The Development and Verification of the Thermal Scattering Cross Section Calculation Module ThermalXS in AXSP

Based on neutron thermal scattering theory, a neutron thermal scattering cross-section calculation module (ThermalXS) was developed independently in the advanced evaluated nuclear cross section processing program AXSP. Different types of neutron thermal scattering cross-sections were calculated using the thermal scattering law files of nuclides such as U, H, and Zr. To verify the reliability of the ThermalXS module for thermal neutron calculations, its results were compared with those obtained from the THERMR module of NJOY2016 program. Compared with the THERMR module, the ThermalXS module employs an adaptive incident energy grid technology, which ensures higher accuracy of thermal scattering cross-sections for metal hydrides. Additionally, it is capable of processing thermal scattering law data incorporating one-phonon corrections. In this study, the variations of the thermal scattering cross-sections of graphite across the ENDF/B-VII.1, ENDF/B-VIII.0, and ENDF/B-VIII.1 evaluated nuclear data libraries were systematically analyzed and validated against experimental values. The results show that the thermal scattering cross section of graphite in ENDF/B-VIII.1, modified using the one-phonon model, shows better agreement with experimental data compared to the graphite crystal model. The primary reason is the elimination of the incoherent approximation in the cross-section calculation. The calculated thermal scattering cross section of reactor graphite in ENDF/B-VIII.1 exhibits a trend of increasing with porosity, yet it remains significantly lower than the experimental data for graphite with porosity.