Abstract:

Nuclear data covariances are important input data for quantificational assessment of nuclear facility design uncertainty and nuclear data adjustment (NDA), which give direct impact on estimated uncertainties and results of NDA. To test the rationality of the newly evaluated nuclear reaction cross sections covariance in smooth region for ²³⁵U which is generated based on the analysis of source of experiments uncertainties and linear least-square method, the data were tested with the NDA benchmark exercises recommended by the OECD/NEA WPEC/SG33. The input data of the NDA generated from JENDL-4.0 library were updated with the cross sections and covariances of ²³⁵U fission, capture and inelastic scattering reactions from ²³⁵U cov, and used in NDA calculation. The new results were compared with the original JENDL-4.0 ones. The test results show that the covariance data from ²³⁵U cov are unreasonable. Too large uncertainties around threshold energy of inelastic scattering reaction were found. The uncertainties of fission and capture cross sections in smooth region are too small to be supported by NDA results.

Key words: nuclear data covariance, nuclear data adjustment, linear least-square method, rationality test, analysis of source of experiment uncertainty

摘要：

核数据协方差是评估核装置设计不确定度和核数据调整的重要输入，直接影响设计不确定度量化评估和核数据调整的结果。为测试基于不确定度源项分析和线性最小二乘法评价的²³⁵U平滑区协方差数据的合理性，采用OECD/NEA WPEC/SG33提出的核数据调整基准例题和自主研发的核数据调整程序NDAC，开展了以JENDL-4.0库为基础的核数据调整测试，得到了应用了²³⁵U cov版²³⁵U数据的调整结果。测试结果显示，²³⁵U cov版²³⁵U数据的非弹性散射截面协方差不合理，阈能附近的不确定度过大；裂变和俘获截面的不确定度偏小。

关键词: 核数据协方差, 核数据调整, 线性最小二乘法, 合理性测试, 不确定度源项分析