Neutronic and thermal-hydraulic fuel design for a dual-salt breed-and-burn molten salt reactor

Highlights: • Breed-and-burn concept proposed with fuel tubes and separate fuel and coolant salts. • Fuel designs with natural, 5%, and 20% enriched uranium feed fuel were evaluated. • Neutronic feasibility of fuel designs was assessed using neutron balance method. • Limiting power densities were determined using thermal-hydraulic design algorithm. A breed-and-burn molten salt reactor (BBMSR) concept is proposed to achieve high uranium utilisation in a once-through fuel cycle. By using separate fuel and coolant molten salts, the BBMSR may overcome key materials limitations of traditional breed-and-burn (B&B) and molten salt reactor designs. A central challenge in design of the BBMSR fuel is balancing the neutronic requirements for B&B operation with thermal-hydraulic requirements for safe and economically competitive reactor operation. Fuel configurations that satisfy both neutronic and thermal-hydraulic objectives were identified for 5% enriched and 20% enriched uranium feed fuel. A neutron balance method and thermal-hydraulic design algorithm were used to evaluate uranium utilisation and maximum allowable power density, respectively, for a range of configurations. B&B operation is achievable in the 5% enriched version with orders of magnitude greater uranium utilisation compared to light water reactors, but with moderately lower power density. Using 20% enriched feed fuel relaxes neutronic constraints so a wider range of fuel configurations can be considered, but there is a strong inverse correlation between power density and uranium utilisation. The fuel design study indicates the flexibility of the BBMSR concept to operate along a spectrum of modes ranging from high fuel utilisation at moderate power density using 5% enriched uranium feed fuel, to high power density and moderate utilisation using 20% uranium enrichment.