A systematic approach to analyzing pre-closure operational performance of the proposed repository for high-level nuclear waste at Yucca Mountain, NV

Abstract

This research aimed to measure the operational impact of various strategies for utility loading behavior for commercial spent nuclear fuel (CSNF), as well as thermal design parameters involving waste transportation and emplacement of CSNF during the pre-closure period at Yucca Mountain, NV (YM). Specific objectives included: (1) generation of probable scenarios for waste stream quantities and thermal properties, (2) identification of performance trade-offs in surface facility design parameters and operating decisions, and (3) evaluation of safety and throughput implications of pre-closure strategies. These objectives were accomplished by modeling the pre-closure phase of YM operations as an integrated waste management system. Through application of this model, a better understanding was gained of how various waste management strategies influence facility design assumptions. Advantages and disadvantages of various operating strategies were identified in terms of safety considerations and throughput of surface facilities. This led to an opportunity for making recommendations that have potential to result in improved performance. Strategies that required fewer canisters to be aged and those that contained fewer dual-purpose canisters (DPCs) resulted in lower frequencies of dropped canisters and spent nuclear fuel assemblies. Results indicate that DOE estimates are within the likely range of frequencies for a drop event that is generated by this analysis. The consequences of these events are low enough that their frequency will not likely impact the ability to meet regulatory requirements. Still, DOE could strengthen its preliminary hazards analyses by adopting a probabilistic approach to estimating the drop frequency in evaluating pre-closure safety. This would help to communicate the risk posed by the drop events, and allow for an analysis that is less reliant on deterministic estimates of waste stream quantities and crane drop rates. Pending future agreements between waste generators and the Department of Energy, the capacity of the Wet Handling Facility may need to be increased in order to efficiently handle assemblies arriving in DPCs and bare-fuel transportation casks. Furthermore, because design goals for throughput have been defined in terms of surface buildings as opposed to functional needs, there is a redundancy in functional capability of the Canister Receipt and Closure Facility and the Receipt Facility which should be taken into account in order to design a more efficient system. An alternative design for throughput requirements, based on functional demands of the system, is proposed.