Generation and analysis of independent fission yield covariances based on GEF model code

Abstract

The fission yield data provided by the evaluated nuclear data files do not contain covariance information, which is not conducive to uncertainty analysis. To generate covariance information, the model parameters of the code GEF which describes the fission process are sampled and the independent fission yield samples are calculated. The covariances of independent fission yields of 235U, 239Pu, and 241Pu thermal neutron-induced fissioning systems are generated individually based on the above samples. This method is verified by comparing the uncertainties of burnup-related responses based on fission yield samples calculated by GEF and based on fission yield samples generated with the covariances. The influence of correlations among fissioning systems is also quantified and the joint covariances among different fissioning systems calculated with GEF are demonstrated correct. In addition, the Bayesian Monte Carlo method is adopted to adjust the model parameters of GEF, and the numerical results prove the effectiveness of the adjustment.