JPH10170688A - Method for preventing contamination of outer surface of radioactive material storage container - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for preventing contamination of the outer surface of a radioactive material storage container, by which, when the decay heat of spent nuclear fuel is removed by natural air cooling, the need for the work of removing radioactive materials in advance from the outer surface of a storage container made of steel can be eliminated. SOLUTION: An O-ring 4 is mounted on the outer surface of the upper end of a thin-walled steel storage container 2 having a sealing function to prevent leakage of radioactive materials, and the steel storage container 2 is enclosed in a shielding container 3, either with the O-ring 4 brought into contact with the inner surface of an opening in the shielding container 3, or with a flange 5 provided at the upper end of the steel storage container to mount the O-ring 4 on the flange 5 to enclose the steel storage container 2 in the shielding container 3. Then the O-ring 4 is brought into contact with the upper end of the shielding container 3 to form a sealed space part 6 between the part of the outer surface of the steel storage container 2 inside the O-ring 4 and the inner surface of the shielding container 3, and then the shielding container 3 enclosing the steel storage container 2 is dipped in a spent fuel storage pool, so that the outer surface of the steel storage container 2 is prevented from making contact with contaminated pool water by the sealed space part 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preventing external contamination of a radioactive substance storage container.

[0002]

2. Description of the Related Art When storing radioactive materials such as spent nuclear fuel, it is called a cask having (1) a sealing function for preventing leakage of radioactive materials and a shielding function for shielding radiation from spent nuclear fuel. When a thick steel storage container is used, and (2) a thin steel storage container having a sealing function to prevent leakage of radioactive materials and a concrete shield having a shielding function surrounding the steel storage container There is a case where a radioactive substance storage container composed of a container for use is used.

A conventional example of the radioactive substance storage container of the above (2) will be described with reference to FIGS. 3 (a) and 3 (b). 1 is a spent nuclear fuel, 21 is a thin steel storage container, and 22 is a thick storage container. A lid, 23 is a concrete shielding container surrounding the steel storage container 21, 24 is an air supply port provided in the concrete shielding container 23, 25 is an exhaust port provided in the concrete shielding container 23, 27 is a steel container The ventilation passage 26 formed between the storage container 21 and the concrete shielding container 23 is an airflow flowing through the ventilation passage 27, and the spent nuclear fuel 1 is loaded and sealed in the thin steel storage container 21. Thin steel storage container 2
1 is placed in a concrete shielding container 23.

At this time, an air flow 26 entering the ventilation passage 27 from the air supply port 24 and heading toward the exhaust port 25 is brought into contact with the outer surface of the thin steel storage container 21 to reduce the decay heat of the spent nuclear fuel 1 by natural air cooling. To remove.

[0005]

The conventional radioactive substance storage container shown in FIG. 3 has the following problems. That is, FIG. 4 shows a process of loading the spent nuclear fuel 1 into the steel storage container 21 in the water of the spent fuel storage pool 28.
Since the steel storage container 21 is thin and has no shielding function,
After storing the steel storage container 21 in the thick-walled shielding container 20 having a shielding function, the crane 29 is operated to move the steel storage container 21 and the shielding container 20 into the underwater of the spent fuel storage pool 28. And then spent fuel storage pool 28
The spent nuclear fuel 1 in the steel storage container 21 is transferred to the steel storage container 21, and then the crane 29 is operated to operate the steel storage container 21.
Further, the shielding container 20 is transported to a fuel pit (not shown) outside the spent fuel storage pool 28, and the steel storage container 21 is set in the concrete shielding container 23. In other words, a thin steel storage container 2 having no shielding function
1 is not handled alone (without a shielding function).

During the above series of operations, the thin steel storage container 2
The outer surface of the container 1 comes into contact with the water in the spent fuel storage pool 28 which is contaminated by radioactive material and is contaminated. Therefore, the crane 29 is operated, and the steel storage container 21 and the shielding container 20 are operated.
Is transported to a fuel pit (not shown) outside the spent fuel storage pool 28, the steel storage container 21 is set in the concrete shielding container 23, and the air is released from the thin steel storage container 2.
Before the decay heat of the spent nuclear fuel 1 is removed by natural air cooling by contact with the outer surface of the
1 must be removed from the outer surface.

At this time, since the steel storage container called the above-mentioned cask is thick and has the shielding function of the steel storage container itself like the shielding container 20, the steel storage container is transported outside the spent fuel storage pool 28. Thereafter, an operator approaches, and the outer surface of the steel storage container can be washed with pure water to wash and remove radioactive substances attached to the outer surface. But steel storage container 2
1 is stored in the shielding container 20, and when the shielding container 20 is transported out of the spent fuel storage pool 28, unless it is taken out of the shielding container 20, the steel storage container 21 is stored.
The radioactive material attached to the outer surface of the device cannot be washed or removed. Moreover, since the steel storage container 21 is thin and does not have a shielding function, it is difficult for workers to approach and without using a remote automatic cleaning device, the radioactive material attached to the outer surface of the steel storage container 21 is cleaned. , Cannot be removed.
Since the storage container lid 22 closing the upper end opening of the steel storage container 21 is thick and has a shielding function, the remote automatic cleaning device does not need to be used only on the outer surface of the storage container lid 22. Can also be decontaminated.

In addition, the contamination inspection after cleaning is performed by wiping. However, it is necessary to use a remote automatic wiping device, which greatly increases the cost. The present invention has been proposed in view of the above problems, and the object thereof is to remove radioactive materials from the outer surface of a steel storage container in advance when removing decay heat of spent nuclear fuel by natural air cooling. It is an object of the present invention to provide a method for preventing contamination of the outer surface of a radioactive substance storage container, which can eliminate the need for an additional operation.

[0009]

SUMMARY OF THE INVENTION In order to achieve the above object, a method for preventing external contamination of a radioactive material storage container according to the present invention comprises a thin steel storage container having a sealing function for preventing radioactive material from leaking. An O-ring is attached to the outer surface of the upper end of the steel container, and the steel storage container is housed in the shielding container. After forming a closed space between the outer surface of the container and the inner surface of the shielding container, the shielding container containing the steel storage container is submerged in the spent nuclear fuel storage pool, and the steel storage container is closed by the closed space. The present invention is characterized in that the outer surface is not brought into contact with the contaminated pool water (claim 1).

In the above method for preventing external contamination of a radioactive substance storage container, a flange is provided at an upper end portion of the steel storage container.
Attach the O-ring to the flange, store the steel storage container in the shielding container, contact the O-ring with the upper end of the shielding container, and shield the outer surface of the steel storage container inside the O-ring. A closed space may be formed between the inner surface of the container and the inner surface of the container (claim 2).

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) Next, a method for preventing external contamination of a radioactive material storage container according to the present invention will be described with reference to a first embodiment shown in FIGS. 1 (a) and 1 (b). Thin steel storage container with sealing function to prevent leakage, 3
Is a shielding container, 4 is an O-ring, and 6 is a sealed space formed between the outer surface of the steel storage container 2 inside the O-ring 4 and the inner surface of the shielding container 3.

When the radioactive material storage container is submerged in the spent fuel storage pool, an O-ring 4 is provided on the outer surface of the upper end portion of the thin steel storage container 2 having a sealing function for preventing leakage of the radioactive material.
, The steel storage container 2 is housed in the shielding container 3, and the O-ring 4 is brought into contact with the inner surface of the opening of the shielding container 3, so that the steel storage container 2 inside the O-ring 4. After forming the closed space portion 6 between the outer surface of the container and the inner surface of the shielding container 3,
The shielding container 3 containing the steel storage container 2 is submerged in the spent fuel storage pool, and the steel storage container 6 is closed by the closed space 6.
Avoid contacting contaminated pool water with the outside surface of the.

(Second Embodiment) Next, a method for preventing external contamination of a radioactive material storage container according to the present invention will be described with reference to a second embodiment shown in FIG. 2. Numeral 1 indicates spent nuclear fuel, and numeral 2 indicates leakage of radioactive material. Thin steel storage container with sealing function
Is a shielding container, 5 is a flange provided at the upper end of the steel storage container 2, 4 is an O-ring attached to the flange 5, 6 is an outer surface of the steel storage container 2 inside the O-ring 4 for shielding. It is a closed space formed between the inner surface of the container 3.

When submerging the radioactive material storage container in the spent fuel storage pool, an O-ring 4 is attached to the flange 5 of the thin steel storage container 2 having a sealing function for preventing the radioactive material from leaking.
Is attached, the steel storage container 2 is stored in the shielding container 3, and the O-ring 4 is brought into contact with the upper end of the shielding container 3,
After forming the closed space 6 between the outer surface of the steel storage container 2 inside the O-ring 4 and the inner surface of the shielding container 3, the shielding container 3 containing the steel storage container 2 has been used. Submerged in the fuel storage pool, the closed space 6 prevents the outer surface of the steel storage container 2 from coming into contact with the contaminated pool water.

[0015]

As described above, the method for preventing external contamination of a radioactive material storage container according to the present invention comprises attaching an O-ring to the outer surface of the upper end portion of a thin steel storage container having a sealing function for preventing radioactive material from leaking. The steel storage container is housed in the shielding container, and the O-ring is brought into contact with the inner surface of the opening of the shielding container, or a flange is provided at the upper end of the steel storage container, and the O-ring is attached to the flange. The storage container made of is stored in the shielding container, and the O-ring is brought into contact with the upper end of the shielding container,
After forming a closed space between the outer surface of the steel storage container inside the O-ring and the inner surface of the shielding container, the shielding container housing the steel storage container is submerged in the spent fuel storage pool. The sealed space prevents the outer surface of the steel storage container from coming into contact with the contaminated pool water, so that when the decay heat of the spent nuclear fuel is removed by natural air cooling, the radioactive material is removed from the outer surface of the steel storage container in advance. The work of removing the sheet can be eliminated.

[Brief description of the drawings]

FIG. 1 (a) is a longitudinal sectional side view showing a first embodiment of a radioactive substance storage container applied to the method for preventing external contamination of a radioactive substance storage container of the present invention, and FIG. 1 (b) is an arrow A- of FIG. FIG. 3 is a cross-sectional plan view along the line A.

FIG. 2 is a longitudinal sectional side view showing a second embodiment of the radioactive substance storage container applied to the method for preventing external contamination of the radioactive substance storage container of the present invention.

FIG. 3A is a longitudinal side view showing a conventional radioactive substance storage container, and FIG. 3B is a cross-sectional plan view taken along line BB in FIG. 3A.

FIG. 4 is an explanatory diagram showing a process of loading a spent nuclear fuel into a steel storage container in water of a spent fuel storage pool.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Spent nuclear fuel 2 Steel storage container 3 Shielding container 4 O-ring 5 Flange 6 Sealed space

Claims (2)

[Claims] 1. An O-ring is attached to an outer surface of an upper end of a thin steel storage container having a sealing function for preventing leakage of radioactive substances, and the steel storage container is stored in a shielding container. To make contact with the inner surface of the opening of the shielding container to form a closed space between the outer surface of the steel storage container inside the O-ring and the inner surface of the shielding container, and then store the steel storage container. A method for preventing external contamination of a radioactive material storage container, wherein the shielded container is submerged in a spent nuclear fuel storage pool, and the outer surface of the steel storage container is prevented from contacting the pool water contaminated by the closed space. . 2. A flange is provided at an upper end portion of the steel storage container, an O-ring is attached to the flange, the steel storage container is housed in a shielding container, and the O-ring contacts an upper end portion of the shielding container. 2. The method according to claim 1, wherein a closed space is formed between the outer surface of the steel storage container inside the O-ring and the inner surface of the shielding container.