Prediction of Waste Package Life for High-Level Radioactive Waste Disposal at Yucca Mountain

Abstract

The U.S. Department of Energy (DOE) has released a Viability Assessment (VA) of the proposed high-level waste (HLW) repository at Yucca Mountain (YM), Nevada. The proposed standard for the repository requires the evaluation of the predicted —over 10,000 yr— performance of the system. In the VA, it is argued that long waste package (WP) lifetimes are responsible for significant containment and delay in release of the HLW. This paper examines the DOE WP lifetime prediction by combining the VA parameters modeling the corrosion behavior of the WP materials with the repository performance assessment code developed by the U.S. Nuclear Regulatory Commission (NRC) and the Center for Nuclear Waste Regulatory Analyses (CNWRA). The objective of the analysis is to exercise and strengthen the NRC review capabilities in preparation for receipt of the DOE license application for the proposed HLW repository. The results indicate that during the first 10,000 yr, radionuclide release depends almost entirely on the fraction of initially defective waste packages (IDWP). Radionuclide release resulting from corrosion of the WPs occurs only beyond 10,000 yr. The long WP lifetimes (>10,000 yr), reported in the VA and in this study, primarily depend on corrosion rates developed from an expert elicitation consensus. Given the importance in the estimation of the onset of radionuclide release and the lifetime of the WP materials, it is suggested the need for a stronger technical basis to assess the fraction of IDWP and to support the low corrosion rates of the WP materials.