JPS606797Y2 - Spent nuclear fuel transport container contamination prevention device - Google Patents

Description

[Detailed description of the invention] Spent nuclear fuel is generally highly radioactive, so it is usually handled underwater using water as a shield, and it is also stored in a pit with a water depth of 1.

When transporting spent nuclear fuel, a cask (container) is submerged in a fuel storage pit or a special pit connected to the pit via a waterway, and the cask is filled with fuel underwater.

The same applies when taking out fuel from the cask.

After filling, the cask is taken out of the water with a lid on and transported to its destination, but since the water in the pit is radioactively contaminated by the fuel, the cask taken out of the water is also contaminated. It is now legally permissible to take the materials out of the controlled area unless they are decontaminated.

However, because the surface of the cask has many heat dissipating fins and other protrusions, decontamination work currently has to rely on the manual labor of workers, which requires a great deal of time and labor. Radiation exposure was a problem.

The present invention was proposed in order to overcome the above-mentioned drawbacks of the conventional method, and by covering most of the cask, which has a complex external shape that makes it difficult to decontaminate radioactivity and has a fuel rod storage space, the cask is contaminated. It is an object of the present invention to provide a contamination prevention device for a container for transporting and storing spent nuclear fuel, which can shorten the working time of decontamination work by insulating the container from pit water.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Reference numeral 1 denotes a cask (container) having a lid and forming a fuel rod storage space inside. It is suspended by a crane, etc.

4 is a bag-shaped cover made of waterproof fabric such as flexible vinyl film that covers most of the cask 1 from below;
The upper edge of the cover 4 is secured 6 through the smooth part 5 of the upper part of the cask 1 so as to be watertight.

The shape of the cover 4 is determined depending on the external shape of the target cask, but it is convenient for handling if the size has some allowance.

On the other hand, attached to the upper part of the force bar 4 are a water injection hose 7 for injecting water into the cover from the outside, and an exhaust hose 8 whose tip is open to the air.

Note that the pipe diameter of the hose 7.8 is the same as that of the cover 4 and the cask 1.
It is determined according to the volume of the space between and the speed at which the cask 1 sinks into the water 9 of the pit.

A drain hose 10 is attached to the lower end of the cover 4, and a drain port 11 at the tip thereof is fixed to the pit water surface 12 or supported above the water surface by a float.

It goes without saying that the diameter of this drainage hose 10 must be larger than the diameter of the water injection hose 7.

Next, to explain the operation, the cask 1 is lowered onto the pit water surface 12 as shown in FIG. 1, and when its lower end reaches the water surface 12, fresh water starts to be injected into the cover 4 from the water injection hose 7.

At this time, the capacity of the drainage hose 10 is sufficient, so if a larger amount of water is continuously injected than the sinking speed of the cask, the excess water will flow out from the drainage hose 10 and the waist cask 1 will be placed in the water 9 of the pit. In the whole process of being submerged in
The internal water level of the cover 4 coincides with the pit water level 12, and the internal and external pressures of the cover 4 are kept in balance.

Furthermore, after the cask 1 is completely submerged, most of the water injected will flow out, but this balance will not be disrupted because the cover internal pressure will increase as the water depth changes.

If the cask 1 is further submerged and reaches the bottom, water injection will be stopped.

In this case, if the drain hose 10 does not have a sufficient length, the drain port 11 will be drawn into the water along with the float due to the descent of the cask 1, but if the length of the hose is longer than that, the drain port 11 will be pulled into the water. There is no problem because the contaminated water will not penetrate inside the cover over time.

Furthermore, once cask 1 reaches the bottom, spent nuclear fuel will be loaded or removed, and then cask 1 will be lifted out of the pit underwater 9 using a crane. Since the water flows out from the drainage hose 10, the water level (or water pressure) inside and outside the cover 1 is always the same.

As explained in detail above, the present invention is for preventing contamination of a cask that has a lid, forms a fuel rod storage space inside, and has a large number of radiation fins protruding from its outer surface.
We have installed a waterproof fabric cover that covers the bottom and sides of the cask and creates a sealed space between it and the cask, so even if the cask is submerged into the pit after being covered with this cover, the bottom part of the cask will remain intact. Most of the outer surface of the cask will not be contaminated with radioactivity, as the entire cask will not come in contact with the contaminated pit water.

Therefore, the decontamination work on the outer surface of the cask only needs to be carried out on the extremely small portions that could not be covered, so the work time for decontamination and the amount of radiation exposure of the workers are greatly reduced.

The present invention also provides a flexible water supply pipe connected to the upper end of the cover and communicating with the sealed space, a flexible exhaust pipe connected to the upper end and communicating with the sealed space, and a flexible exhaust pipe connected to the lower end of the cover and connected to the same sealed space. By providing a flexible drain pipe that communicates with the sealed space and is equipped with a float at the open end, the open end of the drain pipe is maintained above the water surface of the shielding water, and the clean water inside the cover is kept away from the possibility of radioactive contamination. Since it is completely isolated from some shielding water and the pressure inside and outside the cover is balanced, there is no problem of the cover being pressed against the radiation fins and being damaged.

In addition, this allows the use of extremely thin covers, making them easy to attach and remove from the cask, and reducing the volume of the cover that is ultimately disposed of as radioactive solid waste.
It also has excellent practical effects such as ease of handling (solid waste is usually stored after its volume is reduced by compression).

That is, the internal and external pressures applied to the cover can be balanced under any condition, and a cover fabric with low strength can be used.

The fact that such a low-strength cover fabric (for example, vinyl sheet, etc.) can be used is particularly significant in this case.

That is, since spent nuclear fuel is discharged from power plants every one to two years, it would be problematic to leave the contaminated cover in place during that waiting period, and it would probably be necessary to decontaminate it and store it. be.

However, decontaminating a cover that has been exposed to contaminated water several times becomes extremely troublesome.

However, in the case of a bag-shaped cover such as a vinyl sheet, it is extremely inexpensive, so even if it is disposable, there is no problem in terms of cost, and the problem of decontamination of the cover can be easily solved.

[Brief explanation of the drawing]

The drawings show an embodiment of the spent nuclear fuel transport container contamination prevention device of the present invention, and Figure 1 shows the state before sinking into the pit;
FIG. 2 is a front view showing the state in which it is submerged in a pit. Explanation of the main parts of the diagram, 1... Cask (container)
, 3...hanging tool, 4...cover, 6...
... Lashing part, 7 ... Water injection hose (water supply pipe), 8 ... Exhaust hose (exhaust pipe) 10 ...
...Drainage hose (drain pipe).

Claims (1)

[Scope of utility model registration request] A cask that has a lid, forms a fuel rod storage space inside, and has a large number of radiation fins protruding from its outer surface to prevent contamination. a waterproof fabric cover that defines a sealed space in the cover; a flexible water supply pipe connected to the upper end of the cover and communicating with the sealed space; a flexible exhaust pipe connected to the upper end and communicated with the sealed space; 1. A contamination prevention device for a spent nuclear fuel transport container, comprising a flexible drain pipe connected to the lower end, communicating with the same sealed space, and having a float at the open end.