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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 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 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 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 main arguments for renewing the use of nuclear power include:
- carbon dioxide-free generation, and low carbon dioxide production over
the full life-cycle,
- the need for always-available generation, to supplement
renewable energy sources (e.g. wind and solar) that do not work all the time
and are not entirely predictable,
- to replace existing nuclear (and perhaps fossil fuel) power
stations as a stop-gap while development of renewable technologies matures,
- the desire not to be dependent
on imported fossil-fuel supplies as North Sea gas and oil run out,
- new reactor designs that are claimed to be more efficient and inherently
safer in the short-term, more resistant to nuclear proliferation, and which
possibly generate their own fuel in the long-term.
The counter-arguments at the practical level include:
- concern that the actual costs – especially decommissioning – will
(again) turn out to be far higher than expected, and that the government
might have to pick up the bill,
- concern that nuclear power
would divert attention and effort from work to develop new renewable, clean
energy sources,
- doubts that enough new nuclear power stations could be ready soon enough
to act as an effective stop-gap en route to new renewable technologies.
The broader issues that worry many people are:
- safety – especially the risk of even one or two extremely serious
accidents,
- the continuing lack of a
functioning system for long-term storage of nuclear waste,
- the risk that
having more nuclear reactors in unstable regions of the world would lead
to more countries acquiring nuclear weapons, and the associated danger that
they will be used,
- the risk that nuclear fuel or waste might be used in various ways by terrorists.
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Nuclear Power
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
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 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.)
Fission and chain reactions
In nuclear fission the uranium-235 (or plutonium-239) 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 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. This would avoid some of the major problems of nuclear
fission, and is described on our
green energy page.
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Current Status and Plans
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) 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 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 about 50 nuclear reactors under construction, mostly in
Asia. Many more are being planned.
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 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. This dropped further in 2008 due
to problems with some of the older reactors. 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 will all be closed after
2010. 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) 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 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 has now been repaired at considerable expense.
Four others are limited to about two-thirds 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.
Proposals for new reactors in the UK
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 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.
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Arguments in Favour
of New Nuclear Power Stations
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 construction, fuel preparation,
or the 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 fossil-fuel generation.
The need for always-available
power generation, replacing existing facilities
The main renewable technologies now being adopted, mostly 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 to give British examples, 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 – some
of the reactors cannot simply be run flat out but must 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. These currently generate about one-sixth of UK electricity. The
government proposes to replace them with a new generation of reactors, some
of them probably similar to the ones now being built in Finland and France
(see below).
Even more new reactors would be needed if they were to replace some of the
dirtiest of the current 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 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 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
– 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. This is discussed
in the next section.
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New reactor designs
Generation III+
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.
EPR
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 and Flamanville, France (photo), 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 mentioned 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 are plans to build several EPRs in the US.
The EPR is now going through the UK's generic
design approval procedure, based on the proposals mentioned
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 2011.
AP1000 and ESBWR
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 are really 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 2011.
Generation IV
Generation IV reactors are futuristic designs still being researched
– they would 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.
IFR
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 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 use 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 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 after that.
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Concerns about Nuclear Power
Costs
and Timescales
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 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 is a very likely choice
to be used for some of the new power stations proposed for the UK. However,
the Olkiluoto-3 reactor is currently more than three years behind schedule
after a similar time under construction, and at least 50% over budget. 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, and the estimated cost has
risen by 21%. Areva says these are teething problems with a new design.
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.
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.
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Safety of Nuclear Power
Reactors
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. 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. 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. Lack of
information and honesty about the accident contributed to public distrust and
concern.
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 a large area of Europe. The cause was operator errors combined with
an unsafe reactor design.
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 much higher estimates of the number
of casualties, ranging up to 40,000 deaths from cancer. The disagreements
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 fairly low
doses of radiation, which remains controversial and is very difficult to ascertain.
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 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:
- Less serious accidents, incidents and "near misses" have
often not been reported honestly or openly by the operators.
- A number of leaks
and other malfunctions (e.g. in the US) were not repaired
promptly, even after they were detected and known to the safety regulator.
- If there is expanded use of nuclear power, especially combined with pressures
to build quickly, the chances of a major accident will increase.
This is especially true for countries with lower safety standards and/or
less stringent enforcement.
- In a competitive market, costs would be under pressure and safety measures
might well be skimped.
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Disposal of Nuclear Waste
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, 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
US has a designated site in Nevada, but more than 10 years on it looks as if
it may never open due to a variety of legal challenges regarding its suitability.
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. 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.
The UK situation
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.
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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 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; there has been no business from Japan since then.
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". A decision on whether to write the
plant off is expected soon.
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
over the next 110 years
has not yet been accepted.
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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 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
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 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
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 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, have not
signed the treaty (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 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. 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.
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Possibilities for terrorism
A nuclear-related terrorist attack could take various forms:
- A transporter of nuclear material, such as radioactive waste, might be
attacked, sabotaged or hijacked. An explosion or fire could spread the radioactivity.
If there are more nuclear power stations then more nuclear transports will
be needed.
- A plutonium store at a reprocessing plant like Sellafield
might be attacked to spread the
plutonium in it. Plutonium is a very toxic radioactive substance, particularly
when inhaled.
- A nuclear power station might be attacked. A successful
attack to disrupt the operation and cause a nuclear accident seems unlikely.
However, an attack could focus on the local storage for radioactive waste,
which is not protected by containment buildings in the same way as the
reactor.
- A crude nuclear weapon might be built using stolen plutonium (which can
also be separated easily from MOX fuel) and a simple implosion technique.
There is enough plutonium in civil stockpiles world-wide to build up to 40,000
nuclear bombs.
- A so-called dirty bomb might be built. This could be a very primitive
device, using high explosive to spread any type of radioactive material.
Although not necessarily very deadly, the cost and disruption of the required
clean-up operation could be considerable.
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.
Further reading
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 a good starting place for anti-nuclear arguments
is Friends of the
Earth (Australia). A
useful report on the possible
security dangers of nuclear power was commissioned by
the Oxford Research Group, while a thorough report that is neither strictly
pro or con (including much on US safety regulation, but also many other issues)
is available from the Union
of Concerned Scientists in the US.
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