Probabilistic Analysis of Human Intrusion in a High Level Nuclear Waste Repository in Salt Using Draft EPA Assumptions

Abstract

AbstractThe Office of Nuclear Waste Isolation (ONWI) has planned performance assessments that will quantify various performance measures for the eventual licensing of a repository in salt. In addition to studying “expected” conditions, selected discrete event scenarios must be analyzed. This paper presents a probabilistic analysis of a human intrusion scenario in which boreholes may be drilled into the repository, contact nuclear waste, and release the radionuclides to the environment. A stochastic analysis using draft EPA limiting factors regarding probability of drilling and quantities of water flow is compared to the proposed EPA 10,000 year limits. The years in which boreholes penetrate the repository are probabilistically determined in each iteration of the analysis. For each borehole, the probability of contacting radioactivity is an increasing function of time. When a borehole does make contact with radioactivity, the curie release of a given nuclide is a function of solubility limits and current inventory. Prediction intervals and complementary cumulative probability distribution functions are developed for the curie release as a fraction of the EPA limits. Radionuclide releases are small fractions of the EPA limits. This study shows that there is a high expectation that the EPA requirements would be met with a repository in salt.