Work out nuclear fuel burnup instantly with clear inputs, formula shown and shareable results.
Burnup measures energy extracted per unit of fuel, in megawatt-days per tonne of heavy metal. Modern light water reactor fuel reaches 45,000-55,000 MWd/tHM at 4-5% enrichment. Roughly 9500 MWd/tHM corresponds to 1% of the heavy metal atoms having fissioned.
Burnup
Burnup (MWd/tHM) = thermal energy (MWd) / heavy metal mass (t)
Electrical output
Electrical energy = thermal energy x plant thermal efficiency
Nuclear fuel management, burnup limits and criticality safety are governed by the reactor licence and regulatory authority. This is an educational estimate only.
More fissile material must be loaded initially to sustain criticality as fissile atoms are consumed and neutron-absorbing fission products build up. Each extra 10,000 MWd/tHM needs roughly one percentage point of enrichment.
Cladding corrosion and hydrogen pickup, fission gas pressure inside the rod, and fuel pellet swelling. Licensing limits are set on the fuel rod's mechanical integrity.