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Comments on the status of modern covariance data based on different fission and fusion reactor studies

Both the availability and the quality of covariance data improved over the last years and many recent cross-section evaluations, such as JENDL-4.0, ENDF/B-VII.1, JEFF-3.3, etc. include new covariance data compilations. | Comments on the status of modern covariance data based on different fission and fusion reactor studies EPJ Nuclear Sci. Technol. 4 46 2018 Nuclear Sciences I. Kodeli published by EDP Sciences 2018 amp Technologies https doi.org 10.1051 epjn 2018027 Available online at https www.epj-n.org REGULAR ARTICLE Comments on the status of modern covariance data based on different fission and fusion reactor studies Ivan Kodeli Jožef Stefan Institute Jamova 39 Ljubljana Slovenia Received 29 September 2017 Received in final form 6 February 2018 Accepted 14 May 2018 Abstract. Both the availability and the quality of covariance data improved over the last years and many recent cross-section evaluations such as JENDL-4.0 ENDF B-VII.1 JEFF-3.3 etc. include new covariance data compilations. However several gaps and inconsistencies still persist. Although most modern nuclear data evaluations are based on similar or even same sets of experimental data and the agreement in the results obtained using different cross-sections is reasonably good larger discrepancies were observed among the corresponding covariance data. This suggests that the differences in the covariance matrix evaluations reflect more the differences in the mathematical approaches used and possibly in the interpretations of the experimental data rather than the different nuclear experimental data used. Furthermore tuning and adjustments are often used in the process of nuclear data evaluations. In principle if adjustments or tunings are used in the evaluation of cross-section then the covariance matrices should reflect the cross-correlations introduced in this process. However the presently available cross-section covariance matrices include practically no cross-material correlation terms although some evidence indicate that tuning is present. Experience in using covariance matrices of different origin such as JEFF JENDL ENDF TENDL SCALE etc. in sensitivity and uncertainty analysis of vast list of cases ranging from fission