JP2005241314A - Spent fuel storing basket and spent fuel container - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spent fuel storing basket capable of improving criticality prevention performance, without increasing the cask outside diameter, even in the case of a basket having grid-like compartments by a cake-box structure. <P>SOLUTION: In the basket, provided with grid-like compartments for arranging fuels therein formed, by combining grid members having respectively a cavity part inside in the longitudinal and lateral directions, grid members having respectively the narrowest cavity part are arranged in between the fuel in the outermost side row and the fuel in the next inside row, in the longitudinal and lateral directions respectively. Hereby, the number of stored fuel bodies can be increased, while keeping full criticality-preventing performance, as it is. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a storage basket for a transport / storage container for spent fuel generated from the core of a nuclear reactor.

  The spent fuel that has been used in the reactor core for a certain period of time is taken out of the core, temporarily stored in a spent fuel storage pool in the power plant, and cooled. The fuel whose predetermined cooling period has ended is transported to a reprocessing plant and reprocessed to recover reusable nuclear fuel materials such as uranium and plutonium. In recent years, due to delays in the construction of reprocessing plants, there is a possibility that the amount of temporary storage of spent fuel may exceed the storage limit of the spent fuel storage pool. Therefore, it is planned to temporarily store the spent fuel in intermediate storage facilities inside and outside the power plant before the reprocessing step.

  The metal cask storage system is one of intermediate storage systems, and has attracted attention from the viewpoint of cost reduction and long-term stable storage. The metal cask has a structure in which a basket having a plurality of compartments for storing spent fuel is disposed inside a spent fuel container (cask), thereby storing the fuel in a partitioned state. ing.

  FIG. 2 shows an example of a storage basket for a conventional transport / storage container for spent fuel. FIG. 2A is a view showing a horizontal section of the basket, and FIG. 2B is a perspective view of a part of the basket. In the basket shown in FIG. 2, the lattice members 1 are configured by arranging plate-like members 1 a facing each other at intervals, and a plurality of compartments in which fuel is arranged by combining the lattice members. As a specific structure, for example, as disclosed in JP-A-8-136695 [Patent Document 1], the first lattice member group aligned in parallel to one direction and the one direction are described. The second lattice member group aligned in parallel with each other in the direction perpendicular to each other is alternately stacked in the axial direction. Here, slits are provided at portions intersecting at right angles to constitute a so-called confectionery folding structure.

  The basket holds the fuel in the compartment to prevent damage due to collision between the fuels, and transmits heat released from the fuel to the container to keep the fuel temperature below a temperature at which the soundness of the fuel is maintained. In addition, the basket also serves to prevent the stored fuel from reaching criticality. For this purpose, as the material of the lattice member 1 of the basket, stainless steel or aluminum to which boron as a neutron absorber is added is generally used. Moreover, in order to improve the criticality prevention performance, as shown in FIG. Fuel in pressurized water reactors (PWR) is more critical than fuels in boiling water reactors (BWR) because of the high number of fuel rods per fuel assembly and large fuel assembly size It is easy to become. Therefore, the gap 2 is provided in the lattice member of the spent fuel basket of the PWR.

  The effect of this void will be described below. The cask must have a structure that is not critical in any conceivable case. For this reason, when evaluating the subcriticality of the cask, it is assumed that the cask is flooded. This is because neutrons are decelerated by water, so that the reactivity of the fuel becomes high and the condition becomes most critical. At this time, the gap portion of the lattice member is also filled with water. By doing so, when neutrons generated in a certain fuel are not absorbed by the lattice member surrounding the fuel and permeate and leak into the gap, they are decelerated by the water in the gap. Since boron has a property of absorbing neutrons with lower energy better, the more the neutrons are decelerated in the voids, the higher the probability that they will be absorbed by the lattice member when they reach the lattice member again. In addition, since the probability of being absorbed by the water itself in the void portion increases, the criticality prevention performance improves as the void portion becomes wider. On the other hand, when the gap is narrow, it reaches the lattice member before it is sufficiently decelerated, so that there is a high probability that it will permeate without being absorbed by the lattice member and reach the fuel again. In addition, when there is no gap, neutrons that have passed through the lattice member reach the adjacent fuel as they are, which is inferior from the viewpoint of criticality prevention performance.

  Another structure of the PWR spent fuel container basket is disclosed in, for example, Japanese Patent No. 3150676 [Patent Document 2]. The basket shown in Japanese Patent No. 3150676 has a rectangular tubular member formed by bonding plate-like members provided with convex portions so that the convex portions are joined to each other as shown in FIG. Use. The plate member is made of aluminum to which boron, which is a neutron absorber, is added. This square tubular member is provided with a cut portion, and a confectionery folding structure is formed by combining the cut portions at right angles so as to fit each other as shown in FIG. Here, the hollow portion of the square tube plays a role of increasing criticality prevention performance by decelerating neutrons and enhancing the neutron absorption effect in the plate-like member.

  Still another structure of the PWR spent fuel container basket is the NFT-14P type shown on the left side of Figure I.7 on page 140 of the document "All radioactive material transport, 2nd edition" (Nikkan Kogyo Shimbun). Some are like cask. FIG. 13 shows the basket structure of the NFT-14P type cask. The basket of the NFT-14P type cask has a structure in which a rectangular tubular fuel storage member (channel) that holds fuel is fixed by a disk-shaped member (support ring) arranged in the axial direction. The fuel storage members are spaced apart from each other in order to enhance criticality prevention performance. The NFT-14P type cask basket has a greater degree of freedom in fuel placement than the basket with a confectionery fold structure as disclosed in JP-A-8-136695 and Japanese Patent No. 3150676. There is an advantage that it can be stored. That is, in the baskets shown in these conventional examples, the section in which the fuel is disposed is limited to a lattice shape, and therefore, when stored in a substantially cylindrical container, a wasteful space is generated between the container and the fuel. However, since the NFT-14P type cask basket is not limited to the lattice arrangement of the fuel, it can be stored without generating the useless space.

  However, in the role of transferring the heat generated by the fuel to the container and keeping the fuel temperature below the temperature at which the soundness of the fuel is maintained, the baskets disclosed in Japanese Patent Application Laid-Open Nos. 8-136695 and 3150676 are disclosed. As described above, a structure in which the fuel partitioning portion and the portion in contact with the container are constituted by one grid plate is more advantageous. In the case of a structure such as an NFT-14P type cask basket, in order to efficiently transmit heat generated by the fuel to the container, a rectangular tubular fuel storage member that partitions the fuel and a disk shape that fixes the fuel storage member It is necessary to prevent a large gap from occurring between the members. For this reason, for example, it is necessary to fix a fuel storage member and a disk-shaped member by welding etc., and there exists a problem which manufacturing cost becomes high.

JP-A-8-136695 Japanese Patent No. 3150676

  In order to reduce transportation costs and storage costs and increase economic efficiency, there is an increasing need to increase the number of stored fuel bodies per metal cask. As the number of stored fuel bodies increases, the temperature of the fuel disposed at the center tends to be higher, so it is important to efficiently transfer heat generated by the fuel to the container. For this reason, a basket with a confectionery fold structure as shown in JP-A-8-136695 and Japanese Patent No. 3150676 is advantageous. However, since the outer diameter of the metal cask is limited by the specifications of the storage facility, in order to increase the number of stored fuel bodies per cask, the distance between the fuels inevitably has to be reduced. For this reason, in the case of a basket having lattice-like sections due to the confectionery folding structure, the gap between the fuels is relatively narrowed, and the performance of keeping the fuel in a subcritical state is lowered.

  An object of the present invention is to provide a spent fuel storage basket that can improve the criticality prevention performance without increasing the cask outer diameter even in a basket having a lattice-like section by a confectionery folding structure based on the above problems. That is.

In order to achieve the above-mentioned object, the present invention is provided in a spent fuel container for storing or transporting spent fuel, and is provided with a compartment for storing spent fuel by combining lattice members. In the fuel storage basket, the lattice member has a void portion inside, and the spent fuel is more than the first lattice member in comparison with the void portion of the first lattice member on the center side in the spent fuel container. The void portion of the second lattice member outside the container is narrowed.
In the spent fuel storage basket, the present invention is characterized in that two plate-like members are arranged face-to-face, and a gap is formed between the two plate-like members to form a gap portion of the lattice member. It is what.
In the spent fuel storage basket, the present invention is characterized in that the lattice member is constituted by a rectangular tubular member having a cavity inside.
Further, in the spent fuel storage basket according to the present invention, the second lattice member is disposed between the fuel placed on the outermost side from the center of the spent fuel container and the fuel placed on the inner side of the fuel. It is characterized by that.
Further, the spent fuel storage basket of the present invention is provided in a spent fuel container for storing or transporting spent fuel, and is a lattice shape for storing spent fuel by combining lattice members vertically and horizontally. In the spent fuel storage basket provided with the section, the lattice member has a gap portion therein, and in at least one of the vertical row and the horizontal row, the first lattice member group that is close to the center of the row And the second lattice member group in a position close to the outer row, the average value of the width of the void portion of the second lattice member group is the average value of the width of the void portion of the first lattice member group. It is characterized by being narrower than.

  Further, the spent fuel storage basket of the present invention includes a lattice member having a narrowest gap in each row in at least one of the vertical row and the horizontal row, the fuel in the outermost row and the inside thereof. It is characterized by being arranged between the fuels in the row.

  In the spent fuel storage basket of the present invention, the lattice member having the narrowest gap in each of the vertical row and the horizontal row is divided into the outermost row fuel and the inner row fuel. It arrange | positions between.

Further, the spent fuel storage basket of the present invention is preferably arranged in the above-described configuration, wherein the width of the gap is arranged closer to the center of each row in at least one of the vertical row and the horizontal row. When g ₁ , g ₂ ,..., G _n−1 , g _n are determined from the lattice members, the following relationship is satisfied.

g ₁ > = g ₂ > = ...> = g _n-1 > g _n
However, g _n denotes an air gap width of the grid member disposed between the fuel outermost fuel and columns in the inner row.

  In the spent fuel storage basket of the present invention, the gap width of the lattice member disposed between the fuel in the outermost row and the fuel in the inner row is preferably g, When g ′ is the narrowest gap width of the lattice members other than the above, the following relationship is satisfied in each of the vertical and horizontal columns.

0.4 <g / g ′ <0.8
By the way, in the spent fuel storage basket of the present invention, the lattice member means, for example, that two plate-like members are arranged in a face-to-face manner, and a gap is formed by providing a gap between the plate-like members, or A square tubular member having a cavity inside may be used as the lattice member.

  According to the spent fuel storage and transport container provided with the spent fuel storage basket of the present invention, it is possible to increase the number of stored fuel bodies while maintaining sufficient heat removal performance and criticality prevention performance.

FIG. 1 shows a horizontal cross section of a spent fuel storage basket in the first embodiment of the present invention. The basket in the first embodiment includes two plate-like members arranged in a face-to-face manner, and is configured by a lattice member that forms a gap by providing a gap between the plate-like members, and is provided in a spent fuel container. It is. Below, let the distance between plate-shaped members be the space | gap part width | variety of a lattice member. By disposing the lattice members vertically and horizontally between the fuels, a lattice-shaped section for storing 24 PWR spent fuels is formed. Here, in FIG. 1, the vertical columns of fuel arranged vertically and horizontally are called the first column, the second column,..., The sixth column from the left side, and the horizontal columns are the first row, the second row,. Let's call it 6 lines. In the present embodiment, the center of the vertical and horizontal columns, that is, the center of the spent fuel container, is between the third column and the fourth column and between the third row and the fourth row, respectively. In the present embodiment, the gap widths of the gap portions 2a of the lattice members disposed between the fuels in the third column and the fourth column and between the fuels in the third row and the fourth row are set to the same g ₁ , The gap widths of the gap portions 2b of the lattice members arranged between the fuel in the third column, the fourth column and the fifth column, the second row and the third row, and the fourth row and the fifth row are the same g ₂ , Further, the gap width of the gap portion 2c of the lattice member disposed between the fuel in the first column and the second column, the fifth column and the sixth column, the first row and the second row, and the fifth row and the sixth row is set. It is the same g _3. When the gap widths are arranged from those of the lattice members arranged closer to the center of the row, g ₁ , g ₂ , and g _{3 are obtained} , and the following relationship is satisfied.

g ₁ > g ₂ > g ₃
Next, the effect by this invention is shown. FIG. 3 shows the result of calculating the change in effective multiplication factor when the relationship between g ₁ , g ₂ , and g ₃ is changed so that the cask outer diameter is constant. At this time, the uranium enrichment of the PWR fuel was 4.2 wt%, and a 15 mm thick stainless steel plate to which 1 wt% boron was added was used as a plate member constituting the lattice member. As is apparent from FIG. 3, the effective multiplication factor can be reduced when the basket structure (g ₁ > g ₂ > g ₃ ) according to the present invention is used as compared with the conventional example (g ₁ = g ₂ = g ₃ ). . Therefore, the criticality prevention performance can be improved without increasing the cask outer diameter. In the analysis shown in FIG. 3, g ₁ = 44 mm, g ₂ = 38 mm, and g ₃ = 22 mm, but the combination of values that can reduce the effective multiplication factor varies depending on the lattice plate thickness and the boron concentration added to the lattice plate. obtain. However, the configuration that satisfies the relationship of g ₁ > g ₂ > g ₃ can still realize the optimum combination.

FIG. 4 shows an example of the lattice member 1 for constituting the present invention. The size of the gap widths g ₁ , g ₂ , and g ₃ of the lattice member can be arbitrarily set by changing the position of the slit 5 (fitting slit) for intersecting another plate member at a right angle.

The operation of the present invention will be described below. FIG. 5 shows the relative neutron amounts in the third row, third column fuel, the second row, third column fuel, and the first row, third column fuel from the side closer to the center of the column. . In the case of the conventional example (g ₁ = g ₂ = g ₃ ), it can be seen that the amount of neutron is closer to the center of the row. On the other hand, according to the present invention, the gap width of the lattice member disposed at a position close to the center of the row is relatively widened to enhance the neutron moderating effect in the gap portion, and neutrons are absorbed more effectively by the lattice member. However, under the condition that the cask outer diameter is constant, the gap width of the lattice member disposed between the fuels in the outer row is relatively narrowed, and the neutron absorption amount is reduced. Therefore, in the case of the basket according to the present invention (g ₁ > g ₂ > g ₃ ), as shown in FIG. 5, the neutron amount of the fuel in the outer column (the fuel in the first row and the third column) is relatively To increase. However, neutrons generated from the fuel in the outer row have a high probability of leaking outside the cask, and the contribution to the neutron chain reaction is relatively small, so the effect on the effective multiplication factor is relatively small. As a result, the basket (g ₁ > g ₂ > g ₃ ) according to the present invention in which the amount of neutrons in the fuel near the center of the row is relatively reduced can reduce the effective multiplication factor and improve the criticality prevention performance. Can do.

  As described above, the essence of the present invention is that the neutron amount of the fuel in the outer row that contributes relatively little to the neutron chain reaction is increased, and is close to the center of the row that contributes relatively much to the neutron chain reaction. The purpose is to reduce the neutron content of the fuel. This phenomenon is realized by relatively widening the gap width of the lattice members arranged closer to the center of the row and relatively narrowing the gap width of the lattice members arranged outside the row. This is because boron absorbs neutrons with lower energy better. That is, if the gap is widened at a position close to the center of the row, the neutron moderating effect is increased and the neutron energy is lowered, so that the amount of neutron absorption by boron increases.

  In the embodiment of FIG. 1, a stainless steel plate added with boron is used as the lattice member. However, from the above viewpoint, it is obvious that the lattice member is not limited to the stainless steel plate in order to obtain the effects of the present invention. . For example, aluminum added with boron may be used as the lattice member. Heat conductivity can be improved by using aluminum with good thermal conductivity as a lattice member. Even in this case, criticality prevention is achieved by relatively widening the gap width of the lattice members arranged closer to the center of the row and relatively narrowing the gap width of the lattice members arranged outside the row. Performance can be increased.

  In addition, from the viewpoint of improving heat transfer, a heat transfer plate made of aluminum, copper, or the like having good heat conductivity may be disposed in at least a part of the gap of the lattice member or between the lattice member and the fuel. is there. Even in the case where the heat transfer plates are arranged in this way, as in the embodiment shown in FIG. 1, the gap width of the lattice members arranged closer to the center of the row is relatively wide and arranged outside the row. The criticality prevention performance can be enhanced by relatively narrowing the gap width of the lattice member. Here, when arrange | positioning a heat exchanger plate in the space | gap part of a lattice member, let the space | gap part between a heat exchanger plate and a lattice member be the space | gap part of a lattice member. In order to improve the criticality prevention performance, aluminum or copper to which boron is added can be used as the heat transfer plate.

  Furthermore, the neutron absorbing material is not limited to boron, and it is clear that the effect of the present invention can be obtained as long as it has a property of absorbing better neutrons with lower energy. For example, it is known that gadolinium added to nuclear reactor uranium fuel as a neutron absorber absorbs neutrons with lower energy better. Therefore, for example, the effect of the present invention can be obtained even when an alloy plate to which gadolinium is added or a plate-like member in which gadolinium or a gadolinium alloy is sandwiched between stainless steels is used as the lattice member.

  Incidentally, in the embodiment of FIG. 1, an example in which the gap width of the lattice member is constant in the cask axial direction and the cask radial direction is shown, but the application target of the present invention is not limited thereto. Even when the gap width of the lattice member is not constant in either the cask axial direction, the radial direction, or both, the average gap width value is obtained, and the average gap width value of the lattice members arranged outside the row is calculated. It is possible to improve the criticality prevention performance by making it relatively narrow. Here, the average value of the gap width of a certain lattice member is calculated as follows, for example.

  Here, da represents the minute area of the lattice member facing the gap, and g (a) represents the gap width between the minute areas. Integration is performed over all of the grid members facing the void.

A spent fuel storage basket according to another embodiment of the present invention is shown in FIG. The basket in this embodiment is an example in which g ₁ = g ₂ > g ₃ . That is, only the gap width of the lattice member disposed between the fuel in the outermost row and the fuel in the innermost row is relatively narrowed, and the gap widths of the other lattice members are made the same. Even when g ₁ = g ₂ > g _3, it is possible to increase the neutron amount of the fuel in the outer row where the neutron leakage is relatively large and to reduce the neutron amount of the fuel near the center of the row. The effect by can be acquired. FIG. 3 also shows the change in effective multiplication factor when the basket in the embodiment of FIG. 6 is used. The analysis conditions are the same as in the embodiment of FIG. 1, the uranium enrichment is 4.2 wt%, the plate member constituting the lattice member is stainless steel with a plate thickness of 15 mm and the boron addition concentration of 1 wt%, and the cask outer diameter is constant. It is said. As can be seen from FIG. 3, even when g ₁ = g ₂ > g ₃ , the effective multiplication factor can be reduced by making g ₁ and g ₂ larger than g ₃ .

In the embodiment of FIG. 1 and FIG. 6, the gap width of the lattice members arranged closer to the center of the row is made wider (the embodiment of FIG. 1) or the same (the embodiment of FIG. 6). However, in order to reduce the effective multiplication factor, the above conditions are not necessarily required. At least the gap width of the lattice member disposed between the fuel in the outermost row and the fuel in the innermost row is set to another lattice. It is only necessary to make it smaller than the gap width of the member. FIG. 3 shows the change in effective multiplication factor when g ₂ > g ₁ > g ₃ . When g ₂ > g ₁ > g ₃ , the effect is smaller than when g ₁ > g ₂ > g ₃ or g ₁ = g ₂ > g ₃ , but the neutron leakage is relative. Since the amount of neutrons in the outer row of fuels can be increased and the amount of neutrons in the fuel near the center of the row can be reduced, the neutron effective multiplication factor can be made smaller than in the conventional example.

By the way, as shown in FIG. 3, the gap width g ₃ of the lattice member disposed between the fuel in the outermost row and the fuel in the inner row and the gap width of the other lattice members are the narrowest. It was found that the effective multiplication factor can be reduced particularly in the following range, where g ′ is the smaller of g ₁ and g ₂ .

0.4 <g / g ′ <0.8
Therefore, in the present invention, it is preferable that the gap portion of the lattice member has a basket structure that satisfies the above relationship.

The embodiment of FIGS. 1 and 6 is an example of a basket using a lattice member in which two plate-like members are arranged in a face-to-face manner and a gap is formed by providing a gap between the plate-like members. as shown in Patent No. 3150676 publication, in the case of a basket using the angular tubular member having a cavity therein applicability of the present invention. FIG. 9 shows an embodiment in which the present invention is applied to a basket constituted by square tubular members. FIG. 9 is a view showing an axial cross section of the basket. As shown in FIG. 9, the horizontal width of the hollow portion of the rectangular tubular member is arranged closer to the center portion of the row to g ₁ , g ₂ ,
If g ₃
g ₁ > g ₂ > g ₃
Thus, the effect of the present invention can be obtained. The basket having such a hollow portion is, for example, a plate-shaped member in which the horizontal lengths d and d ′ (shown in FIG. 8) of the convex portions are d + d ′ = g ₁ , g ₂ and g ₃ . A combination is prepared, and each is bonded to create a rectangular tubular member whose horizontal widths are g ₁ , g ₂ , and g _3, and combined into a confectionery shape as shown in FIG. it can.

Similarly to the embodiment of FIG. 6, when only the hollow portion of the rectangular tubular member disposed between the fuel in the outermost row and the fuel in the inner row is narrowed to satisfy g ₁ = g ₂ > g ₃ However, the effect of the present invention can be obtained. Furthermore, even when g ₂ > g ₁ > g ₃ , the effect is less than when g ₁ > g ₂ > g ₃ or g ₁ = g ₂ > g ₃ , but neutron leakage Since the neutron content of the fuel in the outer row with a relatively large number can be increased and the neutron content in the fuel near the center of the row can be reduced, the effective neutron increase compared to the conventional example (g ₁ = g ₂ = g ₃ ) The magnification can be reduced.

The embodiment described above is an example of a basket that stores 24 spent fuels, but the present invention can be applied to other storage units. FIG. 10 shows an example in which the present invention is applied to a basket for storing 32 spent fuels, and FIG. 11 shows an example in which the present invention is applied to a basket for storing 37 spent fuels. Similarly, in the case of baskets storing 32 and 37 spent fuels, the gap width of the lattice member arranged closer to the center of the row is wider and the gap width of the lattice member arranged outside the row. Can be made narrower and g ₁ > g ₂ > g ₃ to improve the criticality prevention performance. In addition, the gap width of the lattice member disposed at least between the fuel in the outermost row and the fuel in the innermost row is made smaller than the gap width of the other lattice members, for example, g ₁ = g ₂ > g _{If 3} or g ₂ > g ₁ > g ₃ , the amount of neutrons in the outer row of fuel with relatively high neutron leakage can be increased and the amount of neutrons in the fuel near the center of the row can be reduced. The effects of the invention can be obtained.

By the way, all the embodiment shown above showed the example which made the basket a 1/4 rotation symmetrical shape. When 24, 32, and 37 fuels are stored in a substantially cylindrical container, in order to make the inner diameter of the container the smallest, the number of rows in the vertical and horizontal directions is the same. At this time, the vertical and horizontal lattice members are symmetrical, that is, for example, as in the embodiment shown in FIG. 1, the lattice members, the third column, and the fourth row arranged between the fuels in the third row and the fourth row. The gap widths of the lattice members arranged between the fuels in the row are made the same. By doing so, the number of grid members arranged between each row becomes one type in the vertical and horizontal directions, and the number of types of plate-like members for constituting the basket becomes the same as the conventional example, which increases the manufacturing cost of the basket. Can be suppressed. However, in order to obtain the effect of the present invention, it is not always necessary to have a 1/4 rotation symmetry. As shown in FIG. 14, even if the gap portions of all the lattice members have different widths, the gap portion width of the lattice members arranged closer to the center of the row is wider, and the lattice members arranged outside the row If the gap width is narrower, the criticality prevention performance can be improved. Further, the effect of the present invention can be obtained if the gap width of the lattice member disposed at least between the fuel in the outermost row and the fuel in the inner row is made smaller than the gap width of the other lattice members. Can do. That is, in the example shown in FIG. 14, at least g ₄ and g ₅ are narrower than g ₁ , g ₂ and g ₃ , and g ₄ ′ and g ₅ ′ are g ₁ ′, g ₂ ′ and g ₃ ′. It is possible to increase the criticality prevention performance by narrowing it. Here, the magnitudes of g ₄ and g _{5 and} the magnitudes of g ₄ ′ and g ₅ ′ are arbitrary.

Further, the present invention can be applied to a case where the number of rows and columns is different in order to minimize the inner diameter of the container, for example, when the number of fuel bodies is 26. FIG. 12 shows an example in which the present invention is applied when the number of housings is 26. When the number of housings is 26, it is preferable that the maximum number of columns in the vertical and horizontal directions is 5 and 6. FIG. 12 shows an example in which 5 columns are arranged vertically and 6 columns are arranged horizontally. Here, in FIG. 12, the vertical columns of fuel arranged vertically and horizontally are called the first column, the second column,..., The sixth column from the left side, and the horizontal columns are the first row, the second row,. Let's call it 5 lines. At this time, eight bodies of the first row, the second column and the fifth column, the second row, the first column and the sixth column, the fourth row, the first column and the sixth column, the fifth row, the second column, and the fifth column. If the lattice member is arranged so that the fuel is in contact with the inner diameter of the container, the gap portion of the lattice member can be increased on average under the condition of the same container inner diameter, and the criticality prevention performance can be enhanced. In this case, the gap width in the vertical direction with a small number of rows inevitably increases on average, but in each of the vertical and horizontal directions, the gap portion width of the lattice member arranged closer to the center of the row is wider, The effect of the present invention can be obtained if the gap width of the lattice member disposed outside is made narrower and g ₁ > g ₂ and G ₁ > G ₂ > G ₃ . Further, in each of the vertical and horizontal directions, the gap width of the lattice member disposed at least between the fuel in the outermost row and the fuel in the inner row is made smaller than the gap width of the other lattice members, for example, g ₁ > If g ₂ and G ₁ = G ₂ > G ₃ , or g ₁ > g ₂ and G ₂ > G ₁ > G ₃ , then the amount of neutrons in the outer row of fuel with relatively high neutron leakage is increased, Since the amount of fuel neutrons close to the center of the row can be reduced, the effect of the present invention can be obtained. Even in this case, since the number of types of plate members for constituting the basket is the same as that of the conventional example (g ₁ = g ₂ and G ₁ = G ₂ = G ₃ ), the manufacturing cost of the basket is increased. Can be suppressed. Similarly to the example shown in FIG. 14, from the viewpoint of enhancing the criticality prevention performance, at least between the fuel in the outermost row and the fuel in the inner row, even if all the gaps have different widths. What is necessary is just to make the space | gap part width | variety of the lattice member arrange | positioned to be smaller than the space | gap part width of another lattice member.

  By the way, the effect of the present invention can be obtained by increasing the neutron amount of the fuel in the outer row where the neutron leakage is relatively large and reducing the neutron amount of the fuel near the center of the row as shown in FIG. The embodiments are not limited to those described above. In the embodiment shown in FIG. 15, with respect to the lattice members disposed between the vertical rows, the lattice members disposed closer to the center of the row have a larger gap width and the lattice members disposed between the horizontal rows. Has a constant gap width. Even in such a configuration, the neutron amount of the fuel in the outer row where the neutron leakage is relatively large can be increased and the neutron amount of the fuel close to the center of the row can be reduced, so that the criticality prevention performance can be improved. Further, in the embodiment shown in FIG. 16, with respect to the lattice members arranged between the vertical rows, only the gap width of the lattice members arranged at the center of the rows is made wider than the others, and arranged between the horizontal rows. The gap width is constant for the lattice member. Thus, when divided into the first lattice member group located near the center of the row and the second lattice member group located near the outer row, the width of the gap portion of the second lattice member group By making the average value narrower than the average value of the width of the gap portion of the first lattice member group, the amount of neutrons in the outer row of fuel with relatively high neutron leakage is increased, and the fuel near the center of the row is increased. Since the amount of neutrons can be reduced, the criticality prevention performance can be enhanced.

It is a figure which shows the basket structure by this invention. It is a figure which shows the conventional basket structure. It is a figure which shows the effect by this invention. It is a figure which shows the example of the plate-shaped member which comprises this invention. It is a figure which shows the relative neutron amount in a different fuel position. It is a figure which shows the basket structure by this invention. It is a figure which shows a square tubular basket structural member. It is a figure which shows a square tubular basket structural member. FIG. 3 shows a basket structure according to the present invention. It is a figure which shows the basket structure by this invention. It is a figure which shows the basket structure by this invention. It is a figure which shows the basket structure by this invention. It is a figure which shows the conventional basket structure. It is a figure which shows the basket structure by this invention. It is a figure which shows the basket structure by this invention. It is a figure which shows the basket structure by this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Lattice member, 1a ... Plate-shaped member, 2, 2a, 2b, 2c ... Cavity part, 3 ... Fuel, 4 ... Containment container, 5 ... Fit slit, 6 ... Cavity part.

Claims (13)

Provided in a spent fuel container for storing or transporting spent fuel;
In a spent fuel storage basket provided with a compartment for storing spent fuel by combining lattice members,
The lattice member has a gap inside,
Compared to the gap of the first grid member on the center side in the spent fuel container, the gap of the second grid member located outside the spent fuel container from the first grid member. A spent fuel storage basket that is narrowed. The spent fuel storage basket according to claim 1,
2. The spent fuel storage basket according to claim 1, wherein the lattice member includes two plate-like members arranged in a face-to-face manner, and the gap is formed by providing an interval between the two plate-like members. The spent fuel storage basket according to claim 1,
The spent fuel storage basket, wherein the lattice member is a rectangular tubular member having a cavity inside. The spent fuel storage basket according to any one of claims 1 to 3,
The second grid member is disposed between the fuel placed on the outermost side from the center of the spent fuel container and the fuel placed on the inner side of the fuel. For baskets. The spent fuel storage basket according to any one of claims 1 to 4,
From the lattice members disposed closer to the center of the spent fuel container, g ₁ , g ₂ ,.
A spent fuel storage basket satisfying the following relationship when g _n-1 and g _n are satisfied.
g ₁ > = g ₂ > = ...> = g _n-1 > g _n
However, g _n denotes an air gap width of the grid members disposed between the outermost fuel and fuel inside from the center of the spent fuel container. In a spent fuel storage basket provided in a spent fuel container for storing or transporting spent fuel and provided with a grid-like section for storing spent fuel by combining grid members vertically and horizontally,
The lattice member has a gap inside, and in at least one of the vertical row and the horizontal row, the first lattice member group located near the center of the row and the second row located near the outer row. Spent fuel characterized in that, when divided into lattice member groups, the average value of the width of the gap portion of the second lattice member group is narrower than the average value of the width of the gap portion of the first lattice member group Storage basket. In a spent fuel storage basket provided in a spent fuel container for storing or transporting spent fuel and provided with a grid-like section for storing spent fuel by combining grid members vertically and horizontally,
The lattice member has a gap inside, and in at least one of the vertical row and the horizontal row, the lattice member having the narrowest gap in each row is arranged with the fuel in the outermost row and the inside thereof. A spent fuel storage basket, which is disposed between the fuel in a row of the fuel. In a spent fuel storage basket provided in a spent fuel container for storing or transporting spent fuel and provided with a grid-like section for storing spent fuel by combining grid members vertically and horizontally,
The lattice member has a gap inside, and in each of the vertical row and the horizontal row, the lattice member having the narrowest gap portion is divided into an outermost row fuel and an inner row fuel. A spent fuel storage basket, which is arranged in between. The spent fuel storage basket according to any one of claims 7 to 8,
The width of the gap portion, at least one of the vertical columns and horizontal rows, g _1, g ₂ from those of the grid member disposed closer to the center of the column, ... When g _n-1, g n A spent fuel storage basket satisfying the following relationship:
g ₁ > = g ₂ > = ...> = g _n-1 > g _n
However, g _n denotes an air gap width of the grid member disposed between the fuel outermost fuel and columns in the inner row. The spent fuel storage basket according to any one of claims 7 to 9,
When the gap width of the lattice member disposed between the fuel in the outermost row and the fuel in the innermost row is g, and g ′ is the narrowest gap width of the other lattice members, the vertical row And a spent fuel storage basket characterized by satisfying the following relationship in at least one of the horizontal rows.
0.4 <g / g ′ <0.8 The spent fuel storage basket according to any one of claims 6 to 10,
2. The spent fuel storage basket according to claim 1, wherein the lattice member includes two plate-like members arranged in a face-to-face manner, and the gap is formed by providing an interval between the two plate-like members. The spent fuel storage basket according to any one of claims 6 to 11,
The spent fuel storage basket, wherein the lattice member is a rectangular tubular member having a cavity inside. A spent fuel container comprising the spent fuel storage basket according to any one of claims 6 to 12.

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