Sensitivity and uncertainty analysis for eigenvalue and few-group constants of reactor-physics calculations

Abstract

The effects of nuclear-data uncertainties on the predictions of the reactor-physics calculations are quantified in this paper. Uncertainty analysis has been applied to the TMI-1 assembly at both Hot Zero Power (HZP) and Hot Full Power (HFP) conditions, propagating the nuclear-data uncertainties to the eigenvalue and few-group constants. The statistical sampling method has been applied to the uncertainty analysis for lattice calculations of TMI-1 assembly. The 172-group WIMSD-4 formatted microscopic cross-section library and corresponding cross-section covariance matrices based on the ENDF/B-VII.1 have been generated and applied for the uncertainty analysis. From the numerical results of the uncertainty analysis, it can be observed that the relative uncertainties of the eigenvalue and two-group constants at HFP are a little larger than these at HZP. The vt and vp covariance matrices of 235U impact the uncertainty results notably. Both at HZP and HFP, the relative uncertainty of the eigenvalue is about (4.7±0.09)‰ (applying vp covariance of 235U) or (7.1±0.20)‰ (applying vt covariance of 235U); the relative uncertainties of two-group constants vary from about (2.9±0.06)‰ (for Σt,2) to (11.9±0.34)‰ (for Σs,1,2).