JP2000258595A - Monitor for double lid of canister - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to easily and securely inspect the integrity of primary and secondary lids of a canister. SOLUTION: A primary lid 6 is welded to the upper part in the main body 1 of a canister inside which spent fuel assemblies 3 are housed and a helium gas 12 is charged, and a secondary lid 8 is welded above the primary lid 6 in the main body 1 of the canister with a clearance 7, filled with a helium gas 13 whose pressure is higher than that of the helium gas 12 charged into the section where the spent fuel assemblies 3 are housed, intervening between the primary and secondary lids. Then, a pressure detector 10 to detect the pressure in the clearance 7 is connected to the secondary lid 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a double lid monitoring device for a canister.

[0002]

2. Description of the Related Art A canister is used for storing spent fuel, and a lid is attached to the canister so as to confine radioactive materials inside the canister.

[0003] When a welded structure is used for joining the lid, it is necessary to ensure the soundness of the welded portion. For this reason, conventionally, a PT test (liquid permeation inspection) is performed to confirm whether or not the welded portion is sound. However, the monitoring of the welded portion is not particularly performed during storage of the spent fuel. .

However, recently, in the United States, an accident in which a crack occurs in a welded portion has occurred, and standards for the cracking have been reviewed. As a countermeasure, for example, after loading a spent fuel into a canister, an RT inspection (a volume test) of the welded portion is performed. Inspection, ie X
It is conceivable to perform an inspection by radiography.

[0005]

However, since the spent fuel stored in the canister emits radioactive materials, it is technically difficult to perform an RT inspection on a welded portion.

The present invention has been made in view of the above circumstances, and has as its object to easily and reliably monitor the soundness of a welded portion of a lid in a canister.

[0007]

SUMMARY OF THE INVENTION A double lid monitoring apparatus for a canister according to the present invention is characterized in that a primary lid is welded to an upper portion of a canister body in which a spent fuel assembly is housed and a required gas is sealed, At the top of the primary lid in the canister body, a secondary lid is welded through a gap filled with a gas higher in pressure than the gas sealed in the storage section of the spent fuel assembly, A means for detecting the gas pressure in the inside is provided.

In the present invention, when there is no abnormality in the welded portion between the primary lid and the secondary lid, the gas pressure in the gap falls within the fluctuation assumed in advance. Falls out of the fluctuation assumed in advance.

Therefore, by monitoring the gas pressure in the gap by means for detecting the gas pressure in the gap, the soundness of the welded portions of the primary lid and the secondary lid can be easily and quickly confirmed.

[0010]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIGS. 1 and 2 show an embodiment of the present invention. In the drawings, reference numeral 1 denotes a cylindrical canister main body, 2 denotes a secondary lid welded to the bottom of the canister main body 1, and FIG. Inside, the spent fuel assembly 3 is stored.

An annular seat 4 is welded in the canister body 1 so as to be located above the upper end of the spent fuel assembly 3, and a shielding plug 5 is mounted on the upper surface of the annular seat 4. Have been.

Shield plug 5 in canister body 1
A primary lid 6 that is in contact with the upper surface of the shielding plug 5 and that is welded to the inner periphery of the canister body 1 is provided at the upper part of the canister.
A top secondary lid 8 which is disposed with a predetermined gap 7 between the primary lid 6 and is welded to the inner periphery of the canister body 1.
Is provided. Thus, the primary lid 6 and the secondary lid 8 form a double lid.

A guide hole 9 is formed in the secondary lid 8 so as to penetrate the secondary cover 8 in the thickness direction. The guide hole 9 has a conduit 11 having a pressure detector 10 attached to the upper end thereof. It is connected so as to be located above the next lid 8.

A helium gas 12 having a pressure P1 of about 1.7 atm is sealed in a storage section of the spent fuel assembly 3 in the canister body 1, and a gap 7 between the primary lid 6 and the secondary lid 8 is filled in the space. A helium gas 13 having a pressure P2 of about 2.0 atm is sealed from a helium gas inlet 17.

In FIG. 1, reference numeral 14 denotes a welded portion of the primary lid 6 to the inner periphery of the canister body 1, 15 denotes a welded portion of the secondary lid 8 to the canister body 1, and 16a and 16b denote valves.

In order to check the soundness of the welded portion 14 of the primary lid 6 and the welded portion 15 of the secondary lid 8, the pressure detector 10
Thus, the change in the pressure in the gap 7 is monitored. If there is no abnormality in the welds 14 and 15, the pressure detector 10
The value detected by is within the fluctuation assumed in advance in consideration of the time-dependent decay of the calorific value of the spent fuel assembly and the change in the ambient temperature.

On the other hand, when there is an abnormality in the welded portion 14 of the primary lid 6, the pressure P2 of the helium gas 13 sealed in the gap 7 is changed to the helium gas in the storage portion of the spent fuel assembly 3 in the canister body 1. 12 is higher than the pressure P1, the helium gas 13 leaks into the storage portion of the spent fuel assembly 3 in the canister body 1, and if there is an abnormality in the welded portion 15 of the secondary lid 8, the helium gas 13 Since the pressure P2 of the sealed helium gas 13 is higher than the atmospheric pressure outside the canister body 1, the helium gas 13 leaks outside the canister body 1. As a result, the welds 14, 1
5 has an abnormality, the pressure P2 of the gap 7 detected by the pressure detector 10 falls below the fluctuation range assumed in advance, so that the value of the pressure It can be confirmed that there is an abnormality in the welded portion 14 of the secondary lid 8 and the welded portion 15 of the secondary lid 8.

According to the embodiment of the present invention, the soundness of the primary lid 6 and the secondary lid 8 of the canister can be easily and reliably confirmed by monitoring the pressure detector 10.

It should be noted that the present invention is not limited to the above-described embodiment, and it is needless to say that various changes can be made without departing from the spirit of the present invention.

[0021]

According to the double lid monitoring apparatus for a canister of the present invention, an excellent effect that the integrity of the welded portion between the primary lid and the secondary lid of the canister can be easily and reliably confirmed can be obtained.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of an example of an embodiment of a double lid monitoring device for a canister of the present invention.

FIG. 2 is an enlarged view of a portion II in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Canister main body 3 Spent fuel assembly 6 Primary lid 8 Secondary lid 10 Pressure detector (means for detecting gas pressure) 12, 13 Helium gas (gas)

Claims (1)

[Claims] 1. A primary lid is welded to an upper part of a canister body in which a required fuel assembly is accommodated and a required gas is filled, and the spent fuel is mounted on an upper part of the primary lid in the canister body. The secondary lid is welded through a gap in which gas having a higher pressure than the gas sealed in the storage section of the assembly is sealed, and a means for detecting gas pressure in the gap is provided at a required location. The double lid monitoring device of the canister.