JPS5813880B2 - Cask control and decontamination method - Google Patents

Description

[Detailed description of the invention] The present invention relates to a spent nuclear fuel transport container (hereinafter referred to as a cask).

) related to decontamination and prevention methods. A cask is used to store and transport spent nuclear fuel.

The operation of storing spent nuclear fuel inside the cask is carried out with the cask immersed in a contaminated liquid (pool water) into which the spent nuclear fuel has been previously inserted, from the viewpoint of preventing exposure to radiation.

Therefore, the contaminated liquid from the fuel pool will adhere to the outer surface of the cask.

In this case, in order to avoid environmental contamination, it is necessary to decontaminate the outer surface of the cask before transporting it, but since the cask has a large number of fins, trunnions, etc., its shape is complex, and decontamination requires many steps. It takes time and effort, and there are safety issues if it is done manually.

The present invention can prevent or minimize contamination of the cask with pool liquid during or after the operation even if the cask is immersed in the fuel pool water for storing spent nuclear fuel. This paper proposes a method that can efficiently decontaminate contamination even if it is contaminated, and examples thereof will be described below with reference to the drawings.

1 is a spent nuclear fuel (not shown).

) is inserted into the fuel pool, and the pool water is naturally contaminated from the beginning.

2 is an annular slit or a large number of holes, the hole diameter is 0.1 to 3
3 (hereinafter referred to as through holes) provided in the range of mm and the pitch in the range of 10 to 200 mm.

) are arranged in a ring shape, and this air supply pipe 2
Air is supplied to the tank by an air pump 5 through a pipe 4.

The air supply pipe 2 is provided at the bottom of the fuel pool 1, and the air is continuously exhausted from its through hole 3, which becomes a large number of small bubbles and rises in the contaminated liquid 6.

Therefore, a cylindrical air curtain 7 is formed in the contaminated liquid 6.

Reference numeral 8 denotes a liquid supply pipe for uncontaminated liquid (clean water) 9, which is provided in an annular shape below the surrounding portion 10 of the air curtain 7.

A slit or a through hole 11 is also formed in the liquid supply pipe 8,
Fresh water sent from a tank (not shown) through piping 12 can be injected from the lower part of the surrounding part 10.

While water is not being injected into the surrounding area 10 from the water supply pipe 8, the pool water in the surrounding area 10 is contaminated in the same manner as the contaminated liquid 6 outside thereof due to the formation of the air curtain 7.

However, when water injection is started, the water pressure in the surrounding section 10 becomes higher than that outside, so the contaminated liquid is gradually pushed out through the air curtain 7, and the degree of contamination decreases.

If the water injection is continued further, the pool water in the surrounding area 10 will eventually become only uncontaminated liquid, that is, clear water, and thus the surrounding area 10 will become a clear water area Z.

Note that the amount of fresh water injected is 0.1
The amount can be replaced within a range of ~3 hours, and in this case, the degree of contamination of the surrounding portion 10 is 1, assuming the degree of contamination before fresh water injection is 100.

Therefore, the contamination removal rate is 99%.

The cask 13 is immersed in the clear water Z with the upper lid body 14 open.

The spent nuclear fuel is stored in a cask 13 in the clear water area Z.

After storage, the upper lid 14 is attached to seal the cask 13, and then the cask 13 is pulled upward and taken out of the fuel pool 1, and subjected to natural drying or forced drying.

In this way, a clear water area Z is easily formed in the contaminated liquid 6 of the fuel pool 1, and the cask 13 can be immersed therein to store the spent nuclear fuel. 13 and the contaminated liquid 6 do not come into contact with each other.

Therefore, contamination of the outer surface of the cask 13 can be prevented.

Furthermore, even if it is contaminated, the degree of contamination will be extremely low.

Therefore, in the event that the outer surface of the cask 13 is contaminated for some reason, if the cask 13 is left in the clear water area Z for a certain period of time and water injection is continued during that time, the fresh water flow in the clear water area Z will decontaminate the cask 13.

Although fresh water may be constantly injected into the air curtain surrounding section 10, it is not necessary to do so.
It is sufficient to carry out the procedure as needed depending on the fresh water contamination situation.

As is clear from the above description, according to the present invention, although the cask is immersed in the same pool liquid in which the spent nuclear fuel is inserted, without providing a cover or the like,
Contamination of the outer surface of the cask can be prevented, or even if it is contaminated, it can be easily decontaminated.

[Brief explanation of drawings]

The drawings are explanatory diagrams of embodiments of the present invention. 1... Fuel pool, 2... Air supply pipe, 6... Contaminated liquid, 7...
... Air curtain, 8 ... Water supply pipe, 10 ... Surrounding section, 1
3...Cask, Z...Clear water.

Claims (1)

[Claims] 1. A cask characterized by forming an air curtain surrounding a certain area in contaminated liquid, injecting uncontaminated liquid into the surrounding area of the air curtain to make this an uncontaminated liquid area, and immersing the cask in the cask. Prevention and decontamination methods.