Methods for demonstrating moderator exclusion for nuclear criticality safety

A method for an approach that meets the double contingency principle to assure moderator exclusion to prevent nuclear criticality, the approach incorporating sufficient factors of safety to require two unlikely, independent, and concurrent changes in process conditions before a criticality accident is possible, the method comprising:

• incorporating in the approach to meet the double contingency principle an assumption that the transport cask allows moderator ingress;
• nullifying the effects of the assumption that the transport cask allows moderator ingress in the approach to achieve the double contingency principle, wherein by nullifying the effects of the assumption that the transport cask allows moderator ingress, usage of materials placed inside the canister to absorb moderated neutrons is reduced in comparison to the situation where moderator ingress into the canister is assumed, thereby reducing the cost of safe nuclear spent fuel transport:
• the steps of nullifying are accomplished by:
• designing a canister to achieve an application of the double contingency principle to assure moderator exclusion from the canister fuel region,
• providing procedures for fabricating and closing the canister with closure installation to achieve the double contingency principle approach, the closure installation having closure lid weld redundancy, and
• providing procedures for leakage testing of the canister system;
• and
• providing procedures for enclosing the fabricated canister within the transport cask;
• and
• providing procedures for verifying pre-shipment assembly operations to assure that a transport system is properly assembled to meet the as-designed transport configuration.