JPS62197798A - Nuclear reactor fuel storage devcie - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a nuclear fuel storage system for nine nuclear reactors, and particularly to a rack-type storage system for accommodating spent nuclear fuel assemblies.

[Conventional technology]

During regular inspections of nuclear power plants, nuclear fuel assemblies removed from the reactor vessel are stored in the spent nuclear fuel storage pit (hereinafter referred to as via) in the nuclear fuel handling building adjacent to the reactor containment vessel. stored in water. That is, it is housed and stored in a rack cell that constitutes a spent nuclear fuel storage rack (hereinafter referred to as a rack).

An outline of the conventional structure of the rack in the pit is shown in Figure f7 and Figure 1.
1'. In the drawing, a plurality of rack cells 01 are blocked by support members 06 within a pit 02 to form a rack assembly 03. The support member 06 and the embedded metal fittings 04 around the four circumferences of the pit wall 05 are connected by a strong support 07, thereby fixing the rack assembly 'JO3 to the pit wall 05. Nuclear fuel assemblies are stored in rank assembly 03, but contain fissile material so that they do not reach criticality. Conventional rack cell 01ilt is typically made of square steel tubes made of stainless steel (mainly 5US304), but since this cannot be expected to have much of a neutron absorption effect, the distance between adjacent nuclear fuel assemblies is increased to increase criticality. I try not to reach that. Therefore, the limited area (
Rack cell 01 in pit 02 with (or volume)
The reality is that the number of installations is not that large. Furthermore, the strength of the support member 06, as well as the support 07, the embedded hardware 04, the pit wall 05, etc., is determined so as to be able to withstand external forces such as seismic force. These strengths are set to match the total weight of the rack cell 01 and the weight of the nuclear fuel assembly contained therein.

[Problem that the invention seeks to solve]

The raw reactor fuel, that is, the nuclear fuel assembly, becomes a spent nuclear fuel assembly after a predetermined combustion in the nuclear reactor. Due to the smooth operation of nuclear reactors, a large amount of spent nuclear fuel assemblies are being generated recently, and many high-density ranks have been proposed to store them within nuclear power plants. This high-density rack is intended to store more nuclear fuel assemblies by narrowing the spacing between the nuclear fuel assemblies in a pit of the same size as the conventional one. Although there are some differences depending on the type of neutron absorbing material used between the nuclear fuel assemblies, high-density racks are approximately 2 to 4
Since the storage capacity is doubled, when an external force such as an earthquake occurs, the rack reaction force acting on the wall due to the shaking of the rack assembly increases by that amount compared to the conventional system.

In other words, high-density racks are designed to store a large amount of nuclear fuel assemblies by shortening the distance between the nuclear fuel assemblies to be stored, that is, the spacing between the racks, but this increases the weight and reduces the seismic performance. It turns out to be a good experience. For example, if you try to increase the strength of B/) walls, you will need to increase the strength of the building's reinforcing bars, steel frames, etc., and the capacity of the associated equipment will also increase. This results in increased costs.

Furthermore, the rack assembly itself must be made larger in order to increase the seismic strength of the support members that connect the racks together and the supports that fix them, and this increases storage capacity due to higher density. Improvements are also diminished.

Therefore, the present invention aims to provide a lightweight, low-cost nuclear reactor fuel storage device with excellent seismic performance.

[Means for solving problems]

In the present invention, rack cells that individually receive nuclear fuel assemblies are interconnected by support members to form a rack assembly. The rack assembly is placed in the pit, and a spherical support such as a sphere or an ellipsoidal sphere is placed between the rack assembly and the pit floor, and the rack assembly and the stored nuclear fuel are placed between the rack assembly and the pit floor. Transfers the weight of the aggregate to the focus bed.

"Function" The weight of the rank assembly and the weight (static load) Vi of the Haramachi fuel assembly stored in the rack cell are transmitted to the pit floor via the spherical support.
When the pit floor reciprocates (vibrates) in the horizontal direction due to K, the spherical support (d) rotates about its axis.However, the rack assembly and the nuclear fuel assembly remain in position due to the inertia due to their weight. Earthquake force is not transmitted.

In preparation for large seismic forces and amplitudes, horizontal shock absorbers may be interposed between the rack assembly and the pit wall, and the shape of the spherical body and its mounting structure may be changed to convert horizontal displacement into vertical displacement. If so, the amount of horizontal relative displacement is effectively constrained.

〔Example〕

Hereinafter, embodiments of the present invention will be explained using FIG. 1 (plan view) and FIG. 2 (elevation view). In FIGS. 1 and 2, a vertically long rack cell 1 with a rectangular cross section is They are interconnected by horizontal support members or girders 6, which form the rack assembly 3. The illustrated rank assembly 3
are formed in a small size and are connected to each other by a connector 14. The size of the rack assembly 3 is mainly determined by the capacity of the transportation means such as trailers, carriers, cranes, etc., since it is manufactured in a factory and installed after being transported to the installation site of a nuclear power plant, etc. It is determined by taking into consideration. In some cases,
Instead of dividing into 1054 rack assemblies 3 as in this embodiment, one large rack assembly may be used.

In this case, the coupler 14 becomes unnecessary, but even in the illustrated case, a buffer may be used in place of the coupler 14. The pit 2 is formed in a building by a concrete pit wall 5a and a concrete pit bottom 5b. When storing used nuclear fuel assemblies, pit water 2a is used, but when storing new nuclear fuel assemblies, water is not removed from the VC (it is dry).

At the bottom of the rack assembly 3 is a horizontally extending strong base 8.
is fixed (welded or bolted), and a number of spherical supports, ie, steel balls 9, are arranged between this base 8 and the pit bottom 5b. In order to prevent the steel balls 9 from interfering with each other or being unevenly distributed, an appropriate holding member (not shown) may be provided separately from the base 8, if necessary. base 8
An embedded metal fitting 4 is provided in the pit wall 5a facing the edge of the pit wall 5a, and a shock absorbing material or coil spring 10 is interposed between them.

Both ends of the coil spring 100 are connected by a regular locking member (not shown).

In the above embodiment, the steel balls 9 were placed directly on the pit bottom 5b, but the steel balls 9 may be placed on the steel plate after laying it on the pit floor 5b, or an elastic body ( A sheet of rubber sheet, laminated wire mesh, etc.) may be placed, and the steel ball 9 may be placed on top of the sheet.

In the configuration described above, seismic waves are transmitted to the pit wall 5a.

It is transmitted to the pit bottom 5b and shakes horizontally at an extremely fast speed. The steel ball 9 rotates due to the frictional force of the pit bottom 5b, but the rack assembly 3 and the nuclear fuel assembly therein remain stationary, and the collision with the approaching pit wall 5a is prevented by the coil spring 10. is avoided. Instead of the coil spring 10, a hydraulic shock absorber, a laminated metal mesh, or other types of springs can be used as a cushioning material. Even if some vertical waves are applied, they will be absorbed if an elastic sheet is used.

Next, a second embodiment will be explained using FIGS. 3 and 4.

The rack assembly 3 is the same as in the first embodiment, and the same parts are given the same reference numerals, so a description of those parts will be omitted.

A number of steel balls 9 under the base 8 at the bottom of the rack assembly 3 are
They are placed on a holding frame or skid 11 at appropriate intervals. A frame 11a is erected at the outer end of the skid 11, and a buffer member, ie, a coil spring 10, is interposed between the frame 11a and the girder 6. The frame 11a prevents the rack assembly 3 from protruding outward.

Since the skid 11 is in contact with the concrete floor 5b, the seismic force causes the pit 2 (pit wall 5a,
When the bottom 5b) swings horizontally, the skid 11 also moves accordingly.

Therefore, the rotation of the steel ball 9 and the resulting stationary phenomenon of the rank assembly 3 occur in the same manner as in the first embodiment.

Although the contact area between the skids 11 and the pit bottom 5b is large and there is virtually no slippage, an appropriate spacer may be placed between the skids 11 or between the skids 11 and the pit wall 5a just in case.

Of course, as in the modified embodiment of the first embodiment, when there is one rack assembly 3 in the pit 2, there is only one skid 11, so the spacer is connected between the frame 11a of the skid 11 and the pit wall 5a. It is placed only in between.

Next, a third embodiment will be described with reference to FIGS. 5 and 6.

In this embodiment, a steel ball 21 serving as a spherical support is sandwiched between upper and lower concave bodies.

The rack assembly 3 is formed similarly to the first and second embodiments. That is, the rack cells 1 are interconnected by girders 6 to form a rack assembly 3. pit 2
A strong base 8 is fixed to the bottom of each of the four rank assemblies 3 placed inside.

On the lower surface of the center and four corners of the rank assembly 3, swing support devices 20, which will be described later, are arranged between the pit bottom 5b and the base 8.

In this embodiment, five swing support devices 2o are provided for each rack assembly 3, but of course an increased number may be provided.

Next, details of the swing support device 20 will be explained with reference to FIG. 7.

In FIG. 7, the swing support device 2o includes a spherical support, that is, a steel ball 21, an upper concave body 23 fixed to the base 8, and a lower concave body 25 fixed to the pit bottom 5bK.

The W4 ball 21 and the biconcave body 23.25 are each manufactured using one of steel, non-ferrous metal, ceramics, synthetic resin, or two or more types of Vi.

The concave bodies 23, 25 each have a concave rolling surface 23 in the center.
a, 25 a, and a plate portion 23 b, 25 on the outer periphery.
b surrounds the rolling surfaces 23a and 25a from the outside. This prevents the steel ball 21 from moving outward. The opposing surfaces of the plate portions 23 b and 25 b are horizontal and flat, respectively, and in a normal, stationary state (no earthquake occurs), they are in contact as shown in FIG. 7 . Therefore, the weight of the rack assembly 3 and the nuclear fuel assembly therein is transmitted to the pit bottom 5b via the plate portions 23b, 25b, and the cover acting on the steel balls 21 is kept extremely small.

As a result, the spherical rolling surfaces 23a and 25a are always held smoothly without any dents or the like.

Next, the operating principle of this embodiment will be explained with reference to FIGS. 8a to 8C. FIG. 8a is a diagram showing a stationary state before lateral vibration occurs due to an earthquake, in which the rack assembly 3, steel balls 21,
Pit 2 is both stationary. As described above, in the stationary state, as shown in FIG. 8a, the flat part of the concave body 23 attached to the lower surface of the base 8 of the rack assembly 3 is connected to the flat part of the concave body 25 attached to the pit bottom 5b. While cutting,
The weight of the rack assembly 3 and the nuclear fuel assembly therein is supported by the plate portion 25b of the concave body 25. When an earthquake occurs, the pit 2 shakes repeatedly in the horizontal direction and eventually disappears while attenuating. If the pit 2 first swings to the left, the via bottom 5b will shift to the left from the origin (vertical two-dot chain line), and the concave body 25 will also shift to the left at the same time, as shown in FIG. 8b. At this time, the steel ball 21 moves onto the transfer surface 25 of the concave body 25
It rises while rolling on the slope of a, and at the same time rolls with the transfer surface 23a of the concave body 23, pushing up the concave body 23 and the connected rack assembly 3 slightly upwards.Next, the pit 2 passes the origin and When the concave body 25 swings to the right, as shown in FIG. 8C, the steel ball 21 on the concave body 25 also rolls on the rolling surface 25a of the concave body 25 and moves to the right. , the rack assembly 3 is again pushed up a little bit via the concave body 23.The pit 2 is instantly vibrated left and right repeatedly, but each time the steel balls 21
moves between the concave bodies 23 and 25 while rolling, thereby insulating the seismic force of the pit 2 from being transmitted to the rack assembly 3. When the earthquake ends, the pit bottom 5b returns to its origin,
The steel ball 21 that was rolling on the rolling surfaces 23a, 25a in the concave body 23.25 also returns to its origin at the center of the concave body 23.25. Therefore, even after the earthquake has ended, the rack assembly 3
There is no risk of deviating from the origin. Since the concave shape of the transfer surface forms a spherical mirror surface, the steel ball 21 can roll in any horizontal direction (all directions of 360° including north, south, east, and west), and seismic force can be generated from any direction. However, the propagation of seismic force to the rack assembly 3 can be insulated. Even if a slight tremor occurs in the rack assembly 3 due to an earthquake, the rolling surfaces 23a and 25a convert the lateral tremor into potential energy 1, quickly eliminating the lateral tremor and returning the rack assembly 3 to its origin. . Size of steel ball 21 and rolling surface 23a
, 25a, the seismic isolation performance can be controlled by selecting the degree of curvature of . Pit 1 5b due to earthquake
The maximum amount of shaking is 2 even with the largest possible earthquake.
The steel ball 21 is within the concave body 23.25 mm part 23
b, 25 b K There will be no collision. In addition,
In FIGS. 8b and 8C, in order to make the movement of the steel ball 21 easier to understand, the steel ball 21 is shown rolled to the end of the concave body 23.25 in an exaggerated manner; Rolling nearby. Rolling surface 23a of concave body 23.25
, 25a are spherical in this embodiment, but Kid
There is no limitation, and a combination of a spherical surface and a straight line can also be used. FIG. 9 shows a partially modified embodiment of the concave body. The center portions of the rolling surfaces 123a, 125a of the concave bodies 123, 125 are spherical, and are linearly sloped outward from the center portions (so-called upward slopes). According to this, the rolling surface 23 a
, 25 It is possible to obtain different seismic isolation characteristics than when the entire a is made spherical. A concrete structure for attaching the lower concave body 25 to the pit bottom 5b is shown in FIGS. 10 to 12.

FIG. 10 shows an example in which a flange 25d is formed on the concave body 25, and this flange 25d is attached by tightening with a foundation bolt 31 and a nut 32 installed on the pit bottom 5b.

FIG. 11 shows an example in which an embedded plate 34 with a stud dowel 34a attached is installed on the pit bottom 5b and attached to this embedded plate 34 by welding.

FIG. 12 shows an example in which a plurality of concave bodies 25 are fixed to one seat plate 36 by welding, and the gap between the seat plate 36 and the pit wall 5a is filled with a spacer 37.

Next, a fourth embodiment using an ellipsoidal body instead of the swing support device 20 of the third embodiment will be described with reference to FIGS. 13 and 14.

The three rack assemblies are made up of a plurality of rack cells 1, girders 6, and bases 8, similar to the first, second, and third embodiments. Of course, as in the previous embodiment, the rack cell 1 individually receives nuclear fuel assemblies (not shown), and is a vertically elongated box with an open top.

An elliptic sphere 40 having an elliptical vertical cross section is located at 4 of the rack assembly 3.
It is located at the corner and the center between the base 8 and the pit bottom 5b. The outer shape of the elliptical sphere 40 is a chessboard shape, and a stopper 41 protruding from the lower surface of the base 8 prevents it from coming off.

FIG. 15 shows an enlarged view of the attachment portion of the ellipsoidal body 40.

Figures 168 to 16C show the principle of operation of the fourth embodiment. FIG. 16a is a diagram showing a stationary state before lateral vibration occurs, in which the pit bottom 5b, the rack assembly 3, and the elliptical sphere 40 are all stationary. When an earthquake occurs, the pit bottom 5b repeatedly shakes in the horizontal direction and eventually disappears while attenuating. If the pit bottom 5b first swings to the left, the pit bottom 5b will shift leftward from the origin and the elliptical sphere 40 inserted between the pit bottom 5b and the rack assembly 3 will rotate clockwise, as shown in Figure 16b. direction and push the rack assembly 3 upward slightly. Next, when pit 2 passes the origin and swings to the right,
As shown in FIG. 16C, the elliptical sphere 40 also rolls in the counterclockwise rotation direction while passing through the origin and pushes the rank assembly 3 slightly upward again. The pit 2 instantaneously repeatedly vibrates from side to side, and each time the elliptical sphere 40 rolls between the pit bottom 5b and the rack assembly 3, giving a relative displacement to the pit bottom 5b and the rack assembly 3. , the transmission of the seismic force of the pit bottom 5b to the rack assembly 3 is significantly reduced. When the earthquake ends, the rack assembly 3 and the elliptical sphere 40 are moved by the action of the elliptical sphere 40 (the arbitrary-shaped sphere tries to minimize the distance from the ground to the center of gravity of the sphere due to the action of gravity). The state returns to the state shown in Figure 16a, that is, the same state as before the earthquake occurred.

The structure of the elliptical sphere 40 has a perfect circular horizontal cross section and an elliptical cross section in all directions, so that no matter which direction the seismic force is generated, the seismic force will not propagate to the rack assembly 3. can be insulated. The earthquake will end againζ
, U7, L assembly 3 (even if a slight amount of shaking remains, the action of the elliptical sphere 40 converts the kinetic energy into potential energy (/C), which quickly eliminates the shaking, and the L assembly 3 is returned to the origin VC.The seismic isolation performance of the elliptical sphere 40 can be selected by selecting its size or (,1 aspect ratio (length/width ratio of the ellipse).As shown in Fig. 15, , In order to prevent the elliptical sphere 40 from deviating from the base 8 by any chance, several steps are provided.This stopper 41 suppresses the rotation of the elliptical sphere 40 within a certain range during an earthquake. It can also be used for other purposes.

If the aspect ratio of the ellipsoidal sphere 40 is set too high, the rolling friction will increase rapidly after the start of rotation and may exceed the sliding friction, so it is better not to make the aspect ratio extremely large. The elliptical sphere 41 can be appropriately selected from steel, nonferrous metals, synthetic resins, ceramics, crystals such as diamond, and others. Other materials may also be selected as appropriate from among these materials.

In the third and fourth embodiments, the rack assembly 3 was formed in four pieces, but as in the partially modified example of the third embodiment (2), the large rack assembly 3 was formed in one piece (2). τ and 7 may be used.

〔Effect of the invention〕

According to the present invention, even if an earthquake causes vibrations transmitted through the VC (wall, bottom), it is converted into rotational motion of the spherical support (steel ball, ellipsoid) on the bottom, and the earthquake force is removed. Insulated. That is, the rack assembly is held without horizontal displacement.

[Brief explanation of drawings]

1 and 2 are a plan view and an elevation view respectively showing a first embodiment of the present invention, and FIGS. 3 and 4 are a second embodiment of the present invention.
A partial plan view and a partial elevation view of the embodiment, FIGS. 5 and 6 are a plan view and an elevation view respectively showing the third embodiment of the present invention, and FIG. 7 shows the main part of the third embodiment. Partial sectional view shown, No. 8
Fig. a, Fig. 8b, and Fig. 8C are explanatory diagrams of the operation of the third embodiment, Fig. 9 is a sectional view showing a partially modified example of the third embodiment, Fig. 10, Fig. 11, and Fig. 12. 13 and 14 are plan views and elevation views respectively showing the fourth embodiment of the present invention. FIG. 15 is a partial structural diagram of the third embodiment. Partial enlarged view, No. 16a
Figures 16B and 16C are explanatory diagrams of the operation of the fourth embodiment, and t'1 rg and Figures 16A and 16C are plan views and elevation views of the conventional system. DESCRIPTION OF SYMBOLS 1... Rack cell, 2... Pit, 3... Rack assembly, 5a... Pit wall, 5b... Pit bottom, 6
...Girder, 8...Base, 9...Steel ball, 10...Coil spring, 11...Skid, 14...Coupler,
20... Swing support device, 21... Steel ball, 23.25.
・Concave body, 40...Oval sphere No. 10 Fig. 3 Fig. 5 Fig. 7 (0 mouth Fig. 11 Fig. 121

Claims (1)

[Claims] It is characterized by comprising a rack assembly formed by juxtaposing vertical rack cells for individually receiving fuel assemblies, and a plurality of spherical supports interposed between the bottom of the assembly and the floor of the pit. Reactor fuel storage system.