Uncertainty quantification of LWR-PROTEUS Phase II experiments using CASMO-5

Abstract

This paper presents an improved uncertainty quantification technique for the validation of CASMO-5 on the spent fuel reactivity worth experiments of the LWR-PROTEUS Phase II program. In the program, eleven spent fuel samples manufactured from rods irradiated in a Swiss PWR (discharge burnups of 20–120 MWd/kg) were measured in the PROTEUS research reactor. In this work, both irradiation and reactivity worth measurement steps were modeled with CASMO-5 and the uncertainty on the code prediction were calculated using SHARK-X. For the first time in this work, we propagated the nuclear data uncertainties coming from cross-sections and fission yields for all samples in both fuel irradiations and the reactivity worth experiment models. We found that the fission yield and cross section uncertainties have similar contributions to the uncertainty of the reactivity worth prediction and that the reactivity worth probability distribution is non-normal because of the non-normal distribution of the perturbed fission yield data produced by the GEF code. Propagating input uncertainties through fuel irradiation as well as considering fission yield uncertainty led to larger computational uncertainty than previously reported. However, the observed trends with respect to exposure, fuel type, and moderating conditions are similar. In particular, a linear regression analysis showed that the predictions of reactivity with exposure by CASMO-5 are very accurate for various moderating conditions and for very high burnup. Finally, we estimated the effects of the irradiation history specifications on the relative reactivity worth bias and its uncertainty using two independent irradiation histories. While the bias uncertainty coming from uncertain cross sections was similar when considering either irradiation histories, we observed differences in the bias value. The irradiation history specification is a significant source of modeling bias and should be further investigated.