Evaluation of thermal scattering law and cross sections for liquid hydrogen fluoride

• Novel molecular dynamics model of hydrogen fluoride , benchmarked against experimental data for bond length, density, potential energy, dipole moment , and diffusion coefficients . • High fidelity thermal scattering law (TSL)files were evaluated for hydrogen fluoride for use in nuclear criticality applications. • Generated TSL libraries have been accepted in the ENDF/B-VIII.1 nuclear data library and show marked improvement in reactor criticality benchmarks. Liquid anhydrous hydrogen fluoride (HF) is a material commonly used in fuel manufacturing and processing, and as a result it is of particular interest for criticality safety applications. In order to capture the thermal scattering impacts from this hydrogenous material, accurate thermal scattering law (TSL, i.e. S(α,β)) libraries were developed. Using classical molecular dynamics (MD) simulation of the liquid HF system, a parametrized three-site model was developed in the GROMACS MD code to accurately represent the hydrogen bond and capture the liquid’s interatomic structure. This computational model (referenced as the NCSU HF model) was constructed with a massless charge to capture the hydrogen bonds between molecules. The accuracy of the NCSU HF model was verified by comparing its predictions of various HF properties with experimental data for the hydrogen and fluorine bond length, density, potential energy, dipole moment , and diffusion coefficient. From this model, the primary inputs of the phonon density of states (DOS) and liquid diffusion properties were derived for use in the Full Law Analysis Scattering System Hub ( FLASSH ) to evaluate the TSL for both H(HF) and F(HF). These TSL libraries were benchmarked using the ICSBEP HEU-SOL-THERM-039 critical assembly benchmark, showing notable improvement on the order of 1170 pcm. The libraries generated in this work have been accepted in the ENDF/B-VIII.1 nuclear data release.