Nuclear Fuel Cycle
From uranium mine to deep geological repository - every step of the journey that powers nuclear reactors.
Uranium Mining
Uranium ore is extracted from open-pit or underground mines, or leached from the ground using in-situ recovery.
How it works
Uranium is one of the most abundant metals on Earth - more common than silver or gold. The major producing countries are Kazakhstan (43% of world supply), Namibia, Canada, Australia, and Uzbekistan. Uranium ore typically contains just 0.1โ2% uranium by weight. Three methods are used: open-pit mining (for shallow deposits), underground mining (for deep deposits), and in-situ leach (ISL) mining - where a weak acid or alkaline solution is pumped into the ore body underground to dissolve uranium, which is then pumped to the surface. ISL is now the dominant method globally, accounting for about 60% of world production.
Key Facts
- ~60,000 tonnes of uranium produced per year globally
- Kazakhstan produces ~43% of world supply
- In-situ leach (ISL) is the dominant method
- Uranium is ~40x more abundant than silver
Waste: Uranium tailings - the sandy waste left after milling - are mildly radioactive and require long-term management.
Milling & Yellowcake
Crushed ore is processed into "yellowcake" - uranium oxide (UโOโ) - a concentrated uranium product ready for conversion.
How it works
At uranium mills, the ore is crushed and ground, then treated with sulfuric acid or alkaline carbonate solutions to dissolve the uranium. The uranium is then extracted and precipitated as uranium oxide concentrate - called "yellowcake" (UโOโ) due to its yellow colour. Yellowcake contains 70โ90% uranium and is the tradeable commodity on the uranium market, priced in US dollars per pound. It is only mildly radioactive and can be handled and shipped safely in steel drums. A typical 1 GWe nuclear reactor requires about 200 tonnes of yellowcake per year.
Key Facts
- Yellowcake = uranium oxide concentrate (UโOโ)
- Contains 70โ90% uranium by weight
- ~200 tonnes/year needed per 1 GWe reactor
- Uranium spot price: ~$80โ100/lb UโOโ (2024)
Waste: Mill tailings contain radium, thorium, and other decay products. Must be managed for thousands of years.
Conversion to UFโ
Yellowcake is chemically converted to uranium hexafluoride (UFโ) gas - the form required for enrichment.
How it works
Before enrichment, uranium must be converted from yellowcake (UโOโ) into uranium hexafluoride (UFโ) - a gas at moderate temperatures. This is done at conversion facilities (major ones in Canada, France, Russia, UK, and USA). UFโ is highly corrosive and must be handled in specialised equipment, but it is the only uranium compound that is gaseous under conditions suitable for enrichment. The conversion process involves fluorination - reacting uranium oxide with fluorine gas. UFโ is transported in large steel cylinders.
Key Facts
- UFโ is gaseous above 56ยฐC - ideal for enrichment
- Major conversion plants in Canada, France, Russia, UK, USA
- UFโ is highly corrosive to moisture
- Natural uranium contains 0.711% U-235
Waste: Depleted UFโ (DUFโ) cylinders - containing "depleted uranium" (mostly U-238) - are stored at conversion sites. The US has ~700,000 tonnes in storage.
Uranium Enrichment
The concentration of fissile U-235 is increased from 0.7% (natural) to 3โ5% (reactor grade) or 90%+ (weapons grade) using centrifuges.
How it works
Natural uranium contains only 0.711% of the fissile isotope U-235; the rest is mostly U-238. Most nuclear reactors require uranium enriched to 3โ5% U-235 to sustain a chain reaction. Weapons require 90%+ ("highly enriched uranium" or HEU). Enrichment is done almost exclusively using gas centrifuges - spinning UFโ gas at high speed so the slightly heavier U-238 migrates outward, concentrating U-235 in the centre. Thousands of centrifuges are cascaded to achieve the desired enrichment level. Major enrichment countries: Russia (Rosatom), France (Orano), Netherlands/Germany/UK (Urenco), USA (Centrus), China. Enrichment is the most proliferation-sensitive stage - the same technology enriches to reactor grade or weapons grade.
Key Facts
- Natural U-235: 0.711% โ Reactor grade: 3โ5% โ HEU: 90%+
- Gas centrifuges are 50x more efficient than gaseous diffusion
- Russia controls ~46% of global enrichment capacity
- Weapons-usable HEU requires further cascade passes
Waste: "Tails" (depleted uranium, mostly U-238) produced in large quantities - used in DU ammunition, shielding, or stored.
Fuel Fabrication
Enriched UFโ is converted to uranium dioxide (UOโ) powder, pressed into ceramic pellets, and assembled into fuel rods for reactor use.
How it works
Enriched UFโ is converted back to uranium dioxide (UOโ) powder and pressed into small ceramic pellets - about the size of a pencil eraser. Each pellet contains roughly 7โ8 grams of uranium and will generate as much energy as 480 litres of oil. The pellets are loaded into long zirconium alloy tubes (cladding), which are then assembled into fuel bundles or assemblies. A typical PWR fuel assembly contains 264 fuel rods, each about 4 metres long, bundled in a 17ร17 array. A reactor core contains 150โ200 such assemblies. Fuel fabrication is done at specialised plants (in France, Russia, USA, Japan, South Korea, Germany, and others) under strict safeguards.
Key Facts
- 1 UOโ pellet โ 480 litres of oil in energy content
- Zirconium cladding chosen for low neutron absorption
- PWR assembly: 264 rods, 17ร17 array, ~4m tall
- Fuel stays in reactor ~3โ4 years before being replaced
Waste: Fabrication generates uranium-contaminated scrap and liquid waste, which must be managed carefully.
In-Reactor Use
Fuel assemblies are loaded into the reactor, where controlled fission releases heat to generate steam and electricity for 3โ4 years.
How it works
Inside the reactor, the fissile U-235 (and some Pu-239, bred from U-238 during operation) undergoes fission when struck by neutrons - releasing enormous heat and two or three new neutrons, sustaining the chain reaction. This heat converts water to steam, which drives turbines to generate electricity. A 1 GWe reactor operates at ~33% thermal efficiency, meaning about 3 GW of heat produces 1 GW of electricity. Fuel assemblies remain in the reactor for 3โ4 years, after which they are replaced during refuelling outages (typically every 18โ24 months, replacing ~1/3 of the core). During this time, U-235 is consumed and hundreds of fission products and transuranic elements (including plutonium) are created within the fuel pellets.
Key Facts
- 1 kg of U-235 yields ~24 million kWh
- Fuel stays in reactor ~3โ4 years
- During use, ~1% of U-235 fissions per year
- Creates ~30 tonnes of spent fuel per GWe-year
Waste: Spent fuel is intensely radioactive and hot immediately after removal - must be cooled in water pools at the reactor site.
Spent Fuel Storage
Spent fuel is stored in water pools for 5โ10 years to cool, then may be moved to dry cask storage, reprocessed, or awaiting a permanent repository.
How it works
Spent nuclear fuel is highly radioactive and thermally hot when removed from the reactor. It is first stored underwater in spent fuel pools at the reactor site - the water provides cooling and radiation shielding. After 5โ10 years of cooling, the fuel can be transferred to dry cask storage: thick steel and concrete containers that passively cool the fuel by convection. Currently there are approximately 250,000 tonnes of spent nuclear fuel stored worldwide, with ~10,000 tonnes added each year. Two paths exist: reprocessing (extracting plutonium and unused uranium for reuse) or direct disposal (treating spent fuel itself as waste for a geological repository). No country has yet opened a permanent deep geological repository, though Finland's Onkalo repository is under construction.
Key Facts
- ~250,000 tonnes spent fuel in storage worldwide
- ~10,000 tonnes added globally per year
- Finland's Onkalo will be first geological repository
- Spent fuel remains hazardous for ~100,000 years
Waste: The most radioactive and politically contentious waste stream. High-level waste (HLW) requires deep geological disposal.
Reprocessing (Optional)
In countries like France and Russia, spent fuel is chemically reprocessed to extract unused uranium and plutonium for recycling as MOX fuel.
How it works
Reprocessing uses the PUREX process to chemically dissolve spent fuel and separate it into three streams: reusable uranium (~95% of mass), plutonium (~1%, usable in MOX fuel), and high-level liquid waste (~4%). France reprocesses all its spent fuel at La Hague, recovering enough plutonium to make MOX (mixed oxide) fuel that is used in 20 of its reactors. Russia, Japan, and the UK also reprocess. The USA stopped civilian reprocessing in 1977 (President Carter, proliferation concerns). Reprocessing reduces the volume of high-level waste, but remains controversial - it is expensive, produces intermediate-level liquid waste, and the plutonium it recovers creates proliferation concerns.
Key Facts
- France reprocesses ~100% of its spent fuel at La Hague
- PUREX process separates U, Pu, and waste
- MOX fuel uses recovered Pu mixed with depleted U
- USA halted civilian reprocessing in 1977
Waste: Produces high-level liquid waste (HLLW) vitrified into glass logs for long-term storage, plus intermediate and low-level waste streams.
Final Disposal
The ultimate goal: sealing high-level radioactive waste deep underground in stable geological formations for thousands of years.
How it works
High-level radioactive waste (HLW) - whether spent fuel directly or vitrified glass logs from reprocessing - must be isolated from the biosphere for between 10,000 and 100,000 years, far exceeding the lifespan of any human institution. The globally accepted solution is deep geological disposal: burial 300โ1,000 metres underground in stable rock formations (granite, clay, or salt). Finland is the world leader - its Onkalo repository near Eurajoki will begin accepting waste in the late 2020s and will be the world's first operating geological repository. Sweden's repository has been approved. Other countries (France, Canada, UK, USA) are at various stages of site selection. The challenge is not technical (the engineering is understood) but social and political: communities do not want nuclear waste nearby.
Key Facts
- Onkalo (Finland) = world's first geological repository
- HLW requires isolation for ~100,000 years
- Sweden's repository approved at Forsmark site
- US Yucca Mountain project was cancelled (2009)
Waste: Final destination for all nuclear waste. Once sealed, geological barriers (rock, clay, bentonite) provide passive safety without human maintenance.