EXFOR-based simultaneous evaluation of neutron-induced uranium and plutonium fission cross sections for JENDL-5

The neutron-induced fission cross sections were simultaneously evaluated for the JENDL-5 library for ^233,235U and ^239,241Pu from 10 keV to 200 MeV and for ²³⁸U and ²⁴⁰Pu from 100 keV to 200 MeV. Evaluation was performed by least-squares fitting of Schmittroth’s roof function to the logarithms of the experimental cross sections and cross section ratios in the EXFOR library. A simultaneous evaluation code SOK was used with its extension to data in arbitrary unit. The outputs of the code were adopted as the evaluated cross sections without any further corrections. The newly obtained evaluated cross sections were compared with the evaluated cross sections in the JENDL-4.0 library and the IAEA Neutron Data Standards 2017. The evaluated cross sections were also validated against the californium-252 spontaneous fission neutron spectrum averaged cross sections, ΣΣ (coupled thermal/fast uranium and boron carbide spherical assembly) neutron spectrum averaged cross sections, and small-sized LANL fast system criticalities. The changes in the obtained evaluated cross sections from those in the JENDL-4.0 library are within 4% (²⁴¹Pu), 3% (²³³U, ²⁴⁰Pu), or 2% (²³⁵U, ²³⁹Pu). The newly evaluated ²³⁵U, ²³⁸U and ²³⁹Pu cross sections agree with the IAEA Neutron Data Standards 2017 within 2% with some exceptions.