Nuclear power

Origins

The Nuclear binding energy of all natural elements in the periodic table. With higher values translating into more tightly bound nuclei, the greatest nuclear stability. Iron(Fe), is both the end product of nucleosynthesis within the core of hydrogen fusing stars and the production of elements surrounding iron are likewise the fission products of the fissionable actinides(e.g uranium). Iron is also seen as the trough rather than the peak of the graph as shown, were all other elemental nuclei have the potential to be nuclear fuel, much like "a ball rolls down a hill to the valley floor", with the greater numerical separation or "height" difference from iron, the greater nuclear potential energy that could be released.

In 1932 physicist Ernest Rutherford discovered that when lithium atoms were "split" by protons from a proton accelerator, immense amounts of energy were released in accordance with the principle of mass–energy equivalence. However, he and other nuclear physics pioneers Niels Bohr and Albert Einstein believed harnessing the power of the atom for practical purposes anytime in the near future was unlikely, with Rutherford labeling such expectations "moonshine."^[10]

The same year, his doctoral student James Chadwick discovered the neutron,^[11] which was immediately recognized as a potential tool for nuclear experimentation because of its lack of an electric charge. Experimentation with bombardment of materials with neutrons led Frédéric and Irène Joliot-Curie to discover induced radioactivity in 1934, which allowed the creation of radium-like elements at much less the price of natural radium.^[12] Further work by Enrico Fermi in the 1930s focused on using slow neutrons to increase the effectiveness of induced radioactivity. Experiments bombarding uranium with neutrons led Fermi to believe he had created a new, transuranic element, which was dubbed hesperium.^[13]

In 1938, German chemists Otto Hahn^[14] and Fritz Strassmann, along with Austrian physicist Lise Meitner^[15] and Meitner's nephew, Otto Robert Frisch,^[16] conducted experiments with the products of neutron-bombarded uranium, as a means of further investigating Fermi's claims. They determined that the relatively tiny neutron split the nucleus of the massive uranium atoms into two roughly equal pieces, contradicting Fermi.^[13] This was an extremely surprising result: all other forms of nuclear decay involved only small changes to the mass of the nucleus, whereas this process—dubbed "fission" as a reference to biology—involved a complete rupture of the nucleus. Numerous scientists, including Leó Szilárd, who was one of the first, recognized that if fission reactions released additional neutrons, a self-sustaining nuclear chain reaction could result. Once this was experimentally confirmed and announced by Frédéric Joliot-Curie in 1939, scientists in many countries (including the United States, the United Kingdom, France, Germany, and the Soviet Union) petitioned their governments for support of nuclear fission research, just on the cusp of World War II, for the development of a nuclear weapon.^[17]

First nuclear reactor

In the United States, where Fermi and Szilárd had both emigrated, the discovery of the nuclear chain reaction led to the creation of the first man-made reactor, known as Chicago Pile-1, which achieved criticality on December 2, 1942. This work became part of the Manhattan Project, a massive secret U.S. government military project to make enriched uranium and by building large production reactors to produce (breed) plutonium for use in the first nuclear weapons. The United States would test an atom bomb in July 1945 with the Trinity test, and eventually two such weapons were used in the atomic bombings of Hiroshima and Nagasaki.

The first light bulbs ever lit by electricity generated by nuclear power at EBR-1 at Argonne National Laboratory-West, December 20, 1951.

In August 1945, the first widely distributed account of nuclear energy, in the form of the pocketbook The Atomic Age, discussed the peaceful future uses of nuclear energy and depicted a future where fossil fuels would go unused. Nobel laurette Glenn Seaborg, who later chaired the Atomic Energy Commission, is quoted as saying "there will be nuclear powered earth-to-moon shuttles, nuclear powered artificial hearts, plutonium heated swimming pools for SCUBA divers, and much more".^[18]

The United Kingdom, Canada,^[19] and the USSR proceeded to research and develop nuclear industries over the course of the late 1940s and early 1950s. Electricity was generated for the first time by a nuclear reactor on December 20, 1951, at the EBR-I experimental station near Arco, Idaho, which initially produced about 100 kW.^[20][21] Work was also strongly researched in the United States on nuclear marine propulsion, with a test reactor being developed by 1953 (eventually, the USS Nautilus, the first nuclear-powered submarine, would launch in 1955).^[22] In 1953, American President Dwight Eisenhower gave his "Atoms for Peace" speech at the United Nations, emphasizing the need to develop "peaceful" uses of nuclear power quickly. This was followed by the 1954 Amendments to the Atomic Energy Act which allowed rapid declassification of U.S. reactor technology and encouraged development by the private sector.

The controllability of nuclear power reactors depends on the fact that a small fraction of neutrons resulting from fission are delayed, which makes the reactions easier to control. These are neutrons emitted by the decay of certain fission products.^[23] Operating in this delayed critical state, changes in reaction rates occur slowly enough to permit mechanical feedback to control those reaction rates.^[24]

Early years

On June 27, 1954, the USSR's Obninsk Nuclear Power Plant became the world's first nuclear power plant to generate electricity for a power grid, and produced around 5 megawatts of electric power.^[25][26]

Later in 1954, Lewis Strauss, then chairman of the United States Atomic Energy Commission (U.S. AEC, forerunner of the U.S. Nuclear Regulatory Commission and the United States Department of Energy) spoke of electricity in the future being "too cheap to meter".^[27] Strauss was very likely referring to hydrogen fusion^[28] —which was secretly being developed as part of Project Sherwood at the time—but Strauss's statement was interpreted as a promise of very cheap energy from nuclear fission. The U.S. AEC itself had issued far more realistic testimony regarding nuclear fission to the U.S. Congress only months before, projecting that "costs can be brought down... [to]... about the same as the cost of electricity from conventional sources..."^[29]

In 1955 the United Nations' "First Geneva Conference", then the world's largest gathering of scientists and engineers, met to explore the technology. In 1957 EURATOM was launched alongside the European Economic Community (the latter is now the European Union). The same year also saw the launch of the International Atomic Energy Agency (IAEA).

Calder Hall, United Kingdom – The world's first commercial nuclear power station. First connected to the national power grid on 27 August 1956 and officially opened by Queen Elizabeth II on 17 October 1956

The Shippingport Atomic Power Station in Shippingport, Pennsylvania was the first commercial reactor in the United States and was opened in 1957.

The world's first commercial nuclear power station, Calder Hall at Windscale, England, was opened in 1956 with an initial capacity of 50 MW (later 200 MW).^[30][31] The first commercial nuclear generator to become operational in the United States was the Shippingport Reactor (Pennsylvania, December 1957).

One of the first organizations to develop nuclear power was the U.S. Navy, for the purpose of propelling submarines and aircraft carriers. The first nuclear-powered submarine, USS Nautilus, was put to sea in December 1954.^[32] As of 2016, the U.S. Navy submarine fleet is made up entirely of nuclear-powered vessels, with 75 submarines in service. Two U.S. nuclear submarines, USS Scorpion and USS Thresher, have been lost at sea. As of 2016 the Russian Navy was estimated to have 61 nuclear submarines in service; eight Soviet and Russian nuclear submarines have been lost at sea. This includes the Soviet submarine K-19 reactor accident in 1961 which resulted in 8 deaths and more than 30 other people were over-exposed to radiation.^[33] The Soviet submarine K-27 reactor accident in 1968 resulted in 9 fatalities and 83 other injuries.^[34] Moreover, Soviet submarine K-429 sank twice, but was raised after each incident. Several serious nuclear and radiation accidents have involved nuclear submarine mishaps.^[35][34]

The U.S. Army also had a nuclear power program, beginning in 1954. The SM-1 Nuclear Power Plant, at Fort Belvoir, Virginia, was the first power reactor in the United States to supply electrical energy to a commercial grid (VEPCO), in April 1957, before Shippingport. The SL-1 was a U.S. Army experimental nuclear power reactor at the National Reactor Testing Station in eastern Idaho. It underwent a steam explosion and meltdown in January 1961, which killed its three operators.^[36] In the Soviet Union at The Mayak Production Association facility there were a number of accidents, including an explosion, that released 50–100 tonnes of high-level radioactive waste, contaminating a huge territory in the eastern Urals and causing numerous deaths and injuries. The Soviet government kept this accident secret for about 30 years. The event was eventually rated at 6 on the seven-level INES scale (third in severity only to the disasters at Chernobyl and Fukushima).

Development

Washington Public Power Supply System Nuclear Power Plants 3 and 5 were never completed.

Installed nuclear capacity initially rose relatively quickly, rising from less than 1 gigawatt (GW) in 1960 to 100 GW in the late 1970s, and 300 GW in the late 1980s. Since the late 1980s worldwide capacity has risen much more slowly, reaching 366 GW in 2005. Between around 1970 and 1990, more than 50 GW of capacity was under construction (peaking at over 150 GW in the late 1970s and early 1980s) — in 2005, around 25 GW of new capacity was planned. More than two-thirds of all nuclear plants ordered after January 1970 were eventually cancelled.^[32] A total of 63 nuclear units were canceled in the United States between 1975 and 1980.^[37]

During the 1970s and 1980s rising economic costs (related to extended construction times largely due to regulatory changes and pressure-group litigation)^[38] 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 baseload capacity unattractive.

The 1973 oil crisis had a significant effect on countries, such as France and Japan, which had relied more heavily on oil for electric generation (39%^[39] and 73% respectively) to invest in nuclear power.^[40]

Some local opposition to nuclear power emerged in the early 1960s,^[41] and in the late 1960s some members of the scientific community began to express their concerns.^[42] These concerns related to nuclear accidents, nuclear proliferation, high cost of nuclear power plants, nuclear terrorism and radioactive waste disposal.^[43] In the early 1970s, there were large protests about a proposed nuclear power plant in Wyhl, Germany. The project was cancelled in 1975 and anti-nuclear success at Wyhl inspired opposition to nuclear power in other parts of Europe and North America.^[44][45] By the mid-1970s anti-nuclear activism had moved beyond local protests and politics to gain a wider appeal and influence, and nuclear power became an issue of major public protest.^[46] Although it lacked a single co-ordinating organization, and did not have uniform goals, the movement's efforts gained a great deal of attention.^[47] In some countries, the nuclear power conflict "reached an intensity unprecedented in the history of technology controversies".^[48]

120,000 people attended an anti-nuclear protest in Bonn, Germany, on October 14, 1979, following the Three Mile Island accident.^[49]

In France, between 1975 and 1977, some 175,000 people protested against nuclear power in ten demonstrations.^[49] In West Germany, between February 1975 and April 1979, some 280,000 people were involved in seven demonstrations at nuclear sites. Several site occupations were also attempted. In the aftermath of the Three Mile Island accident in 1979, some 120,000 people attended a demonstration against nuclear power in Bonn.^[49] In May 1979, an estimated 70,000 people, including then governor of California Jerry Brown, attended a march and rally against nuclear power in Washington, D.C.^[50] Anti-nuclear power groups emerged in every country that has had a nuclear power programme.

Three Mile Island and Chernobyl

The abandoned city of Pripyat with Chernobyl plant in the distance.

Health and safety concerns, the 1979 accident at Three Mile Island, and the 1986 Chernobyl disaster played a part in stopping new plant construction in many countries,^[42] although the public policy organization, the Brookings Institution states that new nuclear units, at the time of publishing in 2006, had not been built in the United States because of soft demand for electricity, and cost overruns on nuclear plants due to regulatory issues and construction delays.^[51] By the end of the 1970s it became clear that nuclear power would not grow nearly as dramatically as once believed. Eventually, more than 120 reactor orders in the United States were ultimately cancelled^[52] and the construction of new reactors ground to a halt. A cover story in the February 11, 1985, issue of Forbes magazine commented on the overall failure of the U.S. nuclear power program, saying it "ranks as the largest managerial disaster in business history".^[53]

Unlike the Three Mile Island accident, the much more serious Chernobyl accident did not increase regulations affecting Western reactors since the Chernobyl reactors were of the problematic RBMK design only used in the Soviet Union, for example lacking "robust" containment buildings.^[54] Many of these RBMK reactors are still in use today. However, changes were made in both the reactors themselves (use of a safer enrichment of uranium) and in the control system (prevention of disabling safety systems), amongst other things, to reduce the possibility of a duplicate accident.^[55]

An international organization to promote safety awareness and professional development on operators in nuclear facilities was created: World Association of Nuclear Operators (WANO).

Opposition in Ireland and Poland prevented nuclear programs there, while Austria (1978), Sweden (1980) and Italy (1987) (influenced by Chernobyl) voted in referendums to oppose or phase out nuclear power. In July 2009, the Italian Parliament passed a law that cancelled the results of an earlier referendum and allowed the immediate start of the Italian nuclear program.^[56] After the Fukushima Daiichi nuclear disaster a one-year moratorium was placed on nuclear power development,^[57] followed by a referendum in which over 94% of voters (turnout 57%) rejected plans for new nuclear power.^[58]

Nuclear renaissance

Olkiluoto 3 under construction in 2009. It is the first EPR design, but problems with workmanship and supervision have created costly delays which led to an inquiry by the Finnish nuclear regulator STUK.^[59] In December 2012, Areva estimated that the full cost of building the reactor will be about €8.5 billion, or almost three times the original delivery price of €3 billion.^[60][61][62]

Since about 2001 the term nuclear renaissance has been used to refer to a possible nuclear power industry revival, driven by rising fossil fuel prices and new concerns about meeting greenhouse gas emission limits.^[64] Since commercial nuclear energy began in the mid-1950s, 2008 was the first year that no new nuclear power plant was connected to the grid, although two were connected in 2009.^[65][66]

Fukushima Daiichi Nuclear Disaster

Following the Tōhoku earthquake on 11 March 2011, one of the largest earthquakes ever recorded, and a subsequent tsunami off the coast of Japan, the Fukushima Daiichi Nuclear Power Plant suffered multiple core meltdowns due to failure of the emergency cooling system for lack of electricity supply. This resulted in the most serious nuclear accident since the Chernobyl disaster.

The Fukushima Daiichi nuclear accident prompted a re-examination of nuclear safety and nuclear energy policy in many countries^[67] and raised questions among some commentators over the future of the renaissance.^[68][69] Germany approved plans to close all its reactors by 2022, and Italy re-affirmed its ban on nuclear power in a referendum.^[67] China, Switzerland, Israel, Malaysia, Thailand, United Kingdom, and the Philippines reviewed their nuclear power programs.^{[70][71][72][73]}

In 2011 the International Energy Agency halved its prior estimate of new generating capacity to be built by 2035.^[74][75] Nuclear power generation had the biggest ever fall year-on-year in 2012, with nuclear power plants globally producing 2,346 TWh of electricity, a drop of 7% from 2011. This was caused primarily by the majority of Japanese reactors remaining offline that year and the permanent closure of eight reactors in Germany.^[76]

Post-Fukushima

The Fukushima Daiichi nuclear accident sparked controversy about the importance of the accident and its effect on nuclear's future. The crisis prompted countries with nuclear power to review the safety of their reactor fleet and reconsider the speed and scale of planned nuclear expansions.^[77] In 2011, The Economist opined that nuclear power "looks dangerous, unpopular, expensive and risky", and that "it is replaceable with relative ease and could be forgone with no huge structural shifts in the way the world works".^[78] Earth Institute Director Jeffrey Sachs disagreed, claiming combating climate change would require an expansion of nuclear power.^[79] Investment banks were also critical of nuclear soon after the accident.^[80][81]

In September 2011, German engineering giant Siemens announced it will withdraw entirely from the nuclear industry as a response to the Fukushima accident.^[82][83]

In February 2012, the United States Nuclear Regulatory Commission approved the construction of two additional reactors at the Vogtle Electric Generating Plant, the first reactors to be approved in over 30 years since the Three Mile Island accident.^[84] In October 2016, Watts Bar 2 became the first new United States reactor to enter commercial operation since 1996.^[85]

In 2013 Japan signed a deal worth $22 billion, in which Mitsubishi Heavy Industries would build four modern Atmea reactors for Turkey.^[86] In August 2015, following 4 years of near zero fission-electricity generation, Japan began restarting its nuclear reactors, after safety upgrades were completed, beginning with Sendai Nuclear Power Plant.^[87]

By 2015, the IAEA's outlook for nuclear energy had become more promising. "Nuclear power is a critical element in limiting greenhouse gas emissions," the agency noted, and "the prospects for nuclear energy remain positive in the medium to long term despite a negative impact in some countries in the aftermath of the [Fukushima-Daiichi] accident...it is still the second-largest source worldwide of low-carbon electricity. And the 72 reactors under construction at the start of last year were the most in 25 years."^[88] According to the World Nuclear Association, as of 2015 the global trend was for new nuclear power stations coming online to be balanced by the number of old plants being retired.^[89]

As of 2015, 441 reactors had a worldwide net electric capacity of 382,9 GW, with 67 new nuclear reactors under construction.^[90] Over half of the 67 total being built were in Asia, with 28 in China, where there is an urgent need to control pollution from coal plants.^[91] Eight new grid connections were completed by China in 2015.^[92][93]

Future of the industry

The Hanul nuclear power station in South Korea, presently the second largest in the world by output, with six operating power reactors, by 2023 it was planned to eventually consist of ten operating reactors, when two additional and indigenously designed APR-1400 reactors on site, that are presently under construction, similarly received government approval and constructon commenced over the period of 2018-2022. In 2012 the Korean designer exported the APR design to the United Arab Emirates, were four of the Gen III reactors are under construction.

As of 2018, there are over 150 nuclear reactors planned including 50 under construction.^[94] However, while investment on upgrades of existing plant and life-time extensions continues,^[95] investment in new nuclear is declining, reaching a 5-year-low in 2017.

In 2015, the International Energy Agency reported that the Fukushima accident had a strongly negative effect on nuclear power, yet nuclear power prospects are positive in the medium to long term mainly thanks to new construction in Asia.^[96] In 2016, the U.S. Energy Information Administration projected for its “base case” that world nuclear power generation would increase from 2,344 terawatt hours (TWh) in 2012 to 4,501 TWh in 2040. Most of the predicted increase was expected to be in Asia.^[97]

The future of nuclear power varies greatly between countries, depending on government policies. Some countries, many of them in Europe, such as Germany, Belgium, and Lithuania, have adopted policies of nuclear power phase-out. At the same time, some Asian countries, such as China^[98] and India,^[99] have committed to rapid expansion of nuclear power. Many other countries, such as the United Kingdom^[100] and the United States, have policies in between. Japan generated about 30% of its electricity from nuclear power before the Fukushima accident. In 2015 the Japanese government committed to the aim of restarting its fleet of 40 reactors by 2030 after safety upgrades, and to finish the construction of the Generation III Ōma Nuclear Power Plant.^[101] This would mean that appoximately 20% of electricity would come from nuclear power by 2030. As of 2018, some reactors have restarted commercial operation following inspections and upgrades with new regulations.^[102] While South Korea has a large nuclear power industry, the new government in 2017, partly influenced by a large anti-nuclear movement,^[103] committed to halting nuclear development and to gradually phase out nuclear power as reactors that are now operating or under construction close after 40 years of operations.^[104][105]

The nuclear power industry in western nations have a history of construction delays, cost overruns, plant cancellations, and nuclear safety issues, despite significant government subsidies and support.^{[53][106][107][108]} These problems are related to very strict safety requirements, uncertain regulatory environment, slow rate of construction, and large stretches of time with no nuclear construction and consequent loss of know-how. Commentators therefore argue that nuclear power is impractical in western countries because of high costs, popular opposition, and regulatory uncertainty.^{[109][110][111][112]} Recent financial problems of western nuclear companies, most prominently the bankruptcy of Westinghouse in March 2017 because of US$9 billion of losses from nuclear construction projects in the United States, suggest a shift to the East, as the dominant exporter and designer of nuclear fuel and reactors.^[113][114]

The greatest new build activity is occurring in Asian countries like South Korea, India and China. In March 2016, China had 30 reactors in operation, 24 under construction and plans to build more.^{[115][116][117]}

In 2016 the BN-800 sodium cooled fast reactor in Russia, began commercial electricity generation, while plans for a BN-1200 were initially conceived the future of the fast reactor program in Russia awaits the results from MBIR, an under construction multi-loop Generation IV research facility for testing the chemically more inert lead, lead-bismuth and gas coolants, it will similarly run on recycled MOX (mixed uranium and plutonium oxide) fuel. An on-site pyrochemical processing, closed fuel-cycle facility, is planned, to reduce the necessity for a growth in uranium mining and exploration. In 2017 the manufacture program for the reactor commenced with the facility open to collaboration under the "International Project on Innovative Nuclear Reactors and Fuel Cycle", it has a construction schedule, that includes an operational start in 2020. As planned, it will be the world's most-powerful research reactor.^[118]

In the United States, licenses of almost half of the operating nuclear reactors have been extended to 60 years.^[119][120] The U.S. NRC and the U.S. Department of Energy have initiated research into Light water reactor sustainability which is hoped will lead to allowing extensions of reactor licenses beyond 60 years, provided that safety can be maintained, to increase energy security and preserve low-carbon generation sources.^[121] Research into nuclear reactors that can last 100 years, known as Centurion Reactors, is being conducted.^[122]

According to the World Nuclear Association, globally during the 1980s one new nuclear reactor started up every 17 days on average, and in the year 2015 it was estimated that this rate could in theory eventually increase to one every 5 days, although no plans exist for that.^[123]

Conventional fuel resources

Proportions of the isotopes, uranium-238 (blue) and uranium-235 (red) found naturally, versus grades that are enriched. light water reactors require fuel enriched to (3–4%), while others such as the CANDU reactor uses natural uranium.

Uranium is a fairly common element in the Earth's crust: it is approximately as common as tin or germanium, and is about 40 times more common than silver.^[152] Uranium is present in trace concentrations in most rocks, dirt, and ocean water, but can be economically extracted only where it is present in high concentrations. Still, as of 2011 the world's measured resources of uranium, economically recoverable at the arbitrary price ceiling of 130 USD/kg, were enough to last for between 70 and 100 years.^{[153][154][155]}

According to the OECD in 2006, there was an expected 85 years worth of uranium in already identified resources at the then-current utilization rates. In 2007, the OECD estimated 670 years of economically recoverable uranium in total conventional resources and phosphate ores assuming the then-current use rate.^[156] The OECD's red book of 2011 said that known uranium resources had grown by 12.5% since 2008 due to increased exploration, with this increase translating into greater than a century of uranium available if the rate of use were to continue at the 2011 level.^[157][158]

Light water reactors make relatively inefficient use of nuclear fuel, mostly fissioning only the very rare uranium-235 isotope. Nuclear reprocessing can make this waste reusable. Newer Generation III reactors also achieve a more efficient use of the available resources than the generation II reactors which make up the vast majority of reactors worldwide.^[159] With a pure fast reactor fuel cycle with a burn up of all the Uranium and actinides (which presently make up the most hazardous substances in nuclear waste), there is an estimated 160,000 years worth of Uranium in total conventional resources and phosphate ore at the price of 60–100 US$/kg.^[160]

Breeding

As opposed to 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). In 2006 it was estimated that with seawater extraction, there was likely some five billion years' worth of uranium-238 for use in these power plants.^[170]

Breeder technology has been used in several reactors, but the high cost of reprocessing fuel safely, at 2006 technological levels, requires uranium prices of more than 200 USD/kg before becoming justified economically.^[171] Breeder reactors are however being pursued as they have the potential to burn up all of the actinides in the present inventory of nuclear waste while also producing power and creating additional quantities of fuel for more reactors via the breeding process.^[172][173]

As of 2017, there are only two breeder reactors producing commercial power: the BN-600 reactor and the BN-800 reactor, both in Russia.^[174] The BN-600, with a capacity of 600 MW, was built in 1980 in Beloyarsk and is planned to produce power until 2025.^[174] The BN-800 is an updated version of the BN-600, and started operation in 2014 with a net electrical capacity of 789 MW.^[174] The technical design of a yet larger breeder, the BN-1200 reactor was originally scheduled to be finalized in 2013, with construction slated for 2015 but has since been delayed.^[175]

The Phénix breeder reactor in France was powered down in 2009 after 36 years of operation.^[174] Japan's Monju breeder reactor restarted (having been shut down in 1995) in 2010 for 3 months, but shut down again after equipment fell into the reactor during reactor checkups.^[176] The reactor was decommissioned in 2017.^[174]

Both China and India are building breeder reactors. The Indian 500 MWe Prototype Fast Breeder Reactor is in the commissioning phase,^[177] with plans to build five more by 2020.^[178] The China Experimental Fast Reactor began operating in 2011.^[179]

Another alternative to fast breeders is thermal breeder reactors that use uranium-233 bred from thorium as fission fuel in the thorium fuel cycle.^[180] Thorium is about 3.5 times more common than uranium in the Earth's crust, and has different geographic characteristics.^[180] This would extend the total practical fissionable resource base by 450%.^[180] India's three-stage nuclear power programme features the use of a thorium fuel cycle in the third stage, as it has abundant thorium reserves but little uranium.^[180]

Nuclear waste

The most important waste stream from nuclear power plants is spent nuclear fuel. It 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 fission products from nuclear reactions. 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.^[181]

High-level radioactive waste

Main articles: Reactor-grade plutonium § Reuse in reactors, High-level radioactive waste management, and List of nuclear waste treatment technologies

A nuclear fuel rod assembly bundle being inspected before entering a reactor.

Following interim storage in a spent fuel pool, the bundles of used fuel assemblies of a typical nuclear power station are often stored on site in the likes of the eight dry cask storage vessels pictured above.^[182] At Yankee Rowe Nuclear Power Station, which generated 44 billion kilowatt hours of electricity over its lifetime, its complete spent fuel inventory is contained within sixteen casks.^[183]

High-level radioactive waste management concerns management and disposal of highly radioactive materials created during production of nuclear power. The technical issues in accomplishing this are daunting, due to the extremely long periods radioactive wastes remain deadly to living organisms. Of particular concern are two long-lived fission products, Technetium-99 (half-life 220,000 years) and Iodine-129 (half-life 15.7 million years),^[184] which dominate spent nuclear fuel radioactivity after a few thousand years. The most troublesome transuranic elements in spent fuel are Neptunium-237 (half-life two million years) and Plutonium-239 (half-life 24,000 years).^[185] Consequently, high-level radioactive waste requires sophisticated treatment and management to successfully isolate it from the biosphere. This usually necessitates treatment, followed by a long-term management strategy involving permanent storage, disposal or transformation of the waste into a non-toxic form.^[186]

Governments around the world are considering a range of waste management and disposal options, usually involving deep-geologic placement, although there has been limited progress toward implementing long-term waste management solutions.^[187] This is partly because the timeframes in question when dealing with radioactive waste range from 10,000 to millions of years,^[188][189] according to studies based on the effect of estimated radiation doses.^[190]

Some proposed nuclear reactor designs however such as the American Integral Fast Reactor and the Molten salt reactor can use the nuclear waste from light water reactors as a fuel, transmutating it to isotopes that would be safe after hundreds, instead of tens of thousands of years. This offers a potentially more attractive alternative to deep geological disposal.^{[191][192][193]}

Another possibility is the use of thorium in a reactor especially designed for thorium (rather than mixing in thorium with uranium and plutonium (i.e. in existing reactors). Used thorium fuel remains only a few hundreds of years radioactive, instead of tens of thousands of years.^[194]

Since the fraction of a radioisotope's atoms decaying per unit of time is inversely proportional to its half-life, the relative radioactivity of a quantity of buried human radioactive waste would diminish over time compared to natural radioisotopes (such as the decay chains of 120 trillion tons of thorium and 40 trillion tons of uranium which are at relatively trace concentrations of parts per million each over the crust's 3 * 10¹⁹ ton mass).^{[195][196][197]} For instance, over a timeframe of thousands of years, after the most active short half-life radioisotopes decayed, burying U.S. nuclear waste would increase the radioactivity in the top 2000 feet of rock and soil in the United States (10 million km²) by ≈ 1 part in 10 million over the cumulative amount of natural radioisotopes in such a volume, although the vicinity of the site would have a far higher concentration of artificial radioisotopes underground than such an average.^[198]

Reprocessing

Reprocessing can potentially recover up to 95% of the remaining uranium and plutonium in spent nuclear fuel, putting it into new mixed oxide fuel. This produces a reduction in long term radioactivity within the remaining waste, since this is largely short-lived fission products, and reduces its volume by over 90%. Reprocessing of civilian fuel from power reactors is currently done in Europe, Russia, Japan, and India. The full potential of reprocessing had not been achieved as of 2013 because it requires breeder reactors, which were not commercially available at that time.^[211][212]

Nuclear reprocessing reduces the volume of high-level waste, but by itself does not reduce radioactivity or heat generation and therefore does not eliminate the need for a geological waste repository. Reprocessing has been politically controversial because of the potential to contribute to nuclear proliferation, the potential vulnerability to nuclear terrorism, the political challenges of repository siting (a problem that applies equally to direct disposal of spent fuel), and because of its high cost compared to the once-through fuel cycle. Several different methods for reprocessing been tried, but many have had safety and practicality problems which have led to their discontinuation.^[211][213]

In the United States, the Obama administration stepped back from President Bush's plans for commercial-scale reprocessing and reverted to a program focused on reprocessing-related scientific research.^[214] Reprocessing is not allowed in the U.S.^[215][216] In the United States, spent nuclear fuel is currently all treated as waste.^[217] A major recommendation of the Blue Ribbon Commission on America's Nuclear Future 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".^[218]

Accidents

Following the 2011 Fukushima Daiichi nuclear disaster, the world's worst nuclear accident since 1986, 50,000 households were displaced after radiation leaked into the air, soil and sea.^[221] Radiation checks led to bans of some shipments of vegetables and fish.^[222]

Some serious nuclear and radiation accidents have occurred. The severity of nuclear accidents is generally classified using the International Nuclear Event Scale (INES) introduced by the International Atomic Energy Agency (IAEA). The scale ranks anomalous events or accidents on a scale from 0 (a deviation from normal operation that pose no safety risk) to 7 (a major accident with widespread effects). There have been 3 accidents of level 5 or higher in the civilian nuclear power industry, two of which, the Chernobyl accident and the Fukushima accident, are ranked at level 7. The Chernobyl accident in 1986 caused approximately 50 deaths from direct and indirect effects, and many more serious injuries.^[223] The exact death toll due to indirect effects of the widespread radiation contamination is difficult to measure, and depends on the assumptions used. Some studies put the total death toll of the Chernobyl accident from indirect effects much higher, in the order of thousands of people. The Fukushima Daiichi nuclear accident was caused by the 2011 Tohoku earthquake and tsunami. The accident has not caused any radiation related deaths, but resulted in radioactive contamination of surrounding areas. The difficult Fukushima disaster cleanup will take 40 or more years, and is expected to cost tens of billions of dollars.^[224][225] The Three Mile Island accident in 1979 was a smaller scale accident, rated at INES level 5. There were no direct or indirect deaths caused by the accident.^[35]

Other less serious accidents are more common. Benjamin K. Sovacool has reported that worldwide there have been 99 accidents (defined as either resulting in loss of human life or more than $50,000 of property damage) at nuclear power plants.^[226] Fifty-seven accidents have occurred since the Chernobyl disaster, and 57% (56 out of 99) of all nuclear-related accidents have occurred in the United States.^[226]

Military nuclear-powered submarine mishaps include the K-19 reactor accident (1961),^[33] the K-27 reactor accident (1968),^[34] and the K-431 reactor accident (1985).^[35] International research is continuing into safety improvements such as passively safe plants,^[227] and the possible future use of nuclear fusion.

According to Benjamin K. Sovacool, fission energy accidents ranked first among energy sources in terms of their total economic cost, accounting for 41 percent of all property damage attributed to energy accidents.^[228] Another analysis presented in the international journal Human and Ecological Risk Assessment found that coal, oil, Liquid petroleum gas and hydroelectric accidents (primarily due to the Banqiao dam burst) have resulted in greater economic impacts than nuclear power accidents.^[229]

Safety

In terms of lives lost per unit of energy generated, nuclear power has caused fewer accidental deaths per unit of energy generated than all other major sources of energy generation. Energy produced by coal, petroleum, natural gas and hydropower has caused more deaths per unit of energy generated due to air pollution and energy accidents. This is found when comparing the immediate deaths from other energy sources to both the immediate nuclear related deaths from accidents^[230] and also including the latent, or predicted, indirect cancer deaths from nuclear energy accidents.^{[231][229][232]} When the combined immediate and indirect fatalities from nuclear power and all fossil fuels are compared, including fatalities resulting from the mining of the necessary natural resources to power generation and to air pollution,^[9] the use of nuclear power has been calculated to have prevented about 1.8 million deaths between 1971 and 2009, by reducing the proportion of energy that would otherwise have been generated by fossil fuels, and is projected to continue to do so.^[233][234] Following the 2011 Fukushima nuclear disaster, it has been estimated that if Japan had never adopted nuclear power, accidents and pollution from coal or gas plants would have caused more lost years of life.^[235]

Forced evacuation from a nuclear accident may lead to social isolation, anxiety, depression, psychosomatic medical problems, reckless behavior, even suicide. Such was the outcome of the 1986 Chernobyl nuclear disaster in Ukraine. A comprehensive 2005 study concluded that "the mental health impact of Chernobyl is the largest public health problem unleashed by the accident to date".^[236] Frank N. von Hippel, an American scientist, commented on the 2011 Fukushima nuclear disaster, saying that a disproportionate radiophobia, or "fear of ionizing radiation could have long-term psychological effects on a large portion of the population in the contaminated areas".^[237] A 2015 report in Lancet explained that serious impacts of nuclear accidents were often not directly attributable to radiation exposure, but rather social and psychological effects. Evacuation and long-term displacement of affected populations created problems for many people, especially the elderly and hospital patients.^[238] As of 2013, about 160,000 evacuees still live in temporary housing due to the evacuation order following the Fukushima accident.

Attacks and sabotage

Terrorists could target nuclear power plants in an attempt to release radioactive contamination into the community. The United States 9/11 Commission has said that nuclear power plants were potential targets originally considered for the September 11, 2001 attacks. 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.^[239]

If nuclear power use is to expand significantly, nuclear facilities will have to be made extremely safe from attacks that could release massive quantities of radioactivity. New reactor designs have features of passive safety, such as the flooding of the reactor core without active intervention by reactor operators. However, these safety measures have generally been developed and studied with respect to accidents, not to the deliberate reactor attack by a terrorist group. The U.S. Nuclear Regulatory Commission (NRC) does now also require new reactor license applications to consider security during the design stage.^[239] In the United States, the NRC carries out "Force on Force" (FOF) exercises at all Nuclear Power Plant (NPP) sites at least once every three years.^[239] In the United States, plants are surrounded by a double row of tall fences which are electronically monitored. The plant grounds are patrolled by a sizeable force of armed guards.^[240]

Insider sabotage is also a threat because insiders can observe and work around security measures. Successful insider crimes depended on the perpetrators' observation and knowledge of security vulnerabilities.^[241] A fire caused 5–10 million dollars worth of damage to New York's Indian Point Energy Center in 1971. The arsonist turned out to be a plant maintenance worker. Sabotage by workers has been reported at many other reactors in the United States: at Zion Nuclear Power Station (1974), Quad Cities Nuclear Generating Station, Peach Bottom Nuclear Generating Station, Fort St. Vrain Generating Station, Trojan Nuclear Power Plant (1974), Browns Ferry Nuclear Power Plant (1980), and Beaver Valley Nuclear Generating Station (1981). Many reactors overseas have also reported sabotage by workers.^[242]

Carbon emissions

A 2008 meta analysis of 103 studies, published by Benjamin K. Sovacool, estimated that the mean value of CO₂ emissions for nuclear power over the lifecycle of a plant was 66.08 g/kW·h, this 2008 study by Sovacool garnered controversy by comparing statistical mean with median values,^[254] to suggest various renewable energy sources were "two to seven times more effective at combating climate change", by presenting median values of "9–32 g/kW·h" for the latter.^[255] A similar 2012 meta-analysis by Yale University arrived at a different conclusion, with the median value, depending on which reactor design was analyzed, ranging from 11 to 25 g/kW·h of total life cycle nuclear power CO₂ emissions, a figure comparable, and in some instances lower, than a number of renewable energy generation methods.^[256]

Nuclear power is one of the leading low carbon power generation methods of producing electricity, and in terms of total life-cycle greenhouse gas emissions per unit of energy generated, has emission values comparable to or lower than renewable energy.^[5][257] A 2014 analysis of the carbon footprint literature by the Intergovernmental Panel on Climate Change (IPCC) reported that the embodied total life-cycle emission intensity of fission electricity has a median value of 12 g CO₂eq/kWh which is the lowest out of all commercial baseload energy sources.^[258][259] This is contrasted with coal and fossil gas at 820 and 490 g CO₂ eq/kWh.^[258][259] From the beginning of fission-electric power station commercialization in the 1970s, nuclear power prevented the emission of about 64 billion tonnes of carbon dioxide equivalent that would have otherwise resulted from the burning of fossil fuels in thermal power stations.^[6]

Radiation

According to the United Nations (UNSCEAR), regular nuclear power plant operation including the nuclear fuel cycle causes radioisotope releases into the environment amounting to 0.0002 millisieverts (mSv) per year of public exposure as a global average.^[260] This is small compared to variation in natural background radiation, which averages 2.4 mSv/a globally but frequently varies between 1 mSv/a and 13 mSv/a depending on a person's location as determined by UNSCEAR.^[260] As of a 2008 report, the remaining legacy of the worst nuclear power plant accident (Chernobyl) is 0.002 mSv/a in global average exposure (a figure which was 0.04 mSv per person averaged over the entire populace of the Northern Hemisphere in the year of the accident in 1986, although far higher among the most affected local populations and recovery workers).^[260]

Waste heat

Climate change causing weather extremes such as heat waves, reduced precipitation levels and droughts can have a significant impact on all thermal power station infrastructure, including large biomass-electric and fission-electric stations alike, if cooling in these power stations, namely in the steam condenser is provided by certain freshwater sources.^[261] While many thermal stations use indirect seawater cooling or cooling towers that in comparison use little to no freshwater, those that were designed to heat exchange with rivers and lakes, can run into economic problems.

This presently infrequent generic problem may become increasingly significant over time.^[261] This can force nuclear reactors to be shut down, as happened in France during the 2003 and 2006 heat waves. Nuclear power supply was severely diminished by low river flow rates and droughts, which meant rivers had reached the maximum temperatures for cooling reactors.^[261] During the heat waves, 17 reactors had to limit output or shut down. 77% of French electricity is produced by nuclear power and in 2009 a similar situation created a 8GW shortage and forced the French government to import electricity.^[261] Other cases have been reported from Germany, where extreme temperatures have reduced nuclear power production only 9 times due to high temperatures between 1979 and 2007.^[261]

If global warming continues, this disruption is likely to increase or alternatively, station operators could instead retro-fit other means of cooling, like cooling towers, despite these frequently being large structures and therefore sometimes unpopular with the public.

Advanced fission reactor designs

Generation IV roadmap from Argonne National Laboratory

Current fission reactors in operation around the world are second or third generation systems, with most of the first-generation systems having been already retired. Research into advanced generation IV reactor types was officially started by the Generation IV International Forum (GIF) based on eight technology goals, including to improve nuclear safety, improve proliferation resistance, minimize waste, improve natural resource utilization, the ability to consume existing nuclear waste in the production of electricity, and decrease the cost to build and run such plants. Most of these reactors differ significantly from current operating light water reactors, and are generally not expected to be available for commercial construction before 2030.^[308]

One disadvantage of any new reactor technology is that safety risks may be greater initially as reactor operators have little experience with the new design. Nuclear engineer David Lochbaum has explained that almost all serious nuclear accidents have occurred with what was at the time the most recent technology. He argues that "the problem with new reactors and accidents is twofold: scenarios arise that are impossible to plan for in simulations; and humans make mistakes".^[309] As one director of a U.S. research laboratory put it, "fabrication, construction, operation, and maintenance of new reactors will face a steep learning curve: advanced technologies will have a heightened risk of accidents and mistakes. The technology may be proven, but people are not".^[309]

Hybrid nuclear fusion-fission

Hybrid nuclear power is a proposed means of generating power by use of a combination of nuclear fusion and fission processes. The concept dates to the 1950s, and was briefly advocated by Hans Bethe during the 1970s, but largely remained unexplored until a revival of interest in 2009, due to delays in the realization of pure fusion. When a sustained nuclear fusion power plant is built, it has the potential to be capable of extracting all the fission energy that remains in spent fission fuel, reducing the volume of nuclear waste by orders of magnitude, and more importantly, eliminating all actinides present in the spent fuel, substances which cause security concerns.^[310]

Nuclear fusion

Schematic of the ITER tokamak under construction in France.

Nuclear fusion reactions have the potential to be safer and generate less radioactive waste than fission.^[311][312] These reactions appear potentially viable, though technically quite difficult and have yet to be created on a scale that could be used in a functional power plant. Fusion power has been under theoretical and experimental investigation since the 1950s.

Several experimental nuclear fusion reactors and facilities exist. The largest and most ambitious international nuclear fusion project currently in progress is ITER, a large tokamak under construction in France. ITER is planned to pave the way for commercial fusion power by demonstrating self-sustained nuclear fusion reactions with positive energy gain. Construction of the ITER facility began in 2007, but the project has run into many delays and budget overruns. The facility is now not expected to begin operations until the year 2027 – 11 years after initially anticipated.^[313] A follow on commercial nuclear fusion power station, DEMO, has been proposed.^[314][315] There are also suggestions for a power plant based upon a different fusion approach, that of an inertial fusion power plant.

Fusion powered electricity generation was initially believed to be readily achievable, as fission-electric power had been. However, the extreme requirements for continuous reactions and plasma containment led to projections being extended by several decades. In 2010, more than 60 years after the first attempts, commercial power production was still believed to be unlikely before 2050.^[314]