On the reactor physics implications of the use of UB2 as an additive within UN

The addition of UB₂ to UN fuel raises the onset temperature of its reaction with high-temperature steam. Natural boron contains 19.9% B-10, a strong neutron absorber that decays to Li-7 and He-4 upon neutron capture. This study explores the reactor physics implications of UN-UB₂ (10% UB₂) fuel with varying B-10 concentrations. Depletion analysis of an infinite lattice has shown that UN-UB₂ with 0–2% B-10 maintained cycle lengths similar to UN at equivalent U-235 enrichment and exhibited reduced reactivity swings. At 1500 effective full power days (EFPD), noble gas production in UN-UB₂ (1% B-10) was comparable to UO₂, with helium levels similar to krypton. The fuel temperature coefficient (FTC) was consistently negative across all materials, depletion levels, and temperatures. These results indicate that UN-UB₂ (1% B-10) offers comparable performance to UO₂ with benefits in enrichment, thermal conductivity, manageable helium generation, and effective reactivity control for LWRs. • Investigation of B-10 influence on cycle length and fuel composition in UN-UB2 fuels. • Quantification of tolerable B-10 content in UN-UB2 fuels without impacting cycle length. • Comparable cycle length observed for UN-UB2 (1% B-10) compared to UN fuels with the same U-235 enrichment. • Comparable amounts of noble gases for UN-UB2 (1% B-10) and UO2 fuels at 1500 EFPD. • Comparable fuel temperature coefficients for UO2, UN and UN-UB2 fuels over 0–60 MWd/kgU burnup range.