Nuclear Fuel Cycle and Uranium Enrichment

The nuclear fuel cycle is the sequence through which nuclear material passes, from uranium extraction and fuel preparation to reactor use and the management of spent fuel and radioactive waste. It may be operated as an open cycle, in which spent fuel is treated as waste, or as a closed cycle, in which usable uranium and plutonium are recovered for recycling. Enrichment and reprocessing are dual-use because they serve legitimate civilian purposes but can also produce or separate material relevant to nuclear weapons.

Stages of the nuclear fuel cycle

The cycle has a front end that prepares reactor fuel, a reactor stage that releases energy through fission, and a back end that manages irradiated fuel and waste.

• Uranium ore is mined and milled to produce a concentrated uranium product commonly called yellowcake.
• For enrichment, uranium concentrate is converted into a suitable chemical form, commonly uranium hexafluoride gas.
• Enrichment increases the proportion of uranium-235 relative to uranium-238; many light-water power reactors use low-enriched uranium.
• Enriched uranium is converted into fuel material and fabricated into pellets, rods and fuel assemblies.
• Inside a reactor, fission generates heat while the fuel accumulates fission products and newly formed transuranic elements, including plutonium.
• After removal from the reactor, spent fuel is initially stored under cooling and radiation shielding, commonly in water pools, and may later be moved to dry storage.
• In an open or once-through cycle, spent fuel is ultimately intended for disposal without recovery of usable fissile material.
• In a closed cycle, spent fuel is reprocessed to recover uranium and plutonium for possible reuse, while the remaining high-level waste is conditioned for storage and disposal.

Why enrichment is dual-use

Civilian enrichment and weapons-relevant enrichment rely on the same basic objective: increasing the concentration of the fissile isotope uranium-235. The proliferation concern arises from the level of enrichment, installed capacity, technical knowledge and the possibility of undeclared production or facility reconfiguration.

• Natural uranium contains only about 0.7 per cent uranium-235.
• Low-enriched uranium contains less than 20 per cent uranium-235 and is commonly associated with civilian uses, although reactor requirements vary.
• Uranium enriched to 20 per cent or more uranium-235 is classified as highly enriched uranium; sufficiently high enrichment can provide direct-use material for a nuclear explosive.
• Gas-centrifuge enrichment plants employ cascades of centrifuges and can, in principle, be rearranged or operated further to produce progressively higher enrichment.
• A state possessing enrichment technology may therefore acquire technical capability and infrastructure that shorten the path from peaceful fuel production to weapons-usable material.
• Control of enrichment capacity, material accountancy and verification of declared operations are consequently central proliferation concerns.

Why reprocessing is dual-use

Reprocessing chemically separates reusable uranium and plutonium from fission products and other constituents of spent fuel. It can support fuel recycling and waste-management strategies, but separation makes plutonium more accessible than when it remains embedded in intensely radioactive spent fuel.

• Plutonium is produced in reactors when uranium-238 absorbs neutrons and undergoes subsequent nuclear transformations.
• Recovered plutonium can be fabricated with uranium into mixed-oxide fuel or used in other reactor fuel-cycle strategies.
• Separated plutonium can also be used in nuclear explosives, making its production, separation, storage and transfer proliferation-sensitive.
• Reprocessing does not enrich uranium; its proliferation significance arises principally from separating plutonium and recovering uranium-bearing material.
• Civil reprocessing plants, associated hot cells and expertise may create a latent capability that could be diverted, misused or replicated in undeclared facilities.
• Spent-fuel reprocessing also creates streams of high-level radioactive waste that require conditioning, secure storage and eventual disposal.

International safeguards and proliferation control

The nuclear non-proliferation regime seeks to preserve peaceful nuclear cooperation while verifying that nuclear material and facilities are not diverted to nuclear weapons or other nuclear explosive devices.

• Article III of the Nuclear Non-Proliferation Treaty requires non-nuclear-weapon states party to the Treaty to accept International Atomic Energy Agency safeguards in accordance with the Treaty.
• Article IV recognises the inalienable right of parties to develop research, production and use of nuclear energy for peaceful purposes, subject to the Treaty's non-proliferation obligations.
• IAEA safeguards use measures such as nuclear-material accountancy, containment, surveillance and inspections to verify peaceful use.
• Additional Protocol arrangements can give the IAEA broader information and access relevant to detecting undeclared nuclear material and activities.
• Export-control conditions, physical protection and safeguards reduce diversion risks, but possession of sensitive technology may still provide knowledge, infrastructure and a shorter potential route to weapons capability.

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