Phonon parameters fitting for the simulated Thermal-Neutron scattering cross section of H in ZrHx using Unified Monte Carlo method

•A general methodology was proposed to produce such a covariance matrix-associated to the semi-empirical phonon model for H in ZrHx.•Thermal neutron cross sections of H in ZrHx adjustment is accomplished by fitting the computer-simulated scattering data against experimental data using the Unified Monte Carlo (UMC) method.•After fitting definitive improvements occurred in two criticality benchmarks' eigenvalue for TRIGA reactor, preferably with smaller benchmark uncertainty. Thermal-motion behavior of the neutron is characterized by the neutron thermal-scattering cross sections. The thermal-scattering cross sections depend on the Thermal Scattering Laws (TSL) tabulated in terms of S(α,β), which is usually generated by the LEAPR module of NJOY code, using corresponding Phonon Density Of States (PDOS). The ZrHx is a good moderator because of its large fraction of H, hence it is widely used in the nuclear technology. However, the S(α,β) uncertainties of H in ZrHx has not been reported yet. Therefore, a general methodology is proposed in this paper to produce such a covariance matrix-associated to a semi-empirical phonon model. This is accomplished by fitting the computer-simulated scattering data against experimental data using the Unified Monte Carlo (UMC) method. Two TRIGA reactor benchmarks have been analyzed for keff uncertainty from TSL of H in ZrHx. It can be observed that after fitting, the keff error decreased with smaller uncertainty.