Nuclear Fuel Burnup Calculator

Burnup measures how much energy a reactor extracts from its fuel before that fuel is discharged, expressed in megawatt-days per metric ton of uranium (MWd/MTU). This calculator starts from your target burnup and assembly mass (converted to metric tons of uranium) to get energy per assembly, then multiplies by the number of assemblies for total core energy. Dividing that total by the reactor's thermal power gives an estimated cycle length in days — the interval between refuelings. From there it layers on several simplified physics estimates: U-235 consumption assumes roughly 1 gram of U-235 fissions per MWd of energy released, letting the calculator back into a residual enrichment figure by subtracting consumed U-235 as a percentage of the original loading. Plutonium buildup uses a rough industry rule of thumb of about 10 kg of Pu produced per GWd of total core thermal energy for a typical light-water reactor — this figure is applied directly to the thermal energy total computed above, before the electrical conversion step, so it is not scaled by plant efficiency.

Electricity generated assumes a flat 33% thermal-to-electric efficiency, a reasonable but not plant-specific figure, and initial decay heat at shutdown is approximated as 6% of thermal power, a standard first-order estimate for freshly discharged fuel. Homes powered per year uses a fixed 10.5 MWh average annual US household consumption. None of this replaces core-physics modeling: real burnup, enrichment depletion, and plutonium buildup depend on burnable poisons, moderator temperature, spectral history, and fuel management strategy that this calculator doesn't model. Treat the outputs as order-of-magnitude planning estimates for a generic PWR, not as licensing-basis or safety-analysis numbers.