基于贝叶斯更新方法的^(235) U热中子独立裂变产额协方差估计

Covariance Estimation of ^(235) U Thermal Neutron Independent Fission Yields Based on Bayesian Updating Method

基于贝叶斯更新方法,利用ENDF/B-VII.1数据库中^(235) U热中子累积裂变产额的不确定度及裂变系统的物理约束条件,对^(235) U热中子独立裂变产额协方差矩阵进行了估计与分析。结果表明,多数核素独立裂变产额的不确定度与更新前相比均减小约30%,在独立裂变产额较大的两峰处,独立裂变产额不确定度减小的幅度较大。根据更新后的独立裂变产额协方差矩阵,分析认为,多数核素的独立裂变产额间存在弱相关性,相关系数小于0.25,且多数为负相关。其中,由累积裂变产额不确定度引起的相关性多集中在各个独立裂变产额的质量链内,而由裂变系统的物理约束引起的相关性多集中于独立裂变产额较大的两峰处。

Based on Bayesian updating method,the covariance matrix of ^(235) U thermal neutron independent fission yields in ENDF/B-VII.1 database is estimated by using the uncertainty of the cumulative fission yields of ^(235) U and the physical constraints of the fission system.The results show that the uncertainty of the independent fission yield of most nuclides decrease by about 30%compared with that before update,and these decreases are significant in the fission product yields residing in the two-humped part of independent fission product mass yields distribution.Based on the updated independent fission yield covariance matrix,it is found that there is a weak correlation between the independent fission yields of most nuclides,the correlation coefficient is less than 0.25,and most of them are negative correlation.Among them,the correlation caused by the uncertainty of the cumulative fission yields is concentrated in the mass chain of each independent fission yield,while the correlation caused by the physical constraints of the fission system is focused on the two-humped part of the independent fission yields mass distribution.