Uncertainty and importance assessment using differential analysis: an illustration of corrosion depth of spent nuclear fuel canister

Uncertainty of NRC proposed performance assessment for the corrosion depth of storage canister of nuclear spent fuel in time history is preformed using the differential analysis. The method is demonstrated to evaluate uncertainty propagation of a system with incomplete and insufficient data in the preliminary phase of assessment. The result shows that mean corrosion depth presents a non-linear regression while variance demonstrates a first-order linear increase through 1,000-year time history. By incorporating correlation into pitting factor, uniform corrosion factor, oxygen concentration and chlorine concentration, it is found that the covariance of pitting factor and chlorine concentration has the most significant contribution in the variance of total loss. Incorporating assumed covariance into the system, the analytical form of uncertainty and importance for the corrosion depth evaluation can be well demonstrated from the input parameters.