JPS59137894A - Spent fuel storage device - 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 water tank type spent fuel storage facility, and particularly to a used city fuel storage device suitable for easily increasing the storage capacity of spent fuel.

[Prior art]

When spent fuel assemblies from power reactors are removed from the reactor, they are handled underwater to remove a large amount of decay heat generated by radioactive isotopes contained in fission products.
It is stored in water until its decay heat decreases.

A spent fuel assembly having a large number of rod-shaped fuel rods is such that the distance between the fuel assemblies is maintained at a certain value or more in water, and
The fuel assemblies are held vertically in a storage device designed to ensure that the materials required to prevent criticality are interposed between the fuel assemblies.

Conventional rack-shaped storage devices are fixed on the floor of the water tank, and the water surface of the tank can sufficiently attenuate radiation when the spent fuel assemblies are loaded into the rack-shaped storage device, and the spent fuel assemblies can be moved. The tank is configured to have a thickness sufficient to attenuate radiation generated by the fuel assembly when the fuel assembly is loaded into a storage device in the form of a rack.

Typically, the distance from the water surface or the top surface of the storage device to the water surface is determined by setting the highest position of the spent fuel assembly during loading.

In the above-mentioned prior art, as long as there is a space on the floor of the aquarium, the storage capacity can be increased by adding rack-shaped storage devices in the horizontal direction, but if there is no space, the storage capacity cannot be increased.

Spent fuel assemblies from power reactors are normally reprocessed after being cooled in water for several years, but reprocessing is possible if the reprocessing plant's operations are delayed or interrupted. This creates a need to increase the storage capacity of nuclear reactor storage facilities until the

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a lower rack-like storage device that has a mechanism that can be attached and detached as needed between an existing rack-like storage device and the aquarium floor.

[Summary of the invention]

The present invention was developed after careful consideration of the following characteristics of spent fuel storage facilities for power reactors.

B. Since the spent fuel assembly storage facility, which consists of a load-bearing water tank in the spent fuel assembly storage facility, constitutes a part of the reactor building, the load capacity given by the structure of the existing facility is unlimited and storage equipment can be expanded. not allowed.

The tank's shielding capacity The side walls of the tank are usually constructed of concrete, so even if the storage capacity is increased, there are almost no problems with shielding capacity. On the other hand, regarding the handling of spent fuel assemblies underwater, the shielding ability of the water layer existing above the radiation source must be handled strictly for safety reasons.

The shorter the cooling time, the stronger the radiation source and the higher the shielding ability required.

C. Earthquake resistance of rack-shaped storage equipment Since there is a large amount of radioactivity in spent fuel assemblies, even in the event of a disaster, the rack-shaped storage equipment will be destroyed and the sound sealing of the spent fuel assemblies will be compromised. It is necessary to have sufficient earthquake resistance so as not to damage the structure. Of course, the existing storage equipment in the storage facility is being considered, but it is necessary to separately consider the seismic resistance of the configuration of new storage equipment that has been combined with new parts.

2. Removal of Decay Heat In water, decay heat is removed mainly by water convection. Water at a temperature controlled within a certain range is circulated in the tank.

The shorter the cooling time, the greater the amount of decay heat.

E. Fixing method of rack-shaped storage device The rack-shaped storage device can be fixed to the floor of the aquarium in some cases, which can be relatively easily attached and detached using bolts, and in other cases, it cannot be easily attached and detached, such as by welding.

Spare floor space in the storage tank In addition to the floor space occupied by the rack-shaped storage device that stores the spent fuel assemblies in the spent fuel assembly storage tank, there is some spare floor space.

The present invention has been made based on the above-mentioned characteristics of a spent fuel assembly storage facility, and its main points are that it can be attached to and removed from the lower layer of an existing storage device as needed, and that it can be attached to and removed from the lower layer of an existing storage device, and that it can be attached to and detached from the lower layer of an existing storage device as needed. It provides a means of increasing storage capacity that can be easily configured to meet requirements.

[Embodiment of the invention] In a spent fuel assembly storage facility consisting of a water tank with a water depth of 11.4 m, a rack capable of storing 9 and 10 fuel assemblies on each side and a total of 0 fuel assemblies per unit. Consider the case where 23 storage devices are provided. This facility has a storage capacity for a total of 2,070 bodies, but it is necessary to have the capacity to always take out and store the fuel assemblies that make up the reactor core, and the fuel assemblies that make up the reactor core must be able to be taken out and stored at any time.
The storage capacity available for storing 91 replacement fuel assemblies is 1306, which is considered to be 14 storage units.

The weight of the rack-shaped storage device is 14 tons, and the weight of each loaded fuel assembly is 27 tons. The storage device is fixed with a nut to a bolt attached to the floor of the aquarium, and can be attached or detached by remote control from above the water surface. A total of 16 mounting bolts are used, four in each square of the rectangular storage device.

The height of the existing rack-shaped storage device is 4.5 m, and fuel assemblies with a length of 4.35 m are stored inside the rack.

Here, the upper end of the irradiation cylinder fuel pellet, which is considered to be the main radiation source, is located 4.2 m from the bottom of the storage device.

FIG. 1 shows a preferred embodiment of the present invention, showing the configuration of a lower rack-like storage device 3 and existing equipment 1 for increasing storage capacity.

The outer shape and dimensions of the lower rack storage device 3 are the same as the existing equipment except for the top surface and height.

As for the structure, the parts of the rack that house the four fuel assemblies at the four corners are pillars 4 with a strong box-shaped structure.
The nut can be attached through the hole 5 at the top of the nut. Also mounted on the top of the pillar 4 are upper and lower connecting bolts 6 corresponding to the installation legs 2 of the upper rank storage device 1.

The pillars 4, which have a square box-like structure, support the weight of the existing rack-shaped storage device 1 located on the upper stage, and provide an earthquake-resistant connection between the pillars 4 and the aquarium floor.

In this embodiment, 74 bodies can be stored in the new rack-shaped storage device 3 located at the lower level, and from the four corners of the existing rack-shaped storage device 1 located at the upper level when fixed to the new equipment at the lower level. Since 16 spent fuel assemblies must be removed, a total of 1 new rack-like storage device 3 and 9
This means that the storage capacity of 58 bodies has increased.

The new lug-shaped storage device in the lower stage has a capacity of 14 tons, and the load increase corresponding to the increase in the storage amount of fuel assemblies is approximately 17 tons.
5) Yes.

The new rack-shaped storage device 3 in the lower stage is loaded with spent fuel assemblies taken out immediately after the nuclear reactor is shut down.

191 replacement fuel assemblies are generated at a time, so 3 to 4
This means that the new rack-like storage device 3 can be placed on the lower level. The increase in load in the storage facility will be approximately 1 if four new units are installed.
It is 14 tons, and the increase rate with respect to thermal capacity is 12 inches.

Water heated by decay heat flows upward in the rack of the new rack-shaped storage device 3 in the lower tier, and some of it flows into the water tank from the joint between the upper and lower tiers, but the rest passes through the upper rack and exits into the water tank. .

The distance from the upper end of the radiation source made of fuel pellets in the upper rack storage device 1 to the water surface is 2.6 m.

In the case of BWR fuel that has been cooled for 5 years, the gamma dose rate on the water surface is approximately 4 m directly above the upper rack storage device 1.
rem/hr. Even considering the contribution of the upper rack-shaped storage devices 1, which are spaced apart by one storage device, to the gamma ray dose rate above the water surface, it is 5 mre/hr under normal conditions.
It never exceeds.

When installing the upper rack-shaped storage device 1 on the lower rack-shaped storage device (height 4.6 m) 3, the lower end of the upper equipment is moved under the water surface by floating 0.2 m above the upper end of the lower equipment. However, the maximum gamma dose rate above the water surface in this case is 20 mrem/hr.

FIG. 2 shows another embodiment of the present invention, in which air tanks 7 are arranged to surround the upper rack-shaped storage device 1.
shows. The air tank 7 consists of four parts, and in this embodiment, the total drainage volume is about 10 m3. The weight of the air tank 7 is 1.5 tons, and by connecting the air tank 7, a buoyancy of about 8.5 tons is generated. Therefore, the load increase of 31.5 tons due to the installation of the lower rack storage device 3 and the accompanying increase in storage capacity is reduced to 23 tons. When four new units are installed to receive 191 replacement fuel assemblies, the load on the storage facility will increase by approximately 80 tons, and the increase rate relative to the thermal capacity will be 8.4%.

When the air tank 7 that provides buoyancy is connected to and installed in the rack-shaped storage device 1, the stress generated in the structural materials of the device due to the standard vibration is greatly reduced, and the earthquake resistance is improved.

First, the air tank 7 is placed on the aquarium floor, and after submerging the upper rack-shaped storage device 1 into the air tank 7, the air tank 7 and the upper rack-shaped storage device 1 are lifted at the same time, and the lower rack-shaped storage device 3 is lifted up. Move up and bolt 6 through the common mounting hole 5? Pass it through I- and tighten it with a nut.

FIG. 3 shows another embodiment of the present invention, in which the corners of the upper rack storage device 1 that are in contact with each other are connected using a connecting fitting 8.

In either case, the corner of the upper rack storage device 1 is not loaded with fuel assemblies, so it is possible to attach the connecting fitting 8.

As a result, the dynamic rigidity of the storage device against the reference vibration is significantly increased, and the earthquake resistance is improved.

FIG. 4 shows another embodiment of the present invention, in which all storage devices initially installed are composed of lower storage devices 3 according to the present invention, and upper storage devices 1 are installed as necessary. Give an example.

In this case, all adjacent corners of the lower storage device can be connected by connecting fittings 8 to increase dynamic rigidity.

Although the embodiment of the present invention has been shown in relation to a fuel storage facility related to a BW tank, the present invention does not involve fixing a rack-shaped storage container on the floor of a water tank by welding, but also allows it to be attached and detached by remote operation from above the water surface. Any possible bolt-and-nut fixation is also applicable to rack-like storage devices in water tank fuel storage facilities for PWRs or other types of nuclear reactors.

Furthermore, the present invention can be applied to rack-like storage devices having other shapes, regardless of the embodiments.

〔Effect of the invention〕

According to the present invention, after the existing rack-shaped storage device is removed, the lower storage device according to the present invention is fixed in its original position in a state where it is temporarily placed in a spare space, and fuel is loaded, the fuel is already Since the existing storage device loaded with the above is stacked and fixed on top, the storage capacity can be increased as needed without any modification to the existing device. It is possible to minimize the movement of fuel assemblies when they are cut or expanded, thereby preventing accidents during fuel handling.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a spent nuclear fuel storage device that is a preferred embodiment of the present invention, and FIGS. 2, 3, and 4 are perspective views of other embodiments of the present invention, respectively. 1... Upper rack-shaped storage device, 2... Installation legs,
3M/ figure

Claims (1)

[Claims] 1. In a rack-shaped storage device installed on the floor of a water tank for the purpose of vertically holding and storing spent nuclear fuel assemblies consisting of rod-shaped elements in water, The bottom part is fixed to the floor of the aquarium, and the top part is configured to fix and support other rack-shaped storage devices in the lower tier, and can be attached and detached as necessary, and cooperates with the upper tier storage device to store nuclear fuel in the aquarium. A spent nuclear fuel storage device characterized by increasing capacity. 2. Spent nuclear fuel storage according to item 1, characterized in that the upper rack-shaped storage device is surrounded by a tank for removing water, and the weight of the rack-shaped storage device is reduced by buoyancy. Device. 3. In the storage device described in Items 1 and 2, the used storage device is characterized in that the corner portion of the upper rack-shaped storage device is connected to the corner portion of the adjacent storage device by a metal fitting to increase dynamic rigidity. Nuclear fuel storage device. 4. In a storage facility in which storage devices for lower tiers are arranged according to item 1, when the storage devices for upper tiers are fixed, the corners of the rack-shaped storage devices are fixed to the adjacent corners for the purpose of increasing dynamic rigidity. A spent nuclear fuel storage device characterized in that the parts and the parts are connected by metal fittings.