To provide a radioactive material containment vessel or the like such as a cask capable of suppressing manufacturing costs without deteriorating sealing reliability against impact in any case during conveyance or during installation.

In the cask 1 including a bottomed trunk body 5 having an opening part 25, a primary lid structure 2 constituted by mounting a primary lid 6 to the opening part 25, a secondary lid structure 3 constituted by mounting a secondary lid 7 to the opening part 25, and a tertiary lid structure 4 constituted by mounting a tertiary lid 8 to the opening part 25, during conveyance, the primary lid 6, the secondary lid 7, and the tertiary lid 8 are mounted, and the secondary lid 7 and the tertiary lid 8 seal the trunk body 5. During installation, the primary lid 6 and the secondary lid 7 are mounted and the tertiary lid 8 are detached, and the primary lid 6 and the secondary lid 7 seal the trunk body 5. The primary lid 6 is constituted so as to be plastically deformed so that the sealing of the trunk body 5 is allowed to be opened, due to the impact from the contained material of the trunk body 5, which is assumed in the accident case such as falling during conveyance.

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