Nuclear waste storage canisters

A canister for dry storage of nuclear waste material, the canister comprising:

• a steel tubular first shell defining an internal cavity for storing nuclear waste material;
• a lid sealably attached to a first end of the first shell;
• an end closure attached to a second end of the first shell, the end closure comprising a steel base plate and an upturned annular closure flange disposed on a peripheral portion of the base plate;
• a circumferentially-extending butt joint formed between the annular closure flange and the second end of first shell;
• a circumferentially-extending butt weld formed at the butt joint which hermetically seals the annular closure flange to the second end of the first shell;
• a steel annular shell skirt adjoined and welded to a lower portion of the first shell proximate to its second end, the shell skirt extending circumferentially around the lower portion and having a height less than a full height of the first shell, wherein the shell skirt forms a hermetically sealed secondary pressure retention barrier over the butt weld;
• and
• a plurality of circumferentially spaced apart plug welds which secure the annular shell skirt directly to the base plate.