Uncertainty propagation of prompt fission neutron spectrum for physics analysis of fast and thermal reactors

Abstract

This paper presents a strategy for processing the covariance matrix of the prompt fission neutron spectrum (PFNS) and propagating the PFNS uncertainties to the neutronic calculation of fast and thermal reactors. Due to their great significance to the accurate prediction of nuclear criticality, the sensitivity and uncertainty of core parameters for PFNS are analyzed in this study. The propagation of PFNS uncertainties from the evaluated nuclear data files (ENDF) to the core parameters is divided into two phases. In the first phase, the covariance data in the ENDF is transformed into the multi-group form, in which the “zero-sum” constraint is considered and a corresponding functional module is developed in the updated NECP-Atlas nuclear data processing code. In the second phase, the neutron transport code is coupled as a “black box” to propagate the uncertainties in the multi-group form to the core parameters. Sensitivity and uncertainty (S&U) analysis function is implemented in the NECP-UNICORN uncertainty quantification code. As for its application, S&U analysis for PFNS has been performed to the fast and thermal reactors. The numerical results indicate that the influence of PFNS uncertainties to the confidence interval of reactivity prediction and power distribution should be considered in the nuclear reactor analyses.