An application of stochastic modeling to pitting of Spent Nuclear Fuel canisters

Abstract

Chloride induced stress corrosion cracking (CISCC) is one of the main factors affecting the integrity of used nuclear fuel in dry storage canisters, especially at coastal sites. CISCC has complex interactions associated with environment, stress and materials properties. This paper is focused on the development of probability distribution functions for maximum pit depth based on experimental data created at Lawrence Livermore National Laboratory (LLNL) that have not been fully analyzed before. The LLNL report outlined the key variables of pit initiation, termination and growth rate that may lead to CISCC, with the final aim of prediction of canister life and optimization of the time interval inspection of the canisters. The key parameters characterizing the probability distributions of pits at each stage depend on environment, material susceptibility conditions, and residual stress intensity. A basic stochastic approach to estimate probability distributions based on the median and maximum pit depths observed in experimental data succeeds in reproducing the experimental results, and can be used to estimate the distribution of maximum depth at future times.