JPH10227890A - Spent fuel rack - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a spent fuel rack proper for storage of reactor fuel after use by providing a support means supporting a boron containing stainless steel member without transmitting the load from a cell. SOLUTION: In this spent fuel rack 1, a plurality of rectangular tube cells 2 individually containing spent fuel are bundled in square grid shape by spacer grids 3 fixing each cell 2 between adjacent ones. Box shape members 10 consisting of 4 boron containing stainless steel plates in accordance with the inner shape of the cells 2 are inserted in each of cells 2 so that 4 sides of the cell 2 are covered from the inside. At this moment, the box shape member 10 is put on the surface of a pedestal 7 (support means). Therefore, the load of the cells 2 hardly transmits to the box shape member 10. So, the strength problems of the boron containing stainless steel does not affect the strength of the rack 1 body and fuel assemblies can be contained and stored maintaining subcriticality in the cells 21.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spent fuel rack for storing a fuel assembly for a nuclear reactor after use.

[0002]

BACKGROUND OF THE INVENTION Fuel loaded into a commercial nuclear reactor is then stored in a spent fuel pit in an auxiliary building. The number of fuel stores in the pit is several times the capacity of a single core, but for a reactor that has been operating for a long period of time, the number of fuel stores increases and the storage capacity approaches the limit. It is possible.

[0003] Accordingly, in the pit, the distance between adjacent fuels while maintaining the subcriticality, that is, the distance between cells in which each fuel body is stored, that is, the so-called cell pitch, is reduced to minimize the fuel efficiency. Storage is required.

Therefore, a spent fuel rack using a boron-containing stainless steel plate (hereinafter referred to as a boron stainless steel plate) has been developed. As the amount of boron added to the stainless steel plate is increased, the neutron absorption capacity is improved, and the distance between cells can be reduced.

[0005]

The above-mentioned conventional spent fuel rack usually uses a boron stainless plate as a structural material. That is, the cells constituting the rack itself were made of a boron stainless plate.

However, compared to stainless steel, a boron stainless steel plate has low strength against bending and impact and is easily damaged, and the degree of its deterioration is correlated with the boron content. Therefore, in order to avoid a decrease in structural strength, it is necessary to suppress the amount of boron to be added, which is contrary to the above-described pursuit of subcriticality.

[0007] In view of the above problems, an object of the present invention is to provide a spent fuel rack suitable for storing after-use fuel for a nuclear reactor. Another object of the present invention is to use boron-containing stainless steel as a neutron absorber necessary for subcritical control, while maintaining the mechanical strength of the rack itself,
It is an object of the present invention to obtain a spent fuel rack that enables efficient fuel storage.

[0008] In the case of a conventional spent fuel rack, which is stored in a pit and has already reached the limit of the number of fuel storage units, it is necessary to replace the rack with a smaller cell pitch with a so-called re-racking work. However, existing structural materials such as cells and spacers have been radioactive waste.

Each of these radioactive wastes undergoes a washing step for reducing the radioactive level, and is then shredded and stored in a waste storage drum. The amount of radioactive waste generated during a series of re-wrapping works can reach thousands of drums, and the storage space provided at the power plant is expected to be short.

[0010] In view of the above problems, another object of the present invention is to provide:
An object of the present invention is to provide a spent fuel rack that can reduce waste generated during relaking.

[0011]

In order to achieve the above object, a spent fuel rack according to the first aspect of the present invention comprises:
A plurality of substantially rectangular tubular cells formed of a structural material as hollow cells for storing spent fuel assemblies, and the plurality of cells are bound in a square lattice at regular intervals between adjacent cells. A spacer plate, a base plate fixed to the lower ends of all cells bundled by the spacer grid, and having a flow hole for guiding cooling water into each cell and a pedestal serving as a bottom in each cell; and four sides of each cell. A boron-containing stainless steel member covering the inside or outside of the
Support means for supporting the boron-containing stainless member without transmitting the load from the cell.

Further, in the spent fuel rack according to the second aspect of the present invention, in the spent fuel rack according to the first aspect, the boron-containing stainless steel member includes four sheets corresponding to the inner shape of the cell. A box-shaped member formed by splicing boron-containing stainless steel flat plates is included, and the support means is configured by a pedestal surface for mounting the box-shaped member on the pedestal in each cell.

The spent fuel rack according to the third aspect of the present invention is the spent fuel rack according to the first aspect, wherein the boron-containing stainless member covers the outside of four sides of each cell. The support means includes a band member holding the four boron-containing stainless steel flat plates on the outer surface of the cell.

According to a fourth aspect of the present invention, there is provided the spent fuel rack according to the third aspect, wherein the supporting means is provided on the lower part of the cell or on the base plate, and contains each boron. It includes a projection that supports the lower end of the stainless steel flat plate.

According to a fifth aspect of the present invention, there is provided the spent fuel rack according to the first aspect, wherein the substantially square tubular cell is an existing cell taken out of an existing pit. It is reused after washing.

A spent fuel rack according to a sixth aspect of the present invention is the previously used fuel rack according to the fifth aspect, which is previously assembled as a spacer grid for binding the plurality of cells in a square lattice. Using a structural material for cell insertion, the structural material for cell insertion has a plurality of support plates in the longitudinal direction in which openings for inserting existing cells are arranged in a square lattice, and the openings are It has an area approximately matching the outer shape of the cross section of the existing cell and the boron stainless steel plate covering the four sides of the cell.

According to the spent fuel rack of the present invention, the boron-containing stainless steel is not used for a structural part constituting a rack such as a cell or a spacer grid in which a fuel body is accommodated, and the load from the fuel body or the structural part is not used. However, the mechanical strength problem does not affect the rack strength because it is arranged only as a neutron absorber necessary for subcritical control instead of supporting it.

That is, it is not necessary to use a boron-containing stainless steel having a problem in strength in a structural portion of a rack, such as a cell, a spacer grid, and a base plate, and a metal material having excellent mechanical strength such as stainless steel is selected as a structural material. Therefore, a plurality of spent fuel assemblies can be stored in the rack satisfactorily while maintaining the mechanical strength of the rack itself while using boron-containing stainless steel as a neutron absorber required for subcritical control.

Further, the present invention provides a plurality of substantially square tubular cells,
Since the cells are bound in a square lattice with a certain space between adjacent cells by the spacer grid, only the spacer grid is the space, so the cell pitch can be minimized without wasteful space and the volume is limited. The maximum spent fuel can be stored.

The boron-containing stainless steel member used as a neutron absorber necessary for subcritical control used in the present invention may be any material that covers the inside or outside of four sides of each cell without supporting the load from the cell. .

As a specific configuration of the boron-containing stainless steel member, there is a box-shaped member formed by splicing four boron-containing stainless steel plates according to the inner dimensions of the cell. According to such a configuration, by inserting the box-shaped member into the cell, the boron-containing stainless steel plate covers the four side surfaces of the cell from inside.

Here, the reason why the boron-containing stainless steel plate is formed into a box shape by splicing is that, for example, when formed by screwing, there is a risk of cracks due to stress concentration. This is because the problem that the boron content cannot be secured can be avoided. The notch required for splicing both end surfaces of each boron-containing stainless steel plate can be accurately formed by laser cutting.

Further, as another constitution of the spent fuel rack using the boron-containing stainless steel, the four boron-containing stainless steel flat plates are supported on the outer surface of the cell by a band member as a support means. With this configuration, the four boron-containing stainless steel plates cover the four sides of each cell. At this time, the band member is attached to the outer peripheral surface of each cell so that the corresponding boron-containing stainless steel flat plate can be pressed and fixed to each outer surface of the cell independently.

In the state where the boron-containing stainless steel flat plate is pressed by such a band member, the boron-containing stainless steel flat plate may slide down the cell outer peripheral surface by its own weight in some cases. Therefore, if a projection for supporting the lower end of the boron-containing stainless steel plate is provided on the lower portion of the cell or on the base plate on which the cell is mounted, slippage of the flat plate can be prevented.

Of course, in order to prevent the entire boron-containing stainless steel plate from slipping off, a projection is provided at the lower part of the outer four surfaces of each cell or near the base of each cell on the base plate at a position supporting the lower end of each boron-containing stainless steel plate. To form

At the time of re-laking, the existing cells and spacers which are taken out of the pits and after the replacement of spent fuel are usually radioactive waste. By washing and incorporating a boron stainless steel flat plate and reusing it as a spent fuel assembly accommodating cell constituting the spent fuel rack of the present invention, radioactive waste is significantly reduced accordingly.

As described above, when reusing an existing cell,
As described in claim 6, by assembling the existing cell insertion structural material in advance as a module framework, a spent fuel rack can be simply configured simply by inserting the existing cell after recovery and washing. . At this time, the opening of each of the support plates of the structural material into which the cell is inserted needs to substantially match the cross-sectional outer shape of the existing cell, but the four side surfaces of the existing cell are covered with the boron-containing stainless member from the outside. In this case, the opening area takes into account the space of the boron-containing stainless steel member.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1) Next, a spent fuel rack according to a first embodiment of the present invention will be described with reference to FIGS.
In the present spent fuel rack 1, as shown in the schematic configuration diagram of FIG. 1, a plurality of square tubular cells 2 as hollow cells for accommodating spent fuel assemblies are adjacent to each other.
The cells 2 are bound in a square lattice by a spacer grid 3 fixing the cells 2 therebetween.

The group of cells 2 bound by the spacer grid 3 is placed on the base plate 6 by welding the lower ends of the cells 2. The spent fuel rack 1 mainly includes the cells 2, the spacer grit 3, and the base plate 6 as described above. These are formed of a metal material having high mechanical strength such as stainless steel as a structural material.

Here, in order to strengthen the binding between the cells 2 and to provide resistance to the torsion and bending of the entire rack, all the adjacent cells 2 are welded together with the spacer straps 5.

A pedestal 7 serving as the bottom of each cell 2 is mounted on the upper surface of the base plate 6, as can be seen in the partially broken area in FIG. The outer shape of the pedestal 7 fits into the inner shape of the cell 2. At the time of rack assembly, the cell 2 is fixed on the base plate 6 such that the lower end of the cell 2 is fitted into each pedestal 7. In the base plate 6, water holes for introducing cooling water into the cells 2 are formed on the respective pedestal surfaces.

Further, in the present embodiment, when a spent fuel assembly is stored and stored in each cell 2, a boron-containing stainless steel (hereinafter, referred to as a neutron absorbing material for maintaining subcriticality) is used. The member is described so as to cover four sides of each cell, and the side is covered from the inside of each cell.

That is, a boron stainless steel box-shaped member 1 composed of four boron stainless steel flat plates corresponding to the inner shape of the cell 2
0 was inserted into each cell 2 so as to cover four sides of each cell 2 from the inside. At this time, the boron stainless box member 10 is placed on the surface of the pedestal 7. Therefore, when the boron stainless box member 10 is supported by the pedestal surface, the load of the cell 2 is hardly transmitted to the boron stainless box member 10.

The above-mentioned boron stainless steel box-shaped member 10 is formed by forming notches 11 on both end surfaces of four boron stainless steel flat plates to be fitted with the end surfaces of adjacent flat plates, and forming them into a box shape by joining. is there. Forming by such splicing does not have the risk of cracks due to stress concentration appearing when formed by screwing, or the problem that the boron content of the penetration part cannot be ensured when formed by welding. Each notch 11 can be formed by cutting with a laser.

As described above, in the present spent fuel rack 1,
Since the load from the cell (including the load of the fuel assembly when housed in the cell 2) hardly acts on the boron stainless steel box member 10, the above-described strength problem of the boron stainless steel affects the strength of the rack body. Without having to do so, the spent fuel assemblies can be stored and stored while having subcriticality in the cell 2.

When the fuel assemblies 15 are accommodated in each of the cells 2, as shown in the side view of FIG.
It is inserted into the cell 2 so as to be placed on the pedestal 7 with 3 facing down. In addition, near the upper end of the cell 2, the upper nozzle 1 is provided so that the fuel assembly 15 does not fall out of the upper opening of the cell 2.
It is preferable to provide a retaining projection 12 that presses the outer surface of the projection 4.

A plurality of support pads 9 for supporting the rack 1 were mounted on the lower surface side of the base plate 6 by screwing on the spent fuel rack 1. Since the height of the support pad 9 can be changed by adjusting the screw 16, the horizontality of the rack 1 can be ensured even for subtle irregularities on the pit floor surface.

(Embodiment 2) In the first embodiment, the case where the four sides of each cell are covered with boron stainless steel from the inside is shown. Next, the spent fuel according to the second embodiment of the present invention will be described. A configuration in which four sides of each cell are covered from the outside as a rack will be described.

FIG. 3 is a schematic configuration diagram of a spent fuel rack according to the present embodiment. As shown in a perspective view of FIG.
That is, the configurations of the cell 22, the spacer grit 23, and the base plate 26 are the same as in the first embodiment.

A plurality of square tubular cells 22 are adjacent cells 22
The cells 22 are bound in a square lattice by a spacer grid 23 for fixing the cells 22 therebetween, and the group of the bound cells 22 is placed on the base plate 26 by welding the lower ends of the cells 22.

Further, on the upper surface of the base plate 23, similarly to the first embodiment, an outer base (not shown) fitted to the inner shape of the cell 22 is attached so as to be the bottom of each cell 22. When assembling the rack, the lower end of the cell 22 is fitted into each pedestal so that the base plate 2
The cell 22 is fixed on 3. Also, base plate 2
A flow hole for introducing cooling water into the cell 22 is formed in 3.

Further, in this embodiment, when the spent fuel assembly is stored and stored in each cell 22,
In order to arrange the boron stainless steel plate 24 as a neutron absorbing material for maintaining the subcriticality so as to cover the four sides of each cell 22 from the outside, each cell 2
Band members 25 each holding a boron stainless steel plate 24 on the outer periphery of No. 2 were provided.

A plurality of band members 25 are arranged in parallel in the vertical direction on the four outer peripheral surfaces of each cell 22, and each of the four boron stainless steel flat plates 24 abutting on the four outer peripheral surfaces of each cell 22 is independently formed on the cell surface. To the side. More specifically, as shown in FIG. 3B, both ends of a band-shaped member having elasticity, which is a biasing force necessary to hold the boron stainless steel plate 24, extend in the width direction of one outer peripheral side surface of the cell 22. Is fixed to the cell 22.

Each of the boron stainless steel flat plates 24 is
The band member 25 is sandwiched between the outer peripheral surface and the band member 25. In the state where the boron stainless steel plate 24 is held by the band member 25 for a long period of time, the boron stainless steel plate 24 is not fixed to the cell 22. Therefore, the boron stainless steel plate 24 may slip down due to its own weight. There is.

In this embodiment, a support projection 27 for supporting the lower end of the boron stainless steel plate 24 is formed below the outer peripheral side surface of the rack of the cell 22 located at the outermost periphery of the rack.

In the state in which the boron stainless steel plate 24 is supported by the band member 25, the load of the cell 22 and the fuel assembly accommodated in the cell 22 is not transmitted to the boron stainless steel flat plate 24. The storage and storage of the spent fuel assembly can be performed while maintaining the subcriticality in the cell 22 without the strength problem affecting the strength of the rack body.

(Embodiment 3) Next, as a third embodiment of the present invention, a case will be described below in which a spent fuel rack is constituted by reusing an existing cell taken out during relaking. Here, a pre-assembled structural material for cell insertion is used.

As shown in FIG. 4 (a), the cell insertion structural member 41 is formed by fixing a plurality of support plates 41 each serving as a spacer grid to support legs 44 at four corners in the longitudinal direction. is there. In the support plate 41, openings having an area substantially matching the cross-sectional outer shape of the existing cell 42 to be inserted are arranged in a square lattice shape, and the distance between adjacent openings is the cell pitch.

The lowermost support plate 41 has a support pad 45 attached to the lower surface as a base plate. In addition, the existing cell 42 is supported by the support plate 4 at each opening edge so that the inserted existing cell 42 does not slip down.
A pressing metal fitting 46 for fixing the bracket 1 is attached.

In such a structure 41 for inserting cells, a spent fuel rack is constructed simply by inserting existing cells 42 into each opening. Therefore, at the time of relaking, the cell insertion structural material 41 is assembled in advance so that the existing cells 42 taken out of the existing pits and recovered are washed, and can be quickly inserted into the structural material 41.

When the existing cells 42 are collected, the support members and metal fittings that previously bundled the existing cells 42 are cut off, the cells are taken out without being damaged, and the radioactivity level is reduced by washing. The washed existing cell 42 is inserted into the opening of the cell insertion structural material 41 and a plurality of pressing fittings 46 are inserted.
To make a reusable rack.

When storing the spent fuel assemblies, as shown in the first embodiment, four boron stainless steel plates corresponding to the inner shape of the existing cell 42 are formed by joining. Each of the boron stainless steel box-shaped members 50 is used as a neutron absorber to maintain the subcriticality.
By inserting into the inside, the four sides of each existing cell 42 are covered from the inside.

When the existing cells 42 are covered with a boron stainless steel plate 51 from the outside, as shown in FIG. Band members 52 arranged in parallel in a plurality of directions
Then, each of the four boron stainless steel flat plates 51 is independently held on the four sides of the cell, and then inserted into the existing structural member 41 for cell insertion.
Fix 2

In this case, each opening of the pre-assembled existing cell-inserting structural material has an opening area in consideration of not only the outer shape of the cross section of the existing cell 42 but also the space of the boron stainless steel plate 51 attached to the four outer peripheral surfaces. And

As described above, in the spent fuel rack according to the third embodiment, since the existing cells taken out of the existing pits and recovered at the time of re-laking are reused, the amount of radioactive waste is greatly reduced. .

The spent fuel rack according to the present invention is:
As is clear from the spent fuel racks according to the first to third embodiments, since the outer shape of the rack is a substantially rectangular parallelepiped module, a plurality of racks containing spent fuel assemblies are stored in the fuel pit. In this case, the arrangement can be performed efficiently by a required number of modules.

For example, as shown in FIG. 5, by arranging a plurality of frame structures 32 corresponding to the XYZ axes of the racks 31 in the pits and holding the racks 31 in each unit frame structure 32, a plurality of racks 31 are formed. Can be stored efficiently and in a stable fixed state.

As shown in FIG. 5B, a hook formed toward the wall in the frame structure 32 facing the pit wall side is hooked into a hole of a stopper projecting from an anchor plate on the wall surface. The load of the rack 31 is transmitted to the pit wall via the frame structure 32. The holes of the stoppers have a degree of freedom in consideration of thermal expansion. The frame structure 32 is provided with a press fitting for pressing the outer surface of the rack 31 from the frame structure 32 in order to stably hold the rack 31.

As another fixing method of the racks 31, as shown in FIG. 6, a base frame 33 surrounding the lower part of each rack 31 is used, and a plurality of racks 31 are connected via the base frame 33 to form a pit. There is a method in which a predetermined number of support members 34 that urge both sides are provided between the base frame 33 on the wall surface side and the wall. For example, rack 3
Even if a horizontal force acts on the support member 1,
The movement of the rack 31 in the pit is suppressed by the tension of 4, and the rack 31 is always stored in a stable state.

[0060]

As described above, according to the present invention, while using boron-containing stainless steel as a necessary neutron absorbing material, the rack structure such as the cell and the spacer grid can be formed of other structural materials. Since the load and the load of the fuel assembly contained in the cell are not transmitted to the boron stainless steel member, and the problem of the strength of the boron stainless steel does not affect other structural parts, the mechanical strength of the rack itself is reduced. There is an effect that a plurality of spent fuel assemblies can be favorably stored in a rack under subcritical control while maintaining them.

According to the present invention, the amount of radioactive waste can be significantly reduced by reusing an existing cell as a cell for storing a spent fuel assembly, and the waste storage space can be reduced accordingly. The shortage problem is eliminated.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a spent fuel rack according to a first embodiment of the present invention.

FIG. 2 is a side view including a partial cross section of the spent fuel rack according to the first embodiment of the present invention.

FIGS. 3A and 3B are schematic configuration diagrams of a spent fuel rack according to a second embodiment of the present invention, wherein FIG. 3A is a schematic perspective view and FIG. 3B is an explanatory diagram showing a band member.

FIG. 4 is a schematic configuration diagram of a spent fuel rack according to a third embodiment of the present invention.

FIG. 5 is an explanatory view showing an example of a method for stably storing spent fuel racks in pits according to the present invention, wherein (a) and (c) are explanatory views of a rack holding state using a frame structure, and (b).
FIG. 3 is a partially enlarged view of a pit wall side frame structure.

FIG. 6 is an explanatory view showing another example of a method for stably storing a spent fuel rack in a pit according to the present invention.

[Explanation of symbols]

 1,21,31: Spent fuel rack 2,22: Cell 3,23: Spacer grid 4: Protective belt 5: Spacer strap 6,26: Base plate 7: Pedestal 8: Flow hole 9,45: Support pad 16 :( Screw for supporting pad) 10, 50: Boron stainless steel box-shaped member 11: Notch (for splicing) 12: Retaining projection 13: Lower nozzle 14: Upper nozzle 15: Spent fuel assembly 24, 51: Boron stainless steel Flat plate 25, 52: Band member 27: Support projection 32: Frame structure 33: Base frame 34: Support member 41: Structural material for existing cell insertion 42: Existing cell 43: Support plate 44: Support leg 46: Press fitting

Claims (6)

[Claims] 1. A plurality of substantially rectangular tubular cells each formed of a structural material as a hollow cell for storing a spent fuel assembly, and the plurality of cells are squared with a predetermined interval between adjacent cells. A spacer grid that binds in a grid, a base plate that is fixed to the lower ends of all the cells bundled by the spacer grid, and has a pedestal serving as a bottom in each cell and a flow hole for guiding cooling water into each cell; A spent fuel rack comprising: a boron-containing stainless steel member that covers the inside or outside of four sides of each cell; and support means for supporting the boron-containing stainless member without transmitting a load from the cell. . 2. The boron-containing stainless member includes a box-shaped member formed by splicing four boron-containing stainless steel flat plates corresponding to the inner shape of the cell, and the supporting unit includes a box-shaped member. The spent fuel rack according to claim 1, wherein the spent fuel rack is constituted by a pedestal surface mounted on the pedestal in a cell. 3. The boron-containing stainless steel member includes four boron-containing stainless steel plates that respectively cover the four sides of each cell, and the support unit is configured to place the four boron-containing stainless steel plates on the outer surface of the cell. The spent fuel rack according to claim 1, further comprising a band member held by the rack. 4. The spent fuel rack according to claim 3, wherein the supporting means includes a projection provided on a lower portion of the cell or on the base plate and supporting a lower end of each of the boron-containing stainless steel plates. 5. The spent fuel rack according to claim 1, wherein the substantially square tubular cells are existing cells taken out of existing pits and are reused after cleaning. 6. A pre-assembled structural member for cell insertion is used as a spacer grid for binding the plurality of cells in a square lattice. The structural member for cell insertion has an opening for inserting an existing cell. It has a plurality of support plates arranged in a square lattice shape in the vertical axis direction, and the opening has an area substantially matching the outer shape of the cross section of the existing cell and the boron stainless steel plate covering the four sides of the cell. The spent fuel rack according to claim 5, characterized in that: