Investigating the effect of bedrock temperature on the design of a Brazilian deep geological repository for LEU and reprocessed fuel

Abstract

The final stage of the nuclear fuel cycle involves the design of a disposal repository for spent fuel or high-level waste from reprocessing operations. Focusing on the back-end fuel cycle, this study investigated the impact of bedrock temperature on the disposal of traditional low-enriched fuel and two reprocessed fuels, in a hypothetical design of a Brazilian Deep Geological Repository (DGR). The reprocessed fuels taken into consideration in this study were transuranic fuel spiked with thorium oxide and a plutonium/uranium fuel mix. For all fuels, interim storage had previously taken place for 50 years. The appropriate spacing between adjacent canister was determined, and the effect of increasing the bedrock temperature until the maximum allowed temperature at the canister surface were estimated using the ANSYS code. Results showed a linear relationship between the two temperatures. The transuranic fuel cannot be disposed of under assumed conditions, while the plutonium/uranium fuel requires larger disposal areas than traditional low-enriched fuel. We estimated the total area of disposal required for different amounts of spent fuel and identified six regions for further studies based on simulation results, mean bedrock temperature data, and population density, primarily in the southeastern part of Brazil.