| Nuclear energy past, present and future | | Print | |
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Reflections Quick links Nuclear Energy Past, Present and
Future Nuclear energy can be used in two broad ways: civil and military. In the early days these two areas were closely connected. The civil nuclear energy programme grew out of the nuclear weapons programme, and it is therefore right that we should pay some regard to nuclear weapons. In the popular mind, the nuclear age began with the bombs at Hiroshima and Nagasaki in August 1945. However, the story is older than that. Radioactivity was discovered in 1896 by Henri Bequerel, and soon afterwards, in 1905, Einstein formulated his famous equation E=mc2 which showed that, in theory, a very small amount of matter could be converted into a very large amount of energy. The challenge was how to do it in practice, but the idea occurred to many – reputable scientists as well as futurologists – that science had now discovered a way of providing unlimited energy. [ back to top ]
Nuclear fission Everything in the universe is made up of ‘atoms’. At first scientists thought that atoms were the smallest fragments of anything that could exist – the word derives from the Greek word meaning ‘indivisible’. In fact, we now know that atoms themselves are made up of smaller components – a very dense nucleus, made up of ‘protons’ which have a positive electrical charge and ‘neutrons’ which are uncharged, surrounded by a very much lighter cloud of ‘electrons’, which are negatively charged. The chemical behaviour of matter is determined by the electrons, but here we are much more interested in changes in the nucleus. Hydrogen is the lightest atom, consisting of just one proton electron, while uranium is the heaviest naturally occurring atom, consisting of 92 protons and a variable number of neutrons (146 and 143 in the two commonest forms, known as uranium-238 and uranium-235).
In recent years, a number of other atoms, which do not occur naturally on earth, have been produced, of which perhaps plutonium, with 94 protons and usually 145 to 148 neutrons, is the most well known. There are always a small number of free neutrons around in the environment, some of which come from outer space. Usually when neutrons strike the nucleus of an atom, they either just bounce off or they become absorbed by the nucleus in question. However, the nuclei of a very small group of large atoms, such as ‘uranium-235’, behave in a very different way if a neutron strikes them. These easily fissionable (or fissile) materials break up into two smaller atoms, giving off two or three more loose neutrons and a quite extraordinary amount of heat. This process is called ‘nuclear fission’. In principle, each of the neutrons which are produced could then hit another uranium atom and cause another fission, so creating a chain reaction. If we do nothing to control the reaction, then in some circumstances it might accelerate rapidly. One fission may produce three neutrons, which could in theory cause three more fission reactions, giving nine neutrons, which could cause nine more fissions giving twenty-seven neutrons, and so on. This is in effect what happens in an atom bomb. In practice, quite a few of the neutrons are lost at the edges of the material or absorbed harmlessly by other material present. (In a nuclear power reactor, for example, quite a lot of neutrons are absorbed by the more passive kind of uranium, known as uranium-238, which makes up the main part of the fuel.) If on the other hand, all the neutrons get lost or are absorbed somehow, the reaction will stop altogether. The interesting case from the point of view of power production is when all of the neutrons from each fission are absorbed except for one. This one will cause one more fission, and one neutron from this will cause one more fission, and so on. So it is possible to have a controlled fission reaction which will go on for as long as we have fissile material. This is the process that occurs in a nuclear power reactor. The phenomenon which is now known as fission of uranium was first reported in Berlin in December 1938. Four years later on December 1942, the famous Italian-American physicist Enrico Fermi started the world’s first fission reactor, in a Chicago squash court, and it is perhaps this moment that can most fairly be called the beginning of the nuclear age. [ back to top ]
Post-war developments The first UK research reactor – in fact the first in Europe – the Graphite Low Energy Experimental Pile (GLEEP) at Harwell, started up in 1947, and in the same year work began on two air-cooled plutonium-producing reactors (or piles) at Windscale. These began production in 1950 and 1951 respectively, but were never designed to produce electricity. In 1949 it was decided that the next plutonium-producing reactors, to replace the Windscale piles in due course, should also be capable of generating electricity. This decision marks the start of civil nuclear energy in Britain. The first of four such reactors, which were built at Calder Hall near Windscale in Cumbria, was opened by the Queen in 1956. Four more were constructed at Chapelcross, 70 miles away in Dumfries and Galloway, and opened in 1959. Calder Hall and Chapelcross will have had long and successful operating lives (for most of which they were used solely as electricity producers) until closure in 2003 and 2005 respectively. [ back to top ]
How fission reactors
work
The amount of energy released inside a nuclear reactor can be controlled by using ‘control rods’. These are made from substances such as boron steel or silver and fit between the fuel rods. They can be lowered or raised. These control rods absorb neutrons, so lowering them reduces the number of neutrons available to cause fission of uranium. If they are lowered completely, the reactor will shut down. The heat energy released by the nuclear fission process is continually removed from the reactor core by a ‘coolant’. The coolant flows at a high temperature from the core to a heat exchanger (or ‘boiler’), where it converts water into steam. The most common coolants are:
From this point onwards, nuclear reactors are just like coal-fired or gas-fired power stations – the steam (or hot helium) goes to drive large wheels called turbines – and the electricity that is produced is exactly the same. Uranium is an extraordinarily efficient fuel – one tonne of uranium fuel used in a modern nuclear reactor (without recycling) produces the same amount of electricity as about 20,000 tonnes of coal. Unfortunately, the smaller atomic fragments from the process – known as ‘fission products’ – are highly radioactive, so the used or ‘spent’ fuel needs careful handling. Radioactive waste management is discussed in the booklet Nuclear Energy in the Environment, and the effects of radiation are considered in Radiation, Health and Nuclear Safety. [ back to top ]
The first UK
nuclear energy programme
In 1957 there was a fire in one of the military plutonium piles at Windscale. Both Windscale piles, which were reaching the end of their design lives, were closed down after the incident, and in 1959 what is now the Nuclear Installations Inspectorate (NII), part of the Health and Safety Executive, was set up as the independent government watchdog on the industry. Though the Windscale fire did relatively little real damage, it did mark the end of the early euphoria which had accompanied developments up to that point. [ back to top ]
The second
UK nuclear energy programme
Seven AGR stations were built in the UK to four different designs. Experience of the programme has been very mixed – most have operated reasonably well, although the first, Dungeness B, ordered in 1965, only began working properly in 1993, and ran heavily over time and cost, while others had a slow start. In fact, the UK was the only country which pursued gas-cooled reactors at this stage. Most countries, including France and Japan, chose to follow the US lead and use ordinary water as the cooling agent in their reactors, mainly in pressurised water reactors (PWRs) or in boiling water reactors (BWRs). The UK therefore found itself rather isolated from the global mainstream. One result was that the costs of building were higher, as very few individual units were built compared to PWR or BWR; another was that there was no international experience of solving the kind of problems that might arise with AGR technology.
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Prevention of nuclear weapons proliferation
At first the NPT had its critics. It treated the countries which already had nuclear weapons differently from those which did not, and there was suspicion that inspectors might gain access to issues of vital national security. However, things improved with the success of the Strategic Arms Limitation Talks (SALT) in the 1980s and the end of the Cold War after the collapse of the Soviet Union in 1989–90. France and China both signed the Treaty in 1992. By the start of the new century only India, Pakistan, Cuba and Israel were not signatories. In 2002 North Korea became the only country to withdraw from the NPT. The NPT has been very successful in preventing the spread of nuclear weapons. At the time of the Cuban missile crisis, President Kennedy had thought that by the millennium there would be up to 25 nuclear Weapons States. In reality, in addition to the five official Weapons States, only India and Pakistan have tested nuclear weapons (the former for the first time in 1974, the latter in 1997), though it is widely believed that Israel also has nuclear weapons capacity. On joining the Treaty in 1991, South Africa admitted that it had previously developed nuclear weapons, but had dismantled them. The NPT’s most notable failure was the discovery, after the first Gulf War in 1991, that Iraq, despite being a member of the NPT, had a moderately well-advanced secret programme to develop nuclear weapons. As a result, the IAEA took steps to strengthen the safeguards system further. The relationship between the uses of nuclear science for energy and for weapons is a complex one. Both are based on the fission of uranium, although nuclear fuel is very different from ‘weapons grade material’ and it is a difficult (and easily detectable) industrial process to convert one into the other. It follows that it is perfectly possible for a country to have nuclear energy without nuclear weapons, or vice versa. In fact, four of the five Weapons States developed their nuclear weapons well before using nuclear power (the exception being France), and in three cases before there was any nuclear electricity anywhere in the world. There are many countries with nuclear power stations (Belgium, Canada, Brazil, Japan and South Korea, to name just a few) and no nuclear weapons. In practice, all the countries which have developed nuclear weapons have done so through a specific programme largely unconnected with the use of nuclear energy. Ever since they started, the IAEA’s inspectors have had great success in limiting the spread of nuclear weapons or the use of nuclear energy materials for military purposes. However, in the new century attention has to an extent turned to preventing countries or terrorist groups getting hold of highly radioactive materials, say from hospital radiology departments or from old research reactors, and releasing them in such a way as to threaten people’s health or peace of mind. Though not connected with the use of nuclear energy, these threats are likely to require IAEA involvement for the foreseeable future. [ back to top ] Types
of reactor However, gas-cooled reactors only make up about 8% of the world’s nuclear capacity today. The pressurised water reactor (PWR) is the most common nuclear reactor design used in the world (accounting for over 60% of global nuclear power stations), and the UK’s only PWR is at Sizewell B in Suffolk. PWRs use water as both coolant and moderator. Water is pumped under high pressure (to prevent boiling) through the core of the reactor, reaching a high temperature. It is then used to boil other water in a separate circuit, to make steam.
There are other types of reactor in use in the world today. Boiling water reactors allow the water to boil in the reactor circuit and drive turbines directly without using heat exchangers and a separate water circuit. There are other types of thermal reactor, like the Canadian-designed CANDU, and the RBMK, a design unique to the Former Soviet Union which became infamous after the accident at Chernobyl in 1986. Until 1994 an experimental ‘fast reactor’ operated at Dounreay in Scotland. Fast reactors use a plutonium–uranium mix of fuel, produced from the reprocessing of used reactor fuel from normal (‘thermal’) reactors. Because there is no need for moderators to slow neutrons down (hence the name ‘fast’ reactor), these reactors can be more compact, and they are more fuel-efficient than thermal reactors. They can be used to ‘breed’ more plutonium from otherwise useless uranium-238, but can also be used as plutonium burners. Fast reactors could, for example, be used to destroy the world’s stockpile of military plutonium without producing any more, but they are rather more expensive to build than thermal reactors. Few operational fast reactors have been built (in France, Japan, the UK, Germany and the Former Soviet Union) and global experience has been generally disappointing. [ back to top ]
Reprocessing There are two broad options – either the spent fuel can be stored with a view to disposing of it as it is, or it can be recycled into its separate components. As with all recycling, there are arguments for and against.
Against it, reprocessing involves the use of chemicals and plant which become contaminated with radioactivity, causes emission of radioactive materials into the environment (although recent technological advances have reduced such emissions a hundredfold to very low levels), and is expensive. It also produces free plutonium which could represent a risk regarding the proliferation of nuclear weapons. It was initially assumed that plutonium would be needed to fuel a growing number of fast reactors, but this has not proved to be the case. Another way of addressing the issue would be to convert plutonium into mixed oxide fuel (MOX) as soon as it was separated. MOX can be used in pressurised water reactors as an alternative to fresh uranium fuel. Several countries have licensed reactors to use MOX fuel, notably France which has over 20 reactors so licensed. It is not surprising then that some countries have decided to pursue a reprocessing route and some have not. The USA, since the Carter administration (1977–81), has exerted considerable pressure on countries not to reprocess spent fuel, for fear of it helping countries to develop nuclear weapons, although recently there has been a debate about reversing this stance. The UK is one of a small group of countries, France being the main competitor, which can offer the business of reprocessing to other countries through BNFL’s facility at Sellafield in Cumbria. In all contracts signed since 1976, the country which owns the fuel will eventually have to take away all waste products, as well as the reusable uranium and plutonium, although this has not as yet been done. [ back to top ]
Liberalised energy
markets
After the oil price shocks of the 1970s, fuel prices had fallen significantly, in part because of significant oil discoveries outside the OPEC region. There were also major new discoveries of natural gas. As a result, governments in many countries no longer felt that secure energy supplies were under threat, and turned their attention to other aspects of energy policy, and especially to reducing energy costs. The Europe-wide ban on using gas for electricity was lifted in 1990, and private companies in competition replaced the state-owned electricity monopolies like the Central Electricity Generating Board (CEGB) in the UK. The monopolistic CEGB had been given a duty to supply power to any consumer who required it, in return for being able to pass the costs of any investment needed on to their captive customers. The CEGB had proved very effective in keeping the lights on, for example, during the miners’ strike of 1984–5 and after the storms of 1987. However, the government of the day believed that power costs were higher than they should have been because of the absence of competitive pressures, which meant that the CEGB did not necessarily operate as efficiently as possible. The CEGB was therefore broken up into three parts. Two companies with fossil-fuel power stations were privatised in 1990, but the nuclear industry remained in state hands until 1996, when the AGRs and Sizewell B were privatised. The Magnox stations were not privatised, as they were near to the end of their lives. There would not be enough time to raise the finances needed to deal with their decommissioning and waste management costs, which are high, before they closed down. (As might be expected for the world’s first attempt at nuclear power stations, they were not as efficient as modern nuclear stations like Sizewell B, and therefore produced rather more waste per unit of electricity than did their successors.) In 1989 the plans to build more nuclear stations, including Hinkley Point C, were in effect abandoned. This was partly as a result of the disappointing experience of nuclear construction projects in some countries, but also because of changes in the electricity supply market. The accident at Chernobyl in 1986 undoubtedly had important repercussions as well. In the CEGB days, investment in nuclear energy looked attractive. Nuclear plants did not use much fuel – a tonne of uranium fuel in an AGR is worth about 20,000 tonnes of coal – so their costs would not go up much if fuel costs went up. Instead of being concentrated in a small number of countries, global uranium reserves are widespread, being found for example in the USA, Canada, Australia and Africa, so it was unlikely that supplies would be disrupted. Nuclear stations did not contribute to acid rain, one of the main environmental concerns of the 1970s and 1980s. And although it was expensive to build the stations, this investment could be recouped over a long period of time, as customers could not go anywhere else for their power. The introduction of competition had two important effects. First, because nobody had a guaranteed market, investment was more risky in an economic sense. So instead of potential investors being happy with a 5% rate of return on their very safe investment, as they would have been in the monopoly days, they began to demand higher rates of return – 10% or even more. This is more damaging to a technology which is expensive to build but relatively cheap to run, like nuclear energy, than it is for one which is cheap to build but more expensive to run, like CCGT. Second, since nobody has a guaranteed market at attractive prices for their output for very long, investors want their money back as quickly as possible. CCGTs can be built in 18 months (as opposed to about five years for a traditional nuclear station) at about a quarter to a third of the cost, so the financial risk to the investor is far less. As a result, investment in traditional nuclear power plant has declined radically in the developed world, although in countries like those of the Asia-Pacific region, with growing demands for electricity and problems in providing enough coal from their distant coalfields, nuclear investment continues to look attractive. However, introduction of competition into power markets has also had benefits for nuclear energy. Under the discipline of liberalised markets, the output from the UK nuclear power stations has increased significantly. Globalisation of nuclear energy markets raises the possibility of an international market in plant designs and components, rather than each country ploughing its own path at greater expense. And the plant designers themselves have responded to changing market conditions by developing simpler nuclear designs, which will both be cheaper and quicker to build and more reliable in the early days of operation than previous models. Nuclear stations with many of these features have been built successfully in the Asia-Pacific region, and the plant sellers, companies like BNFL-Westinghouse (which owns the AP1000 design) and AECL (advanced CANDU reactor), believe that a series of new nuclear power stations could produce electricity as cheaply as CCGTs using moderately priced gas. [ back to top ]
Future developments The future is very uncertain. Should renewables fail to fulfil the hopes of governments, and should fears about climate change continue to grow, then nuclear investment may well look more attractive. [ back to top ] Fusion
Fusion is the opposite of fission, joining light atoms together rather than splitting heavy ones apart. The sun and stars are powered by fusion. We can reproduce the effect on earth by bringing together two forms (or ‘isotopes’) of hydrogen called deuterium and tritium. The nuclei naturally want to push away from each other because they are both positively charged and repel each other. But if the isotopes are heated to temperatures of millions of degrees – much hotter than the surface of the sun – there is enough energy to force nuclei so close together that they fuse. At very high temperatures matter turns into a new form known as ‘plasma’, where the electrons are stripped away from the nuclei. Plasma cannot be held in a normal container, so the mixture has to be held in what is called a ‘magnetic bottle’, a very strong magnetic field which prevents it escaping. The mixture is heated with a blast of electric current, and at a certain point the nuclei begin to fuse. The products of this fusion are nuclei of helium atoms and neutrons which travel extremely fast (at speeds comparable to the speed of light). The trick will be to capture these neutrons and use their energy to create electricity. If a substance like lithium is used to trap the neutrons, a further product is more tritium which can be used as fuel for more fusion. In due course fusion could, in theory, become another energy option to go alongside fission, renewables and fossil fuels. Deuterium is very widespread in nature, and is found anywhere there is water. Lithium exists in rocks almost everywhere – the name is derived from the Greek word for ‘stone’. Tritium is expensive to make at present but, as noted above, could be produced by neutrons hitting lithium atoms. Fusion offers striking advantages. At any moment a fusion reactor would only require very small amounts of fuel – all of it could escape without being detectable nearby, so there is no danger of a major accident such as a ‘melt-down’. There is no long-lived radioactive waste, although the reactor itself does become radioactive over time. And like nuclear fission, it will not contribute significantly to climate change or rely on limited fossil fuels with other potentially beneficial uses. Research into fusion is well established – the European project, JET (Joint European Torus, the last word referring to the doughnut-shaped reactor) was established in 1978 at Culham in Oxfordshire, and there have been major ventures in the USA, Japan and Russia. These projects have proved that fusion can be made to happen on earth – in other words they have demonstrated the physics of the process. However, that is not the end of it. Indeed, engineers often claim that ‘the science is the easy bit!’ The next stage will be to develop and build a design which can sustain a self-supporting fusion reaction (so far all terrestrial fusion which has taken place has absorbed more energy than it has produced, simply because the reactors are too small for self-sustaining reactions), and which can then generate electricity. This stage will be known as International Thermonuclear Experimental Reactor (ITER). Interest in this step has been expressed by all of the countries presently involved in fusion, as well as by China and a number of others. Assuming the engineering challenges can be met, it will then be necessary to build a commercial prototype which will reveal the economics of the technology. It is far too early to speculate what the results may be, and even if a commercially attractive design should then be available, it would take some time before it established itself as a major source of world energy. Many people today believe it unlikely that fusion will be a major contributor by the year 2050, but it could become an important source of power after that if the technical and economic challenges can be met. |
It was declared at the outset that electricity generated
from Magnox stations would be more expensive than that
generated by burning coal. However, a number of factors
combined to make nuclear energy attractive at that time.
There was a determination among scientists that the
potentially devastating destructive force of the atom which
had been unleashed should be balanced by a force for good.
There was recognition of the importance of developing new
ways of making energy, a topic discussed in
This both reduced the amount of fuel needed, and
therefore waste produced, per unit of electricity
manufactured, and allowed the reactor to operate at a higher
temperature, which is more efficient. 
Successful as the IAEA’s programme of safeguards was,
fears remained. They were fuelled by concerns about the
effects of carrying out nuclear weapons tests above ground
level, and by the deepening of the Cold War, the most
notable nuclear scare being the Cuban missile crisis in
1962. Further efforts to control the arms race led to the
Nuclear Non-Proliferation Treaty (NPT) coming into force in
1970. The NPT accepted that there were five countries with
nuclear weapons (the ‘Weapons States’) at that time,
including France having tested a nuclear device in 1962 and
China in 1964, but declared a goal of preventing any more
from joining them. By signing the Treaty, a country agrees
to allow IAEA weapons inspectors to check as often as they
think fit that material or equipment from nuclear energy
programmes are not being diverted towards military uses.
Initially, reprocessing was introduced to extract
plutonium from spent nuclear fuel for use in nuclear
weapons. It was also recognised that spent Magnox fuel, made
mainly of natural uranium metal, could not be stored under
water for long periods of time as it would corrode. In
principle, reprocessing reduces the amount of fresh uranium
which has to be mined, so extending the lifetime of uranium
reserves and reducing local environmental impact (although
in fact freshly mined uranium has been rather cheaper than
reprocessed uranium in recent years, so removing the
incentive to use the recycled material). Reprocessing also
cuts the volume of highly radioactive material for eventual
disposal.
However, there were significant developments elsewhere
which were to affect the nuclear industry. The two most
important were the development of the combined-cycle gas
turbine (CCGT) which allowed vast, newly discovered gas
reserves to be converted into electricity far more cheaply
than had previously been the case; and the introduction of
competition into the electricity supply industry.
