Patent Application
20090185652
The present invention relates to a recycled fuel assembly storage basket and a recycled fuel assembly storage container that store recycled fuel assemblies.
Nuclear fuel assemblies used in a nuclear power plant and the like, i.e., used nuclear fuel assemblies extracted from a nuclear reactor after being loaded in the nuclear reactor and burned, are referred to as recycled fuel assemblies. The recycled fuel assemblies contain highly radioactive substances such as a fission product (FP). Therefore, usually, the recycled fuel assemblies are cooled for a predetermined period in a cooling pit of the nuclear power plant. Thereafter, the recycled fuel assemblies are stored in a recycled fuel assembly storage container having a radiation shielding function, i.e., a cask used for transportation and storage. The recycled fuel assemblies are transported to a reprocessing plant or an intermediate storage facility by a vehicle or a ship and stored until being reprocessed.
When the recycled fuel assemblies are stored in the cask, a basket called a recycled fuel assembly storage basket that is formed by collecting basket cells having a square pipe-like section as storage spaces is used. The recycled fuel assemblies are respectively inserted in plural storage spaces formed in this recycled fuel assembly storage basket. Consequently, the recycled fuel assemblies during transportation are kept away from one another at appropriate intervals and prevented from reaching a critical point. Further, appropriate holding power against vibration during transportation, assumed events, and the like is secured. As conventional examples of such a basket, various kinds of baskets are disclosed in, for example, Patent Documents 1 to 4.
Patent Document 1: Japanese Patent Application Laid-open No. H09-159796
Patent Document 2: Japanese Patent Application Laid-open No. 2001-133590
Patent Document 3: Japanese Patent Application Laid-open No. 2001-201595
Patent Document 4: Japanese Patent Application Laid-open No. 2003-207593
When the recycled fuel assemblies are transported and stored, the recycled fuel assemblies are stored in the basket to be close to each other. Therefore, a neutron absorber is used for the recycled fuel assembly storage basket for the purpose of imparting neutron absorbing power with some means to prevent the recycled fuel assemblies stored therein from reaching a critical point. As substances having the neutron absorbing power, gadolinium (Dd), samarium (Sm), cadmium (Cd), and the like are known. In general, a function of absorbing neutrons (hereinafter referred to as neutron absorbing power) is obtained by using a boron aluminum alloy or boron stainless steel containing boron or a boron compound as a basket structure material, coating the surface of the basket structure material, sticking a relevant plate material to the surface of the basket structure material or integrating the plate material with the surface with binding means, or providing a sandwich structure holding the basket structure material. A function of preventing criticality (a subcritical function) and heat removing function matching a state of fuel of the loaded recycled fuel assemblies are required. A material and the structure of the basket, an array of the basket cells, and the like are required.
A process for loading the recycled fuel assemblies in the cask is usually performed in a pool for fuel assemblies set in a nuclear power plant or the like (in water). Fuel used in a PWR (Pressurized Water Reactor) has a high degree of burn-up and is highly likely to reach a critical point during loading of the recycled fuel assemblies. Therefore, a presence ratio of 10B having the neutron absorbing power needs to be set high in a basket. The criticality is prevented by increasing the plate thickness of the basket cells, increasing the content (percentage of mass) of 10B, or providing flux traps. Further, because heating value is also large, the basket is required to have satisfactory heat transfer performance. The technology disclosed in Patent Document 1 targets fuel used in a so-called BWR (Boiling Water Reactor). The recycled fuel assemblies having a high degree of burn-up are assumed in a basket for storing the BWR fuel as well. It is surmised that the basket has the structure similar to the basket for the PWR fuel. Because the PWR fuel is bulkier and heavier than the BWR fuel, a basket structure more excellent in the subcritical function and heat transfer performance and having high rigidity is required for the PWR fuel.
To achieve the subcritical function and the heat transfer performance, in recent years, the basket is often make of a B (boron)-Al (aluminum) material. In this case, as an example of a structure obtained by combining tabular boron-aluminum materials in a lattice shape, for example, Japanese Patent Application Laid-open No. 2001-201595 is known. As examples of a structure obtained by combining hollow materials formed by extruding, Japanese Patent Application Laid-open No. 2001-133590 and Japanese Patent Application Laid-open No. H09-159796 are known. There is also a basket made of boron stainless steel that can transfer, with a large temperature difference, heat to a container making use of high heat resistance. In the case of the basket made of boron stainless steel, the temperature of fuel stored therein is kept high. Soundness of the fuel itself needs to be sufficiently taken into account.
For example, in the structure obtained by combining square pipes disclosed in Japanese Patent Application Laid-open No. 2001-133590, a heat transfer area cannot be sufficiently secured in the square pipes arrayed in a zigzag, which is disadvantageous as heat transfer performance. In a basket in which basket cells of a square pipe type are squarely arrayed, a load can be substantially equally received when a horizontal falling accident of a cask occurs, which is advantageous in terms of the structure. However, in the basket in which the square pipes are arrayed in a zigzag, a load is received on sides of the cells depending on a falling posture of the cask and a concentrated load may be generated, which is disadvantageous for securing structural strength. Therefore, there is a demand for a basket structure that can secure, amid restrictions in terms of weight and dimensions, heat transfer performance for removing decay heat of the recycled fuel assemblies and structural strength for securing subcritical performance even in an event such as a falling accident.
Therefore, the present invention has been devised in view of the above description and it is an object of the present invention to provide a recycled fuel assembly storage basket and a recycled fuel assembly storage container that can attain at least one of transferring decay heat of recycled fuel assemblies to a basket and effectively removing the decay heat to the outside from the basket, securing subcritical performance, improving structural strength and heat transfer properties by combining square pipes, and reducing manufacturing man-hour.
To solve above problems and achieve objects, according to the present invention, a recycled fuel assembly storage basket comprising: square pipes, on at least one surfaces on outer sides of opposed sidewalls of which a plurality of projections are provided, the square pipes storing recycled fuel assemblies; and tabular members. A plurality of storage cell rows formed by arraying the projections of the square pipes in contact with each other are provided, and the tabular members are stacked in a plurality of stages among the storage cell rows with long side ends thereof set in contact with each other.
In this recycled fuel assembly storage basket, a plurality of storage cell rows formed by arraying a plurality of projections, which are provided at least on one surfaces on outer sides of sidewalls of square pipes, in contact with each other are provided. Solid or hollow tabular members are stacked in a plurality of stages among the storage cell rows with long side ends thereof set in contact with each other. This makes it possible to increase a heat transfer area between the square pipes and the tabular members and secure sufficient heat transfer performance and a sufficient subcritical function. The tabular members can disperse a load when a horizontal falling accident occurs and prevent a concentrated load on basket cells located below the tabular members from being generated. Therefore, it is possible to reduce the structural strength required for the basket cells. The hollow tabular members can form flux traps among the square pipes that store the recycled fuel assemblies. Therefore, it is possible secure the subcritical function even for a PWR fuel.
According to the next invention, a recycled fuel assembly storage basket comprising: first square pipes, on outer sides of opposed sidewalls of which a plurality of projections are provided, respectively, the first square pipes storing recycled fuel assemblies; second square pipes, on outer sides of one side walls of which a plurality of projections are provided, the second square pipes storing recycled fuel assemblies; and tabular members. A plurality of storage cell rows formed by arraying the projections of the first square pipes in contact with each other and arranging the second square pipes on the outer sides are provided, the projections of the first square pipes and the projections of the second square pipes being in contact with each other, and the tabular members are stacked in a plurality of stages among the storage cell rows with long side ends thereof set in contact with each other.
In this recycled fuel assembly storage basket, a plurality of storage cell rows formed by arraying a plurality of projections, which are provided on outer sides of sidewalls of first square pipes, in contact with each other and arranging second square pipes on the outer sides are provided. Solid or hollow tabular members are stacked in a plurality of stages among the storage cell rows with long side ends thereof set in contact with each other. This makes it possible to increase a heat transfer area between the first and second square pipes and the tabular members and form flux straps among the square pipes that store the recycled fuel assemblies. Therefore, it is possible to secure sufficient heat transfer performance and a sufficient subcritical function. Because the number of projections provided in the square pipes is small, it is possible to secure accuracy of molding even when a material hard to be extruded or a material hard to be rolled such as a boron-aluminum material or boron stainless steel is used. Therefore, it is possible to prevent a fall in manufacturing efficiency. The square pipes and the hollow tabular members can be bent or bonded. However, when hot extrusion molding is possible, it is reasonable to manufacture the square pipes and the hollow tabular members with extrusion molding.
According to the recycled fuel assembly storage basket of the following present invention, in the recycled fuel assembly storage basket, the tabular members are stacked in a longitudinal direction of the square pipes.
According to the recycled fuel assembly storage basket of the following present invention, in the recycled fuel assembly storage basket, a reinforcing member that supports a part of a load on the recycled fuel assembly storage basket and reinforces the recycled fuel assembly storage basket is arranged between the tabular members adjacent to each other. Consequently, the reinforcing member can bear a part of a shock load. Therefore, it is possible to secure the strength of the recycled fuel assembly storage basket without unreasonably increasing the thickness of the tabular members and secure high shock resistance and safety.
According to the recycled fuel assembly storage basket of the following present invention, in the recycled fuel assembly storage basket, the tabular members are hollow members having at least one hole.
According to the recycled fuel assembly storage basket of the following present invention, in the recycled fuel assembly storage basket, a solid or hollow intra-tabular member reinforcing member that supports a part of the load on the recycled fuel assembly storage basket and reinforces the recycled fuel assembly storage basket is arranged in the hole. Consequently, the reinforcing member can bear a part of a shock load. Therefore, it is possible to secure the strength of the recycled fuel assembly storage basket without unreasonably increasing the thickness of the tabular members and secure high shock resistance and safety.
According to the recycled fuel assembly storage basket of the following present invention, in the recycled fuel assembly storage basket, when there are two or more holes, the intra-tabular member reinforcing member is arranged in at least one of the holes.
According to the recycled fuel assembly storage basket of the following present invention, in the recycled fuel assembly storage basket, tapered sections are provided in portions of the projections that are in contact with the projections of the square pipe adjacent thereto.
With such a configuration, it is possible to suppress a shift of the square pipes when the square pipes are combined and further improve heat transfer performance and shock resistance performance. It is easy to assemble the recycled fuel assembly storage basket.
According to the recycled fuel assembly storage basket of the following present invention, in the recycled fuel assembly storage basket, size of a space surrounded by the projections is different depending of places where the square pipes are arranged. This makes it possible to configure the recycled fuel assembly storage basket according to a degree of burn-up of recycled fuel assemblies stored therein.
According to the recycled fuel assembly storage basket of the following present invention, in the recycled fuel assembly storage basket, the size of the space surrounded by the projections of the square pipes and the thickness of the tabular members are increased from an outer side to a center of the recycled fuel assembly storage basket. On the outer side of the recycled fuel assembly storage basket, radiation from recycled fuel is smaller than that in the center. Therefore, it is possible to set a dimension of flux straps on the outer side of the recycled fuel assembly storage basket smaller than that in the center and suppress an increase in mass and an increase in dimensions of the recycled fuel assembly storage basket.
According to the recycled fuel assembly storage basket of the following present invention, in the recycled fuel assembly storage basket, thickness of the tabular members is changed depending on places where the tabular members are arranged.
This makes it possible to configure the recycled fuel assembly storage basket according to a degree of burn-up of recycled fuel assemblies stored therein.
According to the recycled fuel assembly storage basket of the following present invention, in the recycled fuel assembly storage basket, size of a space surrounded by the projections of the square pipes and thickness of the tabular members are changed. This makes it possible to vary pitches of square pipes forming the housing cells. Therefore, it is possible to configure the recycled fuel assembly storage basket according to a degree of burn-up of recycled fuel assemblies stored therein.
According to the recycled fuel assembly storage basket of the following present invention, a recycled fuel assembly storage basket, comprising: square pipes that store recycled fuel assemblies; hollow first tabular members rectangular in a sectional external shape; and hollow second tabular members rectangular in a sectional external shape. A plurality of storage cell rows alternately arrayed in contact with outer sides of sidewalls of square pipes and outer sides of sidewalls of first tabular members, and the second tabular members are stacked in a plurality of stages among the storage cell rows with long side ends thereof set in contact with each other.
In this recycled fuel assembly storage basket, a plurality of storage cell rows are alternately arrayed in contact with outer sides of sidewalls of square pipes and outer sides of sidewalls of first tabular members. Second tabular members are stacked in a plurality of stages among the storage cell rows with long side ends thereof set in contact with each other. This makes it possible to increase a heat transfer area between the square pipes and the tabular members and form flux traps among the square pipes that store the recycled fuel assemblies. Therefore, it is possible to secure sufficient heat transfer performance and a sufficient subcritical function. Because the square pipes do not have projections, even when a material hard to be extruded such as a boron-aluminum material or a material hard to be rolled such as boron stainless steel is used, it is possible to secure accuracy of molding and suppress a fall in manufacturing efficiency. A section of the first tabular members and a section of the second tabular members can have an identical shape and identical dimensions or may have different shapes and different dimensions.
According to the recycled fuel assembly storage basket of the following present invention, in the recycled fuel assembly storage basket, thickness or dimensions of the second tabular members are different from thickness or dimensions of the first tabular members, and the second tabular members are similar to the first tabular members.
According to the recycled fuel assembly storage basket of the following present invention, in the recycled fuel assembly storage basket, in at least a pair of the storage cell rows, corners of the square pipes in one of the storage cell rows are arranged in positions of sidewalls the square pipes in the other storage cell row.
With such a configuration, it is possible to arrange a larger number of square pipes in a limited section (a section orthogonal to an axis of the basket). Therefore, it is possible to increase the number of stored recycled fuel assemblies while suppressing an increase in dimensions of the recycled fuel assembly storage container.
According to the recycled fuel assembly storage basket of the following present invention, in the recycled fuel assembly storage basket, in at least a pair of the storage cell rows, corners of the square pipes in one of the storage cell rows are arranged in positions of corners the square pipes in the other storage cell row.
According to the recycled fuel assembly storage basket of the following present invention, in the recycled fuel assembly storage basket, cutouts are provided at least at the long side ends of the tabular member opposed to a bottom of a recycled fuel assembly storage container that houses the recycled fuel assembly storage basket therein or at ends of the square pipe opposed to the bottom of the recycled fuel assembly storage container. This improves drainage from the recycled fuel assembly storage basket.
According to the recycled fuel assembly storage basket of the following present invention, in the recycled fuel assembly storage basket, the tabular members arranged among the storage cell rows are stacked to have a gradient with respect to a bottom of a recycled fuel assembly storage container that houses the recycled fuel assembly storage basket therein.
This makes it possible to prevent the air and water from being accumulated in the hollow tabular members. As the gradient is steeper, a surer effect can be expected. However, because of easiness of manufacturing of a first tabular member that determines the gradient, it is reasonable to set the gradient to be equal to or larger than 0 degree and equal to or smaller than the height of one stage of the tabular members.
According to the recycled fuel assembly storage basket of the following present invention, in the recycled fuel assembly storage basket, a sectional shape of holes included in the tabular members is a race-track shape.
This makes it possible to eliminate planes in ceilings and bottoms of the holes of the tabular members. Therefore, it is possible to more effectively prevent the air and water from being accumulated in the hollow tabular members.
According to the recycled fuel assembly storage basket of the following present invention, in the recycled fuel assembly storage basket, an area of a portion of the long side end of the tabular member that is in contact with the long side end of the tabular member adjacent thereto is smaller than an area of a section of the tabular member when the tabular member is cut by a plane parallel to a surface forming the long side end of the tabular member. This makes it possible to reduce an area of a portion where the tabular members are in contact with each other. Therefore, it is possible to reduce moisture remaining in the recycled fuel assembly storage basket and reduce time required for vacuum drying.
According to the recycled fuel assembly storage basket of the following present invention, in the recycled fuel assembly storage basket, projections are formed in a portion of the long side end of the tabular member that is in contact with the long side end of the tabular member adjacent thereto. This makes it possible to reduce an area of a portion where the tabular members are in contact with each other. Therefore, it is possible to reduce moisture remaining in the recycled fuel assembly storage basket and reduce time required for vacuum drying.
According to the recycled fuel assembly storage basket of the following present invention, in the recycled fuel assembly storage basket, spaces are formed in a portion of the long side end of the tabular member that is in contact with the long side end of the tabular member adjacent thereto. This space facilitates exhaust. Therefore, it is possible to reduce time required for vacuum drying.
According to the recycled fuel assembly storage basket of the following present invention, in the recycled fuel assembly storage basket, a bottom plate that separates the recycled fuel assembly storage basket and the recycled fuel assembly storage container is provided between the recycled fuel assembly storage basket and the bottom of the recycled fuel assembly storage container. With such a configuration, it is possible to reduce a quantity of heat transmitted from the recycled fuel assembly storage basket to the bottom of the cask. Therefore, it is possible to suppress thermal deterioration of a material having neutron absorbing function (a neutron shielding material) arranged on the bottom side of the cask and cause the material to display neutron shielding performance throughout a storage period of several tens years.
According to the recycled fuel assembly storage basket of the following present invention, in the recycled fuel assembly storage basket, an opening is provided in the bottom plate.
According to the recycled fuel assembly storage basket of the following present invention, in the recycled fuel assembly storage basket, a space is provided between the bottom plate and the bottom of the recycled fuel assembly storage container. This opening makes it possible to improve drainage. Therefore, efficiency of vacuum drying is improved.
According to the recycled fuel assembly storage basket of the following present invention, in the recycled fuel assembly storage basket, at least the square pipes are made of an aluminum alloy containing boron or a boron compound.
According to the recycled fuel assembly storage basket of the following present invention, in the recycled fuel assembly storage basket, at least the tabular members are made of an aluminum alloy containing boron or a boron compound.
According to the recycled fuel assembly storage basket of the following present invention, in the recycled fuel assembly storage basket, at least the square pipes are made of a stainless steel containing boron or a boron compound.
According to the recycled fuel assembly storage basket of the following present invention, in the recycled fuel assembly storage basket, at least the tabular members are made of a stainless steel containing boron or a boron compound.
According to the recycled fuel assembly storage basket of the following present invention, in the recycled fuel assembly storage basket, at least the square pipes are made of a stainless steel containing gadolinium or a gadolinium compound.
According to the recycled fuel assembly storage basket of the following present invention, in the recycled fuel assembly storage basket, at least the tabular members are made of a stainless steel containing gadolinium or a gadolinium compound.
According to the recycled fuel assembly storage basket of the following present invention, the reinforcing member is stainless steel.
According to the recycled fuel assembly storage basket of the following present invention, the intra-tabular member reinforcing member is a material having strength higher than that of the tabular members.
According to the recycled fuel assembly storage basket of the following present invention, the reinforcing member is a material having strength higher than that of the tabular members.
According to the recycled fuel assembly storage basket of the following present invention, the reinforcing member can be configured by a material having strength higher than that of the tabular members.
According to the recycled fuel assembly storage container of the following present invention, a recycled fuel assembly storage container, comprising: a barrel including an opening and a cavity; a lid that is attached to the opening and seals the cavity; and the recycled fuel assembly storage basket arranged in the cavity.
This recycled fuel assembly storage container includes the recycled fuel assembly storage basket. Therefore, it is possible to suppress, while securing heat transfer performance and a subcritical function, a fall in manufacturing efficiency of molding even when a material hard to be extruded such as a boron-aluminum material or a material hard to be rolled such as boron stainless steel is used.
According to the recycled fuel assembly storage container of the following present invention, in the recycled fuel assembly storage container, an outer circumferential surface of the recycled fuel assembly storage basket is in contact with an inner wall of the cavity.
This recycled fuel assembly storage container includes the recycled fuel assembly storage basket. Therefore, because exchange of heat with the container is performed on a wide surface, it is possible to transfer heat with a small temperature difference while securing a subcritical function. This makes it possible to keep the temperature of stored recycled fuel assemblies low even when a B-SUS material inferior in heat transfer properties compared with a B-Al material is used and keep the temperature of the stored recycled fuel assembles lower in the case of the B-Al material.
The recycled fuel assembly storage basket and the recycled fuel assembly storage container according to the present invention can attain at least one of transferring decay heat of recycled fuel assemblies to a basket and effectively removing the decay heat to the outside from the basket, securing subcritical performance, improving structural strength and heat transfer properties by combining square pipes, and reducing manufacturing man-hour.
The present invention is explained in detail below with reference to the drawings. The present invention is not limited by best modes for carrying out the present invention (hereinafter referred to as embodiments). Elements in the embodiments described below include elements that those skilled in the art can easily assumed or elements substantially identical with the elements, i.e., elements in a so-called range of equivalents. A recycled fuel assembly storage basket explained below is mainly used in casters for transportation and storage. However, the recycled fuel assembly storage basket is not limited to this. For example, the recycled fuel assembly storage basket can be used in a concrete cask for storage purpose, a canister, or a rack of a recycled fuel assembly storage pool. The recycled fuel assembly storage basket is abbreviated as basket when necessary.
(First Embodiment)
A recycled fuel assembly storage basket according to the first embodiment is characterized in that a plurality of storage cell rows formed by arraying a plurality of projections, which are provided on outer sides of sidewalls of square pipes, in contact with each other are provided and solid or hollow tabular members are stacked in a plurality of stages among the storage cell rows with long side ends thereof set in contact with each other. Before the recycled fuel assembly storage basket according to the first embodiment is explained, a recycled fuel assembly storage container is explained.
A bottom plate can be attached to the cylindrical barrel main body 201 by welding. The barrel main body 201 and the bottom plate can be integrally molded by inserting a metal billet into a container having an internal shape matched to an outer shape of the barrel main body 201 and hot-forming the metal billet with a perforating punch having an external shape matched to an inner shape of the barrel main body 201. Further, the barrel main body 201 can be manufactured by casting.
The inside of the barrel main body 201 is a cavity 201C in which a basket 1 that stores recycled fuel assemblies is housed. A sectional inner shape perpendicular to an axial direction of the cavity 201C (a direction indicated by Z in the figure) is circular. However, cavities having sectional inner shapes such as an octagonal shape, a substantial cross shape, and a stepped shape can also be used. In this embodiment, because the sectional inner shape of the cavity 201C is circular, when the basket 1 having a polygonal external shape is housed, a first spacer 202a to a fifth spacer 202e are interposed between the basket 1 and the cavity 201C to position the basket 1 in the cavity 201C.
The basket 1 is preferably set such that an outer circumferential surface thereof is in contact with an inner wall of the cavity 201C. Consequently, because exchange of heat with the container is performed on a wide surface, it is possible to transfer heat with a small temperature difference while securing a subcritical function. This makes it possible to keep the temperature of stored recycled fuel assemblies low even when a B-SUS material inferior in heat transfer properties compared with a B-Al material is used and keep the temperature of the stored recycled fuel assembles lower in the case of the B-Al material.
After the recycled fuel assemblies are stored in the cavity 201C, to prevent radioactive substances from leaking from the inside of the cavity 201C, a primary lid 200T1, a secondary lid 200T2, and a tertiary lid T3 (
A plurality of heat transfer fins 207 made of tabular members are radially attached to the outer circumference of the barrel main body 201. The heat transfer fins 207 are made of good heat conductors such as aluminum plates or copper plates. The heat transfer fins 207 are attached to the outer circumference of the barrel main body 201 by welding or other bonding means such that heat is transmitted well. The outer cylinder 205 made of carbon steel having the thickness of several centimeters is attached to the outer side of the heat transfer fins 207 by welding or other bonding means. The recycled fuel assemblies stored in the cavity 201C generate decay heat. This decay heat is transmitted through the basket 1a [translator's comment: “basket 1a” should be corrected to “basket 1”] and the barrel main body 201 and, then, conducted to the outer cylinder 205 via the heat transfer fins 207 and discharged to the atmosphere from the surface of the outer cylinder 205.
A material having a neutron absorbing function for absorbing neutrons is filled in a space 209 surrounded by the barrel main body 201, the outer cylinder 205, and two heat transfer fins 207. As the material having such a function, a neutron absorbing material such as resin, polyurethane, or silicon as a polymeric material containing a large quantity of hydrogen can be used. Neutrons discharged from the recycled fuel assemblies are absorbed by this neutron absorbing materials to reduce neutrons leaking to the outside of the cask 200 to be less than a regulated value.
The cask 200 is used for storing the recycled fuel assemblies and, then, transporting and stocking the recycled fuel assemblies. When the cask is transported, as shown in
At least the first and second square pipes 10 and 11 are made of an Al (aluminum) material containing B10 (boron) (hereinafter referred to as boron-aluminum material) to secure a subcritical function and reduce weight (the same applies in the following explanation). B can be a boron compound such as B4C (boron carbide) . The first and second square pipes 10 and 11 can be manufactured by, for example, hot-rolling or hot-extruding a billet of boron aluminum manufactured by powder metallurgy. A material of the tabular members 20 is not particularly specified and can be a material same as or different from that of the first and second square pipes 10 and 11.
To house the basket 1 in the cavity 201C circular in section (see
In the basket 1, storage cell rows (square pipe rows) 1A, 2A, 3A, 1B, 2B, and 3B that store the recycled fuel assemblies are formed by arraying a plurality of projections, which are provided on outer sides of sidewalls of the first and second square pipes 10 and 11, in contact with each other. The hollow tabular members 20 are stacked in a plurality of stages among the storage cell rows 1A, 1B, and the like with long side ends thereof set in contact with each other (see
As shown in
The projections 11t2 have a function of, besides transmission of heat, supporting loads with the sidewall 10SW of the square pipe 10 adjacent thereto. When a load condition and a condition of heat are gentle, the projections 11t2 can be omitted. When the projections 11t2 are not provided, there is an advantage that molding of the square pipe 10 is easier. The square pipe 10 and the hollow tabular member 20 can be manufactured by bending or bonding a solid tabular member. However, when heat extrusion molding is possible, it is reasonable to manufacture the square pipe 10 and the tabular member 20 with extrusion molding.
When the first square pipes 10 and the second square pipes 11 are arrayed to form the storage cell rows, the projections 10t1 of the first square pipes 10 adjacent to each other are brought into contact with each other and the projections 10t2 thereof are brought into contact with each other to linearly array a plurality of the first square pipes 10 (e.g., #9 to #12 of the storage cell row 1A). The second square pipes 11 are arranged in the outer circumference to bring the projections 10t1 and 10t2 of the first square pipes 10 into contact with the projections 11t1 and 11t2 of the second square pipe 11 (e.g., #8 and #9 of the storage cell row 1A). When a storage cell row is formed by two second square pipes 11 (storage cell rows 3A and 3B), the projections 11t1 of the second square pipes 11 adjacent to each other are brought into contact with each other and the projections 11t2 thereof are brought into contact with each other to linearly array the two second square pipes 11 (#1 and #2 and #25 and #26).
The first square pipes 10 and the second square pipes 11 are arrayed in this way to form the storage cell rows 1A, 2A, 3A, 1B, 2B, and 3B. As it is seen from
This makes it possible to arrange a large number of the first square pipes 10 and the second square pipes 11 in a limited section (a section orthogonal to the axis Z of the basket 1). Therefore, the square pipes 10 and the second square pipes 11 are arranged via the tabular members. The projections of the square pipes 10 and the second square pipes 11 can keep the first square pipes 10 and the second square pipes 11 in optimum positions in the positions of the square pipes 10 and the second square pipes 11. Therefore, it is possible to increase the number of stored recycled fuel assemblies while suppressing an increase in dimensions of the cask 200. In particular, the effect of the increase in the number of stored recycled fuel assemblies is large in recycled fuel assemblies for PWR having large dimensions.
As shown in
As shown in
A basket that stores recycled fuel assemblies by combining tabular members in a cake box shape and using spaces surrounded by the tabular members as storage cells for the recycled fuel assemblies is known. In such a basket, because intervals of the storage cells can be adjusted only by adjusting the thickness of the tabular members, it may be inevitable to set excess spaces depending on positions of the storage cells. In the basket 1 according to this embodiment, intervals of the storage cells can be adjusted by changing both the thickness of the tabular member 20 and the height of the projections 10t1 and 11t1 and the like of the first square pipes 10 and the second square pipes 11. Consequently, even in places where the intervals of the storage cells cannot be adjusted in the basket of the cake box shape in the past, it possible to more appropriately set the intervals of the storage cells than in the past. As a result, the basket 1 according to this embodiment can be formed more compact than the basket of the cake box shape in the past.
As shown in
In the tabular members 20 stacked in a plurality of stages and arranged between the storage cell rows 1A and 2A and the like, the sides S thereof and the sides of the first and second square pipes 10 and 11 are in contact with each other. In the basket 1 according to this embodiment, because a contact area between the tabular members 20 and the first and second square pipes 10 and 11 is large, heat transfer performance is improved. In the basket 1 according to this embodiment, because the shock at the time when the cask 200 falls can be received with a wider area, shock resistance performance is also improved. These points are advantageous when the recycled fuel assemblies having a large heating value and large mass are stored. A first modification of this embodiment is explained below.
Tabular members and square pipes according to the first modification of this embodiment have substantially the same structure as the tabular members and the square pipes described above. However, the tabular members and the square pipes according to the first modification are different in that cutouts are provided in portions opposed to the bottom of a cavity formed in a barrel main body of a cask that houses a basket.
In this way, in the tabular member 20a and the square pipe 10 (11) forming the basket according to this modification, the cutouts 20ac and M_P are provided in the portions opposed to the bottom B of the cask 200. Therefore, drainage from the basket is improved. The cutouts 20ac and M_P function as exhaust passages during vacuum drying as well. Therefore, it is possible to reduce time required for the vacuum drying. Further, it is possible to reduce a contact area between the tabular member 20a and the square pipe 10 (11) forming the basket and the bottom B of the cask 200. Therefore, it is possible to reduce heat transmitted from the basket to the barrel main body 201C with which the tabular member 20a and the square pipe 10 (11) forming the basket is directly in contact. This makes it possible to maintain the temperature of the barrel main body 201C low compared with the temperature at the time when the cutouts 20ac and M_P are not provided in the tabular member 20a and the square pipe 10 (11). As a result, it is possible to suppress thermal deterioration of a material having neutron absorbing function (a neutron shielding material) arranged on the bottom B side of the barrel main body 201C and cause the material to display neutron shielding performance throughout a storage period of several tens years. A shape of the cutouts 20ac and M_P can be a rectangular shape, an arc shape, or a shape obtained by combining the rectangular shape and the arc shape.
A second modification of this embodiment is characterized in that an area of a portion where a long side end of a tabular member forming a basket is in contact with a long side end of a tabular member adjacent thereto is smaller than an area of a section of the tabular member when the tabular member is cut by a plane parallel to a surface forming the long side end of the tabular member. With such a configuration, for example, a projection (a projected streak) extending in a longitudinal direction of the tabular member is formed in the long side end of the tabular member.
By providing the projections 30 at the long side end TL, at the long side end TL of the tabular member 29, an area St of a portion in contact with a long side end of a tabular member adjacent thereto is smaller than an area Sd of a section (a section taken along X-X shown in
As in a tabular member 29a shown in
In the basket 1d shown in
A basket according to a third modification of this embodiment is characterized in that reinforcing members are provided among the tabular members.
Instead of the tabular member 20, a tabular member 20′ having one hollow section 21′ shown in
The tabular members 20 forming the basket 1e are made of, for example, an aluminum alloy containing boron or a boron compound. The reinforcing member 32 is made of a material having strength higher than that of the tabular members 20, for example, stainless steel. When the reinforcing member 32 is made of the material having high strength such as stainless steel, the reinforcing member 32 is preferably made of a material containing boron or a boron compound from the viewpoint of shielding neutrons. In the basket 1e according to this modification, a shock load on the basket 1e can be received mainly by the reinforcing member 32. This makes it unnecessary to increase the thickness of the tabular members 20 and the like made of the aluminum alloy to receive the shock load on the basket 1e. Therefore, it is possible to make the tabular members 20 and the like compact. As a result, it is possible to make dimensions of the basket 1e compact.
The reinforcing member 32 is preferably arranged in, for example, a position corresponding to a supporting lattice for recycled fuel assemblies stored in the basket 1e. This makes it possible to receive, with the reinforcing member 32, a load on the basket 1e caused by the recycled fuel assemblies stored in the basket 1e. Therefore, it is possible to effectively reduce a load born by the tabular members 30.
As in the basket 1f shown in
A basket according to a fourth aspect of this embodiment is characterized in that a reinforcing member is provided as an intra-tabular member reinforcing member in a hollow section formed in a tabular member.
The reinforcing member 32 as an intra-tabular member reinforcing member is provided in at least one of the two hollow sections 21 included in each of the tabular members 20. In this embodiment, the reinforcing member 32 is provided in one of the two hollow sections 21. A hole 32h piercing through the tabular member 20 in the longitudinal direction can be formed as in a reinforcing member 32a serving as an intra-tabular member reinforcing member shown in
In a basket 11h shown in
The tabular members 29 and 29b forming the baskets 1e and 1h are made of, for example, an aluminum alloy containing boron or a boron compound. The reinforcing members 32 and 32a are made of, for example, stainless steel. When the reinforcing members 32 and 32a are made of stainless steel, it is preferable to use stainless steel containing boron or a boron compound from the viewpoint of shielding neutrons. In the baskets le and 1h according to this modification, a shock load on the basket 1e and 1h can be received mainly by the reinforcing members 32 and 32a. This makes it unnecessary to increase the thickness of the tabular members 29 and 29b made of the aluminum alloy to receive a shock load on the baskets 1e and 1h. Therefore, it is possible to make the tabular members 29 and 29b compact. As a result, it is possible to make dimensions of the baskets 1e and 1h compact. The reinforcing members 32 and 32a are arranged in the tabular members 29 and 29b that are in contact with the first and second square pipes 10 and 11 (see
A basket according to a fifth modification of this embodiment is similar to the basket according to the first embodiment (see
As shown in
With such a configuration, when the square pipes 10a are combined, there are an advantage that the square pipes 10a less easily shift from each other and an advantage that a heat transfer area is large. Consequently, heat transfer efficiency and power transmission efficiency between square pipes 10a are improved. Because the square pipes 10a less easily shift from each other, work efficiency in assembling the basket 1a is also improved. A gradient of one surface is shown in the figure. However, if two gradients toward opposite directions are given to one projection, the square pipe can be restrained from turning. Force for causing bend in the projections can be offset when force is transmitted. A sixth modification of this embodiment is explained.
A basket according to a sixth modification of this embodiment is similar to the basket according to the first embodiment (see
As shown in
As shown in
As in the basket 1b according to this modification, it is possible to easily vary dimensions of flux traps in the basket 1b by changing dimensions of the projections formed on outer sides of sidewalls of the square pipes and dimensions of the hollow sections of the tabular members. This makes it possible to change the flux traps according to a degree of burn-up of recycled fuel assemblies stored in the basket 1b. It is preferable to form the dimensions of the flux traps to increase from the outer sides of the basket 1b toward the center.
The center of the basket 1b receives radiation from recycled fuel stored in cells around the center as well. Therefore, it is necessary to set the flux traps larger than those in an outer circumference of the basket 1b. On the other hand, in the outer circumference of the basket 1b, because the number of cells is smaller in the periphery than that in the center, radiation from the recycled fuel is less than that in the center. When flux traps in the entire basket 1b are formed with dimensions of flux traps required in the center, dimensions of the flux traps in the outer circumference are larger than necessary. This causes an increase in mass of the basket and an increase in dimensions. Therefore, the flux traps are formed such that dimensions thereof increase from the outer side toward the center of the basket 1b. In this way, an increase in mass and an increase in dimensions of the basket 1b are suppressed.
As explained above, in this embodiment and the modifications of the embodiment, a plurality of storage cell rows formed by arraying a plurality of projections, which are provided on outer sides of sidewalls of square pipes, in contact with each other are provided and hollow tabular members are stacked in a plurality of stages among the storage cell rows with long side ends thereof set in contact with each other. This makes it possible to increase a heat transfer area between the square pipes and the tabular members and form flux traps among the square pipes in which recycled fuel assemblies are stored. Therefore, even when recycled fuel for PWR is stored, it is possible to secure sufficient heat transfer performance and a sufficient subcritical function. Because the number of projections provided in the square pipes is small, it is possible to secure extrusion accuracy even when a material hard to be extruded such as a boron-aluminum material is used. Therefore, it is possible to prevent a fall in manufacturing efficiency. In particular, in a basket in which tabular members provided with cutouts are combined in a case box shape, cutting-out after obtaining tabular members with extrusion molding or the like is necessary. However, in this embodiment and the modifications of the embodiment, machining cost can be substantially reduced because such cutting-out is unnecessary. Recycled fuel assembly storage baskets having a configuration same as the configuration disclosed in this embodiment and the modifications of the embodiment have actions and effects same as those of this embodiment. The configuration disclosed in this embodiment and the modifications can be applied in embodiments described below as well as appropriate.
A second embodiment is the same as the first embodiment and the like in that square pipes and hollow tabular members are combined. However, the second embodiment is different from the first embodiment and the like in that a plurality of storage cell rows are alternately arrayed in contact with outer sides of sidewalls of square pipes and outer sides of sidewalls of first tabular members and second tabular members are stacked in a plurality of stages among the storage cell rows with long side ends thereof set in contact with each other. Otherwise, the second embodiment is the same as the first embodiment and the like.
As shown in
The square pipes 16 are one kind of square pipes of a simple shape without projections. Therefore, only one kind of dice used for extrusion molding of the square pipes 16 has to be provided. Because the square pipes 16 are formed in the simple shape, yield can be improved and time and labor for manufacturing and managing the square pipes 16 can be reduced. If sectional shapes of the first and second tabular members 24 and 25 (sectional shapes orthogonal to a direction piercing through the hollow sections 26) are formed in the same shape, the first and second tabular members 24 and 25 can be used in common. This makes it possible to reduce labor and time for manufacturing and managing the first and second tabular members 24 and 25. The square pipes 16 and the first and second tabular members 24 and 25 forming the basket 1c are explained and the basket 1c is explained more in detail below.
As shown in
As shown in
As shown in
When the square pipes 16 and the first tabular members 24 are arrayed to form storage cell rows, outer sides of sidewalls of the square pipes 16 and sides S of the first tabular members 24 are set in contact with each other, the square pipes 16 and the first tabular members 24 are alternately arrayed, and the square pipes 16 and the first tabular members 24 are linearly arrayed (storage cell rows 1A and 1B). The first tabular member 24 is arranged between the square pipes 16 adjacent to each other. Therefore, as described above, the hollow sections 26 included in the first tabular member 24 function as flux traps.
The first and second tabular members 24 and 25 are arrayed in this way to form storage cell rows 1A, 2A, 3A, 1B, 2B, and 3B. As it is seen from
As shown in
As shown in
The sides S of the second tabular members 25 stacked in a plurality of stages and arranged between the storage cell rows 1A and 2A and the like are in contact with the ouster sides of the sidewalls of the square pipes 16 and the long side ends TL of the first tabular members 26. In this way, in the basket 1c according to this embodiment, because a contact area between the square pipes 16 and the first and second tabular members 24 and 25 is large, heat transfer performance is improved. In the basket 1c according to this embodiment, because the shock at the time when the cask 200 falls can be received with a wider area, shock resistance performance is also improved. These points are advantageous when recycled fuel assemblies for PWR having a large heating value and large mass are stored.
As explained above, in this embodiment, a plurality of storage cell rows are alternately arrayed in contact with outer sides of sidewalls of square pipes and outer sides of sidewalls of first tabular members. Second tabular members are stacked in a plurality of stages among the storage cell rows with long side ends thereof set in contact with each other. This makes it possible to increase a heat transfer area between the square pipes and the tabular members and form flux traps among the square pipes that store the recycled fuel assemblies. Therefore, it is possible to secure sufficient heat transfer performance and a sufficient subcritical function even when recycled fuel for PWR is stored. Because the square pipes do not have projections, even when a material hard to be extruded such as a boron-aluminum material is used, it is possible to easily secure extrusion accuracy, improve yield, and reduce time and labor for manufacturing and managing the square pipes 16. If the first and second tabular members 24 and 25 are formed in the same sectional shape, the first and second tabular members 24 and 25 can be used in common. This makes it possible to also reduce time and labor for manufacturing and managing the first and second tabular members 24 and 25. Recycled fuel assembly storage baskets having a configuration same as the configuration disclosed in this embodiment and the modifications of the embodiment have actions and effects same as those of this embodiment. The configuration disclosed in this embodiment and the modifications can be applied as appropriate in embodiments described below as well.
A third embodiment is the same as the first embodiment and the like in that square pipes and hollow tabular members are combined. However, the third embodiment is different from the first embodiment and the like in that the tabular members are stacked to have a gradient with respect to the bottom of a cask as a recycled fuel assembly storage container that houses a basket therein. Otherwise, the third embodiment is the same as the first embodiment and the like.
In the basket 1a, the air and water W can be prevented from being accumulated in hollow sections 21A of the tabular members 20 by the configuration described above. As the gradient of the tabular members 20 is steeper, a surer effect can be expected. However, because of easiness of manufacturing of the spacer 20A that determines the gradient, it is reasonable to set the gradient to be equal to or larger than 0 degree and equal to or smaller than the height of one stage of the tabular members 20. The square pipes 10 and the tabular members 20 can be integrally formed by bolts, welding, or the like to make it easy to handle the basket 1a. The square pipes 10 and the tabular members 20 can be integrally bound by binding means such as a wire or a band to make it easy to handle the basket 1a. This is preferable because the basket 1a can be disassembled as required. The tabular members 20 integrated by bolts or welding can be formed integrally with the square pipes 10 by binding means such as a wire or a band. This is preferable because the basket 1a can be treated as one body.
In the basket 1 shown in
When recycled fuel assemblies for PWR are stored, the size of the holes 40h provided in the bottom plate 40 is set such that ends of the recycled fuel assemblies are placed on the bottom plate 40. When recycled fuel assemblies for BWR are stored, the size of the holes 40h is set such that ends of the recycled fuel assemblies pierces through the holes 40h provided in the bottom plate 40. Because ends of the recycled fuel assemblies for PWR are flat, drainage is secured by placing the ends on the bottom plate 40. On the other hand, because ends of the recycled fuel assemblies for BWR are sharp, drainage can be secured even if the ends come into contact with the bottom B of the cask. Therefore, an increase in the total length of the cask can be suppressed by setting the ends to pierce through the holes 40h.
The basket 1a placed on the bottom plate 40 can be handled as one body by providing the bottom plate 40. A quantity of heat transmitted from the basket 1a to the bottom B of the cask can be reduced. Therefore, it is possible to suppress thermal deterioration of a material having a neutron absorbing function (a neutron shielding material) arranged on the bottom B side of the cask and cause the material to display neutron shielding performance throughout a storage period of several tens years. The water W drained from the basket 1a is discharged to the outside through an inner space of the tabular members 20 arranged to be inclined with respect to the bottom B of the cask. The water falling from the basket 1a to the bottom plate 40 is discharged to the spaces 42 formed between the bottom plate 40 and the bottom B of the cask. Because drainage is improved by the spaces 42, it is possible to reduce remaining moisture before vacuum drying and reduce time required for the vacuum drying. Because air permeability is improved by the space 42, efficiency of the vacuum drying is also improved. The basket 1a integrated by the method described above can be fixed to the bottom plate 40 by bolts or welding. This makes it possible to handle the basket 1a as one body together with the bottom plate 40 and facilitates work for arranging the basket 1a in the cask.
When the projections 41 provided in the bottom plate 40 is tabular, as in the tabular member 20a shown in
As described above, the recycled fuel assembly storage basket and the recycled fuel assembly storage container according to the present invention are useful for transportation and storage of recycled fuel assemblies and, in particular, suitable for transportation and storage of recycled fuel assemblies for PWR. The basket can be used in a concrete cask for storage purpose, a canister, or a rack of a recycled fuel assembly storage pool.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-135508 | May 2006 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2007/059983 | 5/15/2007 | WO | 00 | 11/13/2008 |
