JPH11337684A - Cask made of stainless steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of stress-corrosion cracking by forming members constituting stainless steel cask by welding and covering a welding bead both on the outer surface and in a part, where stress-corrosion cracking is likely to occur with a polyphenylene sulfide resin film. SOLUTION: A cask has a cylindrical outer body 1, a cylindrical inner body 2 placed concentrically at intervals inside the outer body 1 and a bottom plate 3 that is fitted into an opening at the lower end of the outer body 1 and closes openings at the lower ends of the outer body 1 and the inner body 2. The outer body 1, the inner body 2 and the bottom plate 3 are made of stainless steel as a strength member. The lower end of the outer body 1 is fixed to the intermediate part of the height in a circumferential surface the bottom plate 3 by fillet welding to form a welding bead 4. The welding bead 4 is covered with a polyphenylene sulfide resin coating film 5 to a prescribed thickness. Moreover, the distance L between both toes of the welding bead 4 and both side edges of the resin coating film 5 is set at 50 mm or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stainless steel cask used for storing radioactive materials such as spent nuclear fuel indoors near a coast, for example.

[0002]

2. Description of the Related Art Conventionally, a stainless steel cask of this kind has been formed by welding a plurality of cask constituent members made of JIS SUS304.

[0003] However, when this cask is installed indoors near the coast, due to sea salt particles flying indoors, the cask component has a portion in the vicinity of the weld bead existing on the outer surface, particularly a cask which is a strength member. Stress corrosion cracking may occur in the vicinity of the weld bead in the component.

[0004] In order to solve such a problem, a cask constituent member is made of JI having excellent stress corrosion cracking resistance.
Although it is conceivable to use SSUS316L, there is a problem that the cost is increased and the occurrence of stress corrosion cracking cannot be completely prevented.

An object of the present invention is to solve the above problems and to provide a stainless steel cask that can completely prevent the occurrence of stress corrosion cracking and is inexpensive.

[0006]

SUMMARY OF THE INVENTION A stainless steel cask according to the present invention is formed by welding a plurality of stainless steel cask components, and the possibility of occurrence of stress corrosion cracking on the outer surface. The weld bead existing in a certain portion is covered with a polyphenylene sulfide resin film.

In the above, the polyphenylene sulfide resin film is excellent in heat resistance and water penetration resistance, and is hardly deteriorated by ultraviolet rays when the cask is installed indoors. In addition, since the internal temperature of the cask is higher than the atmospheric temperature, the penetration of moisture into the resin film is reliably prevented in combination with the water penetration resistance of the resin film itself. According to the cask of the present invention, since the weld bead present on the outer surface and in the portion where stress corrosion cracking may occur is covered with such a polyphenylene sulfide resin film, the cask constituent member The occurrence of stress corrosion cracking can be completely prevented. In addition, since the resin film only covers the weld bead, it does not hinder heat radiation from the outer surface of the cask. Further, the cost is reduced as compared with the case where the cask constituent members are formed of JIS SUS316L. Furthermore, since the polyphenylene sulfide resin film is transparent compared to the metal sprayed film or the resin film containing the pigment, the resin film is peeled off at the time of a periodic visual inspection, and the resin film is formed again after the inspection is completed. No need and maintenance is easy.

In the stainless steel cask of the present invention, it is preferable that the distance between both toes of the weld bead and both side edges of the polyphenylene sulfide resin film is 50 mm or more.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described.
This will be described with reference to the drawings.

FIGS. 1 and 2 show a cask according to the present invention.

In FIGS. 1 and 2, the cask comprises a cylindrical outer shell (1), a cylindrical inner shell (2) concentrically arranged inside the outer shell (1) and spaced apart from the outer shell. A bottom plate (3) is fitted into the lower end opening of the trunk (1) and closes the lower end openings of the outer trunk (1) and the inner trunk (2). The outer shell (1), the inner shell (2) and the bottom plate (3) are the strength members of the cask.
It is formed of JIS SUS304.

The lower end of the outer shell (1) is fixed to a middle part of the height of the peripheral surface of the bottom plate (3) by fillet welding. This weld bead is indicated by (4). And this welding bead (4)
However, it is preferably covered with a polyphenylene sulfide resin coating film (5) (resin film) having a thickness of 100 to 300 μm. The distance L between both toes of the weld bead and both side edges of the polyphenylene sulfide resin coating (5) is 50 mm, respectively.
That is all.

The lower end of the inner body (2) is mounted on an annular upper protruding portion (2a) integrally formed on the upper surface of the bottom plate (3) and fixed by butt welding. Although not shown, a basket containing spent nuclear fuel is arranged in the inner shell (2) and placed on the bottom plate (3). A gamma ray shielding layer (7) made of lead is densely formed between the outer body (1) and the inner body (2). The gamma ray shielding layer (7) is formed by injecting molten lead between the outer shell (1) and the inner shell (2) and then solidifying the molten lead, or by forming a cylindrical body made of a lead plate into the outer shell (1). It is formed by being inserted between the inner body (2).

An upper stepped recess (8) is formed in the lower surface of the bottom plate (3) except for the outer peripheral edge. A neutron shielding layer (9) made of resin is formed in a portion of the recess (8) above the step (8a). A heat insulating layer (10) is provided between the upper surface of the neutron shielding layer (9) and the bottom surface of the recess (8), and between the outer peripheral surface of the neutron shielding layer (9) and the inner peripheral surface of the recess (8). Is formed. Also, the step in the recess (8)
A bottom cover (11) made of JIS SUS304 is placed in a portion below (8a) such that the outer peripheral edge of the upper surface is in contact with the step (8a), and is fixed to the bottom plate (3) by welding. .

[0015] JIS SU at a distance outside the outer shell (1)
A cylindrical outer cover (12) made of S304 is arranged concentrically. At the lower end of the cover (12), a small-diameter
(12b) is formed. An inwardly bent portion (12c) is formed at the lower end of the small diameter portion (12b), and the tip is fixed to the outer body (1) by welding. In the space between the outer shell (1) and the cover (12), radiating fins (13) extending in the vertical direction are arranged at intervals in the circumferential direction, and are mounted on the step (12a). The radiation fins (13) are in contact with the outer peripheral surface of the outer shell (1) and the inner peripheral surface of the cover. A neutron shielding layer (14) made of resin is formed in a portion between the adjacent radiation fins (13) in the space.

[Brief description of the drawings]

FIG. 1 is a vertical longitudinal sectional view showing a part of a cask according to the present invention.

FIG. 2 is a partially enlarged view of FIG.

[Explanation of symbols]

 (1): Outer body (3): Bottom plate (4): Weld bead (5): Polyphenylene sulfide resin coating (resin film)

Claims (2)

[Claims] A weld bead formed by welding a plurality of stainless steel cask constituent members and present on an outer surface and a portion where stress corrosion cracking may occur is covered with a polyphenylene sulfide resin film. Stainless steel cask. 2. The distance between both toes of the weld bead and both side edges of the polyphenylene sulfide resin film is 50 m, respectively.
The stainless steel cask according to claim 1, which is at least m.