Enhancement Concept Reactor Physics Studies to Support HFIR Upgrade Planning Activities

At the request of the US Department of Energy (DOE) Office of Science, the scientific justification for a domestic high-performance reactor-based research facility was assessed to continue providing the scientific community with leading neutron capabilities in support of DOE's missions. The assessment determined that Oak Ridge National Laboratory's High Flux Isotope Reactor (HFIR) is critical to DOE's neutron science capabilities and recommended pursuing scientific enhancement enabling upgrades. The HFIR-Sustaining and Enhancing Neutron Science (SENSe) Initiative was established in response to this assessment. This paper focuses on a select set of enhancement concept reactor physics studies to support HFIR-SENSe upgrade planning activities. The variation of ²⁵²Cf production with reactor power and the impact of perturbing the water-to-metal split on irradiation experiment fluxes were assessed in the flux trap target region. High-fidelity depletion simulations were performed to compare safety and performance metrics at 85 MW and 100 MW operations and to evaluate a newly designed, potentially more fabrication-friendly sector-type fuel assembly. Permanent reflector material perturbations and vertical experiment facility fast neutron flux boosting targets were evaluated to better understand performance gains associated with various concepts. Finally, a horizontal beam tube enlargement study was performed to determine the impact on scattering beamline fluxes. The results of these studies indicate that pursuing scientific enhancement enabling upgrades will support continued world-leading neutron science capabilities at HFIR.