Spent fuel and waste

Used LWR fuel is about 95.6% uranium, 2.9% stable fission products, 0.9% plutonium, 0.3% caesium and strontium, 0.1% iodine and technetium, 0.1% other long-lived fission products and 0.1% minor actinides.

Nuclear fission occurs when a uranium-235 nucleus absorbs a neutron and splits into two lighter fragments, releasing about 200 MeV of energy and, on average, 2.45 further neutrons that can sustain a chain reaction.

About one-third of the fuel is replaced at each refuelling every 12 to 18 months (some plants run 24-month cycles), so an assembly spends roughly three years (18-36 months of cycles) in the core.

Fuel burn-up - the energy extracted per tonne of uranium - has risen from about 40 GWd/tU to over 60 GWd/tU for the best fuel; about 50 GWd/t is typical in the USA.

A 1,000 MWe reactor discharges about 27.6 t of used fuel a year (containing about 280 kg of transuranics, mainly plutonium) when fuelled at 4.5% enrichment, or about 19.1 t at 5%.

About 430,000 t of spent fuel has been discharged worldwide, around 30% of it reprocessed, and about 263,000 t is in storage (IAEA figures as quoted by WNA).

High-level waste accounts for just 3% of the volume but 95% of the total radioactivity of all radioactive waste produced.

US commercial reactors have generated about 90,000 metric tons of spent fuel since the 1950s - enough, if stacked together, to fit on a single football field at a depth of less than 10 yards - and add about 2,000 metric tons a year; it is stored at more than 70 sites in 35 states.

All US commercial spent fuel ever produced (about 90,000 t) would fit on a single football field to a depth of less than 10 yards, according to the US Department of Energy.

More than 90% of the potential energy in nuclear fuel remains after five years of use in a reactor; the US does not recycle spent fuel while France does.

After 40-50 years of storage the heat and radioactivity of high-level waste have fallen by over 99%, which is the technical reason for delaying final disposal for several decades.

Reprocessing used fuel and removing the plutonium and uranium leaves high-level waste that decays to the radioactivity level of the original uranium ore within about 9,000 years, compared with about 300,000 years for unreprocessed used fuel.

Used fuel is first cooled in water pools for at least five years and then can be moved to dry casks holding about 40 assemblies each with up to about 45 kW of decay heat.

More than 25,000 shipments of used nuclear fuel have been made since 1971 without any release of radioactivity.

Finland's Onkalo repository at Olkiluoto will be the world's first industrial-scale final disposal facility for spent fuel: on 10 August 2026 regulator STUK concluded there is no obstacle to granting Posiva an operating licence, a government decision proposal was expected in autumn 2026, Posiva's goal is operational readiness for the start of disposal by the end of 2026, and it seeks a licence through 2070.

Sweden's Government approved SKB's spent fuel repository at Forsmark and encapsulation plant at Oskarshamn on 27 January 2022; the Land and Environment Court granted permission in October 2024, ground was broken on 15 January 2025, and construction will take about ten years before disposal of some 12,000 t of fuel in about 6,000 copper canisters at about 500 m depth can begin in the 2030s.

France's Cigeo deep repository near Bure (Meuse/Haute-Marne clay, about 500 m deep) is to hold about 83,000 m3 of waste (about 10,000 m3 high-level and 73,000 m3 long-lived intermediate-level); Andra applied for the construction licence in January 2023, ASNR issued a favourable opinion announced on 4 December 2025, a public inquiry is scheduled for the second half of 2026, the authorisation decree is expected in late 2027/early 2028 and first waste packages are planned for 2050.

Switzerland's Nagra submitted the general licence applications for a deep geological repository at Nördlich Lägern (surface facility in Stadel, Canton Zurich) and an encapsulation plant at Würenlingen to the Swiss Federal Office of Energy on 19 November 2024; the cantons plan to submit their statements in autumn 2027.

The US Yucca Mountain repository licence application was filed in June 2008 but the project has been suspended.

Two consolidated interim storage facilities were licensed by the NRC - Interim Storage Partners in Texas (September 2021) and Holtec's HI-STORE in New Mexico (May 2023, 8,680 tU); Holtec cancelled HI-STORE in 2025 and the US Supreme Court ruled on the Texas licence in June 2025.

Commercial reprocessing capacity is about 1,700 t/yr at La Hague (France), 800 t/yr design capacity at Rokkasho (Japan) and 400 t/yr at Mayak RT-1 (Russia); about 30% of all used fuel has been reprocessed and MOX fabrication capacity is about 480 t/yr.

Fast neutron reactors can burn the long-lived actinides recovered from used fuel, and reactors designed to produce more plutonium than they consume are fast breeder reactors.

Fast neutron reactors have no moderator and use a liquid-metal coolant (normally sodium) at around 500-550 C and near-atmospheric pressure; they can breed plutonium from U-238 or burn long-lived actinides, extracting about 60 times more energy from uranium than a conventional reactor.

Iodine-131 has a half-life of 8.0252 days.

Strontium-90 has a half-life of 28.91 years.

Caesium-137 has a half-life of 30.08 years.

Plutonium-239 has a half-life of 24,110 years.

Uranium-235 has a half-life of 7.04 x 10^8 years (704 million years).

Uranium-238 has a half-life of 4.468 x 10^9 years (about 4.47 billion years, roughly the age of the Earth).