JPS6117099A - Cask storage system for storing spent 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 long-term storage system for spent fuel generated from a nuclear reactor, and is particularly suitable for long-term cooling in dry cask storage and for preventing cask overturning. The present invention relates to a cask storage system for storing spent fuel.

[Background of the invention]

Currently, more than 150 units of spent fuel are generated per year from each nuclear reactor, but due to an imbalance with the processing capacity of the spent reprocessing facility, most of the spent fuel is spent within the plant. Stored in the pool. However, because the spent fuel storage pool within the plant has a limited storage capacity, there is currently a need for a facility that can safely store and store spent fuel for a long period of time until it is reprocessed.

There are two methods for long-term spent fuel storage: the storage pool method and the cask method.The storage pool method takes into consideration the cumulative increase in the number of fuel bodies, and the final storage amount is determined from the beginning of the pool construction. The storage capacity, cooling capacity, and other equipment must be large-scale to meet the demand, and the disadvantage is that the initial construction cost is extremely high. Therefore, with the current trend in the world, storage methods using dry casks for transportation and storage are being considered.

An example of the conceptual design of a dry cask for transportation and storage is shown in Figure 1. The cask has a cylindrical shape with an outer diameter of 12 m and a length of approximately 6 m, and accommodates 52 spent fuel assemblies inside. The inside of the cask is filled with gas such as He. The cask body is made of forged steel and has a thickness of approximately 256 nm, and serves as a pressure-resistant container for containing spent fuel and shielding it from R-rays.

The lid is secured with two bolts and sealed by welding to maintain airtightness. A plastic shield is wrapped around the main body for the purpose of shielding neutrons.

Detachable trunnions are installed at eight locations above and below the cask for transportation and handling, and protective covers for transportation are attached to the head and butt of the cask to prevent injury from falling during transportation. There is. Casks containing spent fuel are transported and stored within the site or to a cask storage facility on another site. Cask storage facilities are a type of storage that is lined up and stored in an indoor or outdoor yard. The number of casks stored is, for example, 1100M.
At a site where four We-class nuclear reactors are installed, 190 spent fuel assemblies (4 casks) are produced per plant per year.
occurs, so by the time the operation is stopped 30 years later,
A total of nearly 480 casks will be stored. The cask is designed to store fuel that has been cooled for more than five years after being removed from the reactor, but as shown in Figure 2, the fuel emits decay heat of about ZsMW/MTU. occurs.

The heat is then released to the outside through the sealed gas and the wall of the container. On the other hand, according to the technical standards of cask,
The maximum permissible temperature of fuel is 400C (limited amount of inflow air or under non-oxidizing atmosphere conditions). Therefore, it is necessary to use some method to remove heat from the outer wall of the cask over a long period of several decades during cask storage.

In the conventional technology, heat radiation from the cask takes into consideration heat radiation from the outer wall and air cooling by natural convection using the outer wall or air cooling fins. However, if casks are installed closely spaced in a cask storage facility, thermal radiation from adjacent casks cannot be ignored. Furthermore, air convection deteriorates near the center of the storage cask group, and the cooling performance due to convection also deteriorates. As a result, the temperature of the outer wall of the cask will rise, and the temperature of the fuel rods will also rise, potentially making it impossible to satisfy the allowable value. Therefore, conventional designs are designed to install casks with sufficient space.

In the conventional example, an arrangement as shown in FIG. 3 is considered, but the cask surface temperature in this case is about 1300°C. In this case, the area occupied by each cask is as follows.

However, since the purpose of cask storage facilities is to carry out long-term storage until fuel reprocessing is operated at a scale that is in balance with the number of spent fuels generated, the space factor is reduced from the perspective of land cultivation. is important, and it is desirable to arrange the casks as closely as possible.

[Purpose of the invention]

An object of the present invention is to provide an economical cask storage system in which casks can be installed closely while effectively removing decay heat emitted from the casks.

[Summary of the invention]

The present invention cools the outer wall of the cask by wrapping a water-cooling jacket around a spent fuel transport and storage cask and connecting the jacket to the jacket of an adjacent cask.

[Embodiments of the invention]

An embodiment of the present invention will be described with reference to FIG. A water jacket 15 is installed so as to surround the cask body 1. A cooling pipe 16 is installed in a spiral shape inside the water jacket 15. The water jacket 15 has a structure that can be divided by 7 lunges 18 around the hinge 17. When installing the water jacket 15 on the cask body IK, the 7
Tighten the two bolts 18 with the ports 19 to fix them to the trunk of the cask body. Furthermore, the piping drawn out from the upper and lower parts of the water jacket 15 has flanges 20 and 7 langes 2.
1 is installed, thereby connecting it to the water jacket of the adjacent cask.

When the cask 1 is carried into the cask storage facility, a water jacket 15 is attached to it at the work site, and the cask 1 is transported to the cask storage yard. Then, connect the flanges 20 and 21 with the flanges of the cask that were previously placed, and pump 2
2, cooling water is supplied to the cooling pipe through the pipe 23.

This method makes it possible to cool multiple casks with one pump. In addition, the cooling water after cooling the cask is passed through the flange 24 to the temporary pipe 25.
Drain by. If you want to bring in more casks,
The temporary piping 25 is removed and the next cask is connected behind it.

Here, as shown in Figure 2, decay heat of approximately 2.5 KW/MTU is generated from the fuel assembly after cooling for 5 years, so
The calorific value of a cask containing 52 aggregates is approximately 20K.
It becomes W. Here, the number of casks that can be connected in series and the required amount of cooling water are calculated as follows.

Calorific value per cask 20KW = 20 x 10” x 4.2 = &4 x
10' d/S ・(1) Now, if we are to flow about 50 t/s of cooling water, the temperature rise of the cooling water per cask will be B, 4 x 1 o' m, s ÷ 50 x 10
"cm" / S, 1.7c - C2). If the inlet temperature of the cooling water is about 25C, the number of casks that can be arranged in series is (60C -
25CΣ÷1.7 C-1 = about 20 bodies. According to the present invention, casks can be water-cooled using only a pump and simple piping, and therefore can be stored densely in a storage yard without requiring large-scale equipment such as a cooling pool.

Another embodiment of the present invention will be described with reference to FIG. In this embodiment, the water jacket 15 is shaped like a rectangular parallelepiped with a plurality of projections and depressions cut on its four sides. At the top of the water jacket, there are provided seven water supply flanges 26 and seven water drainage flanges 27. Additionally, holes 28 are bored along the concave and convex portions of the water jacket from the top to the bottom.

When the cask is delivered to the cask storage yard, the cask is placed in contact with the previously stored cask so that the unevenness overlaps with the cask. And water supply 7 lunge 2
6 and the drain 7 flange 27 are connected, and a bolt 29 is passed through the hole 28 and tightened to fix the cask to the adjacent cask. If there are adjacent casks in the lateral direction, fix them with bolts in the same way. Adjacent casks are fixed to each other in the manner described above, taking into account the layout of the yard and the allowance for cooling pumps.

According to this embodiment, the effective floor contact area is increased by fixing the casks to each other to prevent the cask from falling over during an earthquake, which may occur when the casks are placed vertically. This eliminates the need for structures such as supporting casks, making it possible to construct cask storage facilities more economically, and since there are no structures in the yard, there is greater freedom in cask placement. This has the advantage that handling such as cask transfer becomes easier.

〔Effect of the invention〕

According to the present invention, in a spent fuel cask storage facility,
Because the casks can be arranged densely without cooling constraints, the space in the storage facility can be used effectively, and an economical cask storage system can be provided.

[Brief explanation of drawings]

Figure 1 (a) is a front view showing a part of a conventional dry cask for transportation and storage, (b) is a cross-sectional view of part of (a), and f → is the sealing structure of (a). An explanatory diagram, FIG. 2 is an explanatory diagram of the relationship between the cooling period of fuel and decay heat, FIG. 3 is an explanatory diagram of the conventional cask arrangement, and FIGS. 4 and 5 are respectively the cask storage system for storing spent fuel of the present invention. (A) is a front view, and (B) is a plan view of (A). 2... Trunnion, 3... Drain pipe, 4... Vent and drain orifice, 5... Transportation cover, 6...
...Storage cover, 7...Emergency cover, 8...
Lid, 9... Shell, 10... Fuel rack, 11...
・Neutron shielding material, 12...Copper plate, 13...Cask, 14...Concrete pad, 25...Drain piping, 26...Water supply 7 lunge, 27...Drainage 7 lunge, 28... ...hole, 29...bolt. Basket 1 Mouth (A) (B) Cooling Asama C year] 3rd Snake 4 Snake (Ino

Claims (1)

[Claims] 1. A cask storage system for spent fuel storage, characterized in that a cask cooling pipe through which a refrigerant is passed is wrapped around the outer circumference of the cask.