NUCLEAR POWER- ALTERNATIVE
ENERGY SOURCE?
Nuclear power is the controlled use of nuclear
reactions to release energy for work including propulsion, heat,
and the generation of electricity. Human use of nuclear power to
do significant useful work is currently limited to nuclear fission
and radioactive decay. Nuclear energy is produced when a fissile
material, such as uranium-235 (235U), is concentrated such that
nuclear fission takes place in a controlled chain reaction and creates
heat — which is used to boil water, produce steam, and drive a steam
turbine. The turbine can be used for mechanical work and also to
generate electricity. Nuclear power is used to power most military
submarines and aircraft carriers and provides 7% of the world’s
energy and 15.7% of the world’s electricity.
The United States produces the most nuclear energy,
with nuclear power providing 20% of the electricity it consumes,
while France produces the highest percentage of its electrical energy
from nuclear reactors—80% as of 2006. Nuclear energy policy differs
between countries.
Advantages of nuclear energy for climate change
Nuclear energy uses an abundant, widely distributed
fuel, and mitigates the greenhouse effect if used to replace fossil-fuel-derived
electricity. International research is ongoing into various safety
improvements, the use of nuclear fusion and additional uses such
as the generation of hydrogen (in support of hydrogen economy schemes),
for desalinating sea water, and for use in district heating systems.
Construction of nuclear power plants in the U.S.
declined following the 1979 Three Mile Island accident and the 1986
disaster at Chernobyl. Lately, there has been renewed interest in
nuclear energy from national governments due to economic and environmental
concerns. Other reasons for interest include the public, some notable
environmentalists due to increased oil prices, new passively safe
designs of plants, and the low emission rate of greenhouse gas which
some governments need to meet the standards of the Kyoto Protocol.
Despite their misgivings, some environmental groups are increasingly
supporting nuclear power as it is seen as the lesser of two evils
when looking at greenhouse gas emissions from burning coal and fossil
fuels.
Issues surrounding nuclear energy
The use of nuclear power is controversial because
of the problem of storing radioactive waste for indefinite periods,
the potential for possibly severe radioactive contamination by accident
or sabotage, and the possibility that its use in some countries
could lead to the proliferation of nuclear weapons. Proponents believe
that these risks are small and can be further reduced by the technology
in the new reactors. They further claim that the safety record is
already good when compared to other fossil-fuel plants, that it
releases much less radioactive waste than coal power, and that nuclear
power is a sustainable energy source. Critics, including most major
environmental groups, believe nuclear power is an uneconomic, unsound
and potentially dangerous energy source, especially compared to
renewable energy, and dispute whether the costs and risks can be
reduced through new technology. There is concern in some countries
over North Korea and Iran operating research reactors and fuel enrichment
plants, since those countries refuse adequate IAEA oversight and
are believed to be trying to develop nuclear weapons. North Korea
has now developed nuclear weapons, while the Iranian government
vehemently denies the claims against Iran.
BRIEF HISTORY OF nuclear energy USE
Installed nuclear capacity initially rose relatively
quickly, rising from less than 1 gigawatt (GW) in 1960 to 100GW
in the late 1970s, and 300GW in the late 1980s. Since the late 1980s
capacity has risen much more slowly, reaching 366GW in 2005, primarily
due to Chinese expansion of nuclear power. Between around 1970 and
1990, more than 50GW of capacity was under construction (peaking
at over 150GW in the late 70s and early 80s) — in 2005, around 25GW
of new capacity was planned. More than two-thirds of all nuclear
plants ordered after January 1970 were eventually cancelled.
During the 1970s and 1980s rising economic costs
(related to vastly extended construction times largely due to regulatory
delays) and falling fossil fuel prices made nuclear power plants
then under construction less attractive. In the 1980s (U.S.) and
1990s (Europe), flat load growth and electricity liberalization
also made the addition of large new base load capacity unnecessary.
Washington Public Power Supply System Nuclear
Power Plants 3 and 5 were never completed. A general movement against
nuclear power arose during the last third of the 20th century, based
on the fear of a possible nuclear accident and on fears of latent
radiation, and on the opposition to nuclear waste production, transport
and final storage. Perceived risks on the citizens health and safety,
the 1979 accident at Three Mile Island and the 1986 Chernobyl accident
played a key part in stopping new plant construction in many countries.
Austria (1978), Sweden (1980) and Italy (1987) voted in referendums
to oppose or phase out nuclear power, while opposition in Ireland
prevented a nuclear program there. However, the Brookings Institution
suggests that new nuclear units have not been ordered primarily
for economic reasons rather than fears of accidents.
Financing for new reactors dried up when Wall
Street’s enthusiasm ended. Disillusionment was complete when new
research discredited the claim (previously accepted as fact even
by opponents) that nuclear power was still, despite all its problems,
the most cost-effective source of electricity. Industry figures
had omitted the factor of downtime. During the 1980s and early 1990s,
the newest and biggest U.S. plants were actually producing only
half the energy they were supposed to, due to shutdowns for refueling,
routine maintenance, retrofitting, and frequent minor mishaps. Since
that time, the capacity factor of existing nuclear power plants
has increased dramatically, and has been near 90% in the current
decade.
how nuclear power works
The key components common to most types of nuclear
power plants are:
Nuclear fuel
Neutron moderator
Coolant
Control rods
Pressure vessel
Emergency core cooling systems
Reactor protective system
Steam generators (not in BWRs)
Containment building
Boiler feedwater pump
Turbine
Electrical generator
Condenser.
Conventional thermal power plants all have a heat
source. Examples are gas, coal, or oil. For a nuclear power plant,
this heat is provided by nuclear fission inside the nuclear reactor.
When a relatively large fissile atomic nucleus (usually uranium-235
or plutonium-239) is struck by a neutron it forms two or more smaller
nuclei as fission products, releasing energy and neutrons in a process
called nuclear fission. The neutrons then trigger further fission.
And so on. When this nuclear chain reaction is controlled, the energy
released can be used to heat water, produce steam and drive a turbine
that generates electricity. It should be noted that a nuclear explosive
involves an uncontrolled chain reaction, and the rate of fission
in a reactor is not capable of reaching sufficient levels to trigger
a nuclear explosion because commercial reactor grade nuclear fuel
is not enriched to a high enough level.
The chain reaction is controlled through the use
of materials that absorb and moderate neutrons. In uranium-fueled
reactors, neutrons must be moderated (slowed down) because slow
neutrons are more likely to cause fission when colliding with a
uranium-235 nucleus. Light water reactors use ordinary water to
moderate and cool the reactors. When at operating temperatures if
the temperature of the water increases, its density drops, and less
neutrons passing through it are slowed enough to trigger further
reactions. That negative feedback stabilizes the reaction rate.
Experimental technologies
A number of other designs for nuclear power generation,
the Generation IV reactors, are the subject of active research and
may be used for practical power generation in the future. A number
of the advanced nuclear reactor designs could also make critical
fission reactors much cleaner, much safer and/or much less of a
risk to the proliferation of nuclear weapons.
Integral Fast Reactor has advantages
over current reactor design, especially in the areas of safety,
efficient nuclear fuel usage and reduced waste. The IFR was built,
tested and evaluated during the 1980s and then retired under the
Clinton administration in the 1990s due to nuclear non-proliferation
policies of the administration. Recycling spent fuel is the core
of its design and it therefore produces a fraction of the waste
of current reactors.
The Pebble Bed Reactor is designed
so high temperatures reduce power output by doppler broadening of
the fuel’s neutron cross-section. It uses ceramic fuels so its safe
operating temperatures exceed the power-reduction temperature range.
Most designs are cooled by inert helium, which cannot have steam
explosions, and which does not easily absorb neutrons and become
radioactive, or dissolve contaminants that can become radioactive.
Typical designs have more layers (up to 7) of passive containment
than light water reactors (usually 3). A unique feature that might
aid safety is that the fuel-balls actually form the core’s mechanism,
and are replaced one-by-one as they age. The design of the fuel
makes fuel reprocessing expensive.
SSTAR, Small, Sealed, Transportable,
Autonomous Reactor is being primarily researched and developed in
the US, intended as a fast breeder reactor that is tamper resistant
and passively safe. Subcritical reactors are designed to be safer
and more stable, but pose a number of engineering and economic difficulties.
Controlled nuclear fusion could in principle be used in fusion power
plants to produce safer, cleaner power, but significant scientific
and technical obstacles remain. Several fusion reactors have been
built, but as yet none has ‘produced’ more thermal energy than electrical
energy consumed. Despite research having started in the 1950s, no
commercial fusion reactor is expected before 2050. The ITER project
is currently leading the effort to commercialize fusion power.
Thorium based reactors make it
possible to convert Thorium-232 into U-233 in reactors specially
designed for the purpose. In this way, Thorium, which is more plentiful
than uranium, can be used to breed U-233 nuclear fuel. U-233 is
also believed to have favorable nuclear properties as compared to
traditionally used U-235, including better neutron economy and lower
production of long lived transuranic waste.
Advanced Heavy Water Reactor is a proposed heavy
water moderated nuclear power reactor that will be the next generation
design of the PHWR type. Under development in the Bhabha Atomic
Research Centre (BARC).
The Nuclear Fuel Cycle
The Nuclear Fuel Cycle begins when uranium is
mined, enriched, and manufactured into nuclear fuel, which is delivered
to a nuclear power plant. After usage in the power plant, the spent
fuel is delivered to a reprocessing plant or to a final repository
for geological disposition. In reprocessing 95% of spent fuel can
be recycled to be returned to usage in a power plant.
A nuclear reactor is only a small part of the
life-cycle for nuclear power. The process starts with mining. Generally,
uranium mines are either open-pit strip mines, or in-situ leach
mines. In either case, the uranium ore is extracted, usually converted
into a stable and compact form such as yellowcake, and then transported
to a processing facility. At the reprocessing facility, the yellowcake
is converted to uranium hexafluoride, which is then enriched using
various techniques. At this point, the enriched uranium, containing
more than the natural 0.7% U-235, is used to make rods of the proper
composition and geometry for the particular reactor that the fuel
is destined for. The fuel rods will spend about 3 years inside the
reactor, generally until about 3% of their uranium has been fissioned,
then they will be moved to a spent fuel pool where the short lived
isotopes generated by fission can decay away. After about 5 years
in a cooling pond, the spent fuel is radioactively cool enough to
handle, and it can be moved to dry storage casks or reprocessed.
fuel sources for nuclear energy
Uranium is a common element, occurring almost
everywhere on land and in the oceans. It is about as common as tin,
and 500 times more common than gold. Most types of rocks and soils
contain uranium, although often in low concentrations. At present,
economically viable deposits are regarded as being those with concentrations
of at least 0.1% uranium. At this cost level, available reserves
would last for 50 years at the present rate of use. Doubling the
price of uranium, which would have only little effect on the overall
cost of nuclear power, would increase reserves to hundreds of years.
To put this in perspective; a doubling in the cost of natural uranium
would increase the total cost of nuclear power by 5%. On the other
hand, if the price of natural gas was doubled, the cost of gas-fired
power would increase by about 60%. Doubling the price of coal would
increase the cost of power production in a large coal-fired power
station by about 30%.
Current light water reactors make relatively inefficient
use of nuclear fuel, leading to energy waste. More efficient reactor
designs or nuclear reprocessing would reduce the amount of waste
material generated and allow better use of the available resources.
As opposed to current light water reactors which use uranium-235
(0.7% of all natural uranium), fast breeder reactors use uranium-238
(99.3% of all natural uranium). It has been estimated that there
is anywhere from ten-thousand to five-billion years’ worth of uranium-238
for use in these power plants. Breeder technology has been used
in several reactors. In 2006, the only breeder reactor producing
power was BN-600 in Beloyarsk, Russia. (The electricity output of
BN-600 is 600 MW — Russia has planned to build another unit, BN-800,
at Beloyarsk nuclear power plant.) Also, Japan’s Monju reactor is
planned for restart (having been shut down since 1995), and both
China and India intend to build breeder reactors.
Another alternative would be to use uranium-233
bred from thorium as fission fuel — the thorium fuel cycle. Thorium
is three times more abundant in the Earth’s crust than uranium,
and (theoretically) all of it can be used for breeding, making the
potential thorium resource orders of magnitude larger than the uranium
fuel cycle operated without breeding. Unlike the breeding of U-238
into plutonium, fast breeder reactors are not necessary — it can
be performed satisfactorily in more conventional plants.
Proposed fusion reactors assume the use of deuterium,
an isotope of hydrogen, as fuel and in most current designs also
lithium. Assuming a fusion energy output equal to the current global
output and that this does not increase in the future, then the known
current lithium reserves would last 3,000 years, lithium from sea
water would last 60 million years, and a more complicated fusion
process using only deuterium from sea water would have fuel for
150 billion years. For comparison, the Sun has an estimated remaining
life of 5 billion years.
Reprocessing of nuclear waste
Reprocessing can recover up to 95% of the remaining
uranium and plutonium in spent nuclear fuel, putting it into new
mixed oxide fuel. Reprocessing of civilian fuel from power reactors
is currently done on large scale in Britain, France and (formerly)
Russia, will be in China and perhaps India, and is being done on
an expanding scale in Japan. Iran has announced its intention to
complete the nuclear fuel cycle via reprocessing, a move which has
led to criticism from the United States and the International Atomic
Energy Agency. Reprocessing of civilian nuclear fuel is not done
in the United States due to proliferation concerns.
Solid waste
Nuclear power produces spent fuel, a unique solid
waste problem. Highly radioactive spent fuel needs to be handled
with great care and forethought due to the long half-lives of the
radioactive isotopes in the waste. In fact, fresh spent fuel is
so radioactive that less than a minute’s exposure to it will cause
death. However, spent nuclear fuel becomes less radioactive over
time. After 40 years, the radiation flux is 99.9% lower than it
was the moment the reactor was last shut off, although still dangerously
radioactive.
Spent fuel is primarily composed of unconverted
uranium, as well as significant quantities of transuranic actinides
(plutonium and curium, mostly). In addition, about 3% of it is made
of fission products. The actinides (uranium, plutonium, and curium)
are responsible for the bulk of the long term radioactivity, whereas
the fission products are responsible for the bulk of the short term
radioactivity. It is possible through reprocessing to separate out
the actinides and use them again for fuel, but this often requires
special fast spectrum reactors, which produce a reduction in long
term radioactivity within the remaining waste. In any case, the
remaining waste will be substantially radioactive for at least 300
years even if the actinides are removed, and for up to thousands
of years if the actinides are left in. Even in the most optimistic
scenarios, complete consumption of all actinides, and using fast
spectrum reactors to destroy some of the long-lived non-actinides
as well, the waste must be segregated from the environment for at
least several hundred years, and therefore this is properly categorized
as a long-term problem. There are, however, chemical plants which
also produce hazardous waste staying in the environment for hundreds
of years.
A large nuclear reactor produces 3 cubic meters
(25-30 tonnes) of spent fuel each year. As of 2003, the United States
had accumulated about 49,000 metric tons of spent nuclear fuel from
nuclear reactors. Unlike other countries, U.S. policy forbids recycling
of used fuel and it is all treated as waste. After 10,000 years
of radioactive decay, according to United States Environmental Protection
Agency standards, the spent nuclear fuel will no longer pose a threat
to public health and safety.
The safe storage and disposal of nuclear waste
is a difficult challenge. Because of potential harm from radiation,
spent nuclear fuel must be stored in shielded basins of water, or
in dry storage vaults or dry cask storage until its radioactivity
decreases naturally (“decays”) to safe levels. This can take days
or thousands of years, depending on the type of fuel. Most waste
is currently stored in temporary storage sites, requiring constant
maintenance, while suitable permanent disposal methods are discussed.
Underground storage at Yucca Mountain in U.S. has been proposed
as permanent storage.
The nuclear industry produces a volume of low-level
radioactive waste in the form of contaminated items like clothing,
hand tools, water purifier resins, and (upon decommissioning) the
materials of which the reactor itself is built. In the United States,
the Nuclear Regulatory Commission has repeatedly attempted to allow
low-level materials to be handled as normal waste: landfilled, recycled
into consumer items, etc. Much low-level waste releases very low
levels of radioactivity and is essentially considered radioactive
waste because of its history. For example, according to the standards
of the NRC, the radiation released by coffee is enough to treat
it as low level waste. Overall, nuclear power produces far less
waste material than fossil-fuel based power plants. Coal-burning
plants are particularly noted for producing large amounts of radioactive
ash due to concentrating naturally occurring radioactive material
in the coal.
In addition, the nuclear industry fuel cycle produces
many tons of depleted uranium (DU) which consists of U-238 with
the easily fissile U-235 isotope removed. U-238 is a tough metal
with several commercial uses — for example, aircraft production,
radiation shielding, and making bullets and armor — as it has a
higher density than lead. There are concerns that U-238 may lead
to health problems in groups exposed to this material excessively,
like tank crews and civilians living in areas where large quantities
of DU ammunition have been used.
The amounts of waste can be reduced in several
ways. Both nuclear reprocessing and fast breeder reactors can reduce
the amounts of waste and increase the amount of energy gained per
fuel unit. Subcritical reactors or fusion reactors could greatly
reduce the time the waste has to be stored. Subcritical reactors
may also be able to do the same to already existing waste. It has
been argued that the best solution for the nuclear waste is above
ground temporary storage since technology is rapidly changing. The
current waste may well become valuable fuel in the future, particularly
if it is not reprocessed, as in the U.S.
In countries with nuclear power, radioactive wastes
comprise less than 1% of total industrial toxic wastes, which remain
hazardous indefinitely unless they decompose or are treated so that
they are less toxic or, ideally, completely non-toxic.
Economy of nuclear energy
Opponents of nuclear power argue that any of the
environmental benefits are outweighed by safety compromises and
by the costs related to construction and operation of nuclear power
plants, including costs for spent-fuel disposal and plant retirement.
Proponents of nuclear power respond that nuclear energy is the only
power source which explicitly factors the estimated costs for waste
containment and plant decommissioning into its overall cost, and
that the quoted cost of fossil fuel plants is deceptively low for
this reason. The cost of some renewables would be increased too
if they included necessary back-up due to their intermittent nature.
A UK Royal Academy of Engineering report in 2004
looked at electricity generation costs from new plants in the UK.
In particular it aimed to develop “a robust approach to compare
directly the costs of intermittent generation with more dependable
sources of generation”. This meant adding the cost of standby capacity
for wind, as well as carbon values up to £30 (€45.44) per tonne
CO2 for coal and gas. Wind power was calculated to be more than
twice as expensive as nuclear power. Without a carbon tax, the cost
of production through coal, nuclear and gas ranged £0.022-0.026/kWh
and coal gasification was £0.032/kWh. When carbon tax was added
(up to £0.025) coal came close to onshore wind (including back-up
power) at £0.054/kWh — offshore wind is £0.072/kWh.
Nuclear power remained at £0.023/kWh either way,
as it produces negligible amounts of CO2. Nuclear figures included
decommissioning costs.
In one study, certain gas cogeneration plants
were calculated to be three to four times more cost-effective than
nuclear power, if all the heat produced was used onsite or in a
local heating system. However, the study estimated only 25 year
plant lifetimes (60 is now common), 68% capacity factors were assumed
(above 90% is now common), other conservatisms were applied, and
nuclear power also produces heat which could be used in similar
ways (although most nuclear power plants are located in remote areas).
The study then found similar costs for nuclear power and most other
forms of generation if not including external costs (such as back-up
power).
Capital costs of nuclear energy
Generally, a nuclear power plant is significantly
more expensive to build than an equivalent coal-fueled or gas-fueled
plant. Coal is significantly more expensive than nuclear fuel, and
natural gas significantly more expensive than coal — thus, capital
costs aside, natural gas-generated power is the most expensive.
However, servicing the capital costs for a nuclear power dominate
the costs of nuclear-generated electricity, contributing about 70%
of costs (assuming a 10% discount rate).
The recent liberalization of the electricity market
in many countries has made the economics of nuclear power generation
less attractive. Previously a monopolistic provider could guarantee
output requirements decades into the future. Private generating
companies have to accept shorter output contracts and the risks
of future competition, so desire a shorter return on investment
period which favors generation plants with lower capital costs.
In many countries, licensing, inspection and certification
of nuclear power plants has added delays and construction costs
to their construction. In the U.S. many new regulations were put
in place after the Three Mile Island partial meltdown. Gas-fired
and coal-fired plants do not face such regulations. Because a power
plant does not yield profits during construction, longer construction
times translate directly into higher interest charges on borrowed
construction funds. However, the regulatory processes for siting,
licensing, and constructing have been standardized since their introduction,
to make construction of newer and safer designs more attractive
to companies.
In Japan and France, construction costs and delays
are significantly diminished because of streamlined government licensing
and certification procedures. In France, one model of reactor was
type-certified, using a safety engineering process similar to the
process used to certify aircraft models for safety. That is, rather
than licensing individual reactors, the regulatory agency certified
a particular design and its construction process to produce safe
reactors. U.S. law permits type-licensing of reactors, a process
which is about to be used.
To encourage development of nuclear power, under
the Nuclear Power 2010 Program the U.S. Department of Energy (DOE)
has offered interested parties the opportunity to introduce France’s
model for licensing and to subsidize 25% to 50% of the construction
cost overruns due to delays for the first six new plants. Several
applications were made, two sites have been chosen to receive new
plants, and other projects are pending.
Operating costs of nuclear energy
In general, coal and nuclear plants have the same
types of operating costs (operations and maintenance plus fuel costs).
However, nuclear and coal differ in the relative size of those costs.
Nuclear has lower fuel costs but higher operating and maintenance
costs. In recent times in the United States savings due to lower
fuel cost have not been low enough for nuclear to repay its higher
investment cost. Thus no new nuclear reactors have been ordered
in the United States since the 1970s. Coal’s operating cost advantages
have only rarely been sufficient to encourage the construction of
new coal based power generation. Around 90 to 95 percent of new
power plant construction in the United States has been natural gas-fired.
To be competitive in the current market, both
the nuclear and coal industries must reduce new plant investment
costs and construction time. The burden is clearly greater for nuclear
producers than for coal producers, because investment costs are
higher for nuclear plants. Operation and maintenance costs are particularly
important because they represent a large portion of costs for nuclear
power.
One of the primary reasons for the uncompetitiveness
of the U.S. nuclear industry has been the lack of any measure that
provides an economic incentive to reduce carbon emissions (carbon
tax). Many economists and environmentalists have called for a mechanism
to take into account the negative externalities of coal and gas
consumption. In such an environment, it is argued that nuclear will
become cost-competitive in the United States.
Subsidies for nuclear energy
Critics of nuclear power claim that it is the
beneficiary of inappropriately large economic subsidies — mainly
taking the forms of taxpayer-funded research and development and
limitations on disaster liability — and that these subsidies, being
subtle and indirect, are often overlooked when comparing the economics
of nuclear against other forms of power generation. However, competing
energy sources also receive subsidies. Fossil fuels receive large
direct and indirect subsidies, such as tax benefits and not having
to pay for the Greenhouse gases they emit. Renewables receive large
direct production subsidies and tax breaks in many nations.
Energy research and development (R&D) for
nuclear power has and continues to receive much larger state subsidies
than R&D for renewable energy or fossil fuels. However, today
most of this takes places in Japan and France: in most other nations
renewable R&D get more money. In the U.S., public research money
for nuclear fission declined from 2,179 to 35 million dollars between
1980 and 2000. However, in order to restart the industry, the next
six U.S. reactors will receive subsidies equal to those of renewables
and, in the event of cost overruns due to delays, at least partial
compensation for the overruns.
According to the DOE, insurance for nuclear or
radiological incidents in the U.S., is subsidized by the Price-Anderson
Nuclear Industries Indemnity Act. In July 2005, Congress extended
this Act to newer facilities. In the UK, the Nuclear Installations
Act of 1965 governs liability for nuclear damage for which a UK
nuclear licensee is responsible. The Vienna Convention on Civil
Liability for Nuclear Damage puts in place an international framework
for nuclear liability.
Other economic issues
Nuclear Power plants tend to be most competitive
in areas where other fuel resources are not readily available —
France, most notably, has almost no native supplies of fossil fuels.
The province of Ontario, Canada is already using all of its best
sites for hydroelectric power, and has minimal supplies of fossil
fuels, so a number of nuclear plants have been built there. India
too has few resources and is building new nuclear plants. Conversely,
in the United Kingdom, according to the government’s Department
Of Trade And Industry, no further nuclear power stations are to
be built, due to the high cost per unit of nuclear power compared
to fossil fuels. However, the British government’s chief scientific
advisor David King reports that building one more generation of
nuclear power plants may be necessary. China tops the list of planned
new plants, due to its rapidly expanding economy and fervent construction
in many types of energy projects.
Most new gas-fired plants are intended for peak
supply. The larger nuclear and coal plants cannot quickly adjust
their instantaneous power production, and are generally intended
for baseline supply. The market price for baseline power has not
increased as rapidly as that for peak demand. Some new experimental
reactors, notably pebble bed modular reactors, are specifically
designed for peaking power.
Any effort to construct a new nuclear facility
around the world, whether an older design or a newer experimental
design, must deal with NIMBY objections. Given the high profile
of both the Three Mile Island and Chernobyl accidents, few municipalities
welcome a new nuclear reactor, processing plant, transportation
route, or experimental nuclear burial ground within their borders,
and many have issued local ordinances prohibiting the development
of nuclear power. However, a few U.S. areas with nuclear units are
campaigning for more.
Current nuclear reactors return around 40-60 times
the invested energy when using life cycle analysis. This is better
than coal, natural gas, and current renewables except hydropower.
The Rocky Mountain Institute gives other reasons
why nuclear power plants may not be economical. In the U.S. this
includes long lead times on risky investments, and the more cost-effective
approach of investing in efficiency instead of new power plants.
Nuclear power, coal, and wind power are currently
the only realistic large scale energy sources that would be able
to replace oil and natural gas after a peak in global oil and gas
production has been reached. However, The Rocky Mountain Institute
claims that in the U.S. increases in transportation efficiency and
stronger, lighter cars would replace most oil usage with what it
calls negawatts. Biofuels can then substitute for a significant
portion of the remaining oil use. Efficiency, insulation, solar
thermal, and solar photovoltaic technologies can substitute for
most natural gas usage after a peak in production.
Nuclear proponents often assert that renewable
sources of power have not solved problems like intermittent output,
high costs, and diffuse output which requires the use of large surface
areas and much construction material and which increases distribution
losses. For example, studies in Britain have shown that increasing
wind power production contribution to 20% of all energy production,
without costly pumped hydro or electrolysis/fuel cell storage, would
only reduce coal or nuclear power plant capacity by 6.7% (from 59
to 55 GWe) since they must remain as backup in the absence of power
storage. Nuclear proponents often claim that increasing the contribution
of intermittent energy sources above that is not possible with current
technology. Some renewable energy sources, such as solar, overlap
well with peak electrical production and reduce the need of spare
generating capacity. Future applications that use electricity when
it is available (e.g. for pressurizing water systems, desalination,
or hydrogen generation) would help to reduce the spare generation
capacity required by both nuclear and renewable energy sources.
Concerns about nuclear power
Accident or attack
The Ignalina nuclear power plant in Lithuania
contains two RBMK reactors. Because of the safety flaws of the design,
the closure of the plant was a condition of Lithuania’s entry into
the EU. The first of the two reactors was closed down in 2004 and
the second is scheduled for shutdown by 2009.Opponents argue that
a major disadvantage of the use of nuclear reactors is the threat
of a nuclear accident or terrorist attack and the possible resulting
exposure to radiation.
Proponents argue that the potential for a meltdown
in non-Russian-designed reactors is very small due to the care taken
in designing adequate safety systems, and that the nuclear industry
has much better statistics regarding humans deaths from occupational
accidents than coal or hydropower. While the Chernobyl accident
caused great negative health, economic, environmental and psychological
effects in a widespread area, the accident at Chernobyl was caused
by a combination of the faulty RBMK reactor design, the lack of
a properly designed containment building, poorly trained operators,
and a non-existent safety culture. The RBMK design, unlike nearly
all designs used in the Western world, featured a positive void
coefficient, meaning that a malfunction could result in ever-increasing
generation of heat and radiation until the reactor was breached.
Even at Three Mile Island, the most severe civilian nuclear accident
in the non-Soviet world, the reactor vessel and containment building
were never breached, even though it had suffered a core meltdown,
so that very little radiation (well below natural background radiation
levels) was released into the environment.
Design changes are being pursued in the hope of
lessening some of the risks of fission reactors; in particular,
automated and passively safe designs are being pursued. Fusion reactors
which may come to exist in the future theoretically have little
risk since the fuel contained in the reaction chamber is only enough
to sustain the reaction for about a minute, whereas a fission reactor
contains about a year’s supply of fuel. Subcritical reactors never
have a self sustained nuclear chain reaction.
Opponents of nuclear power express concerns that
nuclear waste is not well protected, and that it can be released
in the event of terrorist attack, quoting a 1999 Russian incident
where workers were caught trying to sell 5 grams of radioactive
material on the open market, or the incident in 1993 where Russian
workers were caught selling 4.5 kilograms of enriched uranium. The
UN has since called upon world leaders to improve security in order
to prevent radioactive material falling into the hands of terrorists,
sometimes leading to the guarding of nuclear shipments by thousands
of police. Other energy sources, such as hydropower plants and LNG
carriers, are more vulnerable to accidents and attacks. Proponents
of nuclear power contend, however, that nuclear waste is already
well protected, and state their argument that there has been no
accident involving any form of nuclear waste from a civilian program
worldwide. In addition, they point to large studies carried out
by NRC and other agencies that tested the robustness of both reactor
and waste fuel storage, and found that they should be able to sustain
a terrorist attack comparable to the September 11 terrorist attacks.
Spent fuel is usually housed inside the plant’s “protected zone”
or a spent nuclear fuel shipping cask; stealing it for use in a
“dirty bomb” is extremely difficult. Exposure to the intense radiation
would almost certainly quickly incapacitate or kill any terrorists
who attempt to do so.
According to the Nuclear Regulatory Commission,
20 American states have requested stocks of potassium iodide which
the NRC suggests should be available for those living within 10
miles of a nuclear power plant in the unlikely event of a severe
accident.
Health effects on populations
Most of the human exposure to radiation comes
from natural background radiation. Most of the remaining exposure
comes from medical procedures. Several large studies in the U.S.,
Canada, and Europe have found no evidence of any increase in cancer
mortality among people living near nuclear facilities. For example,
in 1990, the National Cancer Institute (NCI) of the National Institutes
of Health announced that, after doing a large-scale study which
evaluated the mortality rates from 16 types of cancer, no increased
incidence of cancer mortality was found for people living near 62
nuclear installations in the United States. The study also showed
no increase in the incidence of childhood leukemia mortality in
the study of surrounding counties after the start-up of the nuclear
facilities. The NCI study, the broadest of its kind ever conducted,
surveyed 900,000 cancer deaths in counties near nuclear facilities.
Aside from the immediate effects of the Chernobyl
accident, there is continuing impact from soils containing radioactivity
in Ukraine and Belarus. For this reason a Zone of alienation was
established around the Chernobyl plant.
In March, 2006, safety reviews found that several
nuclear plants in the United States have been leaking water contaminated
with tritium into the ground. (The discharges were intended to go
through discharge pipes into rivers, at levels which would be below
regulatory limits. However, by leaking into the ground, very low
levels of tritium reached drinking water supplies.) The attorney
general of Illinois announced that she was filing a lawsuit against
Exelon because of six such leaks, demanding that the utility provide
substitute water supplies to residents although no well outside
company property shows levels that exceed drinking water standards.
According to the NRC, “The inspection determined that public health
and safety has not been adversely affected and the dose consequence
to the public that can be attributed to current onsite conditions
is negligible with respect to NRC regulatory limits.” However, the
chairman of the Nuclear Regulatory Commission, said, “They’re going
to have to fix it.”
Nuclear proliferation
Opponents of nuclear power point out that nuclear
technology is often dual-use, and much of the same materials and
knowledge used in a civilian nuclear program can be used to develop
nuclear weapons. This concern is known as nuclear proliferation
and is a major reactor design criterion.
The military and civil purposes for nuclear energy
are intertwined in most countries with nuclear capabilities. In
the U.S., for example, the first goal of the Department of Energy
is “to advance the national, economic, and energy security of the
United States; to promote scientific and technological innovation
in support of that mission; and to ensure the environmental cleanup
of the national nuclear weapons complex.”
The enriched uranium used in most nuclear reactors
is not concentrated enough to build a bomb. Most nuclear reactors
run on 4% enriched uranium; Little Boy used 90% enriched uranium;
while lower enrichment levels could be used, the minimum bomb size
would rapidly become unfeasibly large as the level was decreased.
However, the same plants and technology used to enrich uranium for
power generation can be used to make the highly enriched uranium
needed to build a bomb.
In addition, the plutonium produced in power reactors,
if concentrated through reprocessing, can be used for a bomb. While
the plutonium resulting from normal reactor fueling cycles is less
than ideal for weapons use because of the concentration of Pu-240,
a usable weapon can be produced from it. If the reactor is operated
on very short fueling cycles, bomb-grade plutonium can be produced.
However, such operation would be virtually impossible to camouflage
in many reactor designs, as the frequent shutdowns for refueling
would be obvious, for instance in satellite photographs.
It is widely believed that the nuclear programs
of India and Pakistan used CANDU reactors to produce fissionable
materials for their weapons; however, this is not entirely accurate.
Both Canada (by supplying the 40 MW research reactor) and the United
States (by supplying 21 tons of heavy water) supplied India with
the technology necessary to create a nuclear weapons program, dubbed
CIRUS (Canada-India Reactor, United States). Because international
policies did not dictate usage of nuclear technology transfers,
India was able to use the technology to create a nuclear weapon.
Pakistan is believed to have produced the material for its weapons
from an indigenous enrichment program.
To prevent weapons proliferation, safeguards on
nuclear technology were published in the Nuclear Non-Proliferation
Treaty (NPT) and monitored since 1968 by the International Atomic
Energy Agency (IAEA). Nations signing the treaty are required to
report to the IAEA what nuclear materials they hold and their location.
They agree to accept visits by IAEA auditors and inspectors to verify
independently their material reports and physically inspect the
nuclear materials concerned to confirm physical inventories of them
in exchange for access to nuclear materials and equipment on the
global market.
Several states did not sign the treaty and were
able to use international nuclear technology (often procured for
civilian purposes) to develop nuclear weapons (India, Pakistan,
Israel, and South Africa). South Africa has since signed the NPT,
and now holds the distinction of being the only known state to have
indigenously produced nuclear weapons, and then verifiably dismantled
them. Of those who have signed the treaty and received shipments
of nuclear paraphernalia, many states have either claimed to, or
been accused of, attempting to use supposedly civilian nuclear power
plants for developing weapons, including Iran and North Korea. Certain
types of reactors are more conducive to producing nuclear weapons
materials than others, and a number of international disputes over
proliferation have centered on the specific model of reactor being
contracted for in a country suspected of nuclear weapon ambitions.
New technology, like SSTAR, may lessen the risk
of nuclear proliferation by providing sealed reactors with a limited
self-contained fuel supply and with restrictions against tampering.
One possible obstacle for expanding the use of
nuclear power might be a limited supply of uranium ore, without
which it would become necessary to build and operate breeder reactors.
However, at current usage there is sufficient uranium for an extended
period — “In summary, the actual recoverable uranium supply is likely
to be enough to last several hundred (up to 1000) years, even using
standard reactors.” Breeder reactors have been banned in the U.S.
since President Jimmy Carter’s administration prohibited reprocessing
because of what it regarded as the unacceptable risk of proliferation
of weapons-grade materials.
Some proponents of nuclear power agree that the
risk of nuclear proliferation may be a reason to prevent non democratic
developing nations from gaining any nuclear technology but argue
that this is no reason for democratic developed nations to abandon
their nuclear power plants, especially since it seems that democracies
refrain from war against each other.
Proponents also note that nuclear power, like
some other power sources, provides steady energy at a consistent
price without competing for energy resources from other countries,
something that may contribute to wars.
In February, 2006, a new U.S. initiative, the
Global Nuclear Energy Partnership was announced. It would be an
international effort to reprocess fuel in a manner making proliferation
infeasible, while making nuclear power available to developing countries.
Environmental effects
Non-radioactive water vapor is the significant
operating emission from nuclear power plants. Fission produces gases
such as iodine-131 or Xenon-133. These primarily remain within the
fuel rods, but with some postulated fuel failure, small amounts
of the gasses can be released in to the reactor coolant. The chemical
control systems isolate the radioactive gasses which have to be
stored on-site for several half-lives until they have decayed to
safe levels.
Nuclear generation does not directly produce sulphur
dioxide, nitrogen oxides, mercury or other pollutants associated
with the combustion of fossil fuels (pollution from fossil fuels
is blamed for many deaths each year in the U.S. alone). It also
does not directly produce carbon dioxide, which has led some environmentalists
to advocate increased reliance on nuclear energy as a means to reduce
greenhouse gas emissions (which contribute to global warming).
Like any power source (including renewables like
wind and solar energy), the facilities to produce and distribute
the electricity require energy to build and subsequently decommission.
Mineral ores must be collected and processed to produce nuclear
fuel. These processes are either directly powered by diesel and
gasoline engines, or draw electricity from the power grid, which
may be generated from fossil fuels. Life cycle analyses assess the
amount of energy consumed by these processes (given today’s mix
of energy resources) and calculate, over the lifetime of a nuclear
power plant, the amount of carbon dioxide saved (related to the
amount of electricity produced by the plant) vs. the amount of carbon
dioxide used (related to construction and fuel acquisition).
Several life cycle analyses show similar emissions
per kilowatt-hour from nuclear power and from renewables such as
wind power. According to one life cycle study by van Leeuwen and
Smith from 2001–2005, carbon dioxide emissions from nuclear power
per kilowatt hour could range from 20% to 120% of those for natural
gas-fired power stations depending on the availability of high grade
ores. The study was critiqued by World Nuclear Association (WNA),
rebutted in 2003, then dismissed by the WNA in 2006 based on its
own life-cycle-energy calculation (with comparisons).
In 2006, a UK government advisory panel, The Sustainable
Development Commission, concluded that if the UK’s existing nuclear
capacity were doubled, it would provide an 8% decrease in total
UK CO2 emissions by 2035. This can be compared to the country’s
goal to reduce greenhouse gas emissions by 60 % by 2050. As of 2006,
the UK government was to publish its official findings later in
the year.
Waste heat in water systems
Nuclear reactors require cooling, typically with
water (sometimes indirectly). The process of extracting energy from
a heat source, called the Rankine cycle, requires the steam to be
cooled down. Rivers are the most common source of cooling water,
as well as the destination for waste heat. The temperature of exhaust
water must be regulated to avoid killing fish; long-term impact
of hotter-than-natural water on ecosystems is an environmental concern.
In most new facilities, this problem is solved by implementing cooling
towers. This is true of all traditional power plant designs, including
coal, oil, and natural gas plants, which also rely on the Rankine
cycle to produce their energy. All four types of plant simply differ
in their heat source, be it nuclear fission or burning fossil fuels.
The need to regulate exhaust temperature also
limits generation capacity. On extremely hot days, which is when
demand can be at its highest, the capacity of a nuclear plant may
go down because the incoming water is warmer to begin with and is
thus less effective as a coolant, per unit volume. This was a significant
factor during the European heat wave of 2003. Engineers consider
this in making improved power plant designs because increased cooling
capacity will increase costs. The global increase in average temperature
has required some plants in the southeast United States to revise
their technical specifications to allow operation with their cooling
water sources at higher temperatures.
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