Spent nuclear fuel
Fuel assemblies removed from a reactor after use, highly radioactive and thermally hot, containing uranium, plutonium, fission products and minor actinides.
Discharged light-water fuel at about 50 GWd/t is still roughly 93–94% uranium (around 0.8% U-235), 1% plutonium, 4–5% fission products and about 0.1% minor actinides such as neptunium, americium and curium. Fission products dominate radioactivity and heat for the first few centuries; actinides dominate long-term radiotoxicity, which falls to the level of the original uranium ore after roughly 100,000–300,000 years without recycling, or a few thousand years with actinide recycling.
Management steps:
- Wet storage in pools for 5–10 years to remove decay heat.
- Dry cask storage in steel and concrete containers, licensed for decades.
- Reprocessing (France at La Hague, Russia, Japan's Rokkasho under commissioning) separates uranium and plutonium for MOX fuel.
- Deep geological disposal: Finland's Onkalo repository, about 430 m deep in granite, is the world's first and began trial operation in 2024–2025; Sweden's Forsmark repository is under construction.
A 1 GWe light-water reactor discharges roughly 20–25 t of spent fuel per year. The world inventory is around 400,000 t heavy metal, of which about one-third has been reprocessed. The volume is small per unit of electricity, about 3 grams per MWh. Higher burnup lowers the mass discharged.
Related terms
All terms →- Burnup
The thermal energy extracted from nuclear fuel per unit mass of initial heavy metal, usually expressed in gigawatt-days per tonne (GWd/tHM).
- Nuclear fission
The splitting of a heavy atomic nucleus such as uranium-235 or plutonium-239 into lighter nuclei after absorbing a neutron, releasing about 200 MeV of energy and further neutrons.
- Pressurised water reactor (PWR)
The most common nuclear reactor type, in which water under high pressure cools the core without boiling and transfers heat to a separate steam circuit.
- Thorium fuel cycle
A nuclear fuel cycle that uses fertile thorium-232, which absorbs a neutron and decays to fissile uranium-233, as an alternative to uranium-plutonium fuel.
- Sievert (radiation dose)
The SI unit of effective dose, weighting absorbed radiation energy by radiation type and tissue sensitivity to estimate stochastic health risk; 1 Sv = 1 J/kg.