Abstract
To understand how compensation errors occur in a nuclear data adjustment mostly devoted to U-Pu fuelled fast critical experiments and with only limited information on U-235 data, a stress test on 235 U(n,f) was suggested, using critical benchmarks sensitive to 235 U(n,f) in 1∼ 10 keV region. The adjustment benchmark exercise with 20 integral data suggested by the NEA WPEC/SG33 was used as the reference, where practically only one experiment did give information on U-235 data. The keff of HCI4.1 and HCI6.2 experimental benchmarks were used as the 21st and 22nd integral data separately to perform stress tests. The adjusted integral values and cross sections based on 20, 21 and 22 integral data using the same nuclear data and covariance data sets were compared. The results confirm that compensation errors can be created by missing essential constraints.
Highlights
According to the study of the NEA WPEC (Working Party on International Nuclear Data Evaluation Cooperation) /SG26 [1], a strategy of combined use of integral and differential measurements should be pursued to meet the accuracy requirements of nuclear data for Gen-IV innovative systems
It was noticed that some adjusted integral results after adjustment get worse, which was suspected to be caused by compensations in the adjustments. To prove this hypothesis and to understand how compensation errors occur in a nuclear data adjustment mostly devoted to U-Pu fuelled fast critical experiments and with only limited information on U-235 data, a stress test on 235U(n,f) cross section was suggested
If we look into the sensitivity coefficients of these integral parameters to 235U(n,f) cross section, as shown in Fig. 2 and Fig. 3, we can notice that the calculated spectra index ZPPR-9 F28/F25, which has larger bias before adjustment than the former three indices in Fig. 1, have strong sensitivity to 235U(n,f) cross section in several keV region
Summary
According to the study of the NEA WPEC (Working Party on International Nuclear Data Evaluation Cooperation) /SG26 [1], a strategy of combined use of integral and differential measurements should be pursued to meet the accuracy requirements of nuclear data for Gen-IV innovative systems. It was noticed that some adjusted integral results after adjustment get worse, which was suspected to be caused by compensations in the adjustments To prove this hypothesis and to understand how compensation errors occur in a nuclear data adjustment mostly devoted to U-Pu fuelled fast critical experiments and with only limited information on U-235 data, a stress test on 235U(n,f) cross section was suggested. In this test, two additional benchmarks with inter-mediate energy spectrum were added to extend the benchmark exercises of SG33 and to study the influence of changing constraint conditions in the adjustment
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