JPS6021490A - Method of storing nuclear fuel - 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 Application of the Invention] The present invention relates to a method for storing spent nuclear fuel used in a nuclear power plant in fuel storage racks.

[Background of the invention]

In nuclear power plants, fuel exchange is performed approximately once a year, and a certain number of fuels are removed as spent fuel each year, and the same number of new fuels are loaded. All irradiated fuel being refueled is handled underwater for shielding and cooling. Spent fuel is cooled and stored in reactor fuel storage racks (hereinafter referred to as fuel racks) installed in water within the spent fuel pool (hereinafter referred to as fuel pools) to remove decay heat. The fuel is placed in a fuel transport container and transported to a reprocessing plant.

In recent years, there has been concern about the lack of spent fuel reprocessing capacity, and a long-term, efficient method for storing spent fuel in fuel pools inside reactor buildings is desired.

Figures 1 and 2 show the plan and cross-section of a fuel pool in which a fuel rack for a boiling water reactor is installed, Figure 3 shows the external shape of a conventional fuel rack, and Figure 4 shows how the fuel rack is installed.

The fuel pool 1 is located on the top floor of the reactor building and is a facility for storing radioactive solid waste including spent fuel. The fuel pool 1 has a passage 4 provided with a gate 7 as shown in FIG.
It is connected to the reactor well 2 via the reactor well 2, and is constantly filled with water for radiation protection and cooling of the fuel 8.

In the fuel pool 1, a fuel rack 1 is provided to store fuel 8 whose storage capacity is at least equal to the amount for each core and for one replacement.
2 will be installed.

The structure of the fuel rack 12 must be such that the fuel 8 does not reach criticality due to mutual influence between the stored fuels 8. The fuel 8 must be stored at appropriate storage intervals to ensure subcriticality. The fuel 2 tank 12 uses a stainless steel ring square via '13 with good neutron absorption properties to achieve high density storage, and forms a neutron absorption wall between the fuel 8 and the fuel 80. The square pipe 13 has a fuel 8 length of 4.5
It has a length that covers m and is welded and connected to the reinforcement material 14,
Furthermore, it is welded to the seat plate 15. Further, a base 16 is attached to the lower part of the seat plate 15, and is fixedly installed by a rack mounting pole 17 provided on the fuel pool floor 3.

Next, a conventional fuel exchange procedure will be explained below.

The fuel pool 1 is always filled with water, and at the time of fuel exchange, water is also poured into the reactor well 2 up to the water level in the fuel pool 1. After that, the reactor containment vessel head and reactor pressure vessel head are removed, and the steam dryer and steam separator of the reactor internals are removed and temporarily placed in the designated position. Furthermore, the gate 7 separating the fuel Pnir 1 and the reactor well 2 is removed.

A fuel pick-up device 10 attached to a heat exchanger truck 9 lifts the fuel 8 from inside the reactor core 6 to the fuel transfer height. The lifted fuel 8 is transferred to the fuel pool 1 side through the passage 4 by the heat exchange truck 9. After the fuel 8 is transferred to a predetermined storage position, it is suspended from the top of the fuel tank 12 into the polygonal pipe 13 and stored.

As explained above, the height of the conventional fuel rack 12 is 8
Since the length is 4.5 m and the same volume, the pool depth shown below is required.

Figure 5 shows the water depth of a cross section of the fuel pool in which the fuel rack of a boiling water reactor is installed. Fuel pool 1 is approximately 11.5m
The structure is as follows: storage fuel height a, clearance between the stored fuel and transferred fuel b, transfer fuel height C1, transfer fuel shielding water depth d, approximately 4.6 m and 0.2 m, respectively. 4
．． 5m and 2.2m.

Therefore, the water depth is required to be approximately 2.5 times as large as the height of the stored fuel, which is 4.6 m, and there is still room for improvement in terms of effective use of the fuel pool space.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a nuclear fuel storage method that allows the water depth of a fuel storage pool to be made shallow by lowering the upper end of a fuel storage rack when carrying in spent fuel.

[Summary of the invention]

In order to achieve the above object, the nuclear fuel storage method of the present invention includes:
The square pipe that serves as the neutron absorption wall can be removed independently from the fixed part of the fuel storage pool, and after storing the spent fuel in a low-height fuel storage rack, the square pipe is installed to remove the spent fuel. It is characterized by a covering and seven.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to FIGS. 6 to 15.

FIG. 6 shows the outer shape of a fuel rack according to the invention.

The structure of the present fuel rack 20 is that a flat plate is welded to the upper part in a lattice shape, and an upper grid 2 whose outer periphery is constructed by welding shaped steel.
There is 1. The interstitial dimension of this upper grid 21 is such that it ensures a gap with the external dimension of the square pipe 22 of the neutron absorption wall and allows the square pipe 22 to pass through. At the bottom, there is a lower grid 23 having the same structure as the upper grid 21 . A seat plate 24 is attached to the lower grid 23 for seating the fuel 8 and the square pipe 22.

The seat plate 24 is composed of a single plate provided with a plurality of holes 25 that are inclined to match the shape of the lower tie plate 29 of the fuel 8. The pitch of the holes 25 is the same as the lattice pitch of the upper grid 21 and the lower grid 23, and welding is performed so that the center of the hole 25 provided in the sheet plate 24 coincides with the lattice center of the lower grid 23. Furthermore, a base 26 is welded to the lower surface of the top plate 24 and is constructed by welding the plates together.

The upper grid 21 and lower grid 23 of the structural members are welded to the diagonal support 27 and the vertical support 28 so that their grid centers coincide. Stability can be maintained if the height of the upper grid 21 is set to the height of the center of gravity of the fuel 8 with the fuel 8 and square pipe 22 seated on the seat plate 24.

The fuel rack 2o constructed as described above is fixedly installed by a rack mounting port 17 provided on the fuel pool floor 3, similar to the conventional structure.

Incidentally, the details of the mutual relationship between the 21 parts of the upper grout #+8 and the square pipe 22 are shown in FIG. Also, seat plate 2
FIG. 8 shows details of the mutual relationship between the fuel 8 of the lower grid 23 and the square pipe 22.

The procedure for exchanging the fuel 8 using the fuel thick 20 configured as described above will be described below.

The fuel 8 taken out from the reactor core 6 of the reactor pressure vessel 5 is transferred to the fuel pool 1 side and kept stationary on the grid center of the upper grid 21 of the fuel rack 20, and the fuel clamp device 10 is lowered to remove the fuel 8. It is seated and installed on the seat plate 24 of the fuel rack 20. Next, a square pipe special clamp is attached in advance to the overhead crane or the jib crane 11 mounted on the heat exchanger truck 9, and the square pipe 22 is grasped and inserted into the stored fuel 8 from above. Furthermore, it is installed on the sheet plate 24 using the upper grid 21 and the lower grid 23 as guides. Incidentally, the storage order is from the back of the fuel pool. Further, when carrying out the fuel 8 to the outside of the fuel pool 1, the procedure is reversed to the above-mentioned transfer and storage procedure.

In the structure of the fuel rack 30 shown in FIG. 10, a square pipe is divided into an upper stage and a lower stage to constitute a neutron absorption wall. The lower square pipe 31 is welded to a reinforcing member 33 and welded to a seat plate 34. This sheet plate 34 has a fuel 8
It consists of a single plate provided with a plurality of holes that are inclined to match the shape of the lower tie plate 29. Note that the lower square pipe 31 is welded so that the hole in the seat plate 34 and the center of the lower square pipe 31 coincide with each other. Further, a base 35, which is constructed by welding the plates together, is attached to the lower surface of the seat plate 34 by welding. A stopper 36 when the upper square pipe 32 is inserted is welded to the upper end of the inner surface of the lower square pipe 31 of the component. The height of the lower square pipe 31 is set to the height of the center of gravity of the fuel 8 when the fuel 8 is seated on the seat plate 34. The fuel rack 3o constructed as described above has rack mounting bolts 1 provided on the fuel pool floor 3 as in the conventional structure.
7 is fixedly installed.

A procedure for exchanging the fuel 8 using the fuel rack 3o configured as described above will be described below.

Similar to the fuel exchange procedure for the fuel rack 2o described above, the fuel 8 is transferred to the fuel pool 1 side, and is then made to rest on the center of the lower square pipe 31 of the fuel rack 30, and the fuel clamp device 10 is lowered. The fuel 8 is seated on the seat plate 34 of the fuel rank 30. Next, a square pipe special clamp is attached in advance to the overhead crane or the jib crane 11 of the heat exchanger truck 9, the upper square pipe 32 is grasped, and the fuel 8 is inserted from above into the stored fuel 8. Furthermore, a stopper 36 is attached to the inner surface of the upper part of the lower square perve 31.
Insert and install the upper square pipe 32 until the end. Note that the storage order and the carrying out of the fuel pool to the outside of the fuel pool are the same as those for the fuel rack 20 described above.

The structure of the fuel rack 40 shown in FIG. 10 is the same as the structure of the fuel rack 30 described above, but unlike the method in which the upper square pipe 32 is inserted into the lower square pipe 31 after the fuel 8 is installed, the neutron absorption wall The square pipe has a double pipe structure, and the fuel 8
After installation, the inner square pipe is pulled up to form a neutron absorption wall.

Figures 13 to 15 show details of the double pipe structure of the present fuel rack 40. At the upper end of the lower square pipe 41, there are a ball 43 that stops the vertical movement of the upper square pipe 42, a spring 44 that presses the ball 43, and a spring 44.
A stopper 45 consisting of a plate 46 that confines the air is attached by welding. In order to reduce the distance between the lower square pipes 41, the stopper 46 is provided between the lower square pipes 4 as shown in FIG.
1. Can be installed in 2 places on both sides with different struts. A groove 47 into which a ball 43 pressed by a spring 44 is inserted is provided in the lower part of the upper square pipe 42.

This groove 47 position is a position into which the ball 43 enters when the upper square pipe 42 is pulled up to a predetermined pull-up position after the fuel 8 is seated and installed.

The procedure for exchanging the fuel 8 using the fuel rack 40 configured as described above is almost the same as when using the fuel rack 3o. After the fuel 8 is seated on the seat plate 34, The square pipe 42 is pulled up to a predetermined pull-up position using a square pipe special hook and stored.

FIG. 9 shows the water depth breakdown of the cross section of the fuel pool when the fuel rack 20 according to the present invention is used (the same applies when the fuel rack 30 and fuel thick 4o are used). As explained above, since the fuel 8 is installed in the fuel rack 20 using a rectangular pipe that serves as a neutron absorption wall, and is set to be inserted, inserted, and pulled up, the height of the fuel rank 20 at the time of installation of the fuel 8 is the same as that of a conventional fuel rack. Since the height of 12 is 4.5 m, only about half the height is required, so the fuel pool depth is 9.2 m.

Its configuration is a fuel rack height e, a clearance f between the fuel rack and the transferred fuel, a transferred fuel height g, and a transferred fuel shielding water depth of 2.3 m and 4.5 m, respectively.

It is 2.2m. Therefore, the depth of the fuel pool is shallower by about 22 m, with the fuel rack height lowered, and the water depth is only about twice as large as the height of the stored fuel, which is 4.6 m. Furthermore, regarding the fuel rank 20 of the present invention, since the square pipe is inserted later and the square pipe itself is not attached to the fuel rack 20 by welding, the conventional fuel rack 12 can also have a very simple structure. It is.

Figures 16 and 17 show an example of application of the present invention, which allows fuel 8 to be stored in two stages while maintaining the conventional fuel pool depth. The difference from the fuel rank 40 shown in FIG. 13 is that the length of the lower square pipe 51 is different from that of the conventional fuel rack 1.
The length of the upper stage square pipe 52 is the same as that of the square pipe 13 of No. 2, and the length of the upper stage square pipe 52 has a length necessary to store the upper stage fuel 8 on the lower stage fuel 8. The lower rectangular pipe 51 has a double pipe structure with the upper rectangular pipe 52 and is welded to the reinforcing member 54, and further welded to the sheet plate 55. Further, a base 56 is welded to the lower surface of the seat plate 55, and is fixedly installed on a rack mounting port 17 provided on the pool floor 3. FIG. 17 shows details of the double pipe structure of an applied example of the present invention. A stopper is attached to the upper end of the lower square pipe 51 to stop the vertical movement of the upper square pipe 52, similar to the fuel rack 40 shown in FIG. It is the same as. However, in order to seat the fuel 8 in the upper stage, a swingable plate 53 is attached to both sides of the inner surface of the upper square pipe 52 in two parts. A fuel rack 50 that can be stacked and stored in two stages is constructed from the above-mentioned components.

In the above-configured refueling procedure for the fuel 8 using the fuel rack 50, the fuel 8 taken out from the core 6 of the reactor pressure vessel 5 is transferred to the fuel pool 1llIll. fuel 8
is made to rest on the lower square pipe 51 of the fuel rank 50, and the fuel knob device 10 is lowered to seat the fuel 8 on the seat plate 55 of the fuel rack 50. At this time, the upper square pipe 52 is housed within the lower square pipe 51. By repeating this procedure, in order to store the second stage fuel 8 on top of the first stage fuel 8 after the storage in the lower stage square pipe 51 is completed, the second stage fuel 8 is stored on top of the first stage fuel 8. The fuel 8 is transferred onto the first stage fuel 8 already stored and placed there. Next, a square pipe special clamp is attached to the overhead crane, the upper square pipe 52 is grabbed, the upper square pipe 52 is pulled up to a predetermined position, and the fuel 8 of the second stage, which is being transferred and stationary, is wrapped therein. After confirming that the plate 53 attached to the lower inner surface of the upper square pipe 52 can be seated, the fuel 8 is inserted into the plate 5.
3, and the storage is completed.

When a fuel rack is used according to the applied example of the present invention, the fuel 8 in the second stage can be stored in the transferred state, so the fuel pool depth is approximately 11.5 m, and its configuration is similar to that in the 16th stage.
As shown in the figure, the height of the stored fuel in the first stage, the clearance t between the stored fuel in the first stage and the transferred fuel in the second stage, the height m of the transferred fuel, and the water depth n for shielding the transferred fuel, each of which is approximately 4.6
m, 0.2 m.

They will be 4.5m and 2.2m. Therefore, twice as much fuel can be stored while maintaining the conventional fuel pool depth.

〔Effect of the invention〕

According to the present invention, the structure of the fuel rack is simple, and the space within the fuel pool can be used for sounding, and the depth can be reduced, thereby providing an inexpensive fuel storage facility.

[Brief explanation of the drawing]

FIG. 1 is a plan view of the spent fuel pool and reactor well. FIG. 2 is a sectional view taken along line A--A in FIG. 1. Third
The figure is an external view of a conventional spent fuel storage rack. Fourth
The figure is a detailed partial view of FIG. 3, showing the attachment of the spent fuel storage rack to the spent fuel pool. Figure $5 shows the state of fuel transfer in a conventional spent fuel pool. FIG. 6 is an external view of a spent fuel storage rack according to the present invention. FIG. 7 is a sectional view taken along the line A--A in FIG. 6. FIG. 8 is a sectional view taken along the line B--B in FIG. 6. FIG. 9 shows the state of fuel transfer in the spent fuel pool according to HOMEKI. FIG. 1O is an outline drawing of a spent fuel storage rack according to the present invention. Figure 11 is a detailed view of section G in Figure 10.
FIG. 6 is a state diagram in which a neutron absorption wall is installed after fuel is inserted. 1st
FIG. 2 is a D-Draft view of FIG. 11. FIG. 13 is a detailed view of section G in FIG. 10, and is a diagram showing the state in which the neutron absorption wall is pulled up and installed after fuel is inserted. Figure 14 is E of Figure 13.
-E line sectional view. FIG. 15 is a detailed view of section F in FIG. 13. FIG. 16 is an example of application of the present invention to FIG. 13. FIG. 17 is a detailed view of part G in FIG. 16 and shows the operation of an applied example. 20...Fuel rack, 21 Upper river grid, 22...
・Square pipe, 23... Lower grid, 24... Jidobu L/-1, 30... Fuel rack, 31... Lower square pipe, 32... Upper square pipe, 40... Fuel rack , 41...Lower stage square pipe, 42...Upper stage square pipe, 47...Groove, 50...Fuel rack, 51...
Lower square pipe, 52... 3 Invitation 4 Invitation S Sho'13 G Ink 7121 also 8 Ink 13 Mouth 45 ￥14 Ichi, 5th sword 1st G El

Claims (1)

[Scope of Claims] 1. In a nuclear fuel storage method in which spent fuel generated in a nuclear reactor is held in an upright position at predetermined intervals, the spent fuel is stored at a height similar to that of the spent fuel. 1. A nuclear fuel storage method comprising storing the spent fuel in a short fuel storage rack, and then covering at least the spent fuel protruding from the fuel storage rack with a square pipe. 2. After installing a lower square pipe in the fuel storage rack in advance, store the spent fuel in the lower square pipe, and then insert the upper square pipe into the lower square pipe to measure the entire length of the spent fuel. The nuclear fuel storage method according to claim 1, characterized in that the nuclear fuel is covered. 3. In the fuel storage rack, after installing two square pipes in upper and lower stages in a double structure, storing the spent fuel in the square pipes, and then pulling up the upper square pipe, The nuclear fuel storage method according to claim 1, characterized in that the entire length of the spent fuel is covered.