Estimating the Frequencies of Drop Events During the Preclosure Emplacement Period at Yucca Mountain, Nevada

This research estimates the likelihood of the number of occurrences of three internal events involving crane transfers during the potential 50-year preclosure operational period of Yucca Mountain (YM): (a) drop of a bare-fuel assembly, (b) drop of a transport, aging, and disposal canister, and (c) drop of a dual-purpose canister. The analysis employs a model developed by the authors for predicting the packaging and thermal characteristics of waste streams arriving at YM and is related to a study on throughput for the surface facilities that was also conducted by the authors using the model. The model generates waste streams for commercial spent nuclear fuel as a function of repository design parameters and operating strategies.

Waste streams arriving at the repository are assumed to be routed for processing in the surface facilities based on the thermal properties of the packages. This allows for estimation of the number of material crane transfers associated with each waste stream. The number of drops over the preclosure period is described as a binomial distribution, where each crane transfer is treated as an identical, independent trial with an outcome of drop or no drop.

Results indicate that the drop events are not expected to occur one or more times during the preclosure operational period. This paper demonstrates an approach for estimating the likely distributions for frequencies of drop events, accounting for uncertainty in waste stream quantities in addition to changing assumptions about the crane drop rate. While it is recognized that results of this analysis are specific to YM surface facility design, the approach can be adapted for similar systems designed for centralized interim storage.