Thermal-Hydrologic Model Study for an Alternative Waste Package Design for Yucca Mountain Repository

The long-term thermal, hydrologic, and psychrometric storage environment of nuclear waste is analyzed within an emplacement drift at Yucca Mountain Repository in Nevada. Pertinent issues regarding temperature, relative humidity, and liquid water in contact with the waste packages are studied for a modified design currently considered by the U.S. Department of Energy (DOE). For cost reduction and improved repository performance, the proposed design implements a slight modification in the waste package emplacement sequence and thermal load. The main change is an increase from 44 boiling water reactor (BWR) to 52 BWR fuel assemblies to reduce the number of waste packages for the same storage capacity. The results of the analysis show that acceptable temperature, moderate relative humidity, and no liquid water are expected on the hot waste package including the new BWR containers of the proposed design for the 5000-yr study period. The cold DOE high-level waste and the colder defense spent nuclear fuel containers in the alternative design will experience about the same amount of condensates as those in the DOE baseline design.