PRISM reference fuel design

Highlights: • PRISM uses metallic fuel for its reference cores (471–840 MWth). • Metallic fuel is compatible with sodium whereas oxide chemically reacts with sodium. • Incorporating actinides in a metallic alloy is easier than into an oxide matrix. • Metallic fuel's high thermal conductivity enhances the inherent safety of the core. - Abstract: The basis for GE-Hitachi Nuclear Energy America's, LLC (GEH's) decision to select metallic fuel as the reference core for its sodium-cooled fast reactors (SFRs), such as PRISM (Power Reactor Inherently Safe Module), is based on the fuel's physical properties, manufacturability, and accident response. The ideal fuel for a fast reactor has high thermal conductivity, a high melting temperature, chemical compatibility with the coolant, dimensional stability during irradiation, high fissile atom density, and few moderating atoms. Though each material has unique benefits, metallic fuel was chosen because 1) its high heat transport capability throughout its irradiation life, while still maintaining similar margin to melt as oxide fuel, 2) it is completely compatible with the coolant, making run beyond cladding breach a feasible operational strategy, and 3) it avoids the potential for core-wide boiling by providing a lower accident condition fuel centerline temperature and low Doppler reactivity feedback in stabilization of the core power during transient events. Metallic fuel is judged to have a more robust implementation for multiple SFR missions due to the relatively limited impact on overall thermo-mechanical properties with varying isotopic content, and therefore aligns PRISM better with the GEN-IV and PRISM's original design goals of economic power generation, transuranic recycle and plutonium disposition, which in turn makes the commercialization of an advanced SFR possible in the near-term.