Blewbury Energy Initiative - Nuclear Fission

The Role of Nuclear Fission Power Stations

After an introduction, we describe nuclear power and the current status and plans in the UK. Then the complex issues and problems raised by using nuclear fission to generate electricity are discussed. We start with the arguments in favour of building new nuclear power stations in the UK and elsewhere:

low carbon dioxide emissions,
the need for always-available generation,
the desire for energy security, and
the possibility of new reactor types (including thorium) that might be safer and perhaps renewable.

Then we cover the serious concerns that make nuclear power more controversial than other options:

costs and timescales,
safety, including information and comments on Fukushima,
disposal of radioactive waste,
the spread of nuclear weapons, and
the risk of nuclear-related terrorism.

Finally, a brief list of further reading.

The very different concepts and situation regarding nuclear fusion are discussed on our green energy page.

A new generation of nuclear fission power stations is planned in the UK in response to the retirement of existing nuclear power stations. Nuclear fission in its present form is not a renewable energy source, since it uses uranium and does not generate more fuel from its nuclear reactions. 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. Considered over all, it is therefore a low-carbon, not a no-carbon, technology.

The energy comes from the reduction in mass when certain very 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 very 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 only one exception (Sizewell B, pictured at left) these are old and will soon have to be phased out. A new generation of reactors has been proposed. However, the use of nuclear fission reactors to generate electricity raises much broader and more controversial issues than other technologies, so opinions 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 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 turbines to generate electricity. At present, the atom that is split is usually a fairly rare isotope of uranium (uranium-235, which has 92 protons and 143 neutrons 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. This is despite substantial development programmes – virtually all of which have now been terminated. Another future possibility is to obtain nuclear fuel from thorium, which is more abundant than uranium and has other possible advantages – there is more on thorium reactors below.

The process of preparing the reactor fuel requires a great deal of energy, and generates carbon dioxide. 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. The original gaseous diffusion method uses huge amounts of energy, but it is now being replaced by the use of large numbers of very big and sophisticated gas centrifuges, which consumes only about 2.5% as much energy. 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 can be used to make nuclear fission bombs, more often called atomic bombs. Atomic bombs can also be made using plutonium-239, an element which does not occur in nature – it is manufactured in nuclear reactors. (The even more powerful thermonuclear, or hydrogen, bombs are based on nuclear fusion but require fission bombs as a trigger.)

In nuclear fission the uranium-235 (or plutonium-239) nuclei are bombarded by neutrons, and split into two lighter nuclei, as 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 law. 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 by burning 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-239 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, regulated by control rods that can absorb excess neutrons. However, in a nuclear fission bomb the chain reaction occurs in a fraction of a second and is uncontrolled, causing an explosion. The chain reaction in current reactors cannot trigger a full nuclear explosion because they are constructed completely differently from a nuclear weapon, and also the uranium is not highly enriched – even if the fission reactions in a reactor were to go out of control, the reactor assembly would melt (which would still be extremely serious) rather than cause a nuclear explosion.

At present, all operating power reactors are so-called thermal reactors. In a thermal reactor the high-energy neutrons produced in fission are slowed down by collisions with the light atoms of a moderator such as water, or sometimes graphite, to speeds where they are more likely to be captured by a uranium-235 or plutonium-239 nucleus. This means that only a relatively small fraction of the fuel needs to be fissile material (uranium-235 or plutonium-239). In contrast, the chain reaction in a fast reactor is sustained by fast neutrons. No neutron moderator is needed, but the fuel must be richer in fissile material than in a thermal reactor.

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 to generate energy is by using nuclear fusion, a process that combines light atoms. (The Sun’s energy comes from fusion.) 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 58 reactors produce more than 75% of the electricity. Other big users include the US (which actually generates more nuclear power than France, though it’s a smaller fraction of their total electricity) and Japan. However, few new nuclear power stations have been built since the Three Mile Island accident in 1979 and the much more serious Chernobyl accident in 1986. The first two reactors 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 on the order of 50 nuclear reactors under construction, mostly in Asia (notably China). Many more are being planned, but some may be influenced by the events at Fukushima in 2011.

The UK was the first country to use nuclear reactors to generate electricity commercially. This began in 1956 using the Calder Hall reactor at Windscale (now called 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 to manufacture plutonium for nuclear weapons, with electric power generation as a by-product.

In the UK there are currently 18 functioning nuclear power stations, all but one of which will be retired by 2023. In 2006 they generated 19%, and in 2007–2010 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 18 are three remaining reactors of the Magnox design, which was developed by the UK Atomic Energy Authority. They were commissioned between 1968 and 1971, and will all be closed in 2011 and 2012. Fourteen are Advanced Gas-cooled Reactors (AGRs), commissioned between 1976 and 1989 and due to close between 2014 and 2023. The final one is a Pressurised Water Reactor (PWR), Sizewell B, commissioned in 1995, which is due to be decommissioned in 2035. All but the Magnox reactors are now run by British Energy, a company previously owned by the government and which has had a rocky financial history.

Four of the AGRs did not operate from late 2007 to early 2009 due to corrosion problems, which have now been repaired at considerable expense. Four others are limited to about two-thirds of their rated output. Sizewell B, the most modern reactor, was off for nearly a year in 2010 and early 2011 due to technical problems.

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.

The UK government has a policy to (at minimum) replace the existing reactors that must be shut down with new ones. This would be done by private companies, with the aim of generating at least 20% of the UK’s electricity. The government would ideally like to have at least two operators and two reactor designs for this programme. There is more information below, in the section on new reactor designs.

In 2008 British Energy, which runs most of the UK’s nuclear power stations, was sold by the government to Electricité de France (EDF); in 2009 EDF then sold 20% to UK energy retailer Centrica. EDF proposes to have the French government-owned company Areva build four EPRs, two at Sizewell in Suffolk and two at Hinkley Point in Somerset. These would generate 6400 megawatts, about 13% of UK electricity, by the early 2020s.

At the same time E.ON and RWE npower, in a joint venture with several other utilities, propose to build either Westinghouse AP1000s or Areva EPRs. There would be two each at Oldbury in Gloucestershire and Wylfa in Wales, and could generate as much as 6000 megawatts.

In November 2009 the government named 10 sites as possible locations for new reactors, including the four mentioned above. Eight of the sites already have reactors (either operating or closed), while two others are new sites in Cumbria, near Sellafield. Four proposed sites were rejected, one of which (Dungeness) has existing reactors. The government wants to avoid very lengthy public inquiries such as the three-year one for the UK’s most recent reactor, Sizewell B. It has therefore proposed a new centralised planning system for large infrastructure projects, based on the newly established Infrastructure Planning Commission.

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 construction, fuel preparation, waste disposal and decommissioning operations. Also, as better-quality uranium ore runs out, it will take more energy and chemical processing to purify the uranium, and this will probably produce more carbon dioxide. However, the total carbon dioxide emissions over the full nuclear power life-cycle should remain well below those of generation using fossil fuels.

Two main renewable technologies now being adopted, wind and solar power, have the obvious problem that they only work some of the time. The amount of wind is variable. Solar power works only in daylight, and varies with the seasons and whether or not it’s sunny. Other possibilities for the future such as tidal power also have time constraints. At present the capacity for storing energy until it is needed, such as the pumped-storage hydro-electricity facilities at Dinorwig in Wales and Cruachan in Scotland, is very small. 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.
(In France, where most of the electricity is nuclear-generated, the problem is in fact the opposite – nuclear reactors work best when running flat-out, but some of the reactors must vary their outputs to follow the load. This is inefficient, making the electricity more expensive to produce.)

As already mentioned (see current status), all but one of the UK’s nuclear power reactors will be closed down between now and 2023. The government proposes to replace them with a new generation of reactors, some of them probably similar to the EPRs now being built in Finland and France. Even more new reactors would be needed if they were also to replace some of the UK’s dirtiest power stations, which burn coal. The stated goal is to use nuclear fission as a low-carbon energy source for the relatively short-term, with the hope that renewable technologies (described on our green energy page) 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 really serious programme of energy efficiency measures, the demand for electricity might be met without needing the nuclear power contribution to the base load, and at the same time reducing fossil-fuel generation. There is also a serious problem of timescale, since all or most of the replacement reactors would not be ready until well after the existing ones are shut down. There is more on this below.

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 – this has already become a serious concern elsewhere in Europe.

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-239 reactor fuel from the more abundant isotope uranium-238 would make the nuclear fuel cycle renewable, but that raises difficult problems of 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. Another possibility is reactors based on the more abundant element thorium. These options are discussed in the next section.

Most currently operating reactors are classed as Generation II, to distinguish them from early designs such as Magnox in the UK. These typically generate between 600 and 1300 megawatts each. Various newer designs (Generation III) were then proposed, in order to improve efficiency and safety, generate less waste, and to lower costs. However, due to the lack of orders after Chernobyl, few Generation III reactors were built. More recent designs with further improvements are called Generation III+. These include the reactors currently being proposed for the UK, the two most likely types being the EPR and the AP1000.

The EPR (originally called European Pressurised Reactor in Europe and Evolutionary Power Reactor in the US and elsewhere) is a 1600 megawatt design by the French firm Areva. The two currently being built, in Olkiluoto, Finland (photo) and Flamanville, France, are the first reactors ordered in western Europe since the Chernobyl disaster in 1986. The design includes improved safety features such as a double-walled containment structure. The performance of these reactors is, of course, not yet proven. Their construction is currently running very late and well over budget, as discussed below.

Two EPRs, uprated to 1750 megawatts, are being built in Taishan, China. Construction on the first began in 2009 and the second in 2010; they are due to be completed at the end of 2013 and in 2015, respectively. There won’t be any more – China has opted mainly for the AP1000 (see below).

France plans to replace its 58 existing reactors with about 40 EPRs, starting in 2020. There were plans to build several EPRs in the US, but that now seems doubtful.

The EPR is now going through the UK’s generic design approval procedure, based on the proposalss (above) by EDF and E.ON/RWE to build new power stations. The Health and Safety Executive has raised questions about the EPR’s control and instrumentation systems (among other items), and is working together with the Finnish regulator which has already raised similar points regarding the Olkiluoto reactor. The major issue concerns making the reactor protection system fully independent of the normal operating controls. It is predicted that these questions will be resolved and UK approval granted by the end of 2011.

In the US, the Generation III+ designs are the 1100 megawatt AP1000 (by Westinghouse, which was previously owned by British Nuclear Fuels and then sold to Toshiba), and the 1500 megawatt ESBWR (Economic Simplified Boiling Water Reactor, by General Electric-Hitachi). These improve safety by making more of the systems passive and fail-safe. However, critics say that the containment is less robust in order to cut costs, and there is less redundancy in the safety systems than in previous designs. Thus it is not clear whether they really are safer.

In the US, 14 applications to build AP1000s on seven sites have been filed. They will be the first new reactors in the US since the Three Mile Island accident. There are also plans to build several ESBWRs in the US; the ESBWR is no longer being proposed for the UK.

The AP1000 is the main reactor design adopted for expanding China’s nuclear generation. The first four AP1000s in the world are already being built at Sanmen and Haiyang, in China, and there are firm plans for eight more, with about a further 30 proposed. Construction on Sanmen 1 commenced in 2009, and it is expected to begin operation in 2013 with the second about one year later. Haiyang 1 was also started in 2009, and the Haiyang units are expected to start operation in 2014 and 2015.

The AP1000 is going through UK generic design approval, aimed at the proposals (above) by E.ON and RWE to build power stations based on either the AP1000 or the EPR. The Health and Safety Executive has raised points related to the AP1000’s civil and mechanical engineering, structural integrity, and many other safety-related issues. There are more unresolved serious points than with the EPR, and major progress will be required in order to obtain UK approval by the end of 2011.

Generation IV reactors are futuristic designs still being researched – they could not be built for at least 20 years due to the need for research and development. The main aims are to improve safety, to make it difficult to use the fuel or waste for nuclear weapons, and to minimise waste and reduce its radioactive lifetime. Some designs would breed fuel, making them sustainable and avoiding the problem of uranium running out.

Opponents of these long-term developments say that they are not a good use of money and effort. They feel that the nuclear option is best avoided because its problems can never be eliminated completely, and that longer-term research should concentrate on cleaner, safer new ways to generate energy.

Recently, a number of prominent scientists and commentators who had been opposed to nuclear power announced that they now conclude that nuclear power should be reconsidered, because climate change appears to be happening more rapidly and with more serious effects than previously thought. In order to minimise the consequences, the use of coal must be phased out as quickly as possible. They believe that the problems associated with nuclear power are outweighed by the threats posed by carbon dioxide. The Generation IV reactor design called the Integral Fast Reactor (IFR) is seen as the most favoured solution.

The IFR would be a fast reactor – unlike reactors in use now, the neutrons are not slowed down by a moderator. The fuel is an alloy of uranium and plutonium, and cooling is by liquid sodium. After an initial load of conventional uranium fuel the waste would be reprocessed, ideally on-site (hence ‘integral’), using a new type of reprocessing to extract uranium and plutonium that have been bred inside the reactor in order to provide subsequent fuel loads. This fuel would also include many of the longer-lived waste products, so the residual waste would be much shorter-lived and less dangerous than waste from present-day reactors. Fuel could also include waste from conventional reactors, and from existing stockpiles of plutonium. Thus the inefficient once-through fuel cycle of conventional reactors would be avoided, and the problem of peak uranium would be avoided. The fuel cycle is designed to make extraction of uranium or plutonium in a form useful for nuclear weapons very difficult, and the on-site reprocessing would minimise the transport of large quantities of radioactive waste or nuclear fuel.

Critics point out that this very impressive-sounding list of IFR features has flaws. The concept has never been tried – a prototype IFR was under construction at Argonne National Laboratory in the US, but the programme was cancelled in 1994 three years from completion. Using liquid sodium as the coolant is highly problematic because it is very reactive chemically – if it comes into contact with air it burns, and with water it explodes. A number of fast reactors in the US, UK, France, etc. tried to use sodium cooling, but there were numerous problems with leaks and reliability, and all are now shut down. The new form of pyro-reprocessing required by the fuel cycle has never been tested. On nuclear weapons proliferation, the plutonium used in the IFR could make inefficient bombs, and the operation of such a reactor could be changed to produce plutonium that would work well in nuclear weapons. The costs of the reactor, reprocessing plant and fuel all seem to be very high. Finally, it seems that prototype IFRs could not be operating until about 2020, and useful amounts of power might not follow for at least a decade and probably more after that.

In addition to uranium and plutonium, thorium is another element that can be used as a nuclear fuel. It is roughly three times more abundant than uranium, and the deposits are easier to mine and process as they are more concentrated. Countries with very large thorium deposits include India, the USA, Australia, Brazil, Venezuela and Turkey. Unlike uranium, which has to be enriched to increase the concentration of the fissile uranium-235, natural thorium consists almost entirely of one isotope, thorium-232 (which has 90 protons and 142 neutrons), and does not need enrichment – a major point in favour of thorium.

Thorium-232 itself is not fissile, but it can absorb a slow neutron to produce (via two beta decays) the fissile isotope uranium-233, and this is the fissile material used to produce energy. To start the process some uranium-233, uranium-235 or plutonium-239 is needed, but once started it can be self-sustaining.

A claimed advantage of thorium reactors is that there is far less long-lived radioactive waste than from uranium reactors. This would greatly reduce the size, cost and required lifetime of storage facilities for the waste.

Another claimed advantage of thorium reactors is that it would be quite difficult to use their uranium-233 to produce nuclear weapons. The main reason is that along with uranium-233 some uranium-232 is produced, and its decay chain produces strong gamma radiation which not only makes handling very difficult, but also makes it harder to do in a clandestine way. However, some critics say that this advantage may be overstated and that there may be feasible methods for making bombs using thorium reactors. This gamma radiation also makes routine processing of separated uranium-233 much more difficult than for uranium-235, as remote handling in heavily shielded facilities is required.

Proposals for using thorium include various types of reactors. The quickest to implement would be to use solid-fuel reactors similar to those used at present with uranium. However, even for that case the fuel fabrication and waste handling have some technical difficulties to overcome, and would need further research and development. So even fairly conventional thorium reactors probably could not be available for at least 10–15 years, and more advanced designs would take far longer.

India, having large deposits of thorium ore but little uranium, has the most well-established thorium research and development programme. It has been using some thorium in its two Kakrapar pressurised heavy-water reactors. ThorEnergy in Norway has undertaken an extensive research effort and is promoting thorium fuels for both current and future reactors. Both these programmes are for solid-fuel reactors.

More advanced proposals tend to use thorium in reactors that breed nuclear fuel. A big advantage over uranium is that thorium does not need to use fast neutrons. However, as discussed earlier breeder reactors are decades away at best.

Thorium reactors using liquid fuel may be promising: an example is the Liquid Fluoride Thorium Reactor (LFTR). This is an advanced breeder reactor concept in which the core is uranium-233 surrounded by a thorium blanket. Both the core and blanket are liquids at atmospheric pressure, and consist of compounds (e.g. fluorides) of uranium-233 and thorium, respectively, as well as other compounds. The liquids cool the reactor. Uranium-233 is bred in the thorium blanket and continuously removed to add to the core. Manufacturing the fuel and processing the waste might be easier in such a liquid-fuel reactor, and interesting safety advantages are claimed:

This approach was researched in the 1960s and is now being revived. There is interest in liquid fuel reactors in China, Canada, Russia, France, and in the USA where enthusiast Kirk Sorenson has started a company called Flibe Energy, calling thorium the ‘next giant leap’ in energy technology.

Enthusiasts for thorium nuclear power claim that it offers a truly sustainable and abundant energy source. However, advanced types of thorium reactors need to go through considerable research and development before even a demonstration phase is possible, and therefore must be at least decades off even if problems can be overcome. To learn more, we suggest Wikipedia, an article in favour from the World Nuclear Association, and a more sceptical report from the UK National Nuclear Laboratory.

Unlike electricity generation using fossil fuels, nuclear reactors require so little fuel that, despite the fuel being very difficult and expensive to produce, 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 EPRs, being built by the French firm Areva in two locations, one in France (Flamanville; photo) and the other in Finland (Olkiluoto). These are a new pressurised-water design that is claimed to be more efficient and safer than previous reactors. This design is the choice to be used for some of the new power stations proposed for the UK. However, the Olkiluoto reactor is currently about four years behind schedule after a similar time under construction – start-up is estimated for mid-2013 at the earliest, and the cost has risen from 3 to 6.6 billion euros. It has also been criticised repeatedly by the Finnish nuclear safety regulator: first over problems with concrete, then with welds, and now its control system (which is also an issue with the UK Health and Safety Executive).

The Flamanville reactor was started more recently, but there have been delays in construction due to safety issues with concrete and steel quality. It is also about four years late, and the estimated cost has risen from 3.3 to 6 billion euros. Areva says these are teething problems with a new design.

The cost increases for Olkiluoto and Flamanville mean that the price of the electricity they generate will be perhaps 33% to 45% higher than expected. Proposals to build EPRs in a number of other countries have failed, due to the cost being much higher than for competing designs.

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 rose to £73 billion from £53 billion within just two years, 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. However, the liability of the owners in case of serious problems such as an accident will be limited.

The disaster at Fukushima has triggered a nuclear safety review in the UK. This is likely to delay the timescale for approving and building new EPR and AP1000 reactors. It is not yet known whether it will also raise safety requirements and thus increase the cost of new reactors.

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. On current planning, the first few new ones cannot be ready before about 2018–2020. The government is trying to speed up the planning and regulatory processes, 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 long gap since the last ones were built.

Like air travel, nuclear reactor safety is tightly regulated, and incidents are investigated not just to apportion blame but 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 in 1986. 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 Cumbria in 1957, and Three Mile Island in the US in 1979. Twenty-five years after Chernobyl, the disaster at Fukushima in 2011 has again focused attention on the issue.

At Windscale (now Sellafield) in 1957 the graphite core of a reactor used to produce plutonium for nuclear weapons caught fire 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.

Lack of information, and dishonesty in the information available during and after the accident, contributed to public distrust and concern.

The accident in the Three Mile Island power station in 1979 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 doses of radiation. 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 reactor accident in history (photo at right). A huge power excursion and the resulting steam explosion and fire spread radioactive contamination across a large area of Europe. The cause was operator errors combined with a reactor design that was unsafe – among other things there was no containment vessel.

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 permanent resettlement of about 220,000 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.

A United Nations report in 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. However, there are also far higher estimates of the number of casualties, ranging up to hundreds of thousands of deaths from cancer. The differences in the estimates have not been resolved because most of these would be hidden as relatively small increases in cancer incidence among millions of people spread over much of Europe.

A key issue in making such estimates is the effect of low doses of radiation, which is very difficult to ascertain and remains controversial. The disagreement concerns whether there is a threshold below which the damage caused by a low dose can be repaired by the body, or whether even very small doses are ultimately harmful. A careful, long-term, wide-ranging study would help to resolve the huge disagreements in the estimates of the effects of the Chernobyl accident, and also help to resolve the uncertainty about the effects of low-level radiation exposure. Unfortunately, such a study has not been done. There is now an EU-based proposal to do one, but it is not yet funded and if it goes ahead there will be many difficulties – it’s a long time since accident, and there are many complicating factors related to the break-up of Soviet Union and the psychological effects of Chernobyl. In the absence of accepted conclusions, the pro-nuclear camp quotes reports that Chernobyl hardly killed anyone, while the anti-nuclear camp seizes on the worst estimates. The very large uncertainties in the numbers are often not mentioned.

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. About 200 tonnes of highly radioactive material remain deep within it, and this poses a serious environmental hazard until it is better contained. A huge, new 32,000 tonne structure 257 metres wide, 105 metres high, and costing about £1.4 billion, has been designed. After years of delay most of the funding now seems to be available, and the completion date is estimated to be 2015. The structure will be constructed 500 metres from the reactor due to radiation, and then moved into place. It is estimated that the clean-up of the site will take about 50 years.

The second worst nuclear reactor accident to date was caused by the huge earthquake and tsunami in north-east Japan in March 2011. However, to keep things in perspective, the serious problems at the Fukushima nuclear power station were part of a much bigger catastrophe, which killed many thousands of people and did an enormous amount of damage. Radiation from Fukushima has not, so far, killed anyone, although the danger is not over.

The earthquake was one of the 10 most powerful ever measured, and the tsunami was about 14 metres high at Fukushima. The area had been considered to be at relatively low risk – the Fukushima reactors were designed to withstand less serious earthquakes, and tsunamis up to 5.7 metres. This raises the general question of how rare an event to design for, while keeping increasing costs in mind.

The affected plant was Fukushima Daiichi (‘number one’), Japan’s biggest reactor complex, which has six reactors: reactors 1 to 4 are very close together, with 5 and 6 in a separate building (see left-hand photo below). These are Boiling Water Reactors (BWRs), a 1960s General Electric design (Generation II), commissioned in the 1970s. This type of reactor is in wide use, especially in the US. Concentrating six reactors in one place made Fukushima Daiichi one of the 15 largest nuclear generation sites in the world; in view of what happened some people have questioned the wisdom of building nuclear reactors in large clusters like this.

When the earthquake occurred, reactors 4–6 were off for maintenance and reactor 4’s fuel had been removed. Reactors 1–3 switched off when the earthquake cut off electric power. Even when off, the radioactive materials in the reactors generate considerable heat and pumps are needed to cool them. In case of a power failure there are emergency diesel generators, but the tsunami swamped them. The pumps operated using backup batteries until they were depleted, and then the cooling failed. The resulting overheating caused most of the subsequent problems.

In 1990 the US Nuclear Regulatory Commission listed failure of the emergency generators – and hence failure of the cooling system – of plants in seismically active regions as one of the most likely risks. The Japanese Nuclear and Industrial Safety Agency cited this in 2004, but Fukushima’s operator, the Tokyo Electric Power Company (which already had a poor safety record), did not respond to these warnings. The newer Fukushima Daiini (‘number two’) plant, a few miles away, survived the earthquake and tsunami because its emergency generators were better protected against flooding.

Another problematic feature of these reactors is the storage of highly radioactive spent fuel very close to the reactors, in water pools to cool them. Reactor 4’s pool also contained all of its fuel, which had been unloaded. Due to lack of capacity on-site, the no. 2 and no. 4 ponds contained more spent fuel than normal. These pools also overheated after the earthquake, so much of their cooling water boiled off.

The overheating in reactors 1–3 generated hydrogen gas. Fire engines pumped in seawater to cool the reactors and prevent complete meltdown of the fuel and serious explosions. The excess pressure caused by the hydrogen had to be vented off, and over the following weeks there were hydrogen explosions at all three reactors. The one in reactor 2 caused a leak in its containment vessel, now claimed to be sealed although contaminated water continues to leak out. Reactors 1–3 have all suffered partial meltdowns, and there are indications that all three may have leaks in their containment vessels. In addition, the material in the spent fuel pools of reactors 1, 3 and 4 was partly uncovered – reactor 4’s had an explosion and then a fire, which caused damage to the reactor itself. Reactors 1–4 have been written off; reactors 5 and 6 will probably never run again either. A ‘cold’, i.e. safe, shutdown of reactors 1–3 is predicted to be at least six to nine months off.

The photos below show: (left) the Fukushima Daiichi plant before the accident, with reactors 1-4 at left and 5–6 at right a short distance away; (centre) the damaged reactor 3; (right) the damaged reactor 4.

As a result of the explosion and leaking containment vessels, radioactive material was released to the air, contaminating the surrounding area and some ‘hotspots’ further away, and a lot of highly radioactive cooling water drained into the sea. The radioactive material was mainly iodine-131, which has a half-life of 8 days, and caesium-137, with a half-life of 30 years. However, there may also be longer-lived materials such as plutonium. There are severe problems working on the site due to the high level of radiation near the reactors, which severely limits the time workers can spend there. An exclusion zone of 20 km around the plant led to 80,000 people being evacuated, and there is concern about food and water supplies in the area. Some experts have urged increasing the zone to 30 km due to the hotspots of radiation outside the 20 km zone; this would more than double the number of people affected. It is not known how long the area around the reactors will be uninhabitable, and some of the nearby villages will probably have to be abandoned for decades if not permanently.

No one has so far been killed by radiation from Fukushima Daiichi. However, reactors 1–3 are not yet stable and the spent fuel pool of reactor 4 may still be dangerous. The local population is homeless for an unknown period, a substantial part of Japan’s electricity generating capacity has been written-off, and there is very costly damage, including the need to make the destroyed reactors safe for a long time to come – cleaning up the Fukushima area will take many years. The majority of the other reactors in Japan have been turned off pending tests of how well they would cope with problems, leading to a shortage in Japan’s electricity supplies, and some of the reactors may never be turned on again. Fukushima raises serious questions about the safety of nuclear reactors and the cost of dealing with failures, especially in earthquake zones but also in dealing with the unexpected in general. The possibility that this sort of thing can happen, even very rarely, in a well-regulated and advanced country, makes nuclear power look like a less attractive and more expensive option, and should focus attention on the possible risk factors.

Recent reactors have more comprehensive safety features than Chernobyl and Fukushima, and new designs claim to be safer still. However, a number of factors undermine public confidence:

Following Fukushima, a number of countries have temporarily suspended work towards new nuclear installations or turned off very old reactors in order to review their safety. Germany and Switzerland have announced that they will eventually stop using nuclear power, and Japan has cancelled plans to increase nuclear generation from about 30% to 50% of its electricity. In the UK, a safety review published interim findings in May 2011. This pointed out that such a huge earthquake and tsunami are very unlikely in the UK and that newer reactors have improved safety features. It found no need to curtail the operations of nuclear plants in the UK. The report listed 25 areas for review, though some people felt that its headline conclusions seemed somewhat complacent and/or premature.

It has been said that nuclear reactors are a ‘brittle’ technology, in the sense that a rare but not impossible disaster can have huge and long-term consequences and costs. Fukushima was hit by an earthquake and tsunami far more serious than it had been designed to cope with, and about a fifth of all existing reactors and others that are being planned world-wide are also in seismically active areas. Climate change is predicted to cause a rise in sea level and more violent weather, which could affect some of the many reactors located on sea coasts. Will reactors be able to deal safely with the most extreme earthquakes, tsunamis, fires, storms, floods and tornados?

There is also the human element. Safety is not just a matter of rules, and it is not easy or cheap to implement. It requires an open, honest culture and good oversight, covering the regulators, the reactor operators, and the rest of the workforce. There must not be corruption in construction or operation. Even advanced, democratic countries have had failings. What about the many reactors now planned for countries that might have bigger problems with this, such as Belarus, Chile, Egypt, Indonesia, Jordan, Lithuania, Malaysia, Morocco and Turkey?

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 isotopes in the waste, such as iodine-131, are intensely radioactive but have very short half-lives (8 days for iodine-131). Others, such as plutonium-239 (half-life 24,000 years), 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 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, sea-level rise, earthquakes, and other natural forces, as well as political interference, on a timescale comparable to the entire history of human civilisation.

No country has a fully implemented waste disposal policy actually working yet. A few, such as Finland and Sweden, have earmarked sites for underground low-term storage and begun construction, but not yet started to use them. The first to go into operation will be Onkalo, in Finland, in 2020. The US had a designated site in Nevada, but after more than 10 years and a variety of legal challenges the project has been cancelled. The UK has a policy of disposal deep underground, see below.

In the interim, waste from reactors is stored on the surface, most often at the reactor sites. This is done for a number of years with fresh waste in any case, to allow the initial intense radiation to decrease. Much of the waste is stored in pools of water, to provide cooling for the heat generated. However, this can lead to problems with corrosion and leaks, which can contaminate groundwater and also, if the pool drains rapidly by accident, cause a fire that releases radioactive material. (This happened at Fukushima.) A better solution is to use dry, sealed casks inside concrete vaults. A serious concern is that most waste storage at present is not secure, and is more vulnerable to terrorist attacks than the reactors themselves.

One of the reasons for developing new types of reactors is that it may be possible to use fuel cycles that produce waste in smaller quantities, and/or are made up of isotopes with shorter half-lives, which would reduce the waste disposal problem.

Used reactor fuel still contains much of its original uranium. In the UK, some of the used fuel is sent to Sellafield for reprocessing to recover the usable fuel. High-level wastes arising from this, as well as many tonnes of plutonium, 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) considered what to do about the UK’s waste. It also looked into the implications of possibly abandoning any reprocessing of used fuel (see the next section). CoRWM recommended deep geological disposal of high and intermediate-level wastes long-term, and the government has accepted its key recommendations. CoRWM said that the government should move swiftly to implement its proposals, but it acknowledges that actually commissioning a repository could take decades. 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.

About one-third of the UK appears to be geologically suitable. The location of the repository would be on basis of community agreement, with incentives for communities to volunteer. However, a recent call for local authorities willing to do this has had a poor response, and a site has not yet been identified.

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 serious disadvantage of reprocessing is that it is relatively easy to recover plutonium in order to use it for nuclear weapons. Unprocessed reactor waste is highly radioactive and dangerous to work with, but once the plutonium it contains has been extracted it is not so radioactive and is relatively easy to handle without elaborate equipment. (The main danger is inhalation of plutonium particles, which causes cancer years later.) If such plutonium were stolen, it would be relatively easy to make a nuclear bomb. That is why the US stopped civilian reprocessing as part of its non-proliferation policy, but that US policy may soon be reversed. It is also why it is very disturbing when countries cannot account for all the uranium and plutonium in their possession, as has happened in Japan and at Sellafield (see below).

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, but it only began operation in 1997. In 2004–2005 THORP suffered a large leak of a highly radioactive solution. An inquiry determined that a design error had led to the leak, while a complacent culture at the plant delayed its 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. However, it is of great concern that enough uranium and plutonium to make perhaps 30 nuclear bombs went missing without being noticed. Production eventually restarted at the plant in 2008, but various other problems have limited its capacity.

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. Trouble began early on, in 1999, when Japan returned a shipment of fuel because its inspection records had been falsified; business from Japan was suspended. The MOX plant was designed to produce 120 tonnes of fuel per year, then downrated to 40 tonnes per year. But over its first ten years of operation its total output was only 5 tonnes, and continuing technical problems have prevented any output at all in some years. In 2008 orders for the plant had to be fulfilled in France, and the plant was reported in the media as having ‘failed’. In May 2010 a new agreement was signed with Japanese customers for future MOX supplies. However, in August 2011 the Nuclear Decommissioning Authority announced that the MOX Plant would close, due to the loss of Japanese orders following the Fukushima disaster.

Reports from the Health and Safety Executive continue to mention problems due to various leaks, inadequate staff training, and failure to fix identified defects promptly. The latest ‘lifetime plan’ for decommissioning of old facilities at Sellafield over the next 110 years has not yet been accepted.

An important reason for considering nuclear power differently from other energy technologies is its 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. The same methods (e.g. centrifuges) used to enrich fuel for power reactors can also be used to continue the enrichment process to produce highly enriched uranium for use in atomic bombs. 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 world’s first commercial electricity-generating reactors (British Magnox) were built primarily to produce plutonium, and electricity was only a by-product.

There is serious concern that if more countries have nuclear electricity it could also assist some of them 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 at Sellafield), 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 easily be used for weapons.

Two of the 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 have not signed the treaty, including three nuclear weapons states (India, Pakistan, and Israel), 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 and Libya abandoned programmes 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. For a while it seemed that North Korea (which signed the NPT but then withdrew) was abandoning its nuclear weapons programme, but it has recently tested two atomic bombs. The current tense situation concerning Iran is centred on accusations that it is developing nuclear weapons.

Most of the discussion about building new reactors in the UK and other developed countries makes little or no mention of the situation world-wide. But 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 some countries should renew or increase their nuclear power capabilities, but that others should not have it. But spreading and encouraging nuclear power increases the danger that more countries will develop nuclear weapons, which makes their eventual use (whether by governments or other organisations who obtain them) more likely.

Some new reactor designs are designed to make nuclear weapon production more difficult, by using fuel cycles which do not allow easy separation of plutonium. However, in the short term the nuclear power options being proposed are not based on these options.

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.

There is a huge amount of material available on nuclear power. Unfortunately, much of it – both for and against – is very biased. There are quite a few good and useful articles in the Wikipedia. These give more detailed explanations of most of the areas covered here, and provide many other references. A useful website for numbers, basic information, and country-by-country summaries (very much pro-nuclear) is the World Nuclear Association, while good starting places for anti-nuclear arguments are Friends of the Earth (Australia) (for general arguments) and Nuclear Consult (more UK-oriented). A useful report on the possible security dangers of nuclear power was commissioned by the Oxford Research Group. A thorough report that is neither strictly pro or con (with many details on US safety regulation, but also covering many other issues) is available from the Union of Concerned Scientists in the US – their website also includes a great deal of other useful material, covering nuclear and many other important issues.