Generic Sodium-Potassium-Cooled Thermal Microreactor Reference Design with Sizing-Burnup Tradeoff Study

Abstract

Thermal liquid metal designs can afford low uranium loading, and hence compact core sizing which are desirable qualities for microreactor concepts. In particular, the utilization of thermal sodium - potassium cooled designs capitalize on these qualities through metal hydrides and refractory metal reflectors, enabling a more efficient neutron economy. These features are being investigated and advanced through national laboratory projects, for which commercialization of such designs are being pursued. Thus, there is interest in understanding economic tradeoffs for design choices, such as fuel enrichment, core sizing, etc., and to provide a comparison across other microreactor concepts. However, there is little public domain work on cost tradeoff for such systems and limited publicly available reference designs from which to study. For this reason, a reference configuration is built from a previous Systems for Nuclear Auxiliary Power (SNAP) 8 Experimental Reactor benchmark model to utilize 19.75% HALEU fuel in the form Uranium Zirconium Hydride. A critical mass of 135 kg uranium loading was determined for the reference design. The thermal spectra and power distributions are consistent with HALEU adoption into benchmark model. Burnup studies with varied fuel loading via core heights and fixed power density showed maximal discharge burnup of 25 MWd/kgU with 650 kg of uranium loaded, higher than other fast and thermal systems sodium-potassium cooled concepts for slightly lower lifetimes. Future work will investigate tradeoffs of reactor features as they pertain to cost, of which minimizing HALEU loading while maintaining a compact core and economic viability is of primary interest.