Implementation of an adaptive energy grid routine in NDEX for the processing of thermal neutron scattering cross sections

Abstract

Thermal neutron scattering laws tabulated in File 7 for various materials the ENDF/B database require processing to generate the cross section and distribution data needed for use in Monte Carlo reactor simulations. Typically, the total scattering cross section is calculated on a fixed energy grid and interpolated on this grid. Nevertheless, this method may result in the loss of physical features in the cross section related to the details of the thermal scattering law, especially the oscillatory behavior of solid hydride moderators (e.g., ZrH, YH2). An adaptive energy grid has been implemented in the NDEX nuclear data code, initialized from the tabulated β grid of the processed evaluation. Cross section libraries for Monte Carlo codes generated using this adaptive grid demonstrate greatly improved prediction of oscillations in solid metal hydride moderators when compared to the fixed grid method.