Generation of the Thermal Scattering Law of Uranium Dioxide with Ab Initio Lattice Dynamics to Capture Crystal Binding Effects on Neutron Interactions

Abstract

Scattering of thermal neutrons and Doppler broadening of epithermal neutron resonances in uranium and its compounds may be sensitive to crystal binding. The thermal scattering law (TSL) for uranium dioxide, which captures crystal binding effects, has been reevaluated for ENDF/B-VIII.0. Phonon spectra were generated using ab initio lattice dynamics for the paramagnetic phase and validated against experiment. Improved agreement with the Debye-Waller coefficient as a function of temperature is found relative to the spectrum used for the ENDF/B-VII.1 evaluation. The TSL was generated using the phonon expansion method within the NJOY nuclear data processing package and was found to be in reasonable agreement with inelastic neutron scattering measurements. The present evaluation predicts a reduction in the inelastic scattering cross section relative to ENDF/B-VII.1 and a total scattering cross section consistent with neutron transmission experiments.

Keywords:

• Uranium dioxide
• thermal scattering law
• phonons
• resonances
• ENDF/B-VIII.0

Acknowledgments

This work was supported by funding from the U.S. Department of Energy’s Nuclear Energy University Program, the Nuclear Criticality Safety Program, and the Naval Nuclear Propulsion Program. The submitted manuscript has been authored by contractors of the U.S. Government under contract No. DOE-89233018CNR000004.

Data Availability Statement

The data that support the findings of this work include ENDF evaluations, which are publicly available through the U.S. National Nuclear Data Center (NNDC) using the ENDF web-based retrieval tool: https://www.nndc.bnl.gov/exfor/endf00.jsp. The ENDF/B-VIII.0 TSL evaluation and input files may also be downloaded from the NNDC within the TSL sublibrary at https://www.nndc.bnl.gov/endf/b8.0/download.html.