Breeding Ratio
Ratio of fissile atoms produced to fissile atoms consumed in reactor core.
BR >1 indicates net gain, as in fast breeders converting U-238 to Pu-239 via (n,γ) then β-decay. LWRs have BR~0.6, wasting 80% uranium; breeders target 1.1-1.5. Conversion ratio is similar for thermal reactors.
Why it matters now
Breeding ratios >1 are key for fast spectrum SMRs closing fuel cycle, mitigating 2030 HALEU shortages for sustained data center expansion.