Evaluation of Codisposal Viability for Aluminum-Clad DOE-Owned Spent Fuel: Phase II Degraded Codisposal Waste Package Internal Criticality

This report presents the analysis and conclusions with respect to disposal criticality for canisters containing aluminum-based fuels from research reactors. The analysis has been divided into three phases. Phase I, dealt with breached and flooded waste packages containing relatively intact canisters and intact internal (basket) structures; Phase II, the subject of this report, covers the degradation of the spent nuclear fuel (SNF) and structures internal to the codisposal waste package including high level waste (HLW), canisters, and critically control material. Massachusetts Institute of Technology (MIT) Uranium aluminide (U-Al) fuel with 93.5% enriched uranium and Oak Ridge Research Reactor (ORR) uranium silicide (U-Si-Al) fuel with 20.56% enriched uranium were selected by the Alternative Technology Program of the Westinghouse Savannah River Company (SRS) as being representative of the high enriched uranium (HEU) and medium enriched uranium (MEU) fuel inventories, respectively. Phase III will consider the possibility of external criticality, which can arise from a flow of water carrying fissile material out of the waste package.