The evaluation of corrosion processes for engineered barrier systems

The U.S. Nuclear Regulatory Commission (NRC) established a corrosion program to evaluate the predicted performance of the U.S. Department of Energy’s proposed engineered barrier system for the potential high-level waste geologic repository at Yucca Mountain, Nevada. The risk-informed, performance-based regulation established by the NRC for the potential licensing of the proposed repository is introduced in this article with a discussion of resolution methods for various technical issues. These resolution methods include probability or consequence screening, deterministic confirmatory research investigations, and the use of the Total-System Performance Assessment Code to determine the risk significance of specific materials degradation processes on the total system performance. An example of the deterministic analysis method is the evaluation of the susceptibility of mill-annealed and gas-tungsten-arc welded alloy 22 to lead-assisted stress corrosion cracking in deaerated PbCl2 and Pb(NO3)2 solutions at 95°C. Also in this article is an evaluation of the risk significance of high-temperature deliquescence-induced localized corrosion of the alloy 22 waste package outer barrier on the total system performance.