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The Role of Nuclear Fission Power Stations After a brief introduction, we describe nuclear power and its current status. Then the issues raised by using nuclear fission to generate electricity are discussed. These include the arguments in favour of building new nuclear power stations in the UK, and the serious concerns about costs and timescales, safety, waste disposal, and the possible spread of nuclear weapons. The very different situation regarding nuclear fusion is discussed on our green energy page. |
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Introduction to Nuclear Fission Electricity Generation A new generation of nuclear fission power stations is being promoted in the UK in response to the retirement of existing nuclear power stations. Nuclear fission is not a renewable energy source, since it uses uranium and, at least at present, does not replace it. No greenhouse gases are produced in the electricity generating phase, but preparing the nuclear fuel, decommissioning old power stations, and storing the radioactive waste does generate some carbon dioxide. Overall it is a low-carbon, not no-carbon, technology. 
The energy comes from the reduction in mass when certain heavy atoms are split to form different chemical elements. This mass is converted to energy according to Einstein's famous law E = mc2. The energy generated from a very small amount of fuel is enormous, so although the fuel is expensive to produce the total fuel cost is relatively low. The main costs are the construction of the power stations, and later decommissioning them as well as dealing with the radioactive waste. At present about one-sixth of the UK's electricity is generated by British nuclear power stations, but (with one exception, Sizewell B, pictured at left) these are old and will soon have to be phased out. A new generation of reactors is being proposed. However, the use of nuclear fission reactors to generate electricity raises broader and more controversial issues than other technologies, so opinions about this are strongly polarised. The need to replace existing nuclear power stations quite soon, if they are to be replaced at all, adds urgency to this discussion. The main arguments for renewing the use of nuclear power include:
The counter-arguments at the practical level include:
The broader issues that worry many people are:
The energy produced by nuclear fission is an established source for generating electricity. The fission produces heat, and in a nuclear reactor the heat is transferred to steam which drives a turbine to generate electricity. Normally, the atom that is split is a fairly rare isotope of uranium (uranium-235, which has 92 protons and 143 neutron in its nucleus); the artificially created element plutonium can also be used. It is also possible to use a nuclear reactor to convert the more common isotope of uranium (uranium-238, which instead has 146 neutrons) into fuel, and this would make the cycle renewable. However, such breeder reactors are not a mature technology despite development programmes that have now been terminated. Another possibility, with advantages that might be realised in the future, is to obtain nuclear fuel from thorium, which is more abundant than uranium. The process of preparing the reactor fuel does generate carbon dioxide, and requires a great deal of energy. Uranium fuel for nuclear reactors is mined (e.g. in Australia and Canada), and the ore contains only a very small fraction of uranium (about 1% at best). The mines themselves contain toxic materials and radioactive radon gas. Extracting and purifying the uranium is a relatively dirty process. Then the natural concentration of uranium-235, which is only 0.7%, must be increased. This enrichment process is very difficult, because uranium-235 and 238 are essentially identical chemically, and it uses a huge amount of energy. The original gaseous diffusion method has now mostly been replaced by the use of large numbers of very large and sophisticated gas centrifuges, which is more efficient. After some enrichment, typically to 3–5% uranium-235, the uranium can be used to fuel reactors. After much more enrichment, usually to more than 85% uranium-235, it to be used to make atomic (i.e. nuclear fission) bombs. Atomic bombs can also be made using plutonium-239, an element which does not occur in nature – it is manufactured in nuclear reactors. Fission and chain reactions 
In nuclear fission the uranium-235 (or plutonium) nuclei are bombarded by neutrons, and split into two lighter nuclei, as shown in the upper picture at right. In addition to these lighter nuclei, more neutrons are released, typically an average of 2.5. The total mass of the two lighter nuclei plus the neutrons is less than the total mass of the uranium nucleus, and the difference is converted to energy according to Einstein's equation. In a nuclear reactor this energy is converted to heat, and is transferred to the reactor's working fluid, usually water, which is then used to produce steam. Weight for weight, the energy produced from fuel in this way is millions of times more than what is obtained from a fossil fuel. What makes nuclear fission special in uranium-235 and plutonium is their ability to sustain a chain reaction, as in the lower picture at right. Some of the neutrons produced will impact with other nuclei and induce further fission reactions, releasing yet more neutrons. If enough uranium-235 or plutonium is assembled in one place then these freshly generated neutrons outnumber neutrons that escape, and a sustained nuclear reaction will occur. An assembly that allows such a sustained chain reaction is called a critical assembly or critical mass. In a nuclear reactor, chain reactions are initiated, controlled, and sustained at a steady rate. However, in a nuclear bomb the chain reaction occurs in a fraction of a second and is uncontrolled, causing an explosion. The chain reaction in a reactor cannot trigger a full nuclear explosion because the uranium is not highly enriched – even if the fission reactions were to go out of control, the reactor assembly would melt (which would still be extremely serious) rather than cause a nuclear explosion. What keeps a reactor under control is a moderator, usually water or sometimes graphite, to reduce the number of neutrons with energies capable of causing fission reactions and so slow down the chain reaction. In addition, control rods that can absorb excess neutrons are used to regulate the rate of the chain reaction. Nuclear reactors produce waste that remains radioactive for an extremely long time, and what to do with it is one of the most serious and still unresolved issues surrounding nuclear power. Decommissioning old power stations at the end of their working lifetimes is a long, difficult, and expensive process. Both dealing with the waste and decommissioning generate some carbon dioxide. For the long-term future, another possible way of generating energy is by using nuclear fusion, a process that combines light atoms. This would avoid some of the major problems of nuclear fission, and is described on our green energy page. Nuclear power reactors are used to generate roughly 15% of the world's electricity, and currently there are about 440 reactors operating in about three dozen countries. The most notable is perhaps France, where they produce more than 75% of the electricity. Other big users include the US and Japan. However, few new nuclear power stations have been built since the Three Mile Island accident (1979) and the much more serious Chernobyl accident (1986). The first two to be ordered in western Europe since then are currently under construction in Finland and France. Some countries have rejected all use of nuclear power, while others have a revived interest in order to reduce dependence on imported fossil fuel. World-wide, there are currently about two dozen nuclear reactors under construction, nearly half of which are in India and China. Many more are planned. 
The UK was the first country to use nuclear reactors to generate electricity in commercial quantities. This began in 1956 using the Calder Hall reactor at Windscale (now Sellafield), pictured at left. However, as an example of the broader issues surrounding nuclear power, the primary use of the first power-generating reactors was initially to manufacture plutonium for nuclear weapons. In the UK there are currently 19 functional nuclear power stations, all but one of which will be retired by 2023. In 2006 they generated 19%, and in 2007 about 15%, of all the electricity used. A further 3% of UK electricity is imported from France and is mainly nuclear-generated. The oldest of the 19 are four reactors of the Magnox design, which was developed by the UK Atomic Energy Authority. They were commissioned between 1968 and 1971, and are due to be closed between 2008 and 2010. Fourteen are Advanced Gas-cooled Reactors (AGRs), commissioned between 1976 and 1989 and due to close between 2014 and 2023. The final power station is a Pressurised Water Reactor (PWR) commissioned in 1995, which is due to be decommissioned in 2035. All but the four Magnox reactors are now run by British Energy, a company partly owned by the government and which has had a rocky financial history. Four of the AGRs are currently not operating due to corrosion problems, and four others are limited to 70% of their rated output. If the UK's existing nuclear capacity is to be replaced by new nuclear power stations, a start would need to be made very soon, as the process of design, gaining planning approval and construction is likely to take many years. It is estimated that the first could only be ready by about 2018–2020 at the earliest. The big question is whether a new generation of nuclear power stations is the right way forward or not. Arguments in Favour of New Nuclear Power Stations in the UK 
Low carbon dioxide production Nuclear power is being promoted in the UK as a carbon-free method of electricity generation. As already mentioned above, this is only strictly true for the production phase, not the fuel preparation or the decommissioning and waste disposal operations. Also, as better-quality uranium ore runs out, it will take more energy and chemical processing to purify the uranium, and this would probably produce more carbon dioxide. However, the total carbon dioxide emissions over the full nuclear power life-cycle should remain well below those of fossil-fuel generation. The need for always-on power generation, replacing existing reactors The main renewable technologies now being adopted, mostly wind and some solar power, have the obvious problem that they only work some of the time. The amount of wind is variable, and solar power works only in daylight. Other possibilities for the future such as tidal power also have time constraints. At present the possibilities for storing energy until it is needed, such as the pumped-storage hydro-electricity facilities at Dinorwig in Wales and Cruachan in Scotland, are very limited. Nuclear power, on the other hand, is a low-carbon energy source that works best when it is always on, providing the electrical base-load. As already mentioned in the current status section, all but one of the UK's nuclear power reactors will be closed down between now and 2023. These generate about one-sixth of UK electricity. The government proposes to replace them with a new generation of reactors, probably similar to the ones now being built in Finland and France (see below). The stated goal is use nuclear as a low-carbon energy source for the relatively short-term, with the hope that renewable technologies such as more advanced solar power, tidal power, biomass, or fusion will develop and later be able to take their place. People arguing against using nuclear power point out that the nuclear share of UK electricity is relatively small. If more renewable energy using a variety of sources is combined with a serious programme of energy efficiency measures, the need for electricity could drop by enough not to need nuclear power to provide base load, and at the same time reduce fossil-fuel generation. In addition there is a problem of timescale, since replacement reactors would not be ready until well after the existing ones are shut down. There is more on this below. Energy security North Sea oil and gas are running out, so the UK's fortunate position regarding fossil-fuel resources is ending. The cleanest fossil-fuel technology for electricity generation is currently gas, which is now widely used in the UK to generate electricity. A large proportion of European gas reserves are in Russia and other less stable countries, which might decide to raise prices and/or limit supplies, . Except for raw uranium supplies, the main sources of which are Canada and Australia, the UK has all parts of the chain for producing nuclear fuel and processing the waste. There is enough uranium to provide power for much of the 21st century, but this depends on the extent to which other countries also take up nuclear power. If uranium has to be obtained from ores and other repositories such as sea water where it is in much lower concentrations, the energy to extract it may approach the energy released when it is used, so the long-term future of fission reactors fuelled in this way is doubtful. The use of breeder reactors to produce plutonium reactor fuel from the more abundant isotope uranium-238 would make the nuclear fuel cycle renewable, but that raises difficult problems, such as safety, and other dangers, including nuclear weapons proliferation. The UK, France, and the US have all terminated their breeder-reactor development programmes due to a combination of these problems and a lack of demand. New reactor designs New European Pressurised Water Reactors (EPRs) are currently being built in Olkiluoto, Finland and Flamanville, France. These two are the first to be ordered in western Europe since the Chernobyl disaster in 1986. This design is claimed to be safer and more fuel-efficient than existing ones, and to produce less radioactive waste. The performance of these reactors is, of course, not yet proven. Their construction is currently running late and well over its budget – see the next section. As nuclear reactors require so little fuel, the cost of electricity is dependent mainly on the cost of construction and final decommissioning of the plant. There is also the cost of storing the radioactive residue. Fuel is only very roughly 10% of the cost of the electricity generated, unlike a gas-fired power station where it might be 80% or more. 
The new nuclear power stations under construction in western Europe are being built by the French firm Areva in two locations, one in France and the other in Finland (photo at left). These are a new pressurised-water design that is claimed to be more efficient and safer than previous reactors. This design and company seem the most likely to be used for new power stations in the UK. However, the Olkiluoto-3 reactor is at least 24 months behind schedule after 28 months of construction, and 50% over budget. It has also been criticised by the Finnish nuclear safety regulator. The Flamanville reactor was started more recently, but there have been halts in construction due to safety issues with concrete and steel quality. The estimated cost of new nuclear power stations for the UK seems to be in the range £2.8 to £4.5 billion each. Unfortunately, the history of nuclear power is full of examples of costs going well beyond budgets, timescales being stretched, and the British government paying to prevent financial collapse. For example, the cost of decommissioning the current generation of British reactors is very considerable – the estimate has risen to £73 billion from £53 billion only two years ago, for a programme lasting about 130 years. In response, the government has stated that the full costs of any new nuclear power stations, including radioactive waste disposal and decommissioning, will have to be borne by the owners. It does not seem possible to build new nuclear power stations in the UK quickly enough to replace the existing ones as they are decommissioned, especially in the large numbers needed. The first few new ones cannot be ready, on current planning, before about 2018–2020. The government is trying to speed up the planning and licensing process, but nuclear power stations take much longer to build than fossil-fuel ones. Questions have also been raised regarding the availability of enough people with the engineering skills and experience to build a large number of new nuclear power stations, especially in view of the gap since the last ones were built. Safety of Nuclear Power Reactors Like air travel, nuclear reactor safety is tightly regulated, and incidents are investigated in order to learn from them. And like comparing air travel to road accidents, an accident in a nuclear reactor will hit the headlines, but there are no headlines about the large number of people who die or whose health is damaged by pollution from the burning of fossil fuels. This overall perspective should be borne in mind when discussing the safety of nuclear power. Nuclear accidents range in magnitude from small leaks of radioactive material to the Chernobyl disaster. The industry is relatively safe – Chernobyl was the only accident in the past 50 years that caused significant loss of life. However, Chernobyl was extremely serious, and it is this small risk of a major disaster that mainly worries people. Two other serious accidents before Chernobyl were the Windscale fire in 1957 and Three Mile Island in 1979. At Windscale (now Sellafield) the graphite core of a reactor used to produce plutonium for nuclear weapons burned and was destroyed, releasing large amounts of radioactive material. This was an early reactor with a faulty design, not used for producing electricity. The release of radioactive iodine-131 may have caused more than 200 additional thyroid cancers, most of them treatable. The accident in the Three Mile Island power station was caused by loss of coolant, due to inadequate instrumentation. The reactor core partially melted down. Despite this, there were no verified casualties and no evidence of anyone receiving large radiation dosages. It had a huge effect on public opinion, and a very large number of reactor orders in the US were cancelled. Cleaning up the damage took until 1993 and cost roughly $1 billion. 
The disaster in 1986 at Chernobyl in the Ukrainian Soviet Socialist Republic was the worst nuclear accident in history (photo at right). The power excursion and resulting steam explosion and fire spread radioactive contamination across large portions of Europe. The UN report of 2005 concluded that the death toll included the 47 workers who died of acute radiation syndrome and nine children who died from thyroid cancer. It estimated that there might be 4,000 extra cancer cases among the approximately 600,000 people most highly exposed, and 5,000 among the 6 million living nearby. The radioactive plume drifted over the western Soviet Union, then eastern, western and northern Europe, even reaching the UK and Ireland. Large areas in Ukraine, Belarus, and Russia were badly contaminated. A zone of 30 km radius around the plant was cleared, resulting in the evacuation and resettlement of about 135,000 people including 50,000 from the nearby town of Pripyat. This zone, including Pripyat, remains off limits. The now-independent countries of Russia, Ukraine, and Belarus have been burdened with the continuing and substantial decontamination and health care costs of the accident. The Chernobyl reactor is now enclosed in a large concrete sarcophagus, which was built quickly to allow continuing operation of the other reactors at the plant. However, the structure is not strong or durable. Some 200 tonnes of highly radioactive material remains deep within it, and this poses an environmental hazard until it is better contained. A new structure will be built by the end of 2011. Nuclear reactors used in the west were already safer than Chernobyl, and new designs claim to be safer still. However, a number of factors undermine public confidence:
Spent fuel and the materials that surround the reactor core are highly radioactive. The radioactivity diminishes with time, since ultimately it decays into non-radioactive elements. The timescale is determined by the half-life – the time it takes to lose half of its radioactivity. Some of the elements in the waste, such as iodine-131, are intensely radioactive but have very short half-lives (8 days for iodine). Others, such as plutonium-239, will remain hazardous for hundreds of thousands, and in some cases millions, of years. Thus, these wastes must be shielded for centuries and isolated from the living environment for many thousands of years. To achieve this, the preferred solution is deep and secure burial for the more dangerous wastes. A satisfactory site must be stable against climate, erosion, underground water, earthquakes, and other natural forces, as well as political interference, on a timescale longer than the history of human civilization. No country has a fully implemented waste disposal policy working at present. Some, such as Finland, have earmarked sites for underground low-term storage but not yet started to use them. The US has a designated site in Nevada, but 10 years on it has not opened due to a variety of legal challenges. The UK situation Used reactor fuel still contains much of its original uranium. In the UK, used fuel is sent to Sellafield for reprocessing to recover the usable fuel. High-level wastes arising from this are stored there, in stainless steel canisters in silos. This is to be stored for 50 years before disposal, to allow the short-lived components of the radioactivity to die down. In 2006 the Committee on Radioactive Waste Management (CoRWM) recommended deep geological disposal of high and intermediate-level wastes long-term. It also looked into the implications of possibly abandoning any reprocessing of used fuel (see below). The location of the repository would be on basis of community agreement, with incentives for communities to volunteer. About one-third of the UK appears to be geologically suitable. CoRWM said that the government should move swiftly to implement its recommendations, though it acknowledges that actually commissioning a repository could take decades. The government has accepted CoRWM's key recommendations. In April 2007 the Nuclear Decommissioning Authority (NDA) established the Radioactive Waste Management Directorate (RWMD), to devise "a safe, environmentally sound, publicly acceptable, geological disposal solution" for the UK's high-level wastes – civil and military. This is expected to cost £7.5 billion Reprocessing of nuclear waste 
Instead of simply disposing of all radioactive waste from nuclear reactors, it can be reprocessed to recover uranium and plutonium to use as fuel. This reduces the need to mine, purify and enrich uranium, and at the same time makes the residual waste less radioactive. The fuel produced is a mixture of uranium dioxide and plutonium dioxide, and so is called mixed oxide, or MOX. Reprocessing of civilian fuel from power reactors is currently done in Britain, France, Russia, Japan and India, and may soon be done in China. France is generally cited as the most successful reprocessor, but at present only 28% (by mass) of its nuclear fuel comes from previously used fuel. (7% is MOX produced in France, and 21% is uranium recovered in France and re-enriched in Russia.) A disadvantage of reprocessing is that it is relatively easy to recover plutonium in order to use it for nuclear weapons. The US has stopped civilian reprocessing as part of its non-proliferation policy. The UK's reprocessing programme has had a problematic history. The Thermal Oxide Reprocessing Plant (THORP) at Sellafield processes spent nuclear fuel from nuclear reactors and separates the uranium and plutonium, which can then be reused in mixed oxide fuel. Construction of THORP started in the 1970s, and it began operation in 1997. In 2004–5 THORP suffered a large leak of a highly radioactive solution. An inquiry determined that a design error led to the leak, while a complacent culture at the plant delayed detection for nine months. The spill contained about 20 tonnes of uranium and 160 kilograms of plutonium, but was safely recovered. No radiation leaked to the environment and no one was injured. Production eventually restarted at the plant in 2008, but almost immediately had to be put on hold again, for an underwater lift that takes the fuel for reprocessing to be repaired. The Sellafield MOX Plant, to manufacture mixed-oxide fuel, was completed in 1997, but only began operation in October 2001. MOX fuel behaves similarly to the enriched uranium for which most nuclear reactors were designed. It also provides a means of using excess weapons-grade plutonium (from military sources) to produce electricity. However, MOX fuel is currently much more expensive than normal uranium fuel. The MOX plant was designed to produce 120 tonnes of fuel per year, then downrated to 40 tonnes per year. But over its first five years of operation its total output was only 5 tonnes. In 2008 orders for the plant had to be fulfilled in France, and the plant was reported in the media as having "failed". Proliferation of Nuclear Weapons The relationship between nuclear power and nuclear weapons An important reason for considering nuclear power differently from other energy technologies is the relationship with nuclear weapons, which continue to threaten world peace and stability. There are several areas in which nuclear power generation and the manufacture of nuclear weapons overlap. Highly enriched uranium can be used for atomic bombs, and the same methods (e.g. centrifuges) used to enrich the fuel for power reactors can be used to continue the enrichment process. Plutonium can also be used for atomic bombs, and is preferred because a smaller mass of plutonium produces a more efficient bomb than uranium. The first commercial electricity-generating reactors were built primarily to produce plutonium, and the electricity was a by-product. There is serious concern that having nuclear electricity could also assist more countries in obtaining nuclear weapons, either by enriching uranium or by extracting plutonium produced in the power reactors. In addition, modern reactors can also use mixed oxide fuel (for example produced by the Sellafield MOX facility, see above), which contains a great deal of plutonium that can easily be extracted for making bombs. And if nuclear power continues to develop and uranium starts to become expensive, future reactors my well be fuelled entirely with plutonium, which can be used for weapons. 
Nuclear proliferation Two of the great successes of the past decades have been the Nuclear Proliferation Treaty (NPT) of 1968, which aims to limit the spread of nuclear weapons, and the International Atomic Energy Agency (IAEA) which won the 2005 Nobel Peace Prize for its efforts in this area. Although several significant countries, including nuclear weapons states (India, Pakistan, and Israel), have not signed the treaty, and although the nuclear countries at the time of signing it (US, UK, France, Soviet Union, China) have not reduced their nuclear arsenals in the way the treaty requires, it is strongly believed that the NPT has helped in discouraging countries from developing nuclear weapons. For example, South Africa, Libya, and now probably North Korea, have abandoned plans to obtain nuclear weapons. On the other hand, India and Pakistan now have nuclear weapons, and although not openly declared it is generally acknowledged that Israel has them as well. The current tense situation concerning Iran is centred on accusations that it is developing atomic weapons, while Iran claims it is merely developing nuclear power generation. Most of the discussion about building new reactors in the UK makes no mention of the situation in other countries. The views of the UK are influential in many places. If the UK advocates the use of nuclear power, and also the use of reprocessed fuel that contains plutonium, then other countries (including some with less careful regulation, less stable governments, or in less stable parts of the world) may also want it. It seems inconsistent to say that the UK will renew its nuclear power capabilities, but that other countries should not have it. Possibilities for terrorism A nuclear terrorist attack could take various forms:
At present it would probably be easiest to acquire radioactive materials, such as nuclear waste. If nuclear power is more widely used and developed further, there will of course be more radioactive materials in circulation. But in addition, large quantities of separated plutonium will exist after the highly radioactive fuel rods are reprocessed, for example by the Sellafield mixed-oxide (MOX) plant, and this could fall into the wrong hands. |
