Thermal Design of an Alternative Boiling Water Reactor Spent Nuclear Fuel Package for Yucca Mountain Repository

Thermal analysis of an alternative boiling water reactor (BWR) waste package design for permanent disposal in the Yucca Mountain Repository is reported in this paper. The new design implements an increase in the holding capacity of the BWR waste packages from 44 to 52 assemblies and a modified arrangement sequence of waste packages in the emplacement drift. The design is favorable from the perspective of a generally drier emplacement drift due to an increase in heat load in the waste packages and the resulting higher temperatures. The analysis addresses heat transfer issues inside the waste package and those pertinent to satisfying the safe thermal limits for the waste package components. Key parameters in the analysis are the spent nuclear fuel assembly effective conductivities, the number of aluminum shunts, and the gap backfill with pressurized helium inside the waste packages. The feasibility of the proposed design is demonstrated by the internal waste package thermal model and the thermal-hydrologic environment in the emplacement drift. The conformity of the alternative thermal design to safe temperatures, in spite of the additional heat load, led to another innovative design with radial arrangement of assemblies in the waste packages that would further support the sustenance of drier emplacement drifts. These radial configurations are also discussed in this paper.