Sensitivity analysis of a final repository model with quasi-discrete behaviour using quasi-random sampling and a metamodel approach in comparison to other variance-based techniques

Abstract

This paper contributes to the investigation of recent computationally efficient variance-based methods for sensitivity analysis and sampling schemes on the basis of a Performance Assessment (PA) model for a repository for Low- and Intermediate-Level Radioactive Waste (LILW) in an abandonned salt mine. The PA model takes account of typical characteristics of repository systems including a quasi-discrete nature.The results indicate best convergence of the State-Dependent-Parameter (SDP) metamodel method and the simple first-order sensitivity indices (SI1) calculation scheme (EASI) if combined with the LpTau low discrepancy sampling method. The SI1 indices obtained from the SDP and EASI methods are very similar. The Fourier Amplitude Sensitivity Test (EFAST) seems to have some convergence problems, likely due to the quasi-discrete behaviour of the PA model. Due to parameter interactions, none of the investigated methods, however, could directly determine all significant parameters. This is illustrated by means of a simplified way of factor fixing.