skip to contentsThe Nuclear Fuel Chain

The phrase "the nuclear fuel cycle" is commonly used to mean the processes that the fuel goes through, from the mined uranium ore to its waste products and reprocessing. The word 'cycle' implies that all or most of the fuel is recycled - which is not true - and avoids thinking about the details of what this 'cycle' requires, and its other products. This 'cycle' cannot occur without other activities, such as building power stations, nor without other consequences, such as creating massive dumps of radioactive ore and decommissioning those power stations.

A more realistic term is "the nuclear fuel chain". To get the true picture of what nuclear power means, we also need to include the other uses of products from the fuel chain - nuclear weapons - since they are intimately linked, both as the initial motivation for nuclear power stations and continuing proliferation. It is crucial to look at the bigger picture because other parts of the fuel chain have significant human and monetary costs. The nuclear industry likes to focus exclusively on the power generation stage and thus claim that nuclear power is 'clean' and "carbon free"; whereas in fact several of the stages in the fuel chain produce large quantities of radioactive waste and carbon dioxide. It's a dirty business.

Most people have some picture of what is involved in the fuel chain for electricity production by coal or gas. Coal is mined, sorted, then transported to a coal-fired power station; perhaps they can also picture a slag heap. Oil is extracted, piped or transported to a refinery, then transported to a gas-fired power station. But for nuclear power most people just have a picture of the power station, typically a clean white dome. The other parts of the nuclear fuel chain do not easily come to mind, but they are far more complex than for coal or gas, and involve several more stages. In the UK we sometimes see coal mines (working or defunct) but we never see uranium mines; enrichment and fuel fabrication plants are not noticeable as they look like other industrial plants; the Sellafield reprocessing plant is not near a large population centre or main rail line; and the nuclear power stations are mostly in remote coastal locations with little tourism and no nearby industry. Thus it is that, as yet, most people do not have any clear idea of what is involved in nuclear power. (Wind power is perhaps the opposite of this: the turbine is very visible, but that's pretty much all there is - the environmental costs are plain to see, not hidden.)

The nuclear fuel chain is far more complex than for coal, oil or renewable sources. So there is a diagram which shows the links between the main stages. These stages are described below. Some aspects are described in more detail in other sections of this website [see infopack topics list].

Uranium mine blank local girl blank feet of local

Uranium mining & Milling

Uranium is found in rocks in various parts of the world. The USA, Canada, S. Africa, Australia and France are among those countries with large enough amounts to make mining worthwhile. High grade ores contain up to 4% uranium but sources of this quality have largely been used up, and ores of 0.4% and lower are now being mined. Thus the cost of extraction has significantly increased, and there is a limited supply - perhaps 35 years at the present rates of use. So this energy source is not a sustainable one.

When the ore is mined, other radioactive and hazardous materials are brought to the surface besides uranium. During the mining and milling, Radon-222 (an alpha emitter, and one of the decay products of Uranium-238) escapes into the air. Uranium miners working underground face this daily hazard and are particularly susceptible to lung cancer (this fact was established by 1930). It is estimated that about 1 in 6 miners die from this cause. The pictures above show some of the effects on locals near a uranium mine in India.

Uranium mining is an often ignored part of the fuel chain, partly because it is unglamourous, partly because of its horrendous environmental and human costs, but mostly because it doesn't happen in the UK - it's somebody else's problem. Responsibility for the results of this mining should not be ignored, and cannot be dismissed, just because they do not immediately affect users of UK nuclear energy.

For example, the CO2 produced in uranium mining, the transport of ore, and milling, will be part of the carbon tax budget of the country where it is mined - not the country which uses the ore to produce energy. But whoever pays for this (if anyone), the CO2 goes into the atmosphere and affects us all.


The crude ore is transported to a mill (usually by trucks or diesel trains as mines tend to be in remote locations) where it is crushed to a fine sand. Chemical solvents are used to separate the uranium, producing 'yellowcake'. This contains 85% uranium and consists of oxides of various uranium isotopes: 99.3% U-238 and only 0.7% U-235.

The residual waste - about 100 times as much as the yellowcake produced - is called 'tailings', and contains radioactive radium (which decays to radon). Radium is a bone-seeking radionuclide even more dangerous than Strontium-90, and has a half-life of 1670 years. It was discovered in 1960 that radioactive tailings had been used in the foundations of many buildings (notably Grand Junction, Colorado), including homes, schools and hospitals, permanently exposing the occupants to radon gas.

In the USA alone there are estimated to be 90 million tonnes of tailings, much of it piled on river banks. So radioactive dust is blown about and also washed into waterways.

Another by-product is 3700 litres of liquid waste per tonne of ore, which is both chemically toxic and radioactive. Many of the solvents used in the fuel chain are highly corrosive (hydrofluoric acid, sulphuric acid, nitric acid)

enrichment plant


The proportion of only 0.7% fissile U-235 is insufficient to support a chain reaction. So the yellowcake must be refined or 'enriched' by some means. Separating isotopes of the same element is difficult because chemically they are virtually identical, moreover U-235 and U-238 are only slightly different in mass.

One method of separation is diffusion through a thin porous membrane, and to do this the yellowcake is processed into uranium hexafluoride (or 'hex') which can be vapourized. This gas is viciously corrosive and reactive, and requires high quality materials and careful handling. This separation process produces a lot of waste heat, so it needs large scale cooling systems, consumes energy and increases global warming. For example the Oak Ridge military enrichment plant uses some 2000 megawatts of electricity - enough for a sizeable city - and this electricity is generated by fossil fuels (power plants which burn strip-mined coal).

For military purposes highly enriched Uranium (HEU) is preferred (about 90% U-235) but most reactors require much less: 2% to 5%.

An alternative method of enrichment is to spin the hex gas in a centrifuge. It is claimed that this requires only one tenth the energy of gas diffusion. Other techniques are under development. If a better one is found, this may provide a quicker route for producing weapons grade material - maybe one that any small country can afford, thus having serious implications for nuclear proliferation.

(The heavy water designs of reactors do not require enriched fuel and are highly efficient in producing Plutonium. The Canadian CANDU reactor is one such and has been sold to India and Pakistan. It is ironic that a state without nuclear weapons has been instrumental in providing the means to two other countries to build them - but that's just business to the nuclear industry.)

fabrication plant

Fuel fabrication

The enriched uranium hexafluoride is turned back into uranium dioxide (as pellets) and packed into metal clad cylinders called "fuel rods". For Magnox reactors the cladding is a magnesium alloy called 'Magnox'. Fabrication of plutonium as a fuel is much more difficult and dangerous. A mixture of uranium dioxide and plutonium dioxide can also be used as a nuclear fuel, called 'MOX' (mixed oxide). Why didn't they call it 'pox'?

Fuel fabrication and enrichment are done at different sites, as are uranium mining/milling and the following stages of electricity generation, reprocessing and waste storage. This means there are significant transport costs, some of which require carbon-based fuels because they are in remote areas.

Unlike France, the UK has no Uranium mining or enrichment plants, and so relies on import of enriched Uranium. But it does have fuel fabrication plant, at Springfields (Lancashire).

nuclear power station

Electricity generation

This is the stage which the nuclear industry focuses on, because it is the only one with any possible benefit.

During the normal running of a nuclear power station, radioactive materials are routinely released into the air and/or water. In addition, accidents (often described as 'incidents') are not rare; some of these result in localized contamination, but others release significant radioactivity into our environment.

While it is true that reactors are designed so that no accident can result in a nuclear explosion, they are capable of creating intense heat which can create a steam explosion, or a hydrogen explosion (due to either hot graphite or hot uranium stripping the oxygen from water and releasing hydrogen gas). Both of these occurred at Chernobyl, but they have also happened in several other quite different reactor designs. Such explosions can spread large amounts of radioactive materials over a very wide area. Chernobyl could have released up to 400 times as much radiation as it did. Even so it was a catastrophe.

The second (or third) worst nuclear reactor accident was the Windscale (renamed Sellafield) fire in 1957. Calder Hall (opened in 1956), adjacent to Windscale, was touted as "the world's first nuclear power station" but was built to produce plutonium for nuclear weapons, and probably consumed more energy than it ever generated.

nuclear waste train


Between each of these stages of the nuclear fuel chain, transport is usually required. The uranium ore is the bulkiest form, and mines are usually in remote locations. Milling may take place near the mine, but enrichment most likely will not. So the yellowcake, and perhaps the ore, will have to be transported long distances, usually by diesel powered trains (ie. using fossil fuels emitting CO2).

Enrichment plants, fuel fabrication plants and power stations are usually in different locations, requiring further transport. Transport between these and later stages in the fuel chain may take relatively little energy compared to the transport of the ore (or of coal or oil) since the fuel is more concentrated.

After nuclear fuel has been used it is highly radioactive and requires heavy shielding. If fuel rods are sent for reprocessing, two tons of fuel may need a 50 ton cask (called 'flasks' because they contain water coolant). Used fuel rods are taken from cooling ponds at the power station and placed in water-filled steel 'flasks' some 14" thick. A lid is bolted on top, the flask is washed down to remove surface contamination, then loaded on to a lorry and taken to a railhead to be loaded onto a flat-bed wagon. (If the water coolant was lost, the fuel rods would overheat then combust, dispersing a massive dose of radioactivity into the atmosphere.)

Although there is no danger of a nuclear explosion, an accident could be catastrophic and hence this transport may be a target for terrorists. So the costs of safety and security in transport at this stage may be significant. In the UK the trains carrying hazardous nuclear waste are routed through large centres of population - for commercial reasons - against the advice of a WHO report.

(The nuclear trains and their risks are described in more detail in the sections "What Travels on the Trains" and "Accidents and Risks in Transport".)

reprocessing plant


After some time in a nuclear reactor the fuel rods (like any fuel) must be replaced. The used fuel rods are highly radioactive. They can either be stored or reprocessed, but in either case there is no way to reduce the total radioactivity - only time will do that.

The early reactors were built primarily to convert Uranium-238 to Plutonium-239 for making bombs. So this plutonium had to be recovered from the fuel rods - this was the main reason for reprocessing. Uranium-235 was in short supply, so it was economic to also recover the unused U-235. (About 20% of the U-235 remains in "spent fuel".) This has given the impression that fuel rods must always be 'reprocessed', and that the used fuel rods are a valuable asset. However, there is now a glut of Plutonium and it should be given a negative monetary value (the costs to contain it as a highly toxic waste). The uranium oxide recovered by reprocessing is stored for possible future use, so it too has no immediate value. The nuclear industry insist on calling the used fuel rods "spent fuel" but they are really just nuclear waste.

During reprocessing the radioactive gas Krypton-85 (a gamma emitter with half-life 10.8 years) is discharged into the air. Radiobiologists did not consider it a hazard, though they have since changed their opinion. It is also thought to be a greenhouse gas. Sellafield (Windscale) also routinely discharges radioactive waste into the Irish Sea - some 500,000 litres per day.

Reprocessing is a complex and dangerous process. For magnox fuel, the cladding of the fuel rod, which has become radioactive, is stripped off, and the bare fuel rod is dissolved in nitric acid and other corrosive solvents. The extracted plutonium is converted to a solid oxide, or kept in a nitrate solution ready to be made into weapons or into fuel for a fast-breeder reactor. But the UK fast breeder reactor program at Dounreay has now been abandoned. In theory the extracted uranium and plutonium go back into the nuclear fuel 'cycle', but in practice there never was a cycle, and there is little sign of there being one in the future.

Reprocessing one tonne of fuel produces about 5 cubic metres of high-level liquid waste containing nitric acid and radioactive materials at high temperatures. This waste must be continuously cooled. The total volume of high-level waste at Sellafield is now thousands of cubic metres. A storage tank has a lifetime of at most 25 years - which is less than the half-life of some of the isotopes it may contain. In similar storage tanks at Hanford (USA) there are 250,000 cubic metres of high-level liquid waste. In 1973 one tank leaked 400,000 litres into the earth, containing 40,000 curies of Caesium-137 and 14,000 curies of Strontium-90. Official investigators declared that the leak could not reach ground-water, but test drilling to locate the waste had to be stopped for fear of helping the waste to migrate downward. This was neither the first nor the last leak.

Some 'experts' in the nuclear industry say that magnox fuel must be reprocessed because it will be dangerous if it deteriorates. But this is misleading - magnox spent fuel from the Wylfa power station is kept in dry-storage. The reason the fuel rods deteriorate is because they have been immersed in cooling ponds, but this is a choice not a necessity.

The nuclear industry likes to portray reprocessing as a good thing, and to pass it off as recycling. The fact is that it is both unnecessary and uneconomic. The whole process does not reduce the total radioactivity; it produces a much larger volume of waste to handle - some of it in corrosive liquid form - and in the process it releases radioactive materials into the environment. The reasons for reprocessing are (a) the historical link with nuclear weapons, (b) the government subsidies and underwriting the costs of mistakes, (c) the high-tech image and public relations value. (For example BNFL had a poster campaign based on the idea that a match can burn twice, implying that we can get something for nothing.)

The only real benefits in reprocessing are to the people making profits or salaries from it, and to the countries which can get rid of their nuclear waste by exporting it to another country for reprocessing.

Dounreay plant

Decommissioning & radioactive scrap metal

A nuclear reactor is designed for a limited lifetime. Accidents may result in it being shut down prematurely. Whether shut down at the end of its lifetime or earlier, the reactor, ancillary equipment and the building itself will be contaminated by radioactivity. This complicates the dismantling and safe disposal of the plant as a whole (known as 'decommissioning'). During this process - which may take a hundred years or more - the site must be under surveillance, and entry by the public prevented. (Children have a tendency to get into abandoned buildings, and warning notices and fences are not always a deterrent.) No one has any experience of the whole process of decommissioning, so the costs and problems can only be guessed at. Current estimates have already escalated and could inrease further if unforeseen problems arise.

The decommissioning of power stations and other nuclear plant will have to handle a lot of radioactive contaminated metal. Decommissioned X-ray machines and other non-reactor equipment have already resulted in deadly radioactive metals getting into the environment. There have been several incidents in the UK where radioactive metal has been found in scrapyards. But even more worryingly, contaminated metals have been found in new products (eg. steel pipes in apartment buildings).

The regulations governing disposal of radioactive metals are based on a level of radioactivity. This level is set as a compromise between safety to health and cost (or profits) to industry. There is continual pressure from the nuclear industry to relax controls. The regulation only limits the level of radioactivity not the total quantity, so companies can legally release radioactivity by the cynical tactic of "dilute and pollute". But it is now generally accepted that there is no safe minimum of radiation - the more total radiation in our environment, however released, the worse it is for our health.

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Waste storage

Radioactivity tends to contaminate everything that comes within its range: not just the metal cladding of fuel rods, but containers, clothing, cleaning materials and living creatures. All these then become sources of radioactivity. When the radioactivity is relatively little, the materials are called "low-level waste". In the past these have been casually incinerated (sending the radioactivity into the air) or dumped (risking contamination of ground water supplies). For over two decades this was not seen as a problem, but the growing quantity of low-level waste means that sites for dumping are harder to find. It was belatedly realized that some low-level wastes contain long-lived isotopes. These isotopes are difficult and expensive to remove, so the waste must be kept virtually indefinitely. Records of the contents of the waste are sometimes incomplete or missing, making it difficult to decide exactly how to handle the waste. Again and again we see examples of the industry's attitude to waste: sweep the problem under the carpet, or into next-door's back yard - out of sight out of mind.

High-level waste is initially in a smaller range of materials, but reprocessing means that some of it becomes mixed with highly active chemicals. Radioactivity can also affect chemical reactions, and so it is not always easy to predict the reaction of such mixtures. High-level waste requires very long term storage. There is still much debate about whether it is safer to store this on the surface (where it is visible and easily accessed) or deep underground. Bearing in mind industry's tendency to ignore problems, it would seem safer to keep the problem in view. We have no experience of safely storing such active wastes as Plutonium for their lifetime of thousands of years. Well within that time scale geological formations can change and the languages on warning signs unintelligible.

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Nuclear weapons

Until the last decade or so, nuclear weapons meant bombs. Nuclear bombs were tested (both in the atmosphere and underground) not only to see whether they worked but also for their political impact. The countries which demonstrably possessed nuclear weapons gained extra status in the United Nations. Every one of the atmospheric weapons test in the 50's and 60's will cause thousands of deaths from cancer, eventually totalling many millions. How can the 'scientists', politicians and military in charge have been so stupid and unconcerned?

The increasing spread and availability of nuclear weapons and nuclear material ('proliferation') pose an increasing risk, not only from a nuclear bomb, but also from a conventional 'dirty' bomb which disperses radioactive material. Such weapons do not have an attractive image to high-tech countries, but might be used by terrorists. Even if they are never used, nuclear weapons (and nuclear-powered submarines) leave a legacy of nuclear waste.

More recently, radioactive material has been used in shells - depleted uranium (DU). DU is used because uranium is a very heavy (dense) metal, and because it is relatively cheap since it is a by-product from the enrichment of nuclear fuel. But one effect of a DU shell is to spread many tiny fragments of radioactive material. This affects not only the immediate combatants but also the civilian population. Several countries have denied using DU, but recent evidence contradicts this.


The "nuclear fuel cycle" is a misnomer. There would be more logic in the term "the fossil fuel cycle" since the carbon from the burning of coal will be taken up by trees (if there are any left) and eventually deposited as coal - whereas the U-238, once transformed into its fission products will never return to U-238. The term is a public relations exercise.

The main points are:

skip to contents updated: 21-Mar-08