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

TL;DR

This paper presents a comprehensive evaluation of neutron-induced fission cross sections for uranium and plutonium isotopes in the JENDL-5 library, using experimental data and advanced fitting techniques to improve accuracy.

Contribution

The study introduces a simultaneous evaluation method using the SOK code with an extension for arbitrary units, providing updated cross sections that are consistent with experimental data and standards.

Findings

Evaluated cross sections differ by up to 4% from previous JENDL-4.0 values.

New cross sections agree within 2% with IAEA standards.

Validation confirms improved accuracy of the evaluated data.

Abstract

The neutron-induced fission cross sections were simultaneously evaluated for the JENDL-5 library for $^{233,235}$U and $^{239,241}$Pu from 10 keV to 200 MeV and for $^{238}$U and $^{240}$Pu 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, $\Sigma\Sigma$ (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% ($^{241}$Pu), 3% ($^{233}$U, $^{240}$Pu), or 2% ($^{235}$U, $^{239}$Pu). The newly evaluated $^{235}$U, $^{238}$U and $^{239}$Pu cross sections agree with the IAEA Neutron Data Standards 2017 within 2% with some exceptions.