Evaluation For Cross-section And Covariance Of The Fast Neutron Induced Reaction Of ²³⁹Pu

As one of the six key nuclides in nuclear engineering applications,²³⁹Pu is widely utilized in fast breeder reactors and accelerator-driven subcritical systems.The accuracy of its sub-reaction cross-sections,particularly the fission cross-section,directly impacts the design,operation,charging and disposal of spent fuel from nuclear devices.In regards to the ²³⁹Pu fission section,when neutron energy ranges between 0.2～10 Me V,agreement among five major evaluation nuclear databases is crucial.However,there are differences between data above 10 Me V,and the maximum energy is also not the same.Additionally,CENDL3.2 database which updated in 2020 did not update the²³⁹Pu fission cross-section.This study evaluated experimental measurement data of ²³⁹Pu（n,f）in the fast neutron energy range and calculated their covariance.（1）The experimental measurement data of 79 ²³⁹Pu neutron fission cross sections and 42 ²³⁹Pu/²³⁵U neutron fission cross section ratios included in the International Atomic Energy Agency（IAEA）EXFOR experimental database were systematically collated and analyzed,as well as the measured ²³⁹Pu（n,f）cross-sectional data of China Spallation Neutron Source（CSNS）published by Lan Changlin’s Research group from the School of Nuclear Science and Technology of Lanzhou University in 2023.The experimental data were compiled and compared based on various factors,including measurement time,authorship,neutron energy range,energy points,measurement method,neutron source type,product activity measurement method,monitor reaction,sample size and uncertainty.（2）Analysis of Sources of Experimental Uncertainty was conducted on the experimental process and measurement data in the literature that can be downloaded in full,and the reliability of the cross-sectional data was evaluated.Some data with low reliability such as obvious errors and insufficient error analysis were discarded,and the parts with errors in the EXFOR compilation results were corrected.（3）The cross-section calculation data of the supervised reaction used in the 0.2-200 Me V energy range experiment after screening were corrected using the latest standard database data IAEA-STd17.The modified data were fitted using Orgin polynomial segmentation and SPCC fitting programs to obtain the ²³⁹Pu（n,f）excitation function curve in the 0.2-200 Me V energy range;（4）The ASEU2.0 program was utilized to compute the correlation covariance matrix of energy points for ²³⁹Pu（n,f）in the 0.2-200 Me V range.（5）TALYS and FUNF were used to calculate the reaction cross section of ²³⁹Pu（n,f）,which was then compared with evaluation data from the TENDL-2021 database.（6）A suggested value and covariance for fast neutron-induced ²³⁹Pu cross sections in the 0.2-200 Me V range are provided with a relative uncertainty of 1.12%.This work provides an evaluation of the ²³⁹Pu（n,f）cross section excitation function in the energy range of 0.2-200 Me V,along with covariance data.Additionally,it offers valuable information to supplement the ²³⁹Pu（n,f）cross-section covariance data for the Chinese Evaluation Nuclear Database（CENDL）.