TRANSPORT CRITICALITY ASSESSMENT METHODOLOGIES FOR THE RWMD SPENT FUEL DISPOSAL CANISTER TRANSPORT CONTAINER - Presentation

Over the past four decades or so, the UK has operated a number of reactor systems, including Magnox reactors, AGR and PWR. The UK’s Nuclear Decommissioning Authority is looking at several options for the disposal of spent fuel (SF) to a Generic Disposal Facility (GDF). One concept is based on the KBS-3 design by SKB. In this the SF would be packed into copper canisters, each containing an integral cast-iron insert. The canisters would be transported to a GDF in a transport container and at the GDF, the copper canister and SF would be unloaded and disposed of, with the transport container being re-used. The transport container, referred to as the “Disposal Canister Transport Container” (DCTC), is currently being designed. Under the IAEA Regulations there are several ways to ensure the nuclear criticality safety of a package. The purpose of this paper is to report initial findings on the transport criticality safety issues that may arise in the assessment of the DCTC concept. The following design variants have been examined: • Restricting the payload of the package. • Amending the package design to include neutron absorbing materials in the insert or flux traps in the package. • Incorporating multiple water barriers in the package. • Taking credit for fuel irradiation (“burn-up credit”) in the criticality assessment. • Hybrid approaches. The paper describes the work method and summarises the nuclear criticality safety issues, together with the arguments for and against each option.