Neutronics simulations of ²³⁷Np targets to support safety-basis and ²³⁸Pu production assessment efforts at the high flux isotope reactor

Fueled by two highly enriched uranium-bearing fuel elements surrounded by a large concentric ring of beryllium reflector, the High Flux Isotope Reactor (HFIR) provides one of the highest neutron fluxes in the world and is used to produce unique isotopes like ²³⁸Pu. The National Aeronautics and Space Administration use radioisotope thermoelectric generators powered by ²³⁸Pu for deep-space missions. As part of the US Department of Energy's task to reestablish the domestic production of ²³⁸Pu, a technology demonstration sub-project has been initiated to establish a new ²³⁸Pu supply chain. HFIR safety-basis neutronics calculations are being performed to ensure the target irradiations have no adverse impacts on reactor performance and to calculate data required as input to follow-on thermal-structural, thermal-hydraulic, radionuclide/dose, and production yield estimation analyses. ²³⁸Pu production assessments are being performed to estimate the amount of ²³⁸Pu that can be produced in HFIR's permanent beryllium reflector. It is estimated that a total of 0.96-1.12 kg ²³⁸Pu (∼1.28-1.49 kg PuO₂ at 85% ²³⁸Pu/Pu purity) could be produced per year in HFIR's permanent beryllium reflector irradiation facilities if they are all utilized.