Modeling and simulation of a High Flux Isotope Reactor representative core model for updated performance and safety basis assessments

Abstract A high-fidelity neutronics model of the Oak Ridge National Laboratory High Flux Isotope Reactor (HFIR) with a representative core and experiment loading was developed to serve as the new basis for performance and safety basis assessments. HFIR provides one of the highest steady-state neutron fluxes of any research reactor in the world to support high-impact applied and basic neutron science research. The newly developed model better characterizes ongoing and envisioned research activities at HFIR, in comparison to the legacy Cycle 400 (operated in 2004) model. The new reactor model serves as the reference for safety basis, reactor operation, in-core experiment, reactor upgrade, and other research activities. It also serves as the reference for high-enriched uranium to low-enriched uranium conversion studies, enabling consistent performance and safety metrics comparisons. Neutronic performance and safety metrics calculational methods and results including, but not limited to, cycle length estimates, flux and fission distributions, point kinetics data, reactivity coefficients, intra cycle and post shutdown source terms, and control element worths are documented herein. These neutronics results provide essential input to higher accuracy follow-on heat deposition, thermal–hydraulic, thermal-structural, reactor transient, and severe accident analyses and directly support safety analysis upgrades, startup and operations calculations, and fuel storage and transportation evaluations. Furthermore, thermal–hydraulic safety limit calculations for inlet coolant temperature, flux-to-flow, and inlet vessel pressure that utilized the neutronics results obtained with the new reactor model are discussed herein. The use of the new neutronics results led to a significant gain in thermal safety margin and enabled the removal of previous conservatism based on low-fidelity calculations.