Neutron activation is the only common way that a stable material
can be induced into becoming intrinsically radioactive. All naturally
occurring materials, including air, water, and soil, can be induced
(activated) by neutron capture into some amount of radioactivity in
varying degrees, as a result of the production of neutron-rich radioisotopes.
Some atoms require more than one neutron to become unstable, which
makes them harder to activate because the probability of a double or
triple capture by a nucleus is below that of single capture. Water, for
example, is made up of hydrogen and oxygen. Hydrogen requires a double capture to attain instability as tritium (hydrogen-3), while natural oxygen (oxygen-16) requires three captures to become unstable oxygen-19. Thus water is relatively difficult to activate, as compared to sodium chloride (NaCl),
in which both the sodium and chlorine atoms become unstable with a
single capture each. These facts were experienced first-hand at the Operation Crossroads atomic test series in 1946.
In other cases, and depending on the kinetic energy of the neutron, the capture of a neutron can cause nuclear fission—the
splitting of the atomic nucleus into two smaller nuclei. If the fission
requires an input of energy, that comes from the kinetic energy of the
neutron. An example of this kind of fission in a light element can occur
when the stable isotope of lithium, lithium-7, is bombarded with fast neutrons and undergoes the following nuclear reaction:
In other words, the capture of a neutron by lithium-7 causes it to split into an energetic helium nucleus (alpha particle), a hydrogen-3 (tritium) nucleus and a free neutron. The Castle Bravo accident, in which the thermonuclear bomb test at Bikini Atoll in 1954 exploded with 2.5 times the expected yield, was caused by the unexpectedly high probability of this reaction.
In the area around a pressurized water reactor or boiling water reactor during normal operation, a significant amount of radiation is produced due to the fast neutron activation of coolant water oxygen via a (n,p) reaction.
The activated oxygen-16 nucleus emits a proton (hydrogen nucleus), and
transmutes to nitrogen-16, which has a very short life (7.13 seconds)
before decaying back to oxygen-16 (emitting 6.13 MeV beta particles).
This activation of the coolant water requires extra biological shielding
around the nuclear reactor plant. It is the high energy gamma ray in
the second reaction that causes the major concern. This is why water
that has recently been inside a nuclear reactor core must be shielded
until this radiation subsides. One to two minutes is generally
sufficient.
In facilities that housed a cyclotron, the reinforced concrete foundation can become radioactive due to neutron activation. Six important long-lived radioactive isotopes (54Mn, 55Fe, 60Co, 65Zn, 133Ba, and 152Eu) can be found within concrete nuclei affected by neutrons.
The residual radioactivity is predominantly due to trace elements
present, and thus the amount of radioactivity derived from cyclotron
activation is minuscule, i.e., pCi/g or Bq/g. The release limit for facilities with residual radioactivity is 25 mrem/year. An example of 55Fe production from the activation of iron in reinforcement bars found in concrete is shown below:
Neutron
activation is the only common way that a stable material can be induced
into becoming intrinsically radioactive. Neutrons are only free in
quantity in the microseconds of a nuclear weapon's explosion, in an
active nuclear reactor, or in a spallation neutron source.
In an atomic weapon neutrons are only generated for from 1 to 50
microseconds, but in huge numbers. Most are absorbed by the metallic
bomb casing, which is only just starting to be affected by the explosion
within it. The neutron activation of the soon-to-be vaporized metal is
responsible for a significant portion of the nuclear fallout
in nuclear bursts high in the atmosphere. In other types of activation,
neutrons may irradiate soil that is dispersed in a mushroom cloud at
or near the Earth's surface, resulting in fallout from activation of
soil chemical elements.
Effects on materials over time
In any location with high neutron fluxes,
such as within the cores of nuclear reactors, neutron activation
contributes to material erosion and periodically the lining materials
themselves must be disposed of, as low-level radioactive waste.
Some materials are more subject to neutron activation than others, so a
suitably chosen low-activation material can significantly reduce this
problem (see International Fusion Materials Irradiation Facility). For example, Chromium-51 will form by neutron activation in chrome steel (which contains Cr-50) that is exposed to a typical reactor neutron flux.
Carbon-14, most frequently but not solely, generated by the neutron activation of atmospheric nitrogen-14 with a thermal neutron, is (together with its dominant natural production pathway from cosmic ray-air interactions and historical production from atmospheric nuclear testing)
also generated in comparatively minute amounts inside many designs of
nuclear reactors which contain nitrogen gas impurities in their fuel cladding, coolant water and by neutron activation of the oxygen contained in the water itself. Fast breeder reactors (FBR) produce about an order of magnitude less C-14 than the most common reactor type, the pressurized water reactor, as FBRs do not use water as a primary coolant.
Uses
Radiation safety
For
physicians and radiation safety officers, activation of sodium in the
human body to sodium-24, and phosphorus to phosphorus-32, can give a
good immediate estimate of acute accidental neutron exposure.
In the ICF
fusion approach, the fusion yield of the experiment (directly
proportional to neutron production) is usually determined by measuring
the gamma-ray emissions of aluminium or copper neutron activation
targets. Aluminium can capture a neutron and generate radioactive sodium-24, which has a half life of 15 hours and a beta decay energy of 5.514 MeV.
Neutron activation analysis
is one of the most sensitive and precise methods of trace element
analysis. It requires no sample preparation or solubilization and can
therefore be applied to objects that need to be kept intact such as a
valuable piece of art. Although the activation induces radioactivity in
the object, its level is typically low and its lifetime may be short, so
that its effects soon disappear. In this sense, neutron activation is a
non-destructive analysis method.
Neutron activation analysis can be done in situ. For example,
aluminium (Al-27) can be activated by capturing relatively low-energy
neutrons to produce the isotope Al-28, which decays with a half-life of 2.3 minutes with a decay energy of 4.642 MeV. This activated isotope is used in oil drilling to determine the clay content (clay is generally an alumino-silicate) of the underground area under exploration.
Historians can use accidental neutron activation to authenticate
atomic artifacts and materials subjected to neutron fluxes from fission
incidents. For example, one of the rare isotopes found in trinitite, and therefore with its absence likely signifying a fake sample of the mineral, is a barium neutron activation product, the barium in the Trinity device coming from the slow explosivelens employed in the device, known as Baratol.
Semiconductor production
Neutron irradiation may be used for float-zone silicon slices (wafers) to trigger fractional transmutation of Si atoms into phosphorus (P) and therefore doping it into n-type silicon
Greenhouse gas emissions per energy source. Nuclear power is one of the sources with the least greenhouse gas emissions.Nuclear power activities involving the environment; mining, enrichment, generation and geological disposal.
Nuclear power has various environmental impacts, both positive and negative, including the construction and operation of the plant, the nuclear fuel cycle, and the effects of nuclear accidents. Nuclear power plants do not burn fossil fuels and so do not directly emit carbon dioxide. The carbon dioxide emitted during mining, enrichment,
fabrication and transport of fuel is small when compared with the
carbon dioxide emitted by fossil fuels of similar energy yield, however,
these plants still produce other environmentally damaging wastes. Nuclear energy and renewable energy have reduced environmental costs by decreasing CO2 emissions resulting from energy consumption.
There is a catastrophic risk potential if containment fails,
which in nuclear reactors can be brought about by overheated fuels
melting and releasing large quantities of fission products into the
environment. In normal operation, nuclear power plants release less radioactive material than coal power plants whose fly ash contains significant amounts of thorium, uranium and their daughter nuclides.
A large nuclear power plant may reject waste heat to a natural
body of water; this can result in undesirable increase of the water
temperature with adverse effect on aquatic life. Alternatives include cooling towers.
The Onagawa Nuclear Power Plant – a plant that cools by direct use of ocean water, not requiring a cooling tower
Mining of uranium ore can disrupt the environment around the mine. However, with modern in-situ leaching technology this impact can be reduced compared to "classical" underground or open-pit mining. Disposal of spent nuclear fuel is controversial, with many proposed long-term storage schemes under intense review and criticism. Diversion of fresh- or low-burnup spent fuel to weapons production presents a risk of nuclear proliferation, however all nuclear weapons states derived the material for their first nuclear weapon from (non-power) research reactors
or dedicated "production reactors" and/or uranium enrichment. Finally,
some parts the structure of the reactor itself becomes radioactive
through neutron activation
and will require decades of storage before it can be economically
dismantled and in turn disposed of as waste. Measures like reducing the
cobalt content in steel to decrease the amount of cobalt-60
produced by neutron capture can reduce the amount of radioactive
material produced and the radiotoxicity that originates from this
material.
However, part of the issue is not radiological but regulatory as most
countries assume any given object that originates from the "hot"
(radioactive) area of a nuclear power plant or a facility in the nuclear fuel cycle is ipso facto radioactive, even if no contamination or neutron irradiation induced radioactivity is detectable.
Waste streams
Nuclear power has at least three waste streams that may impact the environment:
Releases of ill-defined quantities of radioactive materials during accidents
Nuclear reprocessing and breeder reactors which can decrease the need for storage of spent fuel in a deep geological repository
have faced economic and political hurdles but are in some use in
Russia, India, China, Japan and France, which are among the countries
with the highest nuclear energy production outside the United States.
However, the U.S. has not undertaken significant efforts towards either
reprocessing or breeder reactors since the 1970s instead relying on the once through fuel cycle.
The spent nuclear fuel from uranium-235 and plutonium-239 nuclear fission contains a wide variety of carcinogenicradionuclideisotopes such as strontium-90, iodine-131, and caesium-137. Such waste includes some of the most long-lived transuranic elements such as americium-241 and isotopes of plutonium.
The most long-lived radioactive wastes, including spent nuclear fuel,
usually must be contained and isolated from the environment for a long
period of time. Spent nuclear fuel storage is mostly a problem in the
United States, following a 1977 prohibition by then-President Jimmy Carter
on nuclear fuel recycling. France, The United Kingdom, and Japan are
some of the countries that have rejected the repository solution. Spent
nuclear fuel produced by some types of reactors is a valuable asset, not
simply waste.
Disposal of these wastes in specially-engineered underground repositories is the preferred long-term storage solution. The International Panel on Fissile Materials has said:
It is widely accepted that spent nuclear fuel and high-level
reprocessing and plutonium wastes require well-designed storage for long
periods of time, to minimize releases of the contained radioactivity
into the environment. Safeguards are also required to ensure that
neither plutonium nor highly enriched uranium is diverted to weapon use.
There is general agreement that placing spent nuclear fuel in
repositories hundreds of meters below the surface would be safer than
indefinite storage of spent fuel on the surface.
When designing long-term storage facilities, there are several
crucial considerations, including the specific type of radioactive
waste, the containers enclosing the waste, other engineered barriers or
seals around the containers, the tunnels housing the containers, and the
geologic makeup of the surrounding area.
The ability of natural geologic barriers to isolate radioactive waste is demonstrated by the natural nuclear fission reactors at Oklo, Africa. During their long reaction period, about 5.4 metric tons of fission products, 1.5 metric tons of plutonium, and other transuranic elements
were generated in the uranium ore body. These elements remain immobile
and stable to this day, a span of almost 2 billion years.
Despite long-standing agreement among many experts that
geological disposal can be safe, technologically feasible, and
environmentally sound, a large part of the general public in many
countries remains skeptical.
One of the challenges facing the supporters of these efforts is to
demonstrate confidently that a repository will contain waste for so long
that future containment breaches will pose no significant health or environmental risks.
Nuclear reprocessing
does not eliminate the need for a repository, but it reduces the
required volume, the need for long-term heat dissipation, and the
long-term radiation hazard. Reprocessing does not eliminate the
political and social challenges to repository siting.
The countries that have made the most progress towards a
repository for high-level radioactive waste have typically started with public consultations
and made voluntary siting a necessary condition. This consensus-seeking
approach is believed to have a greater chance of success than top-down
modes of decision making, but the process is necessarily slow, and there
is "inadequate experience around the world to know if it will succeed
in all existing and aspiring nuclear nations." Moreover, many communities do not want to host
a nuclear waste repository as they are "concerned about their community
becoming a de facto site for waste for thousands of years, the health
and environmental consequences of an accident, and lower property
values."
In a 2010 Presidential Memorandum, U.S. President Obama established the Blue Ribbon Commission on America's Nuclear Future. The commission, composed of fifteen members, conducted an extensive two-year study of nuclear waste disposal.
During their research, the Commission visited Finland, France, Japan,
Russia, Sweden, and the UK, and in 2012, the Commission submitted its
final report.
The Commission did not issue recommendations for a specific site but
rather presented a comprehensive recommendation for disposal strategies.
One major recommendation was that "the United States should undertake
an integrated nuclear waste management program that leads to the timely
development of one or more permanent deep geological facilities for the
safe disposal of spent fuel and high-level nuclear waste."
Pressurized heavy water reactors like the Canadian CANDU or the Indian IPHWR do not need enriched fuel and can operate using natural uranium. This allows better use of the energy contained in the initial uranium ore (while higher enrichment allows higher burnup, the amount of natural uranium needed to produce this fuel increases faster than the achievable burnup) and reduces the energy needed in fuel manufacturing as the conversion of the yellowcake to uranium hexafluoride and back into an oxide fuel as well as the energy-intensive enrichment process can be skipped.
Other waste
Moderate
amounts of low-level waste are managed through a chemical and volume
control system (CVCS). This includes gas, liquid, and solid waste
produced via the process of purifying the water through evaporation.
Liquid waste is reprocessed continuously, and gas waste is filtered,
compressed, stored to allow decay, diluted, and then discharged. The
rate at which this is allowed is regulated and studies must prove that
such discharge does not pose public health risks (see radioactive effluent emissions).
Solid waste can be disposed of simply by placing it where it will
not be disturbed for a few years. There are three low-level waste
disposal sites in the United States, in South Carolina, Utah, and
Washington. Solid waste from the CVCS is combined with solid waste that comes from handling materials before it is buried off-site.
Most
commercial nuclear power plants release gaseous and liquid radiological
effluents into the environment as a byproduct of the Chemical Volume
Control System. These effluents are monitored in the US by the EPA and
the NRC. Civilians living within 50 miles (80 km) of a nuclear power
plant typically receive about 0.1 μSv per year. For comparison, the average person living at or above sea level receives at least 260 μSv per year from cosmic radiation.
All reactors in the United States are required by law to have a
containment building. The walls of containment buildings are several
feet thick and made of concrete designed to stop the release of any
radiation emitted by the reactor into the environment. For comparison:
The waste produced by coal plants
is actually more radioactive than that generated by their nuclear
counterparts. In fact, the fly ash emitted by a [coal] power plant—a
by-product from burning coal for electricity—carries into the
surrounding environment 100 times more radiation than a nuclear power
plant producing the same amount of energy. . . . Estimated radiation
doses ingested by people living near the coal plants were equal to or
higher than doses for people living around the nuclear facilities. At
one extreme, the scientists estimated fly ash radiation in individuals'
bones at around 18 millirems (thousandths of a rem, a unit for measuring
doses of ionizing radiation) a year. Doses for the two nuclear plants,
by contrast, ranged from between three and six millirems for the same
period. And when all food was grown in the area, radiation doses were 50
to 200 percent higher around the coal plants.
The total amount of radioactivity released through the CVCS depends
on the power plant, the regulatory requirements, and the plant's
performance. Atmospheric dispersion models combined with pathway models
are employed to accurately approximate the exposure to a member of the
public from the effluents emitted. Effluent monitoring is conducted continuously at the plant.
Tritium
Tritium Effluent Limits
Country
Limit (Bq/L)
Australia
76,103
Finland
30,000
WHO
10,000
Switzerland
10,000
Russia
7,700
Ontario, Canada
7,000
European Union
1001
United States
740
California Public Health Goal
14.8
A leak of radioactive water at Vermont Yankee
in 2010, along with similar incidents at more than 20 other US nuclear
plants in recent years, has kindled doubts about the reliability,
durability, and maintenance of aging nuclear installations in the United
States.
Tritium is a radioactive isotope of hydrogen that emits a low-energy beta particle and is usually measured in becquerels
(i.e. atoms decaying per second) per liter (Bq/L). Tritium can be
contained in water released from a nuclear plant. The primary concern
for tritium release is its presence in drinking water, in addition to
biological magnification leading to tritium in crops and animals
consumed for food.
Legal concentration limits of tritium have differed greatly from
place to place (see table right). For example, in June 2009 the Ontario
Drinking Water Advisory Council recommended lowering the limit from
7,000 Bq/L to 20 Bq/L.
According to the NRC, tritium is the least dangerous radionuclide
because it emits very weak radiation and leaves the body relatively
quickly.
A drum of yellowcakeRössing open pit uranium mine, Namibia
Uranium mining is the process of extracting uranium ore from the ground. Kazakhstan, Canada, and Australia are the top three producers and together account for 63% of world uranium production. A prominent use of uranium is as fuel for nuclear power plants. The mining and milling of uranium present significant dangers to the environment.
In 2010, 41% of the world's uranium production was produced by in-situ leaching, which uses solutions to dissolve the uranium while leaving the rock in place.
The remainder was produced by conventional mining, in which the mined
uranium ore is ground to a uniform particle size and then the uranium
extracted by chemical leaching. The product is a powder of unenriched uranium, "yellowcake," which is sold on the uranium market as U3O8. Uranium mining can use large amounts of water—for example, the Roxby DownsOlympic Dam mine in South Australia uses 35,000 m³ of water each day and plans to increase this to 150,000 m³ per day.
The Church Rock uranium mill spill occurred in New Mexico on July 16, 1979, when the tailings disposal pond breached its dam. Over 1,000 tons of solid radioactive mill waste and 93 million gallons of acidic, radioactive tailings solution flowed into the Puerco River, and contaminants traveled 80 miles (130 km) downstream to Navajo County, Arizona and onto the Navajo Nation. The accident released more radiation than the Three Mile Island accident
that occurred four months earlier and was the largest release of
radioactive material in U.S. history, although the radioactive material
was diluted by the 93 million gallons of water and sulfuric acid. Groundwater
near the spill was contaminated and the Puerco rendered unusable by
local residents, who were not immediately aware of the toxic danger.
Despite efforts made in cleaning up Cold War nuclear arms race
uranium sites, significant problems stemming from the legacy of uranium
development still exist today on the Navajo Nation and in the states of
Utah, Colorado, New Mexico, and Arizona. Hundreds of abandoned mines,
primarily used for the US arms race and not nuclear energy production, have not been cleaned up and present environmental and health risks in many communities.
The Environmental Protection Agency estimates that there are 4,000
mines with documented uranium production, and another 15,000 locations
with uranium occurrences in 14 western states, most found in the Four Corners area and Wyoming. The Uranium Mill Tailings Radiation Control Act is a United States environmental law that amended the Atomic Energy Act of 1954 and gave the Environmental Protection Agency the authority to establish health and environmental standards for the stabilization, restoration, and disposal of uranium mill waste.
Numerous studies have been done on the possible relationship between
nuclear power and cancer. Such studies have looked for excess cancers in
both plant workers and surrounding populations due to releases during
normal operations of nuclear plants and other parts of the nuclear power
industry, as well as excess cancers in workers and the public due to
accidental releases. There is agreement that excess cancers in both
plant workers and the surrounding public have been caused by accidental
releases such as the Chernobyl accident.
There is also agreement that some workers in other parts of the nuclear
fuel cycle (most notably uranium mining) have had elevated rates of
cancer, at least in past decades. Excess mortality is associated with all mining activity and is not unique to uranium mining.
However, numerous studies of possible cancers caused by nuclear power
plants in normal operation have come to opposing conclusions, and the
issue is a matter of scientific controversy and ongoing study.
Several epidemiological studies have found that there is an
increased risk of various diseases, especially cancers, among people who
live near nuclear facilities. A widely cited 2007 meta-analysis by Baker et al. of 17 research papers was published in the European Journal of Cancer Care. It offered evidence of elevated leukemia
rates among children living near 136 nuclear facilities in the United
Kingdom, Canada, France, United States, Germany, Japan, and Spain.
However, this study has been criticized for several reasons, such as its
combination of heterogeneous data (different age groups, sites that
were not nuclear power plants, different zone definitions), arbitrary
selection of 17 out of 37 individual studies, and exclusion of sites
with zero observed cases or deaths.
Elevated leukemia rates among children were also found in a 2008 German study by Kaatsch et al. that examined residents living near 16 major nuclear power plants in Germany. This study has also been criticized for reasons similar to those described above. These 2007 and 2008 results are not consistent with many other studies that have tended not to show such associations. The British Committee on Medical Aspects of Radiation in the
Environment issued a study in 2011 of children under five living near 13
nuclear power plants in the UK during the period 1969–2004. The
committee found that children living near power plants in Britain are no
more likely to develop leukemia than those living elsewhere.
Similarly, a 1991 study for the National Cancer Institute found no
excess cancer mortalities in 107 US counties close to nuclear power
plants.
However, in view of the ongoing controversy, the US Nuclear Regulatory
Commission has requested the National Academy of Sciences to oversee a
state-of-the-art study of cancer risk in populations near NRC-licensed
facilities.
A subculture of frequently undocumented nuclear workers do the dirty, difficult, and potentially dangerous work often shunned by regular employees. The World Nuclear Association
states that the transient workforce of "nuclear gypsies"—casual workers
employed by subcontractors—has been "part of the nuclear scene for at
least four decades." Existing labor laws regarding worker health are not always properly enforced.
A 15-country collaborative cohort study of cancer risks due to exposure
to low-dose ionizing radiation, involving 407,391 nuclear industry
workers, showed significant increase in cancer mortality. The study
evaluated 31 types of cancers, primary and secondary.
Nuclear power reactor accidents can result in a variety of radioisotopes being released into the environment. The health impact of each radioisotope depends on a variety of factors. Iodine-131
is potentially an important source of morbidity in accidental
discharges because of its prevalence and because it settles on the
ground. When iodine-131 is released, it can be inhaled or consumed after
it enters the food chain, primarily through contaminated fruits,
vegetables, milk, and groundwater. Iodine-131 in the body rapidly
accumulates in the thyroid gland, becoming a source of beta radiation.
The 2011 Fukushima Daiichi nuclear disaster, the most serious nuclear accident since 1986, resulted in the displacement of 50,000 households. Radiation checks led to bans of some shipments of vegetables and fish. However, according to UN reports, the radiation leaks were small and did not cause any health problems in residents. Evacuation of residents was criticized as not scientifically justified.
Production of nuclear power relies on the nuclear fuel cycle,
which includes uranium mining and milling. Uranium workers are routinely
exposed to low levels of radon decay products and gamma radiation. Risks of leukemia
from acute and high doses of gamma radiation are well-known, but there
is debate about risks from lower doses. Only a few studies have examined
the risks of other hematological cancers in uranium workers.
Comparison to coal-fired power generation
In terms of net radioactive release, the National Council on Radiation Protection and Measurements (NCRP) estimated the average radioactivity per short ton of coal is 17,100 millicuries per 4,000,000 tons. With 154 coal plants in the United States, this amounts to emissions of 0.6319 TBq per year, per plant.
It is sometimes cited that coal plants release 100 times the
radioactivity of nuclear plants. This comes from NCRP Reports No. 92 and
No. 95, which estimate the dose to the population from 1000 MWe coal
and nuclear plants at 4.9 man-Sv/year and 0.048 man-Sv/year, respectively (a typical Chest x-ray gives a dose of about 0.06 mSv, for comparison). The Environmental Protection Agency
estimates an added dose of 0.3 µSv per year for living within 50 miles
(80 km) of a coal plant and 0.009 milli-rem per year for those living
within the same distance of a nuclear plant. Nuclear power plants in normal operation emit less radioactivity than coal power plants.
Unlike coal-fired or oil-fired power generation, nuclear power generation does not directly produce any sulfur dioxide, nitrogen oxides, or mercury (pollution from fossil fuels is blamed for 24,000 early deaths each year in the U.S. alone).
However, as with all energy sources, there is some pollution associated
with support activities such as mining, manufacturing, and
transportation.
A major European Union-funded research study known as ExternE, or Externalities
of Energy, undertaken from 1995 to 2005 found that the environmental
and health costs of nuclear power, per unit of energy delivered, was
€0.0019/kWh. This is lower than that of many renewable sources, including the environmental impact caused by biomass use and the manufacture of photovoltaic solar panels, and was over thirty times lower than coal's impact of €0.06/kWh, or 6 cents/kWh. However, wind power's impact was €0.0009/kWh, just under half the price of nuclear power.
In May 2023, the Washington Post wrote, "Had Germany kept its
nuclear plants running from 2010, it could have slashed its use of coal
for electricity to 13 percent by now. Today’s figure is 31 percent...
Already more lives might have been lost just in Germany because of air
pollution from coal power than from all of the world’s nuclear accidents
to date, Fukushima and Chernobyl included."
Contrast of radioactive accident emissions with industrial emissions
Proponents
of nuclear power argue that the problems of nuclear waste "do not come
anywhere close" to approaching the problems of fossil fuel waste. A 2004 article from the BBC states: "The World Health Organization
(WHO) says 3 million people are killed worldwide by outdoor air
pollution annually from vehicles and industrial emissions, and 1.6
million indoors through using solid fuel." In the U.S. alone, fossil fuel waste kills 20,000 people each year. A coal power plant releases 100 times as much radiation as a nuclear power plant of the same wattage. It is estimated that during 1982, US coal burning released 155 times as much radioactivity into the atmosphere as the Three Mile Island accident. The World Nuclear Association
provides a comparison of deaths due to accidents among different forms
of energy production. In their life-cycle comparison, deaths per TW-yr
of electricity produced from 1970 to 1992 are quoted as 885 for
hydropower, 342 for coal, 85 for natural gas, and 8 for nuclear. The figures include uranium mining, which can be a hazardous industry, with many accidents and fatalities.
The North Anna plant uses direct exchange cooling into an artificial lake.
As with all thermoelectric plants, nuclear power plants need cooling
systems. The most common systems for thermal power plants, including
nuclear, are:
Once-through cooling, in which water is drawn from a large body,
passes through the cooling system, and then flows back into the water
body.
Cooling pond, in which water is drawn from a pond dedicated to the
purpose, passes through the cooling system, then returns to the pond.
Examples include the South Texas Nuclear Generating Station and the North Anna Nuclear Generating Station.
The latter uses a cooling pond or artificial lake, which at the plant
discharge canal is often about 30 °F warmer than in the other parts of
the lake or in normal lakes (this is cited as an attraction of the area
by some residents).
The environmental effects of the artificial lakes are often weighted in
arguments against construction of new plants, and during droughts such
lakes have drawn media attention. The Turkey Point Nuclear Generating Station is credited with helping the conservation status of the American Crocodile, largely an effect of the waste heat produced.
Cooling towers, in which water recirculates through the cooling system until it evaporates from the tower. Examples include the Shearon Harris Nuclear Power Plant.
A 2011 study by the National Renewable Energy Laboratory determined
that the median nuclear plant with cooling towers consumed 672 gallons
of water per megawatt-hour, less than the median consumption of
concentrating solar power (865 gal/MWhr for trough type, and 786
gal/MWhr for power tower type), slightly less than coal (687 gal/MWhr),
but more than that for natural gas (198 gal/MWhr). Once-through cooling
systems use more water, but less water is lost to evaporation. In the
median US nuclear plant with once-through cooling, 44,350 gal/MWhr pass
through the cooling system, but only 269 gal/MWhr (less than 1 percent)
is consumed by evaporation.
Nuclear plants exchange 60 to 70% of their thermal energy by cycling with a body of water or by evaporating water through a cooling tower. This thermal efficiency is somewhat lower than that of coal-fired power plants, thus creating more waste heat.
It is possible to use waste heat in cogeneration applications such as district heating. The principles of cogeneration and district heating with nuclear power are the same as any other form of thermal power production. The Ågesta Nuclear Power Plant in Sweden provides nuclear heat generation. In Switzerland, the Beznau Nuclear Power Plant provides heat to about 20,000 people.
However, district heating with nuclear power plants is less common than
with other modes of waste heat generation; because of either siting regulations and/or the NIMBY
effect, nuclear stations are generally not built in densely populated
areas. Waste heat is more commonly used in industrial applications.
As district heating has a seasonal demand curve it is often only a
seasonal solution of the waste heat problem. Furthermore, district
heating is less efficient in less densely populated areas and as nuclear
power plants are often constructed far out of population centers due to
NIMBY and safety concerns, the usage of nuclear district heating hasn't been widespread.
During Europe's 2003 and 2006 heat waves,
French, Spanish, and German utilities had to secure exemptions from
regulations in order to discharge overheated water into the environment.
Some nuclear reactors shut down.
With climate change causing weather extremes such as heat waves, reduced precipitation levels and droughts can have a significant impact on thermal power station
infrastructure, including large biomass-electric and fission-electric
stations if cooling in these power stations is provided by certain freshwater sources. A number of thermal stations use indirect seawater cooling or cooling towers that use little to no freshwater. During heat waves, some stations designed to heat exchange with rivers and lakes are legally required to reduce output or cease operations to protect water levels and aquatic life.
This presently infrequent problem common among all thermal power stations may become increasingly significant over time. If global warming continues, disruption of electricity may occur if station operators do not have other means of cooling, like cooling towers available.
Nuclear plants, like all thermal power plants including coal, geothermal and biomass power plants,
use special structures to draw in water for cooling. Water is often
drawn through screens to minimize debris. Many aquatic organisms are
trapped and killed against the screens, through a process known as
impingement. Aquatic organisms small enough to pass through the screens
are subject to toxic stress in a process known as entrainment.
Summer shutdowns are especially pronounced in France,
which produces some 70% of electricity with nuclear power plants and
where electric home heating is widespread. However, in regions with high
heating, ventilation, and air conditioning
power use, the summer season, rather than imposing lower power demands,
may be the peak season of electricity demand, complicating scheduled
summer shutdowns.
Over its lifecycle nuclear energy has low greenhouse gas (GHG) emissions. Many stages of the nuclear fuel chain—mining,
milling, transport, fuel fabrication, enrichment, reactor construction,
decommissioning, and waste management—use fossil fuels or involve
changes to land use, and hence emit some carbon dioxide and conventional
pollutants. Nuclear energy produces about 10 grams of carbon dioxide per
kilowatt hour, compared to about 500 for fossil gas and 1000 for coal.
Like all energy sources, various life cycle analysis (LCA) studies have led to a range of estimates on the median value for nuclear power, with most comparisons of carbon dioxide emissions showing that nuclear power is comparable to renewable energy sources.
Many people have argued that an expansion of nuclear power would help combat climate change.
Others have argued that it is one way to reduce emissions, but it comes
with its own problems, such as risks related to severe nuclear accidents, attacks on nuclear sites, and nuclear terrorism.
Some activists also believe that there are better ways of dealing with
climate change than investing in nuclear power, including the improved energy efficiency and greater reliance on decentralized and renewable energy sources.
The 1979 Three Mile Island accident and 1986 Chernobyl disaster,
along with high construction costs and delays resulting from
demonstrations, injunctions, and political actions by anti-nuclear
activists, effectively ended the rapid growth of global nuclear power
capacity. A release of radioactive materials followed the 2011 Japanese tsunami which damaged the Fukushima I Nuclear Power Plant, resulting in hydrogen gas explosions and partial meltdowns. The Fukushima disaster was classified a Level 7
event. The large-scale release of radioactivity resulted in people
being evacuated from a 20 km exclusion zone set up around the power
plant, similar to the 30 km radius Chernobyl Exclusion Zone
still in effect. Published works suggest that the radioactivity levels
around Chernobyl have lowered enough to now have only a limited impact
on wildlife.
In Japan, in July 2016, Fukushima Prefecture announced that the number of evacuees following the Great East Japan earthquake events had fallen below 90,000, in part because of the lifting of evacuation orders issued in some municipalities.
Following the 2011 Japanese Fukushima nuclear disaster, authorities shut down the nation's 54 nuclear power plants. As of 2013, the Fukushima site remains highly radioactive, with some 160,000 evacuees still living in temporary housing, and some land will be unfarmable for centuries. The difficult cleanup job will take 40 or more years, and cost tens of billions of dollars.Japan
towns, villages, and cities around the Fukushima Daiichi nuclear plant.
The 20km and 30km areas had evacuation and sheltering orders, and
additional administrative districts that had an evacuation order are
highlighted.
Since then, radiation levels at the Fukushima I power plant have varied, spiking up to 1,000 mSv/h (millisievert per hour), which can cause radiation sickness to occur following a one-hour exposure.
Significant emissions of radioactive particles took place following
hydrogen explosions at three reactors, as technicians tried to pump in
seawater to keep the uranium fuel rods cool and bled radioactive gas
from the reactors in order to make room for the seawater.
Concerns about the possibility of a large-scale release of
radioactive material resulted in 20 km exclusion zone being set up
around the power plant and people within the 20–30 km band being advised
to stay indoors. Later, the UK, France, and some other countries told
their nationals to consider leaving Tokyo, in response to fears of
spreading nuclear contamination. New Scientist
reported that emissions of radioactive iodine and cesium from the
crippled Fukushima I nuclear plant have approached levels evident after
the Chernobyl disaster in 1986.
On March 24, 2011, Japanese officials announced that "radioactive
iodine-131 exceeding safety limits for infants had been detected at 18
water-purification plants in Tokyo and five other prefectures."
Officials said also that the fallout from the Dai-ichi plant is
"hindering search efforts for victims from the March 11 earthquake and
tsunami."
According to the Federation of Electric Power Companies of Japan,
"by April 27 approximately 55 percent of the fuel in reactor unit 1 had
melted, along with 35 percent of the fuel in unit 2, and 30 percent of
the fuel in unit 3; and overheated spent fuels in the storage pools of
units 3 and 4 probably were also damaged." As of April 2011, water was still being poured into the damaged reactors to cool melting fuel rods. The accident has surpassed the 1979 Three Mile Island accident in seriousness and is comparable to the 1986 Chernobyl disaster. The Economist
reported that the Fukushima disaster is "a bit like three Three Mile
Islands in a row, with added damage in the spent-fuel stores," and that there will be ongoing impacts:
Years of clean-up will drag into decades. A permanent exclusion zone
could end up stretching beyond the plant’s perimeter. Seriously exposed
workers may be at increased risk of cancers for the rest of their
lives...
John Price, a former member of the Safety Policy Unit at the UK's
National Nuclear Corporation, said that it "might be 100 years before
melting fuel rods can be safely removed from Japan's Fukushima nuclear
plant."
In the second half of August 2011, Japanese lawmakers announced that Prime Minister Naoto Kan
would likely visit the Fukushima Prefecture to announce that the large,
contaminated area around the destroyed reactors would be declared
uninhabitable, perhaps for decades. Some of the areas in the temporary
12 miles (19 km) radius evacuation zone around Fukushima were found to
be heavily contaminated with radionuclides, according to a survey
released by the Japanese Ministry of Science and Education.
As of 2016, the government expects to gradually lift the
designation of some “difficult-to-return zones,” a total area of 337
square kilometres (130 sq mi), by 2021. Rain, wind, and natural
dissipation have removed many radioactive contaminants, lowering levels
at the central district of Okuma town to 9 mSv/year, one-fifth the level
recorded in 2011.
However, according to UN reports, radiation leaks were small and did not cause any health damage to residents. Rushed evacuation of residents was criticized as not scientifically justified, driven by radiophobia and causing more harm than the incident itself.
Map showing Caesium-137 contamination in the Chernobyl area in 1996
As of 2013, the 1986 Chernobyl disaster in the Ukraine
remains the world's worst nuclear power plant disaster. Estimates of
its death toll are controversial and range from 62 to 25,000, with the
high projections including deaths that have yet to happen. Peer-reviewed
publications have generally supported a projected total figure in the
low tens of thousands. For example, an estimate of 16,000 excess cancer
deaths are predicted to occur due to the Chernobyl accident out to the
year 2065, whereas, in the same period, several hundred million cancer
cases are expected from other causes.
The IARC also stated in a press release: "To put it in perspective,
tobacco smoking will cause several thousand times more cancers in the
same population," but also, referring to the numbers of different types
of cancers, "The exception is thyroid cancer,
which, over ten years ago, was already shown to be increased in the
most contaminated regions around the site of the accident." The full version of the World Health Organization health effects report adopted by the United Nations, also published in 2006, included the prediction of, in total, no more of 4,000 deaths from cancer. The Union of Concerned Scientists took issue with the report, and they, following the disputed linear no-threshold model (LNT) model of cancer susceptibility, instead estimated that the Chernobyl disaster would cause a total of 25,000 excess cancer deaths worldwide. That would place the total Chernobyl death toll below that of the worst dam failure accident in history, the Banqiao Dam disaster of 1975 in China.
Large amounts of radioactive contamination were spread across Europe due to the Chernobyl disaster; cesium and strontium contaminated many agricultural products, livestock, and soil. The accident necessitated the evacuation of the entire city of Pripyat and of 300,000 people from Kiev, rendering an area of land unusable by humans for an indeterminate period.
As radioactive materials decay, they release particles that can damage the body and lead to cancer, particularly cesium-137 and iodine-131.
In the Chernobyl disaster, releases of cesium-137 contaminated land.
Some communities, including the entire city of Pripyat, were abandoned
indefinitely. One news source reported that thousands of people who
drank milk contaminated with radioactive iodine developed thyroid
cancer.
The exclusion zone (approximately a 30 km radius around Chernobyl) may
have significantly elevated levels of radiation, which is now
predominantly due to the decay of cesium-137. This contamination is expected to last approximately 300 years.
Due to the bioaccumulation
of cesium-137, some mushrooms as well as wild animals which eat them
may have levels which are not considered safe for human consumption. Mandatory radiation testing of sheep in parts of the UK that graze on lands with contaminated peat was lifted in 2012.
In 2007, the Ukrainian government declared much of the Chernobyl Exclusion Zone, almost 490 square kilometres (190 sq mi), a zoological animal reserve.
Many species of animals have experienced population increases since
human influence has largely left the region, including moose, bison, and
wolves. However, other species such as barn swallows and many invertebrates have diminished. There is much controversy among biologists over whether Chernobyl is now a wildlife reserve.
SL-1 meltdown
This image of the SL-1 core served as a sober reminder of the damage that a nuclear meltdown can cause.
The SL-1, or Stationary Low-Power Reactor Number One, was a United States Army experimental nuclear power reactor which underwent a steam explosion and meltdown on January 3, 1961, killing its three operators: John Byrnes, Richard McKinley, and Richard Legg. The direct cause was the improper manual withdrawal of the central control rod,
which was responsible for absorbing neutrons in the reactor core. This
caused the reactor power to surge to about 20,000MW and in turn, an
explosion occurred. The event is the only known fatal reactor accident
in the United States and the first to occur in the world. The accident released about 80 curies (3.0 TBq) of iodine-131, which was not considered significant due to its location in a remote desert of Idaho. About 1,100 curies (41 TBq) of fission products were released into the atmosphere.
Radiation exposure limits prior to the accident were 100 röntgens
to save a life and 25 to save valuable property. During the response to
the accident, 22 people received doses of 3 to 27 röntgens. Removal of radioactive waste and disposal of the three bodies eventually exposed 790 people to harmful levels of radiation. The hands of the initial victims were buried separately from their bodies because of their radiation levels.
Nuclear power plants, uranium enrichment plants, fuel fabrication plants, and even potentially uranium mines are vulnerable to attacks which could lead to widespread radioactive contamination.
The attack threat is of several general types: commando-like
ground-based attacks on equipment which, if disabled, could lead to a
reactor core meltdown
or widespread dispersal of radioactivity; and external attacks such as
an aircraft crash into a reactor complex, or cyber attacks. Terrorists could target nuclear power plants in an attempt to release radioactive contamination into the environment and community.
Nuclear reactors become preferred targets during military conflict and have been repeatedly attacked by military air strikes:
In September 1980, Iran bombed the incomplete Osirak reactor complex in Iraq.
In June 1981, an Israeli air strike completely destroyed Iraq's Osirak reactor.
Between 1984 and 1987, Iraq bombed Iran's incomplete Bushehr nuclear plant six times.
In Iraq in 1991, the U.S. bombed three nuclear reactors and an enrichment pilot facility.
The United States 9/11 Commission said that nuclear power plants were potential targets originally considered for the September 11, 2001 attacks. If terrorist groups could sufficiently damage safety systems to cause a core meltdown
at a nuclear power plant and/or sufficiently damage spent fuel pools,
such an attack could lead to a widespread radioactive contamination.
According to a 2004 report by the U.S. Congressional Budget Office,
"The human, environmental, and economic costs from a successful attack
on a nuclear power plant that results in the release of substantial
quantities of radioactive material to the environment could be great." An attack on a reactor's spent fuel pool
could also be serious, as these pools are less protected than the
reactor core. The release of radioactivity could lead to thousands of
near-term deaths and greater numbers of long-term fatalities.
Insider sabotage occurs because insiders can observe and work
around security measures. In a study of insider crimes, the authors
repeatedly said that successful insider crimes depended on the
perpetrators’ observation and knowledge of security vulnerabilities. Since the atomic age began, the U.S. Department of Energy’s nuclear laboratories have been known for widespread violations of security rules.
A better understanding of the scope of the insider threat will help to
overcome complacency and is critical to getting countries to take
stronger preventative measures.
Researchers have emphasized the need to make nuclear facilities
extremely safe from sabotage and attacks that could release massive
quantities of radioactivity. New reactor designs have passive safety
features, such as automatic flooding of the reactor core without active
intervention by reactor operators. These safety measures have generally
been developed and studied with respect to accidents, not to deliberate
reactor attacks by terrorist groups. However, the US Nuclear Regulatory Commission now requires new reactor license applications to consider security during the design stage.
Following the 2011 Fukushima I nuclear accidents, there has been increased focus on the risks associated with seismic activity and the potential for environmental radioactive release. Genpatsu-shinsai, meaning nuclear power plant earthquake disaster, is a term coined by Japanese seismologist Professor Katsuhiko Ishibashi in 1997. It describes a domino effect scenario in which a major earthquake causes a severe accident at a nuclear power plant
near a major population center, resulting in an uncontrollable release
of radiation that make damage control and rescue impossible. In such a
scenario, earthquake damage severely impedes the evacuation of the
population. Ishibashi predicts that such an event would have a global
impact seriously affecting future generations.[
The 1999 Blayais Nuclear Power Plant flood was a flood
that took place in France on the evening of December 27, 1999. It was
caused when a combination of the tide and high winds from the extratropical storm Martin led to the plant's sea walls being overwhelmed.
The event resulted in the loss of the plant's off-site power supply and
knocked out several safety-related systems, resulting in a Level 2 event on the International Nuclear Event Scale. The incident illustrated the potential for flooding to damage nuclear plants, with the potential for radioactive release.
Nuclear decommissioning is the process by which a nuclear power plant site is dismantled so that it will no longer require measures for radiation protection. The presence of radioactive
material necessitates processes that are occupationally dangerous,
hazardous to the local environment, expensive, and time-intensive.
Most nuclear plants currently operating in the US were originally designed for a life of about 30–40 years and are licensed to operate for 40 years by the US Nuclear Regulatory Commission. The average age of these reactors is 32 years.
Therefore, many reactors are coming to the end of their licensing
period. If their licenses are not renewed, the plants must go through a
decontamination and decommissioning process. As of 2022
debate continues in many countries about how long their nuclear plants
should run for, with some being shut-down earlier than expected when
they were built and others having their lifetimes extended by decades.
Decommissioning is an administrative and technical process. It
includes clean-up of radioactivity and progressive demolition of the
plant. Once a facility is fully decommissioned, no danger of a
radiologic nature should persist. The costs of decommissioning are to be
spread over the lifetime of a facility and saved in a decommissioning
fund. After a facility has been completely decommissioned, it is
released from regulatory control, and the licensee of the plant will no
longer be responsible for its nuclear safety. With some plants, the
intent is to eventually return to "greenfield" status.
