreases exponentially with the passage of time. Moreover, the number of neutron generations has the same tendency.
However, in the conventional cask, the thicknesses of the primary lid and the secondary lid are set by assuming the source intensity on the maintenance side without considering the attenuation of the radiation source during the storage period, and the thickness of the tertiary lid. Was set. For this reason, there has been a problem that the weight of the cask increases.
This is a factor that limits the number of spent fuels that can be accommodated, and also increases the total amount of shielding materials, particularly neutron shielding materials, which is also a factor of high cost.

  The object of the present invention is to reduce the weight while maintaining a predetermined shielding performance, and does not limit the number of spent fuel that can be accommodated, and the total amount of shielding material, particularly neutron shielding material It is an object of the present invention to provide a cask and a method for handling the cask that can reduce costs by reducing the cost.

To achieve the above objects, double the present invention, on the secondary lid for shielding the radiation to seal the upper opening of the body portion for accommodating the spent fuel, furthermore, shielding radiation positionable stacked Since several storage shielding lids are provided , multiple storage shielding lids can be stacked (stacked) according to the radiation dose equivalent rate of the spent fuel to be accommodated, and radiation is suitably shielded. be able to. That is, for example, at the beginning of storage, since the radiation dose equivalent rate is higher than after storage for a predetermined period, the number of storage shielding lids to be laminated is increased, and when the radiation dose equivalent rate decreases after storage for a predetermined period, The number of storage shielding lids can be reduced. That is, according to the cask that enables such handling, it is not necessary to form the primary lid and the secondary lid thickly from the beginning, so that the weight can be reduced. Further, by providing a dent in the bottom of the trunk of the cask and detachably attaching a bottom shielding material for shielding radiation to the dent, the radiation on the bottom side of the cask can be appropriately shielded. Furthermore, by arranging a neutron shielding material on the lower buffer covering the bottom of the body and the upper buffer covering the upper end of the body and the secondary lid, a cask excellent in radiation shielding during transportation can be obtained.
In the cask handling method of the present invention, radiation should be suitably shielded in the process of transporting the cask from the reactor building to the intermediate storage facility, and further to the reprocessing facility, or in the process of storing the cask in the intermediate storage facility. Can do.

  According to the present invention, it is possible to reduce the weight while maintaining a predetermined shielding performance, and it is not a factor that limits the number of spent fuel that can be accommodated, and the total amount of shielding material, particularly neutron shielding material. A cask and a method of handling the cask that can reduce the cost by reducing the cost.

Next, the cask of the present invention will be described in detail with reference to the drawings as appropriate.
(First embodiment)
The cask C of this embodiment includes a cask main body C1 (see FIG. 1) and buffer bodies 20 and 20 (see FIG. 8). As shown in FIG. 1, the cask main body C <b> 1 includes a cylindrical body 10 with a bottom, a primary lid 11 and a secondary lid 12 attached to an upper opening of the trunk 10, and a plurality of cask bodies C <b> 1 on the secondary lid 12. A storage shielding lid 13 (13a to 13d) attached so as to be capable of stacking sheets is provided. Further, a bottom shielding material 14 can be attached to the bottom of the body portion 10. As shown in FIG. 8, the buffer bodies 20, 20 are attached so as to cover the upper and lower portions of the cask main body C1, and protect the cask main body C1 from impact.

  The trunk | drum 10 consists of materials, such as carbon steel, and is exhibiting the bottomed cylindrical shape. A housing portion 10 </ b> A for housing spent fuel (not shown, the same applies hereinafter) is formed inside the body portion 10. The storage portion 10A is provided with a basket 10B that holds spent fuel. A shielding body 10 </ b> D that shields radiation is embedded in the circumferential wall 10 </ b> C of the trunk portion 10 in the entire circumferential direction. A total of eight trunnions 10E used for lifting and suspending the cask main body C1 are provided on the upper and lower portions of the peripheral wall 10C of the trunk portion 10 at a predetermined interval in the circumferential direction.

The primary lid 11 and the secondary lid 12 are made of a material such as carbon steel, and seal the upper opening of the body portion 10 to form a sealed boundary when the cask C is transported and stored.
As shown in FIG. 2, the primary lid 11 is placed on a lower stage 10 a having two upper and lower stages formed on the upper opening edge of the trunk part 10 so as to close the opening of the trunk part 10. 10b. The secondary lid 12 is placed on the upper stage 10c of the step portion so as to cover the primary lid 11, and is attached by a bolt 10d. Here, between the lower step 10a of the stepped portion and the primary lid 11, between the upper step 10c of the stepped portion and the secondary lid 12, or between the primary lid 11 and the secondary lid 12, there is a ring shape (not shown). The seal member is arranged. The primary lid 11 and the secondary lid 12 may be placed in a temporarily placed state on the lower stage 10a and the upper stage 10c in the process of handling the cask C as will be described later. That is, the primary lid 11 and the secondary lid 12 are used for the purpose of temporarily shielding the radiation during the handling operation of the cask C or the like. Thereby, the radiation dose equivalent rate in a work environment etc. can be reduced.

(Storage cover)
The storage shielding lid 13 (13a to 13d) is made of a material such as carbon steel, and is composed of disk-shaped plates having different diameters. As shown in FIG. 3, the storage shielding lid 13 has a structure including a neutron shielding material 13A capable of shielding radiation. It should be noted that the thickness of the storage shielding lid 13 and the material and thickness of the neutron shielding material 13A can be appropriately set in consideration of the type of spent fuel to be accommodated, the shielding ability of the storage building, and the like. As the neutron shielding material 13A, for example, a polymer resin such as polypropylene or polyethylene mixed with boron, or a neutron moderator (hydrogen, carbon, etc.) and a neutron absorber (boron, etc.) such as boric acid water are used. Including can be used. Then, as shown in FIG. 2, when the plurality of storage shielding lids 13 are laminated, the smaller the area away from the secondary lid 12, the smaller ones are sequentially laminated, and as a whole, stepwise in a side view. It is comprised so that it may be laminated | stacked. As a result, the closer to the center O of the cask main body C1, the greater the number of storage shielding lids 13 (13a to 13d) to be stacked, and the closer to the center O, the higher the radiation shielding ability. Yes. Among the storage shielding lids 13, the storage shielding lid 13 a located immediately above the secondary lid 12 is attached to the upper end portion of the body portion 10 by a bolt 10 e, and the other storage shielding lids 13 b to 13 d. Is attached to the upper surface of each of the storage shielding lids 13a, 13b, 13c located on the lower side by the attaching member 13e. Thereby, the storage which prevented the horizontal shift | offset | difference of the shielding cover 13 for storage in an earthquake etc. is realizable.

  FIG. 4 is an example showing the distribution of the radiation dose equivalent rate in the radial direction on the secondary lid 12 when a predetermined spent fuel is accommodated in the cask body C1 of the present embodiment, and the vertical axis represents the radiation dose. The equivalence ratio and the horizontal axis are distances from the center O of the cask main body C1. As shown in the figure, the radiation dose equivalent rate becomes maximum at the center O (distance 0), and gradually decreases as the distance from the center O increases. That is, it can be seen from this graph that the necessary shielding thickness around the secondary lid 12 can be thinner than the central portion. As described above, the storage shielding lid 13 of the present embodiment is laminated stepwise, and the portion closer to the center O is thickened to increase the radiation shielding capability, and therefore matches the characteristics shown in FIG. Therefore, the radiation can be shielded satisfactorily. Therefore, the cask main body C1 having a high radiation shielding capability can be obtained by using such a storage shielding lid 13.

Here, as described above, the radionuclides contained in the spent fuel decay with the passage of time according to the respective half-lives. For example, the number of generated gamma rays (number / second) in the spent fuel of a light water reactor is As shown in FIG. 5, it decreases exponentially with time. In FIG. 5, the vertical axis represents the number of generated gamma rays (relative value), and the horizontal axis represents the elapsed period (cooling period (year)) after the spent fuel is taken out.
Therefore, the storage shielding lid 13 attached to the secondary lid 12 so as to be capable of being laminated is handled so as to reduce the number of laminated layers in accordance with the radiation dose equivalent rate that decreases according to the storage period (information on the storage period). Thus, it is possible to install an appropriate number of sheets according to the handling and situation of the cask main body C1. That is, when the radiation dose equivalent rate at the beginning of storage is high, it is dealt with by stacking a plurality of storage shielding lids 13 corresponding to the radiation dose equivalent rate, and then, depending on the storage period, the storage shielding lid 13 A storage method of reducing the number of stacked layers can be adopted. Thereby, even when the primary lid 11 and the secondary lid 12 have insufficient radiation shielding performance, it is possible to cope with the problem by laminating the storage shielding lid 13. Therefore, it is not necessary to form the primary lid 11 and the secondary lid 12 thickly, and the weight can be reduced accordingly. Further, since an appropriate number of storage shielding lids 13 can be provided according to the situation, for example, the storage shielding lid 13 removed from the secondary lid 12 according to the storage period is replaced with another cask main body C1. It can be used for storage, and the shielding cover 13 for storage can be shared among a plurality of cask bodies C1, which is economical.

In addition, as a handling method of the cask C (cask main body C1), the number of storage shielding lids 13 is set in advance for each storage period, and a predetermined number of storage shields are stored for each storage period according to the setting. A method of reducing the storage shielding lid 13 from above the secondary lid 12 so as to become the lid 13 can also be adopted. In this case, for example, from the relationship between the storage period and the radiation dose equivalent rate, the number of layers of the storage shielding lids 13 for each storage period is set based on a map (not shown) created for each radiation dose equivalent rate at the beginning of storage. be able to. As an example, when the storage period is divided into five periods, the number of stacked layers in each storage period can be set as follows.
(Period 1) From 0 years to a years, four storage cover lids 13 (13a to 13d) are stacked.
(Period 2) From a + 1 year to b year, three storage shielding lids 13 (13a to 13c) are stacked.
(Period 3) From b + 1 year to c year, the two storage shielding lids 13 (13a, 13b) are laminated.
(Period 4) From c + 1 year to d year, only one storage cover 13 (13a) is stacked.
(Period 5) From d to the final year, the storage cover 13 (13a) is removed. That is, the radiation is shielded only by the primary lid 11 and the secondary lid 12.
By doing in this way, the lamination | stacking number of sheets for every storage period can be set easily.
In addition, it is possible to more reliably shield radiation by considering the number of stacked layers based on the measurement result (information on the measurement result) of the radiation dose equivalent rate in each storage period.
Depending on the measurement result of the radiation dose equivalent rate measured before storage, the storage shielding lid 13 may be unnecessary even when the storage is started, that is, even when the storage period is 0 years. In this case, since the primary lid 11 and the secondary lid 12 can cope with this, the storage shielding lid 13 can be used to store another cask body C1.

(Bottom shielding material)
As shown in FIG. 6, the bottom shielding material 14 has a configuration in which a neutron shielding material 14b is provided in a bottomed cylindrical container 14a made of a material such as carbon steel. As the neutron shielding material 14b, the same material as that used for the storage shielding lid 13 can be used. Such a bottom shielding material 14 is designed to be entirely accommodated in a recess 10F formed in the bottom of the body 10 (see FIG. 1, the same applies hereinafter). As a configuration for that purpose, the bottom shielding material 14 is used. 14 height dimension H1 is formed smaller than hollow dimension H2 of hollow part 10F. Accordingly, as shown by a two-dot chain line in FIG. 6, when the bottom shielding material 14 is accommodated and attached in the recess 10 </ b> F, the bottom shielding material 14 has a bottom surface 14 d higher than the bottom surface 10 f of the trunk portion 10. Will be located. In other words, the bottom surface 10f of the bottom shielding material 14 is located in the recess 10F. Such a bottom shielding material 14 is attached to the recess 10F by a bolt 14c.

As shown in FIGS. 7 (a) and 7 (b), the bottom shielding material 14 is usually attached to the hollow portion 10F at the bottom of the trunk portion 10 with the cask body C1 placed horizontally, as shown in FIGS. It is done. For attachment, an attachment tool 30 or the like suspended by a wire W on an overhead crane or the like provided in a receiving area of the reactor building or the like is used. The fixture 30 has a base portion 31 to which the wire W is connected and a holding portion 32 integrally projecting to the side of the base portion 31, and a bottom shielding material through the holding portion 32 from the base portion 31 side. The bottom shielding material 14 is attached to the side surface of the holding portion 32 by bolts 33 inserted into the 14 holding holes 14e (see FIG. 6). The holding | maintenance part 32 is provided with the shape and dimension which can be inserted in the hollow part 10F.
The mounting position of the wire W is such that the posture when the mounting tool 30 is suspended and moved by the wire W in a state where the bottom shielding material 14 is attached to the holding portion 32 is kept vertical. Has been adjusted and balanced. Thereby, when attaching the bottom part shielding material 14 to the hollow part 10F, the opposing surface of the bottom part shielding material 14 with the hollow part 10F does not damage the hollow part 10F due to a one-sided contact or the like.
In addition, with such a fixture 30, the bottom shielding material 14 disposed in the recess 10F is inserted through an insertion hole provided in the fixture 30 (not shown) while being held by the fixture 30. The bolt 14c (see FIG. 6) is fixed to the recess 10F. Then, after fixing, the bolt 33 is removed, and the fixture 30 is pulled away from the bottom shielding material 14.

As shown in FIG. 7C, in the state where the bottom shielding material 14 is attached to the recess 10F, the bottom shielding material 14 has a bottom surface 14d above the bottom surface 10f of the trunk portion 10 as described above (see FIG. 7C). In this case, as seen from the bottom shielding material 14, it is located on the housing portion 10A side on the left side in the drawing, so as shown in FIG. In this case, a gap S is formed between the bottom surface 14d of the bottom shielding material 14 and the floor surface G, and the bottom shielding material 14 is not subjected to external force from the floor surface G and the like, thereby simplifying the structure. it can.
Further, as shown in FIG. 7E, when the shock absorber 20 is attached to the lower portion of the body portion 10, the gap between the opposing surface 20a of the shock absorber 20 and the bottom surface 14d of the bottom shielding material 14 is still. Since the gap S is formed, the bottom shielding material 14 is prevented from coming into close contact with the buffer body 20.

(Buffer)
As shown in FIG. 8, the shock absorber 20 includes a lower shock absorber 20 </ b> A attached so as to wrap the bottom portion of the body portion 10, and an upper shock absorber attached so as to wrap the upper end of the body portion 10 and the secondary lid 12. 20B.
In the lower buffer body 20A and the upper buffer body 20B, a neutron shielding material 21 capable of shielding radiation is disposed at a portion facing the cask body C1. The neutron shielding material 21 is the same as that used for the above-described storage shielding lid 13 (reference numeral 13A, see FIG. 3). In the present embodiment, the lower shock absorber 20A and the upper shock absorber 20B have the same shape or substantially the same shape, and therefore, the lower shock absorber 20A will be described here. As shown in FIG. 9, the lower shock absorber 20 </ b> A has a concave cross section, and the outer shell portion is made of stainless steel or the like, and is filled with wood or a wooden board. The neutron shielding material 21 is disposed in a recess 22 formed in the center. 20 A of lower buffer bodies hold | maintain the state which wraps the surrounding surface of a lower part from the bottom part of the trunk | drum 10 by fitting the recessed part 22 in the bottom part (refer upper part in the upper buffer body 20B) of the trunk | drum 10 (refer FIG. 8), It will play a role in fully mitigating the impact of a fall.
Note that the lower shock absorber 20A and the upper shock absorber 20B are impacted within the allowable deformation amount against the drop in order to prevent a part of the cask body C1 (see FIG. 8) from landing in the event of a drop. Is to be absorbed.

  Such a shock absorber 20 is formed in the reactor building or the like, as shown in FIGS. 10 (a) and 10 (b), in a state where the cask main body C1 is placed horizontally, the bottom portion and the upper portion of the trunk portion 10 of the cask main body C1. (Only the bottom side is shown in the figure). The attachment is performed by being suspended by an overhead crane or the like provided in the carry-out area of the reactor building or the like with a wire W. The buffer body 20 is fixed to the cask main body C1 with a bolt or the like (not shown).

  FIGS. 11A to 11C show attachment to the cask main body C1 using the buffer body 20 'according to the modification. In the buffer body 20 ′ of this example, the neutron shielding material 21 is configured separately, and these are sequentially attached to the cask main body C <b> 1. That is, as shown in FIG. 11A, first, the neutron shielding material 21 is suspended from the cask main body C1 by a wire W or the like, and a bolt (not shown) or the like is attached to the bottom of the trunk portion 10 (the same applies below). Fixed. Thereafter, as shown in FIG. 11 (b), the buffer 20 'is suspended from the wire W or the like so as to approach the bottom of the trunk portion 10, and the neutron shielding material 21 is attached as shown in FIG. 11 (c). From above, it is fixed to the bottom of the body 10 with a bolt or the like (not shown). According to such a modified example, since the buffer 20 ′ and the neutron shielding material 21 are separated, the buffer 20 ′ and the neutron shielding material 21 can be managed individually, and the buffer 20 ′ is damaged. In the case of equality, it is economical because it can be dealt with by replacing only the buffer 20 ′.

Next, handling of such a cask C will be described with reference to FIGS. 12 to 14 (see other drawings as appropriate). In general, as shown in FIG. 12, the cask C is stored and transported to the intermediate storage facility 51 by a trailer T or a ship (not shown) after the spent fuel is accommodated in the nuclear power plant 50. Although it is transported to the reprocessing facility 52 after a predetermined storage period, the handling mainly in the nuclear power plant 50 and the intermediate storage facility 51 will be described in detail below.
As shown in FIG. 13 (a), the cask body C1 manufactured at the manufacturing factory or the cask body C1 (A1) stored in a cask storage (not shown) is connected to the reactor building of the nuclear power plant by the trailer T or the like. (B1). Here, in B1, since the cask main body C1 is horizontally placed on the trailer T and transported, the bottom shielding material 14 is attached to the bottom of the trunk portion 10 in this state. Incidentally, in the subsequent loading of spent fuel (not shown), the cask main body C1 is handled in a vertically placed state, so it is effective to attach the bottom shielding material 14 at this point.

In B2, the suspension arm of the overhead crane provided in the reactor building is held by the trunnion 10E of the cask main body C1, and the cask main body C1 is raised and conveyed to a spent fuel loading area (not shown). Although details in the loading area are not illustrated, in the loading area, the primary lid 11 and the secondary lid 12 are removed, and the primary lid 11 is temporarily tightened after the spent fuel is loaded in the accommodating portion 10A of the cask main body C1. . At this time, an additional shielding body having a radiation shielding function for preventing work exposure (not shown) is continuously mounted on the primary lid 11. Since this additional shielding body is mounted until the primary lid 11 is sealed, radiation can be suitably shielded during that time. Note that one additional shielding body is usually used, and is mounted directly on the primary lid 11 or on the upper end of the trunk portion 10, but a plurality of layers are arranged in a stacked manner like the storage shielding lid 13 of this embodiment. It can be set as a structure.
After that, the primary lid 11 is sealed and the secondary lid 12 is mounted. Here, a shielding body for transport exposure prevention (not shown) may be mounted on the secondary lid 12. This shielding body is particularly effective when using a buffer body to which a general neutron shielding material 21 is not attached in place of the buffer body 20 during transportation described later.

  Thereafter, the sealing of the secondary lid 12 is confirmed, the secondary lid 12 is mounted on the trailer T in the carry-out area, and the cask main body C1 is set on the trailer T so as to lie down (B3). At this time, the bottom side of the cask main body C1 is exposed toward the rear of the trailer. However, since the bottom shielding material 14 is disposed at the bottom, radiation is suitably shielded, and work exposure can be suitably prevented. it can. Thereafter, the cask main body C1 is transported by the trailer T to a cask storage such as in a nuclear power plant (B4), and the buffer body 20 (lower buffer body 20A, upper buffer body 20B) is attached to the cask main body C1 in the cask storage room. (D1). Thereafter, the cask C to which the buffer body 20 is attached is transported to the intermediate storage facility by the trailer T (D2).

  Here, as shown in FIG. 13 (b), in the carry-out area of the reactor building, the buffer body 20 (lower buffer body 20A, upper buffer body 20B) is mounted on the cask body C1 (B5), and the cask C is mounted. You may make it convey to an intermediate storage facility (D2). In this case, time and labor for transporting the cask main body C1 to the cask storage are saved, and the cost is reduced.

As shown in FIG. 14 (a), the cask C transported by the trailer T (E1) is carried into the receiving area of the intermediate storage facility (F1) and loaded and unloaded by a crane or the like (F2). Then, the buffer body 20 (lower buffer body 20A, upper buffer body 20B) is removed (F3). Here, the bottom shielding material 14 (not shown) is removed from the bottom of the cask main body C1, transported to a cask storage or a nuclear power plant, and reused. This is because the cask main body C1 is erected by a crane or the like in the subsequent procedure (F4), and then the cask main body C1 is placed vertically for a long period of time. The raised cask main body C1 is conveyed (F5), mounted on the inspection stand D (F6), and a sensor (not shown) is attached to perform an appearance inspection, a radiation dose equivalent rate inspection, and the like (F7).
At this time, a predetermined number of storage shielding lids 13 are attached on the secondary lid 12 mainly based on the inspection result by the radiation dose equivalent rate inspection. Here, the number of storage shielding lids 13 laminated on the secondary lid 12 is a predetermined number so that the radiation dose equivalent rate on the secondary lid 12 and around the installation location is equal to or less than a predetermined limit value. Laminated. In addition, the number of stacked layers can be set in consideration of the status (information) of radiation shielding facilities around the installation site.

Thereafter, the cask body C1 is transported to the storage area (G1).
And as shown in FIG.14 (b), storage for a predetermined period is performed (G2). During the storage period, the shielding performance inspection is performed. For example, as described above, based on the relationship between the storage period and the radiation dose equivalent rate, the storage performance is determined based on a map (not shown) created for each radiation dose equivalent rate at the beginning of storage. The handling which reduces the lamination | stacking number of sheets of the storage shielding lid | cover 13 for every period is performed. As a result, an accurate number of storage shielding lids 13 corresponding to the storage period can be stacked on the secondary lid 12, and radiation can be reliably shielded with a small number of sheets. The removed storage shielding lid 13 can be used for the cask main body C1 stored later, and the storage shielding lid 13 can be shared without waste.

After storage for a predetermined period, the cask body C1 is transported to a receiving area for transportation (H1). Here, the cask main body C1 is placed on the inspection platform D, and inspection before transportation is performed.
Thereafter, the cask main body C1 is lifted and conveyed (H2, H3), and is placed horizontally (H4). At this time, a bottom shielding material 14 (not shown) is attached to the bottom of the trunk portion 10 in order to prevent exposure during transportation during transportation.

Next, the buffer body 20 (lower buffer body 20A, upper buffer body 20B) is attached to the cask main body C1 (H5) and temporarily stored (H6). Thereafter, the cask C is lifted by a crane or the like, loaded on the trailer T (H7), and transported toward the reprocessing facility (J1).
It should be noted that the bottom shielding material 14 is removed from the cask main body C1 from which spent fuel has been taken out at the reprocessing facility, and is transported to a cask storage or a nuclear power plant (not shown) (A1 shown in FIG. 13A). reference).

Below, the effect acquired in this embodiment is demonstrated.
(1) In this embodiment, a plurality of storage shielding lids 13 for shielding radiation can be stacked on the secondary lid 12 for shielding the radiation by sealing the upper opening of the body portion 10 for containing the spent fuel. Accordingly, a plurality of storage shielding lids 13 can be stacked and attached in accordance with the radiation dose equivalent rate of the spent fuel to be accommodated, and radiation can be suitably shielded. That is, for example, at the beginning of storage, since the radiation dose equivalent rate is higher than after storage for a predetermined period, the number of layers of the storage shielding lid 13 is increased, and when the radiation dose equivalent rate decreases after storage for a predetermined period, The number of storage shielding lids 13 can be reduced. That is, according to the cask C that enables such handling, it is not necessary to form the primary lid 11 and the secondary lid 12 thick from the beginning, so that the weight can be reduced.
(2) Since the weight of the cask C can be reduced, the number of spent fuels that can be accommodated is not limited, and the total amount of the shielding material, particularly the neutron shielding material 13A, does not increase, resulting in high cost. It will never be.
(3) Based on the distribution of the radiation dose equivalent rate on the secondary lid 12, a plurality of storage shielding lids 13 can be stacked in a state in which the radiation dose equivalent rate is higher than other sites. Since it is provided, it is possible to positively shield a part having a high radiation dose equivalent rate, in other words, a part that needs to shield radiation with a storage shielding lid 13 that is laminated in comparison with other parts, Efficient radiation shielding can be realized. In other words, it is not necessary to shield the whole in accordance with the strictest radiation dose equivalent rate uniformly, and a substantial weight reduction can be realized. Further, since it is not necessary to enclose the neutron shielding material 13A in the primary lid 11 and the secondary lid 12, the cost can be reduced correspondingly.
(4) In the present embodiment, since the storage shielding lid 13 is detachably provided on the secondary lid 12, the number of laminated layers is suitable in accordance with the measurement result of the radiation dose equivalent rate. It can be adjusted and attached. In addition, after the storage period has elapsed, the work of reducing the number of the storage shielding lids 13 can be easily performed by removing the attachment member 13e.
(5) A configuration in which a predetermined number of storage shielding lids 13 are stacked on the secondary lid 12 based on a predetermined relationship between the storage period of the cask main body C1 and the radiation dose equivalent rate on the secondary lid 12. In this case, the operator can obtain a suitable number of stacked layers uniformly from the above relationship without performing a complicated inspection as in the prior art, so that the handling of the cask C becomes easier. In this case, more certain radiation shielding can be realized by carrying out a certain type of inspection in combination.
(6) When a configuration is adopted in which a predetermined number of storage shielding lids 13 are stacked on the secondary lid 12 so that the radiation dose equivalent rate around the place where the cask main body C1 is installed is equal to or less than a predetermined limit value. The storage shielding lid 13 can be attached in the number of layers in consideration of the surrounding shielding ability in which the cask main body C1 is stored. Therefore, when the shielding capacity of the intermediate storage facility is high, it is possible to mount the storage shielding lid 13 by reducing the number of laminated layers of the storage shielding lids 13 as compared with the normal one. Therefore, it is possible to prevent the number of the storage shielding lids 13 from being excessively stacked.
(7) The storage shielding lid 13 is composed of disk-shaped plates having different diameters, and when a plurality of layers are laminated, the smaller the area away from the secondary lid 12 is laminated, the whole Therefore, the closer to the center O of the cask main body C1, the more the number of storage shielding lids 13 (13a to 13d) to be stacked, and the closer to the center O, the more capable of shielding radiation. Get higher. Therefore, a part where the radiation dose equivalent rate is higher than other parts, for example, as shown in FIG. 4, preferably matches the characteristics of the cask main body C1 where the radiation dose equivalent rate is maximum at the center O (distance 0). Can be. Thereby, shielding of radiation can be reliably performed with the minimum shielding cover 13 for storage. Further, since the storage shielding lids 13 are stacked stepwise, the operator can visually grasp the current radiation shielding status by the stacked height.
(8) Since the storage shielding lid 13 includes the neutron shielding material 13A, it is not necessary to provide the neutron shielding material 13A on the primary lid 11 and the secondary lid 12, and accordingly, the primary lid 11 and the second lid The weight of the next lid 12 can be reduced. Moreover, since the required number of storage shielding lids 13 are stacked according to the radiation dose equivalent rate, the weight of the cask main body C1 can be reduced as a whole.
(9) Since the storage shielding lid 13 can be mounted and set in advance on the secondary lid 12, it is possible to realize handling of the cask main body C1 in consideration of prevention of work exposure until storage. it can. In addition, based on at least one of the measurement result of the radiation dose equivalent rate on the secondary lid 12 and the storage period, it is handled so that the number of stacked layers is reduced, thereby preventing more reliable work exposure. Can be realized.
(10) Since the bottom shielding material 14 is attached to the bottom portion of the trunk portion 10, the radiation on the bottom side of the cask body C1 is well shielded when the cask body C1 is tilted sideways (such as during transportation). Can do.
(11) Since the bottom shielding material 14 is detachably attached to the bottom depression 10F, it can be attached and used when radiation shielding is necessary in the handling process of the cask body C1. When the bottom shielding member 14 is unnecessary, such as in a vertically placed state where the bottom of the portion 10 faces the floor, it can be removed to reduce the weight of the cask main body C1.
(12) The bottom shielding material 14 is entirely accommodated in the bottom recess 10F, and its bottom surface 14d is positioned above the bottom surface 10f of the body portion 10, so that FIG. As shown in (d), when the trunk portion 10 is placed from the horizontal position to the vertical position, a gap S is formed between the bottom surface 14d of the bottom shielding material 14 and the floor surface G and the like, thereby shielding the bottom portion. Since the material 14 does not receive an external force from the floor G or the like, the structure can be simplified, and the cost can be reduced accordingly.
(13) Since the buffer body 20 (the lower buffer body 20A and the upper buffer body 20B) is provided with the neutron shielding material 21 capable of shielding radiation at the portion facing the cask main body C1, respectively, during transportation Thus, radiation can be shielded reliably. In addition, in the buffer body 20 ′ of the modified example, in which the neutron shielding material 21 is detachably provided, the buffer body 20 ′ and the neutron shielding material 21 can be managed separately. When 20 'is damaged or the like, it can be dealt with by replacing only the buffer 20', which is economical.

(Second Embodiment)
The cask C which is 2nd Embodiment is demonstrated. The cask C of the present embodiment is characterized by a storage shielding lid 13 ′ attached on the secondary lid 12 of the cask main body C 1, and the other points are not changed. As shown in FIGS. 15 (a) and 15 (b), the storage shielding lid 13 '(13a', 13b ', 13c', 13d ') is made of a material such as carbon steel, and has a plan view with different diameters. It is composed of an annular plate. The storage shielding lid 13 'has a structure including a neutron shielding material 13A (not shown) capable of shielding the same radiation as in the above embodiment. Note that the thickness of the storage shielding lid 13 'and the material and thickness of the neutron shielding material 13A can be appropriately set in consideration of the type of spent fuel to be accommodated, the shielding ability of the storage building, and the like.

Further, as shown in FIG. 15 (a), when a plurality of storage shielding lids 13 'are stacked, those having a smaller area are sequentially stacked as they are separated from the secondary lid 12, and as a side view as a whole. It is comprised so that it may laminate | stack in step shape.
FIG. 16 is an example showing the distribution of the radiation dose equivalent rate in the radial direction on the secondary lid 12 when a predetermined spent fuel is accommodated in the cask main body C1 of this embodiment, and the vertical axis represents the radiation dose. The equivalence ratio and the horizontal axis are distances from the center O of the cask main body C1. In this example, spent fuel with a high burnup is arranged around the radial direction of the secondary lid 12, and spent fuel with a low burnup is arranged at the center. As shown in FIG. The dose equivalent rate is maximized at a predetermined distance from the center O (distance 0), and then rapidly decreases. That is, as described above, the radiation dose equivalent is that the storage shielding lid 13 ′ has an annular shape and is stacked in a step shape and is stacked at a predetermined distance from the center O. It is consistent with the rate distribution. Therefore, a cask C having a high radiation shielding capability can be obtained by using such a storage shielding lid 13 '.

This embodiment has the effects described below in addition to the effects (1) to (13).
(14) In the present embodiment, in combination with the radiation dose equivalent rate on the secondary lid 12, the useless area of the storage shielding lid 13 ′ is substantially eliminated, and the weight can be reduced.
Regardless of the arrangement of spent fuel to be accommodated, as a result of the measurement of the radiation dose equivalent rate in the intermediate storage facility, the distribution of the radiation dose equivalent rate shown in FIG. 4 of the first embodiment and the result shown in FIG. When a radiation dose equivalent rate distribution that is a combination of the radiation dose equivalent rate distribution is obtained, the storage shielding lid 13 and the storage shielding lid 13 'shown in the first embodiment are appropriately combined. By configuring the storage shielding lid, it is possible to obtain a cask C having a high radiation shielding capability that flexibly corresponds to the distribution of the radiation dose equivalent rate.

It is sectional drawing which shows the structure of the cask main body in the cask which concerns on 1st Embodiment. It is an expanded sectional view which shows the upper part of the cask main body of FIG. It is a model expanded sectional view of the shielding cover for storage. It is the graph which showed the relationship between the radiation dose equivalent rate and the distance from the center of a cask main body. It is the graph which showed the relationship between the gamma ray generation number and a cooling period. It is an expanded sectional view which shows a bottom part shielding material. (A)-(e) is the schematic diagram which showed the aspect which concerns on a bottom part shielding material. It is sectional drawing of the cask of the state which attached the buffer. It is sectional drawing of the lower buffer body which concerns on 1st Embodiment. (A) (b) is a schematic diagram which shows attachment of a buffer. (A)-(c) is a schematic diagram which shows the attachment of the buffer body of a modification. It is a schematic diagram which shows the outline | summary of handling of a cask. (A) (b) is a schematic diagram which shows the handling of a cask. (A) (b) is a schematic diagram which shows the handling of a cask. (A) is an expanded sectional view which shows the upper part of the cask main body in the cask which concerns on 2nd Embodiment, (b) is a top view similarly. It is the graph which showed the relationship between the radiation dose equivalent rate and the distance from the center of a cask main body.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 trunk | drum 10A accommodating part 10D neutron shielding body 10F hollow part 11 primary lid 12 secondary lid 13 storage shielding lid 13A neutron shielding material 13a-13d storage shielding lid 13e mounting member 14 bottom shielding material 14d bottom surface 14e holding hole 20 Body 20A Lower shock absorber 20B Upper shock absorber 21 Neutron shielding material 22 Recess 30 Attachment tool 31 Base 32 Holding portion 50 Nuclear power plant 51 Intermediate storage facility 52 Reprocessing facility C Cask C1 Cask body

Claims (18)

A cask for transporting or storing spent fuel,
A cylindrical body having a bottom with an accommodating portion for accommodating the spent fuel therein and an upper opening of the trunk are sealed, and radiation from the spent fuel accommodated in the trunk is received. A primary lid and a secondary lid for shielding,
Wherein on the secondary lid further cask, characterized in that it comprises a multiple number of sheets of storage for shielding lid you shielding radiation positionable stacked. A cask for transporting or storing spent fuel,
A cylindrical body having a bottom with an accommodating portion for accommodating the spent fuel therein and an upper opening of the trunk are sealed, and radiation from the spent fuel accommodated in the trunk is received. A primary lid and a secondary lid for shielding,
Based on the distribution of radiation dose equivalent rate on the secondary lid,
On the secondary lid, a plurality of storage shielding lids for shielding radiation that can be placed in a stack .
A cask characterized in that the cask is installed at a position where at least a radiation dose equivalent rate on the secondary lid is higher than other parts. The cask according to claim 1 or 2 , wherein the storage shielding lid is detachably provided on the secondary lid one by one . The storage shielding lid is disposed by stacking a predetermined number on the secondary lid based on a predetermined relationship between a storage period and a radiation dose equivalent rate on the secondary lid. The cask according to any one of claims 1 to 3 . It said storage for shielding lid, as the radiation dose equivalent rate at the location near becomes less pregiven limit values, from claim 1, characterized in that it is arranged in a stack a predetermined number on to the secondary lid cask according to any one of claims 4. Before Symbol storage for shielding lid is composed of different disk-shaped plate diameters mutually, when placed in stacked plurality, smaller ones stacked et al is in the area as a departure from the secondary lid, cask according to any one of claims 1 or we claim 5, characterized in that the overall stepwise stacked. Before Symbol storage for shielding lid, cask according to any one of claims 1 or we claim 6, characterized in that an annular shape in plan view. Before Symbol storage for shielding lid, cask according to any one of claims 1 or we claim 7, characterized in that it comprises a neutron shielding material. A cask for transporting or storing spent fuel,
A cylindrical body having a bottom with an accommodating portion for accommodating the spent fuel therein and an upper opening of the trunk are sealed, and radiation from the spent fuel accommodated in the trunk is received. A primary lid and a secondary lid for shielding,
On the secondary lid further stacked established the storage for shielding lid double several sheets you shield deployable radiation, the measurement of radiation dose equivalent rate on the secondary lid results, and the storage period A cask characterized in that the number of stacked layers is reduced based on at least one of them. A cask for transporting or storing spent fuel,
A cylindrical body having a bottom with an accommodating portion for accommodating the spent fuel therein and an upper opening of the trunk are sealed, and radiation from the spent fuel accommodated in the trunk is received. A primary lid and a secondary lid for shielding,
A hollow portion provided at the bottom of the trunk portion, and provided so as to be attachable to and detachable from the hollow portion, and in a state where the whole is accommodated in the hollow portion, its bottom surface is located in the hollow portion and shields radiation. A cask comprising a bottom shielding material. The cask according to any one of claims 1 to 9 ,
A cask comprising: a hollow portion provided at a bottom portion of the body portion; and a bottom shielding material that is detachably attached to the hollow portion and shields radiation. It said bottom shielding member in a state where whole the recess portion is accommodated, cask according to 請 Motomeko 11 you characterized in that the bottom surface of the bottom shielding member is located within the recess. When the bottom shielding material is attached to and detached from the depression, the bottom shielding material is fixed to the fitting that hangs and moves from the side facing the depression to the depression, while maintaining a vertical posture in the depression. The cask according to any one of claims 10 to 12 , wherein the cask is inserted or pulled out from the recess. A cask for transporting or storing spent fuel,
A cylindrical body having a bottom with an accommodating portion for accommodating the spent fuel therein and an upper opening of the trunk are sealed, and radiation from the spent fuel accommodated in the trunk is received. A cask body including a primary lid and a secondary lid for shielding ,
A lower shock absorber attached to wrapping the bottom of the body,
An upper buffer attached to the upper end of the body and the secondary lid so as to enclose the secondary lid, a portion facing the bottom of the lower buffer, and a portion facing the secondary lid of the upper buffer In addition, neutron shielding materials are respectively arranged ,

The said neutron shielding material is comprised separately from the said lower buffer body and the said upper buffer body, The cask characterized by being provided with respect to the said cask main body so that attachment or detachment was possible . The cask according to any one of claims 10 to 13 ,
A lower shock absorber attached to wrapping the bottom of the body,
An upper buffer attached to the upper end of the body and the secondary lid so as to enclose the secondary lid, a portion facing the bottom of the lower buffer, and a portion facing the secondary lid of the upper buffer In addition, neutron shielding materials are respectively arranged ,
The said neutron shielding material is comprised separately from the said lower buffer body and the said upper buffer body, The cask characterized by being provided with respect to the said cask main body so that attachment or detachment was possible . A cask handling method for handling the cask according to any one of claims 1 to 11,
A loading procedure for loading the cask into the reactor building;
A first transport procedure for transporting spent fuel to the intermediate storage facility after loading spent fuel in a cask pit installed in the reactor building;
An acceptance procedure for accepting the cask into the intermediate storage facility;
A storage procedure for long-term storage of the received cask;
A second transport procedure for transporting the cask to a reprocessing facility after storage;
Including
In the receiving procedure, on the secondary lid of the cask, further stacking a plurality of the shielding lids for storage,
In the storage procedure, based on at least one of the information on the measurement result of the radiation dose equivalent rate around the cask, the information on the radiation shielding equipment situation around the installation site, and the information on the storage period, Reduce the number of storage shielding lids stacked on the next lid to a predetermined number,
In the second transporting procedure, the cask handling method is characterized in that the storage shielding lid is removed from the cask. A cask handling method for handling a cask according to any one of claims 10 to 13 ,
A loading procedure for loading the cask into the reactor building;
A first transport procedure for transporting spent fuel to the intermediate storage facility after loading spent fuel in a cask pit installed in the reactor building;
An acceptance procedure for accepting the cask into the intermediate storage facility;
A storage procedure for long-term storage of the received cask;
A second transport procedure for transporting the cask to a reprocessing facility after storage;
Including
In the carrying-in procedure, the bottom shielding material is attached to the hollow portion provided at the bottom of the trunk portion,
In the receiving procedure, the bottom shielding material is removed from the recess,
In the second conveying procedure, the cask handling method is characterized in that the bottom shielding material is attached to the recess. A cask handling method for handling the cask according to claim 14 or 15 ,
A loading procedure for loading the cask into the reactor building;
A first transport procedure for transporting spent fuel to the intermediate storage facility after loading spent fuel in a cask pit installed in the reactor building;
An acceptance procedure for accepting the cask into the intermediate storage facility;
A storage procedure for long-term storage of the received cask;
A second transport procedure for transporting the cask to a reprocessing facility after storage;
Including
At the time of transporting the cask in the first transport procedure and the second transport procedure, the lower shock absorber is attached to the bottom of the trunk portion of the cask, and the upper portion of the cask is placed on the secondary lid. Attach a buffer,
When receiving the cask in the receiving procedure, the lower shock absorber is removed from the bottom of the trunk portion, and the upper shock absorber is removed from the secondary lid.

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