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Monday, July 31, 2023

Nuclear power in the United States

From Wikipedia, the free encyclopedia
 
A nuclear power plant in Arkansas
 
Nuclear reactors within the Contiguous United States as of October 2021; marker colors indicate respective administrative Regions of the Nuclear Regulatory Commission
 
Net electrical generation from US nuclear power plants 1957–2019
 
Nuclear power compared to other sources of electricity in the US, 1949–2011

In the United States, nuclear power is provided by 92 commercial reactors with a net capacity of 94.7 gigawatts (GW), with 61 pressurized water reactors and 31 boiling water reactors. In 2019, they produced a total of 809.41 terawatt-hours of electricity, which accounted for 20% of the nation's total electric energy generation. In 2018, nuclear comprised nearly 50 percent of US emission-free energy generation.

As of September 2017, there are two new reactors under construction with a gross electrical capacity of 2,500 MW, while 39 reactors have been permanently shut down. The United States is the world's largest producer of commercial nuclear power, and in 2013 generated 33% of the world's nuclear electricity. With the past and future scheduled plant closings, China and Russia could surpass the United States in nuclear energy production.

As of October 2014, the Nuclear Regulatory Commission (NRC) has granted license renewals providing 20-year extensions to a total of 74 reactors. In early 2014, the NRC prepared to receive the first applications of license renewal beyond 60 years of reactor life as early as 2017, a process which by law requires public involvement. Licenses for 22 reactors are due to expire before the end of 2029 if no renewals are granted. Pilgrim Nuclear Power Station in Massachusetts was the most recent nuclear power plant to be decommissioned, on June 1, 2019. Another five aging reactors were permanently closed in 2013 and 2014 before their licenses expired because of high maintenance and repair costs at a time when natural gas prices had fallen: San Onofre 2 and 3 in California, Crystal River 3 in Florida, Vermont Yankee in Vermont, and Kewaunee in Wisconsin. In April 2021, New York State permanently closed Indian Point in Buchanan, 30 miles from New York City.

Most reactors began construction by 1974; following the Three Mile Island accident in 1979 and changing economics, many planned projects were canceled. More than 100 orders for nuclear power reactors, many already under construction, were canceled in the 1970s and 1980s, bankrupting some companies.

In 2006, the Brookings Institution, a public policy organization, stated that new nuclear units had not been built in the United States because of soft demand for electricity, the potential cost overruns on nuclear reactors due to regulatory issues and resulting construction delays.

There was a revival of interest in nuclear power in the 2000s, with talk of a "nuclear renaissance", supported particularly by the Nuclear Power 2010 Program. A number of applications were made, but facing economic challenges, and later in the wake of the 2011 Fukushima Daiichi nuclear disaster, most of these projects have been canceled. Up until 2013, there had also been no ground-breaking on new nuclear reactors at existing power plants since 1977. Then in 2012, the NRC approved construction of four new reactors at existing nuclear plants. Construction of the Virgil C. Summer Nuclear Generating Station Units 2 and 3 began on March 9, 2013, but was abandoned on July 31, 2017, after the reactor supplier Westinghouse filed for bankruptcy protection in March 2017. On March 12, 2013, construction began on the Vogtle Electric Generating Plant Units 3 and 4. The target in-service date for Unit 3 was originally November 2021. In March 2023, the Vogtle reached "initial criticality" and is scheduled to start service in July 2023. On October 19, 2016, TVA's Unit 2 reactor at the Watts Bar Nuclear Generating Station became the first US reactor to enter commercial operation since 1996.

History

Emergence

The Shippingport reactor was the first full-scale PWR nuclear power plant in the United States.
President Jimmy Carter leaving Three Mile Island Nuclear Generating Station for Middletown, Pennsylvania, April 1, 1979

Research into the peaceful uses of nuclear materials began in the United States under the auspices of the Atomic Energy Commission, created by the United States Atomic Energy Act of 1946. Medical scientists were interested in the effect of radiation upon the fast-growing cells of cancer, and materials were given to them, while the military services led research into other peaceful uses.

Power reactor research

Argonne National Laboratory was assigned by the United States Atomic Energy Commission the lead role in developing commercial nuclear energy beginning in the 1940s. Between then and the turn of the 21st century, Argonne designed, built, and operated fourteen reactors at its site southwest of Chicago, and another fourteen reactors at the National Reactors Testing Station in Idaho. These reactors included initial experiments and test reactors that were the progenitors of today's pressurized water reactors (including naval reactors), boiling water reactors, heavy water reactors, graphite-moderated reactors, and liquid-metal cooled fast reactors, one of which was the first reactor in the world to generate electricity. Argonne and a number of other AEC contractors built a total of 52 reactors at the National Reactor Testing Station. Two were never operated; except for the Neutron Radiography Facility, all the other reactors were shut down by 2000.

In the early afternoon of December 20, 1951, Argonne director Walter Zinn and fifteen other Argonne staff members witnessed a row of four light bulbs light up in a nondescript brick building in the eastern Idaho desert. Electricity from a generator connected to Experimental Breeder Reactor I (EBR-I) flowed through them. This was the first time that a usable amount of electrical power had ever been generated from nuclear fission. Only days afterward, the reactor produced all the electricity needed for the entire EBR complex. One ton of natural uranium can produce more than 40 gigawatt-hours of electricity — this is equivalent to burning 16,000 tons of coal or 80,000 barrels of oil. More central to EBR-I's purpose than just generating electricity, however, was its role in proving that a reactor could create more nuclear fuel as a byproduct than it consumed during operation. In 1953, tests verified that this was the case.

The US Navy took the lead, seeing the opportunity to have ships that could steam around the world at high speeds for several decades without needing to refuel, and the possibility of turning submarines into true full-time underwater vehicles. So, the Navy sent their "man in Engineering", then Captain Hyman Rickover, well known for his great technical talents in electrical engineering and propulsion systems in addition to his skill in project management, to the AEC to start the Naval Reactors project. Rickover's work with the AEC led to the development of the Pressurized Water Reactor (PWR), the first naval model of which was installed in the submarine USS Nautilus. This made the boat capable of operating under water full-time – demonstrating this ability by reaching the North Pole and surfacing through the Polar ice cap.

Start of commercial nuclear power

From the successful naval reactor program, plans were quickly developed for the use of reactors to generate steam to drive turbines turning generators. In April 1957, the SM-1 Nuclear Reactor in Fort Belvoir, Virginia was the first atomic power generator to go online and produce electrical energy to the U.S. power grid. On May 26, 1958, the first commercial nuclear power plant in the United States, Shippingport Atomic Power Station, was opened by President Dwight D. Eisenhower as part of his Atoms for Peace program. As nuclear power continued to grow throughout the 1960s, the Atomic Energy Commission anticipated that more than 1,000 reactors would be operating in the United States by 2000. As the industry continued to expand, the Atomic Energy Commission's development and regulatory functions were separated in 1974; the Department of Energy absorbed research and development, while the regulatory branch was spun off and turned into an independent commission known as the U.S. Nuclear Regulatory Commission (USNRC or simply NRC).

Pro-nuclear power stance

Safest forms of energy

As of February 2020, Our World In Data stated that "nuclear energy and renewables are far, far safer than fossil fuels as regards human health, safety and carbon footprint," with nuclear energy resulting in 99.8% fewer deaths than brown coal; 99.7% fewer than coal; 99.6% fewer than oil; and 97.5% fewer than gas.

Under President Obama, the Office of nuclear energy stated in January 2012 that "Nuclear power has safely, reliably, and economically contributed almost 20% of electrical generation in the United States over the past two decades. It remains the single largest contributor (more than 70%) of non-greenhouse-gas- emitting electric power generation in the United States. Domestic demand for electrical energy is expected to grow by more than 30% from 2009 to 2035. At the same time, most of the currently operating nuclear power plants will begin reaching the end of their initial 20-year extension to their original 40-year operating license, for a total of 60 years of operation." It warned that if new plants do not replace those which are retired then the total fraction of generated electrical energy from nuclear power will begin to decline.

The United States Department of Energy web site states that "nuclear power is the most reliable energy source", and to a great degree "has the highest capacity factor. Natural gas and coal capacity factors are generally lower due to routine maintenance and/or refueling at these facilities while renewable plants are considered intermittent or variable sources and are mostly limited by a lack of fuel (i.e. wind, sun, or water)." Nuclear is the largest source of clean power in the United States, generating more than 800 billion kilowatt-hours of electricity each year and producing more than half of the nation's emissions-free electricity. This avoids more than 470 million metric tons of carbon each year, which is the equivalent of removing 100 million cars off of the road. In 2019, nuclear plants operated at full power more than 93% of the time, making it the most reliable energy source on the power grid. The Department of Energy and its national labs are working with industry to develop new reactors and fuels that will increase the overall performance of nuclear technologies and reduce the amount of nuclear waste that is produced.

Advanced nuclear reactors "that are smaller, safer, and more efficient at half the construction cost of today’s reactors" are part of President Biden's clean energy proposals.

Opposition to nuclear power

Anti-nuclear protest at Harrisburg in 1979, following the Three Mile Island accident

There has been considerable opposition to the use of nuclear power in the United States. The first U.S. reactor to face public opposition was Enrico Fermi Nuclear Generating Station in 1957. It was built approximately 30 miles from Detroit and there was opposition from the United Auto Workers Union. Pacific Gas & Electric planned to build the first commercially viable nuclear power plant in the US at Bodega Bay, north of San Francisco. The proposal was controversial and conflict with local citizens began in 1958. The conflict ended in 1964, with the forced abandonment of plans for the power plant. Historian Thomas Wellock traces the birth of the anti-nuclear movement to the controversy over Bodega Bay. Attempts to build a nuclear power plant in Malibu were similar to those at Bodega Bay and were also abandoned.

Nuclear accidents continued into the 1960s with a small test reactor exploding at the Stationary Low-Power Reactor Number One in Idaho Falls in January 1961 and a partial meltdown at the Enrico Fermi Nuclear Generating Station in Michigan in 1966. In his 1963 book Change, Hope and the Bomb, David Lilienthal criticized nuclear developments, particularly the nuclear industry's failure to address the nuclear waste question. J. Samuel Walker, in his book Three Mile Island: A Nuclear Crisis in Historical Perspective, explains that the growth of the nuclear industry in the U.S. occurred in the 1970s as the environmental movement was being formed. Environmentalists saw the advantages of nuclear power in reducing air pollution, but were critical of nuclear technology on other grounds. They were concerned about nuclear accidents, nuclear proliferation, high cost of nuclear power plants, nuclear terrorism and radioactive waste disposal.

There were many anti-nuclear protests in the United States which captured national public attention during the 1970s and 1980s. These included the well-known Clamshell Alliance protests at Seabrook Station Nuclear Power Plant and the Abalone Alliance protests at Diablo Canyon Nuclear Power Plant, where thousands of protesters were arrested. Other large protests followed the 1979 Three Mile Island accident.

In New York City on September 23, 1979, almost 200,000 people attended a protest against nuclear power. Anti-nuclear power protests preceded the shutdown of the Shoreham, Yankee Rowe, Rancho Seco, Maine Yankee, and about a dozen other nuclear power plants.

Historical use of Native land in nuclear energy

Nuclear Energy in the United States has greatly affected Native Americans due to the large amount of mining for uranium, and disposal of nuclear waste done on Native lands over the past century. Environmental Sociologists Chad L. Smith and Gregory Hooks have deemed these areas and tribal lands as a whole "sacrifice zones", due to the prevalence of mishandled nuclear materials. Uranium as a resource has largely been located in the southwestern USA, and large amounts have been found on Native lands, with the estimates being anywhere from 25% to 65% of Uranium being located on Native land. Due to this many mines have been placed on Native land and have been abandoned without proper closing of these mines. Some of these mines have led to large amounts of pollution on Native land which has contaminated the water and ground. This has led to a large uptick in cancer cases. On the Navajo reservation in particular, there has been three separate cleanup efforts done by the EPA, all unsuccessful.

Nuclear waste has been an issue that Native Americans have had to deal with for decades ranging from improper disposal of waste during active mining to the government trying and succeeding to place waste disposal sites on various native lands. In 1986 the US government tried to put a permanent nuclear waste repository on the White Earth Reservation, but the Anishinaabe people who lived there commissioned the Minnesota legislature to prevent it, which worked. However, because there was no permanent place found, the government placed a temporary facility on Yucca Mountain to contain the waste. Yucca Mountain is also on Native Land and is considered a sacred site that the government did not have consent to place nuclear waste on. Yucca Mountain still houses this temporary facility to this day and is being debated over if it should become a permanent facility.

Over-commitment and cancellations

Net summer electrical generation capacity of US nuclear power plants, 1949–2011
Average capacity factor of US nuclear power plants, 1957–2011

By the mid-1970s, it became clear that nuclear power would not grow nearly as quickly as once believed. Cost overruns were sometimes a factor of ten above original industry estimates, and became a major problem. For the 75 nuclear power reactors built from 1966 to 1977, cost overruns averaged 207 percent. Opposition and problems were galvanized by the Three Mile Island accident in 1979.

Over-commitment to nuclear power brought about the financial collapse of the Washington Public Power Supply System, a public agency which undertook to build five large nuclear power plants in the 1970s. By 1983, cost overruns and delays, along with a slowing of electricity demand growth, led to cancellation of two WPPSS plants and a construction halt on two others. Moreover, WPPSS defaulted on $2.25 billion of municipal bonds, which is one of the largest municipal bond defaults in U.S. history. The court case that followed took nearly a decade to resolve.

Eventually, more than 120 reactor orders were canceled, and the construction of new reactors ground to a halt. Al Gore has commented on the historical record and reliability of nuclear power in the United States:

Of the 253 nuclear power reactors originally ordered in the United States from 1953 to 2008, 48 percent were canceled, 11 percent were prematurely shut down, 14 percent experienced at least a one-year-or-more outage, and 27 percent are operating without having a year-plus outage. Thus, only about one fourth of those ordered, or about half of those completed, are still operating and have proved relatively reliable.

Amory Lovins has also commented on the historical record of nuclear power in the United States:

Of all 132 U.S. nuclear plants built (52% of the 253 originally ordered), 21% were permanently and prematurely closed due to reliability or cost problems, while another 27% have completely failed for a year or more at least once. The surviving U.S. nuclear plants produce ~90% of their full-time full-load potential, but even they are not fully dependable. Even reliably operating nuclear plants must shut down, on average, for 39 days every 17 months for refueling and maintenance, and unexpected failures do occur too.

A cover story in the February 11, 1985, issue of Forbes magazine commented on the overall management of the nuclear power program in the United States:

The failure of the U.S. nuclear power program ranks as the largest managerial disaster in business history, a disaster on a monumental scale … only the blind, or the biased, can now think that the money has been well spent. It is a defeat for the U.S. consumer and for the competitiveness of U.S. industry, for the utilities that undertook the program and for the private enterprise system that made it possible.

Three Mile Island and after

Anti-nuclear rally at Harrisburg in April 1979

The NRC reported "(...the Three Mile Island accident...) was the most serious in U.S. commercial nuclear power plant operating history, even though it led to no deaths or injuries to plant workers or members of the nearby community." The World Nuclear Association reports that "...more than a dozen major, independent studies have assessed the radiation releases and possible effects on the people and the environment around TMI since the 1979 accident at TMI-2. The most recent was a 13-year study on 32,000 people. None has found any adverse health effects such as cancers which might be linked to the accident." Other nuclear power incidents within the US (defined as safety-related events in civil nuclear power facilities between INES Levels 1 and 3 include those at the Davis-Besse Nuclear Power Plant, which was the source of two of the top five highest conditional core damage frequency nuclear incidents in the United States since 1979, according to the U.S. Nuclear Regulatory Commission.

Despite the concerns which arose among the public after the Three Mile Island incident, the accident highlights the success of the reactor's safety systems. The radioactivity released as a result of the accident was almost entirely confined within the reinforced concrete containment structure. These containment structures, found at all nuclear power plants, were designed to successfully trap radioactive material in the event of a melt down or accident. At Three Mile Island, the containment structures operated exactly as it was designed to do, emerging successful in containing any radioactive energy. The low levels of radioactivity released post incident is considered harmless, resulting in zero injuries and deaths of residents living in proximity to the plant.

Despite many technical studies which asserted that the probability of a severe nuclear accident was low, numerous surveys showed that the public remained "very deeply distrustful and uneasy about nuclear power". Some commentators have suggested that the public's consistently negative ratings of nuclear power are reflective of the industry's unique connection with nuclear weapons:

[One] reason why nuclear power is seen differently to other technologies lies in its parentage and birth. Nuclear energy was conceived in secrecy, born of war, and first revealed to the world in horror. No matter how many proponents try to separate the peaceful atom from the weapon's atom, the connection is firmly embedded in the mind of the public.

Several US nuclear power plants closed well before their design lifetimes, due to successful campaigns by anti-nuclear activist groups. These include Rancho Seco in 1989 in California and Trojan in 1992 in Oregon. Humboldt Bay in California closed in 1976, 13 years after geologists discovered it was built on the Little Salmon Fault. Shoreham Nuclear Power Plant was completed but never operated commercially as an authorized Emergency Evacuation Plan could not be agreed on due to the political climate after the Three Mile Island accident and Chernobyl disaster. The last permanent closure of a US nuclear power plant was in 1997.

US nuclear reactors were originally licensed to operate for 40-year periods. In the 1980s, the NRC determined that there were no technical issues that would preclude longer service. Over half of US nuclear reactors are over 30 years old and almost all are over twenty years old. As of 2011, more than 60 reactors have received 20-year extensions to their licensed lifetimes. The average capacity factor for all US reactors has improved from below 60% in the 1970s and 1980s, to 92% in 2007.

After the Three Mile Island accident, NRC-issued reactor construction permits, which had averaged more than 12 per year from 1967 through 1978, came to an abrupt halt; no permits were issued between 1979 and 2012 (in 2012, four planned new reactors received construction permits). Many permitted reactors were never built, or the projects were abandoned. Those that were completed after Three Mile island experienced a much longer time lag from construction permit to starting of operations. The Nuclear Regulatory Commission itself described its regulatory oversight of the long-delayed Seabrook Nuclear Power Plant as "a paradigm of fragmented and uncoordinated government decision making," and "a system strangling itself and the economy in red tape." The number of operating power reactors in the US peaked at 112 in 1991, far fewer than the 177 that received construction permits. By 1998 the number of working reactors declined to 104, where it remains as of 2013. The loss of electrical generation from the eight fewer reactors since 1991 has been offset by power uprates of generating capacity at existing reactors.

Despite the problems following Three Mile Island, output of nuclear-generated electricity in the US grew steadily, more than tripling over the next three decades: from 255 billion kilowatt-hours in 1979 (the year of the Three Mile Island accident), to 806 billion kilowatt-hours in 2007. Part of the increase was due to the greater number of operating reactors, which increased by 51%: from 69 reactors in 1979, to 104 in 2007. Another cause was a large increase in the capacity factor over that period. In 1978, nuclear power plants generated electricity at only 64% of their rated output capacity. Performance suffered even further during and after Three Mile Island, as a series of new safety regulations from 1979 through the mid-1980s forced operators to repeatedly shut down reactors for required retrofits. It was not until 1990 that the average capacity factor of US nuclear plants returned to the level of 1978. The capacity factor continued to rise, until 2001. Since 2001, US nuclear power plants have consistently delivered electric power at about 90% of their rated capacity. In 2016, the number of power plants was at 100 with 4 under construction.

Effects of Fukushima

The San Onofre Nuclear Generating Station was shut down in 2013. There is about 1,700 tons of spent nuclear fuel at San Onofre.

Following the 2011 Japanese nuclear accidents, the U.S. Nuclear Regulatory Commission announced it would launch a comprehensive safety review of the 104 nuclear power reactors across the United States, at the request of President Obama. A total of 45 groups and individuals had formally asked the NRC to suspend all licensing and other activities at 21 proposed nuclear reactor projects in 15 states until the NRC had completed a thorough post-Fukushima reactor crisis examination. The petitioners also asked the NRC to supplement its own investigation by establishing an independent commission comparable to that set up in the wake of the serious, though less severe, 1979 Three Mile Island accident. The Obama administration continued "to support the expansion of nuclear power in the United States, despite the crisis in Japan".

An industry observer noted that post-Fukushima costs were likely to go up for both current and new nuclear power plants, due to increased requirements for on-site spent fuel management and elevated design basis threats. License extensions for existing reactors will face additional scrutiny, with outcomes depending on plants meeting new requirements, and some extensions already granted for more than 60 of the 100 operating U.S. reactors could be revisited. On-site storage, consolidated long-term storage, and geological disposal of spent fuel is "likely to be reevaluated in a new light because of the Fukushima storage pool experience". Mark Cooper suggested that the cost of nuclear power, which already had risen sharply in 2010 and 2011, could "climb another 50 percent due to tighter safety oversight and regulatory delays in the wake of the reactor calamity in Japan".

In 2011, London-based bank HSBC said: "With Three Mile Island and Fukushima as a backdrop, the US public may find it difficult to support major nuclear new build and we expect that no new plant extensions will be granted either. Thus we expect the clean energy standard under discussion in US legislative chambers will see a far greater emphasis on gas and renewables plus efficiency".

Competitiveness problems

In May 2015, a senior vice president of General Atomics stated that the U.S. nuclear industry was struggling because of comparatively low U.S. fossil fuel production costs, partly due to the rapid development of shale gas, and high financing costs for nuclear plants.

In July 2016, Toshiba withdrew the U.S. design certification renewal for its Advanced Boiling Water Reactor because "it has become increasingly clear that energy price declines in the US prevent Toshiba from expecting additional opportunities for ABWR construction projects".

In 2016, Governor of New York Andrew Cuomo directed the New York Public Service Commission to consider ratepayer-financed subsidies similar to those for renewable sources to keep nuclear power stations profitable in the competition against natural gas.

In March 2018, FirstEnergy announced plans to deactivate the Beaver Valley, Davis-Besse, and Perry nuclear power plants, which are in the Ohio and Pennsylvania deregulated electricity market, for economic reasons during the next three years.

In 2019, the Energy Information Administration revised the levelized cost of electricity from new advanced nuclear power plants to be $0.0775/kWh before government subsidies, using a 4.3% cost of capital (WACC) over a 30-year cost recovery period. Financial firm Lazard also updated its levelized cost of electricity report costing new nuclear at between $0.118/kWh and $0.192/kWh using a commercial 7.7% cost of capital (WACC) (pre-tax 12% cost for the higher-risk 40% equity finance and 8% cost for the 60% loan finance) over a 40-year lifetime, making it the most expensive privately financed non-peaking generation technology other than residential solar PV.

In August 2020, Exelon decided to close the Byron and Dresden plants in 2021 for economic reasons, despite the plants having licenses to operate for another 20 and 10 years respectively. On September 13, 2021, the Illinois Senate approved a bill containing nearly $700 million in subsidies for the state's nuclear plants, including Byron, causing Exelon to reverse the shutdown order.

Westinghouse Chapter 11 bankruptcy

On March 29, 2017, parent company Toshiba placed Westinghouse Electric Company in Chapter 11 bankruptcy because of $9 billion of losses from its nuclear reactor construction projects. The projects responsible for this loss are mostly the construction of four AP1000 reactors at Vogtle in Georgia and V. C. Summer in South Carolina. The U.S. government had given $8.3 billion of loan guarantees for the financing of the Vogtle nuclear reactors being built in the U.S., which are delayed but remain under construction. In July 2017, the V.C. Summer plant owners, the two largest utilities in South Carolina, terminated the project. Peter A. Bradford, former Nuclear Regulatory Commission member, commented "They placed a big bet on this hallucination of a nuclear renaissance".

The other U.S. new nuclear supplier, General Electric, had already scaled back its nuclear operations as it was concerned about the economic viability of new nuclear.

In the 2000s, interest in nuclear power renewed in the US, spurred by anticipated government curbs on carbon emissions, and a belief that fossil fuels would become more costly. Ultimately however, following Westinghouse's bankruptcy, only two new nuclear reactors were under construction. In addition Watts Bar unit 2, whose construction was started in 1973 but suspended in the 1980s, was completed and commissioned in 2016.

Possible renaissance

US reactor construction permits issued and operating nuclear power reactors, 1955–2011 (data from US EIA)

In 2008, it was reported that The Shaw Group and Westinghouse would construct a factory at the Port of Lake Charles at Lake Charles, Louisiana to build components for the Westinghouse AP1000 nuclear reactor. On October 23, 2008, it was reported that Northrop Grumman and Areva were planning to construct a factory in Newport News, Virginia to build nuclear reactors.

As of March 2009, the NRC had received applications to construct 26 new reactors with applications for another 7 expected. Six of these reactors were ordered. Some applications were made to reserve places in a queue for government incentives available for the first three plants based on each innovative reactor design.

In May 2009, John Rowe, chairman of Exelon, which operates 17 nuclear reactors, stated that he would cancel or delay construction of two new reactors in Texas without federal loan guarantees. Amory Lovins added that "market forces had killed it years earlier".

In July 2009, the proposed Victoria County Nuclear Power Plant was delayed, as the project proved difficult to finance. As of April 2009, AmerenUE has suspended plans to build its proposed plant in Missouri because the state Legislature would not allow it to charge consumers for some of the project's costs before the plant's completion. The New York Times has reported that without that "financial and regulatory certainty" the company has said it could not proceed. Previously, MidAmerican Energy Company decided to "end its pursuit of a nuclear power plant in Payette County, Idaho." MidAmerican cited cost as the primary factor in their decision.

The federal government encouraged development through the Nuclear Power 2010 Program, which coordinates efforts for building new plants, and the Energy Policy Act. In February 2010, President Barack Obama announced loan guarantees for two new reactors at Georgia Power's Vogtle Electric Generating Plant. The reactors are "just the first of what we hope will be many new nuclear projects," said Carol Browner, director of the White House Office of Energy and Climate Change Policy.

In February 2010, the Vermont Senate voted 26 to 4 to block operation of the Vermont Yankee Nuclear Power Plant after 2012, citing radioactive tritium leaks, misstatements in testimony by plant officials, a cooling tower collapse in 2007, and other problems. By state law, the renewal of the operating license must be approved by both houses of the legislature for the nuclear power plant to continue operation.

In 2010, some companies withdrew their applications. In September 2010, Matthew Wald from the New York Times reported that "the nuclear renaissance is looking small and slow at the moment".

In the first quarter of 2011, renewable energy contributed 11.7 percent of total U.S. energy production (2.245 quadrillion BTUs of energy), surpassing energy production from nuclear power (2.125 quadrillion BTUs). 2011 was the first year since 1997 that renewables exceeded nuclear in US total energy production.

In August 2011, the TVA board of directors voted to move forward with the construction of the unit one reactor at the Bellefonte Nuclear Generating Station. In addition, the Tennessee Valley Authority petitioned to restart construction on the first two units at Bellefonte. As of March 2012, many contractors had been laid off and the ultimate cost and timing for Bellefonte 1 will depend on work at another reactor TVA is completing – Watts Bar 2 in Tennessee. In February 2012, TVA said the Watts Bar 2 project was running over budget and behind schedule.

The first two of the newly approved units were Units 3 and 4 at the existing Vogtle Electric Generating Plant. As of December 2011, construction by Southern Company on the two new nuclear units had begun. They were expected to be delivering commercial power by 2016 and 2017, respectively. One week after Southern received its license to begin major construction, a dozen groups sued to stop the expansion project, stating "public safety and environmental problems since Japan's Fukushima Daiichi nuclear reactor accident have not been taken into account". The lawsuit was dismissed in July 2012.

In 2012, The NRC approved construction permits for four new nuclear reactor units at two existing plants, the first permits in 34 years. The first new permits, for two proposed reactors at the Vogtle plant, were approved in February 2012. NRC Chairman Gregory Jaczko cast the lone dissenting vote, citing safety concerns stemming from Japan's 2011 Fukushima nuclear disaster: "I cannot support issuing this license as if Fukushima never happened".

Global status of commercial nuclear deployment as of 2017
  Operating reactors, building new reactors
  Operating reactors, planning new build
  No reactors, building new reactors
  No reactors, new in planning
  Operating reactors, stable
  Operating reactors, decided on phase-out
  Civil nuclear power is illegal
  No commercial reactors

Also in 2012, Units 2 and 3 at the SCANA Virgil C. Summer Nuclear Generating Station in South Carolina were approved, and were scheduled to come online in 2017 and 2018, respectively. After several reforecasted completion dates the project was abandoned in July 2017.

Other reactors were under consideration – a third reactor at the Calvert Cliffs Nuclear Power Plant in Maryland, a third and fourth reactor at South Texas Nuclear Generating Station, together with two other reactors in Texas, four in Florida, and one in Missouri. However, these have all been postponed or canceled.

In August 2012, the US Court of Appeals for the District of Columbia found that the NRC's rules for the temporary storage and permanent disposal of nuclear waste stood in violation of the National Environmental Policy Act, rendering the NRC legally unable to grant final licenses. This ruling was founded on the absence of a final waste repository plan.

In March 2013, the concrete for the basemat of Block 2 of the Virgil C. Summer Nuclear Generating Station was poured. First concrete for Unit 3 was completed on November 4, 2013. Construction on unit 3 of Vogtle Electric Generating Plant started that month. Unit 4 was begun in November 2013. However, following Westinghouse's bankruptcy, the project was abandoned.

In 2015, the Energy Information Administration estimated that nuclear power's share of U.S. generation would fall from 19% to 15% by 2040 in its central estimate (High Oil and Gas Resource case). However, as total generation increases 24% by 2040 in the central estimate, the absolute amount of nuclear generation remains fairly flat.

In 2017, the US Energy Information Administration projected that US nuclear generating capacity would decline 23 percent from its 2016 level of 99.1 GW, to 76.5 GW in 2050, and the nuclear share of electrical generation to go from 20% in 2016 down to 11% in 2050. Driving the decline will be retirements of existing units, to be partially offset by additional units currently under construction and expected capacity expansions of existing reactors.

The Blue Castle Project is set to begin construction near Green River, Utah in 2023. The plant will use 53,500 acre-feet (66 million cubic meters) of water annually from the Green River once both reactors are commissioned. The first reactor is scheduled to come online in 2028, with the second reactor coming online in 2030.

On June 4, 2018, World Nuclear News reported, "President Donald Trump has directed Secretary of Energy Rick Perry to take immediate action to stop the loss of 'fuel-secure power facilities' from the country's power grid, including nuclear power plants that are facing premature retirement."

On August 23, 2020, Forbes reported, that "[the 2020 Democratic Party platform] marks the first time since 1972 that the Democratic Party has said anything positive in its platform about nuclear energy".

In April 2022, the Federal government announced a $6 billion subsidy program targeting the seven plants scheduled for closure as well as others at-risk of closure, to attempt to encourage them to continue operating.Micu, Alexandru (April 20, 2022). "The Biden administration will invest $6bn in keeping nuclear reactors operational". ZME Science. Retrieved April 21, 2022. It will be funded by the Infrastructure Investment and Jobs Act passed in November 2021.

Nuclear power plants

As of 2020, a total of 88 nuclear power plants have been built in the United States, 86 of which have had at least one operational reactor.

In 2019 the NRC approved a second 20-year license extension for Turkey Point units 3 and 4, the first time NRC had extended licenses to 80 years total lifetime. Similar extensions for about 20 reactors are planned or intended, with more expected in the future.

Safety and accidents

A cleanup crew working to remove radioactive contamination after the Three Mile Island accident
Erosion of the 6-inch-thick (150 mm) carbon steel reactor head at Davis-Besse Nuclear Power Plant in 2002, caused by a persistent leak of borated water.

Regulation of nuclear power plants in the United States is conducted by the Nuclear Regulatory Commission, which divides the nation into 4 administrative divisions.

Three Mile Island

On March 28, 1979, equipment failures and operator error contributed to loss of coolant and a partial core meltdown at the Three Mile Island Nuclear Power Plant in Pennsylvania. The mechanical failures were compounded by the initial failure of plant operators to recognize the situation as a loss-of-coolant accident due to inadequate training and human factors, such as human-computer interaction design oversights relating to ambiguous control room indicators in the power plant's user interface. The scope and complexity of the accident became clear over the course of five days, as employees of Met Ed, Pennsylvania state officials, and members of the U.S. Nuclear Regulatory Commission (NRC) tried to understand the problem, communicate the situation to the press and local community, decide whether the accident required an emergency evacuation, and ultimately end the crisis. The NRC's authorization of the release of 40,000 gallons of radioactive waste water directly in the Susquehanna River led to a loss of credibility with the press and community.

The Three Mile Island accident inspired Perrow's book Normal Accidents, where a nuclear accident occurs, resulting from an unanticipated interaction of multiple failures in a complex system. TMI was an example of a normal accident because it was "unexpected, incomprehensible, uncontrollable and unavoidable". The World Nuclear Association has stated that cleanup of the damaged nuclear reactor system at TMI-2 took nearly 12 years and cost approximately US$973 million. Benjamin K. Sovacool, in his 2007 preliminary assessment of major energy accidents, estimated that the TMI accident caused a total of $2.4 billion in property damages. The health effects of the Three Mile Island accident are widely, but not universally, agreed to be very low level. The accident triggered protests around the world.

The 1979 Three Mile Island accident was a pivotal event that led to questions about U.S. nuclear safety. Earlier events had a similar effect, including a 1975 fire at Browns Ferry and the 1976 testimonials of three concerned GE nuclear engineers, the GE Three. In 1981, workers inadvertently reversed pipe restraints at the Diablo Canyon Power Plant reactors, compromising seismic protection systems, which further undermined confidence in nuclear safety. All of these well-publicised events undermined public support for the U.S. nuclear industry in the 1970s and the 1980s.

Other incidents

On March 5, 2002, maintenance workers discovered that corrosion had eaten a football-sized hole into the reactor vessel head of the Davis-Besse plant. Although the corrosion did not lead to an accident, this was considered to be a serious nuclear safety incident. The Nuclear Regulatory Commission kept Davis-Besse shut down until March 2004, so that FirstEnergy was able to perform all the necessary maintenance for safe operations. The NRC imposed its largest fine ever—more than $5 million—against FirstEnergy for the actions that led to the corrosion. The company paid an additional $28 million in fines under a settlement with the U.S. Department of Justice.

In 2013 the San Onofre Nuclear Generating Station was permanently retired when premature wear was found in the Steam Generators which had been replaced in 2010–2011.

The nuclear industry in the United States has maintained one of the best industrial safety records in the world with respect to all kinds of accidents. For 2008, the industry hit a new low of 0.13 industrial accidents per 200,000 worker-hours. This is improved over 0.24 in 2005, which was still a factor of 14.6 less than the 3.5 number for all manufacturing industries. However, more than a quarter of U.S. nuclear plant operators "have failed to properly tell regulators about equipment defects that could imperil reactor safety", according to a Nuclear Regulatory Commission report.

As of February 2009, the NRC requires that the design of new power plants ensures that the reactor containment would remain intact, cooling systems would continue to operate, and spent fuel pools would be protected, in the event of an aircraft crash. This is an issue that has gained attention since the September 11 attacks. The regulation does not apply to the 100 commercial reactors now operating. However, the containment structures of nuclear power plants are among the strongest structures ever built by mankind; independent studies have shown that existing plants would easily survive the impact of a large commercial jetliner without loss of structural integrity.

Recent concerns have been expressed about safety issues affecting a large part of the nuclear fleet of reactors. In 2012, the Union of Concerned Scientists, which tracks ongoing safety issues at operating nuclear plants, found that "leakage of radioactive materials is a pervasive problem at almost 90 percent of all reactors, as are issues that pose a risk of nuclear accidents". The U.S. Nuclear Regulatory Commission reports that radioactive tritium has leaked from 48 of the 65 nuclear sites in the United States.

Post-Fukushima concerns

Following the Japanese Fukushima Daiichi nuclear disaster, according to Black & Veatch’s annual utility survey that took place after the disaster, of the 700 executives from the US electric utility industry that were surveyed, nuclear safety was the top concern. There are likely to be increased requirements for on-site spent fuel management and elevated design basis threats at nuclear power plants. License extensions for existing reactors will face additional scrutiny, with outcomes depending on the degree to which plants can meet new requirements, and some extensions already granted for more than 60 of the 104 operating U.S. reactors could be revisited. On-site storage, consolidated long-term storage, and geological disposal of spent fuel is "likely to be reevaluated in a new light because of the Fukushima storage pool experience". In March 2011, nuclear experts told Congress that spent-fuel pools at US nuclear power plants are too full. They say the entire US spent-fuel policy should be overhauled in light of the Fukushima I nuclear accidents.

David Lochbaum, chief nuclear safety officer with the Union of Concerned Scientists, has repeatedly questioned the safety of the Fukushima I Plant's General Electric Mark 1 reactor design, which is used in almost a quarter of the United States' nuclear fleet.

About one third of reactors in the US are boiling water reactors, the same technology which was involved in the Fukushima Daiichi nuclear disaster. There are also eight nuclear power plants located along the seismically active West coast. Twelve of the American reactors that are of the same vintage as the Fukushima Daiichi plant are in seismically active areas. Earthquake risk is often measured by "Peak Ground Acceleration", or PGA, and the following nuclear power plants have a two percent or greater chance of having PGA over 0.15g in the next 50 years: Diablo Canyon, Calif.; San Onofre, Calif.; Sequoyah, Tenn.; H.B. Robinson, SC.; Watts Bar, Tenn.; Virgil C. Summer, SC.; Vogtle, GA.; Indian Point, NY.; Oconee, SC.; and Seabrook, NH. Most nuclear plants are designed to keep operating up to 0.2g, but can withstand PGA much higher than 0.2.

Security and deliberate attacks

The United States 9/11 Commission has said that nuclear power plants were potential targets originally considered for the September 11 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 widespread radioactive contamination. The research scientist Harold Feiveson has written that nuclear facilities should be made extremely safe from attacks that could release massive quantities of radioactivity into the community. New reactor designs have features of passive nuclear safety, which may help. 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.

Uranium supply

Sources of uranium fuel for the US commercial nuclear power industry in 2012 (US Energy Information Administration)

A 2012 report by the International Atomic Energy Agency concluded: “The currently defined uranium resource base is more than adequate to meet high-case requirements through 2035 and well into the foreseeable future.”

At the start of 2013, the identified remaining worldwide uranium resources stood at 5.90 million tons, enough to supply the world's reactors at current consumption rates for more than 120 years, even if no additional uranium deposits are discovered in the meantime. Undiscovered uranium resources as of 2013 were estimated to be 7.7 million tons. Doubling the price of uranium would increase the identified reserves as of 2013 to 7.64 million tons. Over the decade 2003–2013, the identified reserves of uranium (at the same price of US$130/kg) rose from 4.59 million tons in 2003 to 5.90 million tons in 2013, an increase of 28%.

Fuel cycle

Uranium mining

The United States has the 4th largest uranium reserves in the world. The U.S. has its most prominent uranium reserves in New Mexico, Texas, and Wyoming. The U.S. Department of Energy has approximated there to be at least 300 million pounds of uranium in these areas. Domestic production increased until 1980, after which it declined sharply due to low uranium prices. In 2012, the United States mined 17% of the uranium consumed by its nuclear power plants. The remainder was imported, principally from Canada, Russia and Australia. Uranium is mined using several methods including open-pit mining, underground mining, and in-situ leaching. As of 2017, there are more than 4000 abandoned uranium mines in the western USA, with 520 to over 1000 on Navajo land, and many others being located on other tribal lands.

Uranium enrichment

Location of nuclear reactor fuel processing facilities in the United States (US NRC)

There is one gas centrifuge enrichment plant currently in commercial operation in the US. The National Enrichment Facility, operated by URENCO east of Eunice, New Mexico, was the first uranium enrichment plant in 30 years to be built in the US. The plant started enriching uranium in 2010. Two additional gas centrifuge plants have been licensed by the NRC, but are not operating. The American Centrifuge Plant in Piketown, Ohio broke ground in 2007, but stopped construction in 2009. The Eagle Rock Enrichment Facility in Bonneville County, Idaho was licensed in 2011, but construction is on hold.

Previously (2008), demonstration activities were underway in Oak Ridge, Tennessee for a future centrifugal enrichment plant. The new plant would have been called the American Centrifuge Plant, at an estimated cost of US$2.3 billion.

As of September 30, 2015, the DOE is ending its contract with the American Centrifuge Project and has stopped funding the project.

Reprocessing

Nuclear reprocessing has been politically controversial because of the alleged potential to contribute to nuclear proliferation, the alleged vulnerability to nuclear terrorism, the debate over whether and where to dispose of spent fuel in a deep geological repository, and because of disputes about its economics compared to the once-through fuel cycle. The Obama administration has disallowed reprocessing of spent fuel, citing nuclear proliferation concerns. Opponents of reprocessing contend that the recycled materials could be used for weapons. However, it is unlikely that reprocessed plutonium or other material extracted from commercial spent fuel would be used for nuclear weapons, because it is not weapons-grade material. Nonetheless, according to the Union of Concerned Scientists, it is possible that terrorists could steal these materials, because the reprocessed plutonium is less radiotoxic than spent fuel and therefore much easier to handle. Additionally, it has been argued that reprocessing is more expensive when compared with spent fuel storage. One study by the Boston Consulting Group estimated that reprocessing is six percent more expensive than spent fuel storage while another study by the Kennedy School of Government stated that reprocessing is 100 percent more expensive. Those two data points alone can serve to indicate that calculations as to the cost of nuclear reprocessing and the production of MOX-fuel compared to the "once thru fuel cycle" and disposal in deep geological repository are extremely difficult and results tend to vary widely even among dispassionate expert observers - let alone those whose results are colored by a political or economic agenda. Furthermore, fluctuations on the uranium market can make usage of MOX-fuel or even re-enrichment of reprocessed uranium more or less economical depending on long term price trends.

Waste disposal

The locations across the U.S. where nuclear waste is stored

Recently, as plants continue to age, many on-site spent fuel pools have come near capacity, prompting creation of dry cask storage facilities as well. Several lawsuits between utilities and the government have transpired over the cost of these facilities, because by law the government is required to foot the bill for actions that go beyond the spent fuel pool.

There are some 65,000 tons of nuclear waste now in temporary storage throughout the U.S. Since 1987, Yucca Mountain, in Nevada, had been the proposed site for the Yucca Mountain nuclear waste repository, but the project was shelved in 2009 following years of controversy and legal wrangling. Yucca Mountain is on Native American land and is considered sacred. Native Americans have not consented to having any nuclear waste plants placed in this area. An alternative plan has not been proffered. In June 2018, the Trump administration and some members of Congress again began proposing using Yucca Mountain, with Nevada Senators raising opposition.

At places like Maine Yankee, Connecticut Yankee and Rancho Seco, reactors no longer operate, but the spent fuel remains in small concrete-and-steel silos that require maintenance and monitoring by a guard force. Sometimes the presence of nuclear waste prevents re-use of the sites by industry.

Without a long-term solution to store nuclear waste, a nuclear renaissance in the U.S. remains unlikely. Nine states have "explicit moratoria on new nuclear power until a storage solution emerges".

Some nuclear power advocates argue that the United States should develop factories and reactors that will recycle some spent fuel. But the Blue Ribbon Commission on America's Nuclear Future said in 2012 that "no existing technology was adequate for that purpose, given cost considerations and the risk of nuclear proliferation". A major recommendation was that "the United States should undertake...one or more permanent deep geological facilities for the safe disposal of spent fuel and high-level nuclear waste".

There is an "international consensus on the advisability of storing nuclear waste in deep underground repositories", but no country in the world has yet opened such a site. The Obama administration has disallowed reprocessing of nuclear waste, citing nuclear proliferation concerns.

The U.S Nuclear Waste Policy Act, a fund which previously received $750 million in fee revenues each year from the nation's combined nuclear electric utilities, had an unspent balance of $44.5 billion as of the end of FY2017, when a court ordered the federal government to cease withdrawing the fund, until it provides a destination for the utilities commercial spent fuel.

Horizontal drillhole disposal describes proposals to drill over one kilometer vertically, and two kilometers horizontally in the earth's crust, for the purpose of disposing of high-level waste forms such as spent nuclear fuel, Caesium-137, or Strontium-90. After the emplacement and the retrievability period, drillholes would be backfilled and sealed. A series of tests of the technology were carried out in November 2018 and then again publicly in January 2019 by a U.S. based private company. The test demonstrated the emplacement of a test-canister in a horizontal drillhole and retrieval of the same canister. There was no actual high-level waste used in this test.

Water use in nuclear power production

U.S. 2014 Electricity Generation By Type.

A 2011 NREL study of water use in electricity generation concluded that the median nuclear plant with cooling towers consumed 672 gallons per megawatt-hour (gal/MWh), a usage similar to that of coal plants, but more than other generating technologies, except hydroelectricity (median reservoir evaporation loss of 4,491 gal/MWh) and concentrating solar power (786 gal/MWh for power tower designs, and 865 for trough). Nuclear plants with once-through cooling systems consume only 269 gal/MWh, but require withdrawal of 44,350 gal/MWh. This makes nuclear plants with once-through cooling susceptible to drought.

A 2008 study by the Associated Press found that of the 104 nuclear reactors in the U.S., "... 24 are in areas experiencing the most severe levels of drought. All but two are built on the shores of lakes and rivers and rely on submerged intake pipes to draw billions of gallons of water for use in cooling and condensing steam after it has turned the plants’ turbines," much like all Rankine cycle power plants. During the 2008 southeast drought, reactor output was reduced to lower operating power or forced to shut down for safety.

The Palo Verde Nuclear Generating Station is located in a desert and purchases reclaimed wastewater for cooling.

Plant decommissioning

Nuclear Power plants that have been decommissioned or have announced plans to decommission. The size of the circles indicates the amount of electricity generated
Timeline and operating capacity of plants planned to be decommissioned from 2018 to 2025

The price of energy inputs and the environmental costs of every nuclear power plant continue long after the facility has finished generating its last useful electricity. Both nuclear reactors and uranium enrichment facilities must be decommissioned, returning the facility and its parts to a safe enough level to be entrusted for other uses. After a cooling-off period that may last as long as a century, reactors must be dismantled and cut into small pieces to be packed in containers for final disposal. The process is very expensive, time-consuming, dangerous for workers, hazardous to the natural environment, and presents new opportunities for human error, accidents or sabotage.

The total energy required for decommissioning can be as much as 50% more than the energy needed for the original construction. In most cases, the decommissioning process costs between US$300 million to US$5.6 billion. Decommissioning at nuclear sites which have experienced a serious accident are the most expensive and time-consuming. In the U.S. there are 13 reactors that have permanently shut down and are in some phase of decommissioning, but none of them have completed the process.

New methods for decommissioning have been developed in order to minimize the usual high decommissioning costs. One of these methods is in situ decommissioning (ISD), which was implemented at the U.S. Department of Energy Savannah River Site in South Carolina for the closures of the P and R Reactors. With this tactic, the cost of decommissioning both reactors was $73 million. In comparison, the decommissioning of each reactor using traditional methods would have been an estimated $250 million. This results in a 71% decrease in cost by using ISD.

In the United States a Nuclear Waste Policy Act and Nuclear Decommissioning Trust Fund is legally required, with utilities banking 0.1 to 0.2 cents/kWh during operations to fund future decommissioning. They must report regularly to the Nuclear Regulatory Commission (NRC) on the status of their decommissioning funds. About 70% of the total estimated cost of decommissioning all U.S. nuclear power reactors has already been collected (on the basis of the average cost of $320 million per reactor-steam turbine unit).

As of 2011, there are 13 reactors that had permanently shut down and are in some phase of decommissioning. With Connecticut Yankee Nuclear Power Plant and Yankee Rowe Nuclear Power Station having completed the process in 2006–2007, after ceasing commercial electricity production circa 1992. The majority of the 15 years, was used to allow the station to naturally cool-down on its own, which makes the manual disassembly process both safer and cheaper.

The number of nuclear power reactors are shrinking as they near the end of their life. It is expected that by 2025 many of the reactors will have been shut down due to their age. Because the costs associated with the constructions of nuclear reactors are also continuously increasing, this is expected to be problematic for the provision of energy in the country. When reactors are shut down, stakeholders in the energy sector have often not replaced them with renewable energy resources but rather with coal or natural gas. This is because unlike renewable energy sources such as wind and solar, coal and natural gas can be used to generate electricity on a 24-hour basis.

Organizations

Fuel vendors

The following companies have active Nuclear fuel fabrication facilities in the United States. These are all light water fuel fabrication facilities because only LWRs are operating in the US. The US currently has no MOX fuel fabrication facilities, though Duke Energy has expressed intent of building one of a relatively small capacity.

Framatome (formerly Areva) runs fabrication facilities in Lynchburg, Virginia and Richland, Washington. It also has a Generation III+ plant design, EPR (formerly the Evolutionary Power Reactor), which it plans to market in the US.
Westinghouse operates a fuel fabrication facility in Columbia, South Carolina, which processes 1,600 metric tons Uranium (MTU) per year. It previously operated a nuclear fuel plant in Hematite, Missouri but has since closed it down.
GE pioneered the BWR technology that has become widely used throughout the world. It formed the Global Nuclear Fuel joint venture in 1999 with Hitachi and Toshiba and later restructured into GE-Hitachi Nuclear Energy. It operates the fuel fabrication facility in Wilmington, North Carolina, with a capacity of 1,200 MTU per year.
KazAtomProm and the US company Centrus Energy have a partnership on competitive supplies of Kazakhstan's uranium to the US market.

Industry and academic

The American Nuclear Society (ANS) scientific and educational organization has both academic and industry members. The organization publishes a large amount of literature on nuclear technology in several journals. The ANS also has some offshoot organizations such as North American Young Generation in Nuclear (NA-YGN).

The Nuclear Energy Institute (NEI) is an industry group whose activities include lobbying, experience sharing between companies and plants, and provides data on the industry to a number of outfits.

Anti-nuclear power groups

Anti-nuclear protest, Boston, MA, 1977

Some sixty anti-nuclear power groups are operating, or have operated, in the United States. These include: Abalone Alliance, Clamshell Alliance, Greenpeace USA, Institute for Energy and Environmental Research, Musicians United for Safe Energy, Nuclear Control Institute, Nuclear Information and Resource Service, Public Citizen Energy Program, Shad Alliance, and the Sierra Club.

In 1992, the chairman of the Nuclear Regulatory Commission said that "his agency had been pushed in the right direction on safety issues because of the pleas and protests of nuclear watchdog groups".

Pro-nuclear power groups

Debate

There has been considerable public and scientific debate about the use of nuclear power in the United States, mainly from the 1960s to the late 1980s, but also since about 2001 when talk of a nuclear renaissance began. There has been debate about issues such as nuclear accidents, radioactive waste disposal, nuclear proliferation, nuclear economics, and nuclear terrorism.

Some scientists and engineers have expressed reservations about nuclear power, including Barry Commoner, S. David Freeman, John Gofman, Arnold Gundersen, Mark Z. Jacobson, Amory Lovins, Arjun Makhijani, Gregory Minor, and Joseph Romm. Mark Z. Jacobson, professor of civil and environmental engineering at Stanford University, has said: "If our nation wants to reduce global warming, air pollution and energy instability, we should invest only in the best energy options. Nuclear energy isn't one of them". Arnold Gundersen, chief engineer of Fairewinds Associates and a former nuclear power industry executive, has questioned the safety of the Westinghouse AP1000, a proposed third-generation nuclear reactor. John Gofman, a nuclear chemist and doctor, raised concerns about exposure to low-level radiation in the 1960s and argued against commercial nuclear power in the U.S. In "Nuclear Power: Climate Fix or Folly", Amory Lovins, a physicist with the Rocky Mountain Institute, argued that expanded nuclear power "does not represent a cost-effective solution to global warming and that investors would shun it were it not for generous government subsidies lubricated by intensive lobbying efforts".

Patrick Moore (an early Greenpeace member and former president of Greenpeace Canada) spoke out against nuclear power in 1976, but today he supports it, along with renewable energy sources. In Australian newspaper The Age, he writes "Greenpeace is wrong — we must consider nuclear power". He argues that any realistic plan to reduce reliance on fossil fuels or greenhouse gas emissions requires increased use of nuclear energy. Phil Radford, executive director of Greenpeace US responded that nuclear energy is too risky, takes too long to build to address climate change, and by showing that the can U.S. shift to nearly 100% renewable energy while phasing out nuclear power by 2050.

Environmentalist Stewart Brand wrote the book Whole Earth Discipline, which examines how nuclear power and some other technologies can be used as tools to address global warming. Bernard Cohen, Professor Emeritus of Physics at the University of Pittsburgh, calculates that nuclear power is many times safer than other forms of power generation.

Infographic about the Yucca Mountain nuclear waste repository

President Obama early on included nuclear power as part of his "all of the above" energy strategy. In a speech to the International Brotherhood of Electrical Workers in 2010, he demonstrated his commitment to nuclear power by announcing his approval of an $8 billion loan guarantee to pave the way for construction of the first new US nuclear power plant in nearly 30 years. Then in 2012, his first post-Fukishima state-of-the-union address, Barack Obama said that America needs "an all-out, all-of-the-above strategy that develops every available source of American energy," yet pointedly omitted any mention of nuclear power. But in February 2014, Energy secretary Ernest Moniz announced $6.5 billion in federal loan guarantees to enable construction of two new nuclear reactors, the first in the US since 1996.

According to the Union of Concerned Scientists in March 2013 over one-third of U.S. nuclear power plants suffered safety-related incidents over the past three years, and nuclear regulators and plant operators need to improve inspections to prevent such events.

Pandora's Promise is a 2013 documentary film, directed by Robert Stone. It presents an argument that nuclear energy, typically feared by environmentalists, is in fact the only feasible way of meeting humanity's growing need for energy while also addressing the serious problem of climate change. The movie features several notable individuals (some of whom were once vehemently opposed to nuclear power, but who now speak in support of it), including: Stewart Brand, Gwyneth Cravens, Mark Lynas, Richard Rhodes and Michael Shellenberger. Anti-nuclear advocate Helen Caldicott appears briefly.

As of 2014, the U.S. nuclear industry has begun a new lobbying effort, hiring three former senators — Evan Bayh, a Democrat; Judd Gregg, a Republican; and Spencer Abraham, a Republican — as well as William M. Daley, a former staffer to President Obama. The initiative is called Nuclear Matters, and it has begun a newspaper advertising campaign.

Founder of the Energy Impact Center, a research institute analyzing solutions towards net negative carbon by 2040, Bret Kugelmass believes that “even if we achieved net zero new emissions globally, we’d continue to add extra heat at the same rate we are adding it today,” explaining that we need to remove the already existent carbon dioxide in our atmosphere in order to reverse climate change, not just stop the generation of new emissions. Research efforts conducted by the Energy Impact Center have concluded that nuclear energy is the only energy source that is capable of becoming net-negative and effectively solving global warming.

Public opinion

The Gallup organization, which has periodically polled US opinion on nuclear power since 1994, found in March 2016 that, for the first time, a majority (54%) opposed nuclear power, versus 44% in favor. In polls from 2004 through 2015, a majority had supported nuclear power. support peaked at 62% in 2010, and has been in decline since.

According to a CBS News poll, what had been growing acceptance of nuclear power in the United States was eroded sharply following the 2011 Japanese nuclear accidents, with support for building nuclear power plants in the U.S. dropping slightly lower than it was immediately after the Three Mile Island accident in 1979. Only 43 percent of those polled after the Fukushima nuclear emergency said they would approve building new power plants in the United States. A Washington Post-ABC poll conducted in April 2011 found that 64 percent of Americans opposed the construction of new nuclear reactors. A survey sponsored by the Nuclear Energy Institute, conducted in September 2011, found that "62 percent of respondents said they favor the use of nuclear energy as one of the ways to provide electricity in the United States, with 35 percent opposed".

According to a 2012 Pew Research Center poll, 44 percent of Americans favored and 49 percent opposed the promotion of increased use of nuclear power.

A January 2014 Rasmussen poll found likely US voters split nearly evenly on whether to build more nuclear power plants, 39 percent in favor, versus 37 percent opposed, with an error margin of 3 percent.

Knowledge and familiarity to nuclear power are generally associated with higher support for the technology. A study conducted by Ann Bisconti shows that those who feel more educated about nuclear power also have a more positive opinion towards it; in addition, people who live near nuclear power plants also tend to be largely more in support of nuclear power than the general public.

Decreasing public support is seen as one of the causes for the premature closure of many plants in the United States.

Economics

George W. Bush signing the Energy Policy Act of 2005, which was designed to promote US nuclear reactor construction, through incentives and subsidies, including cost-overrun support up to a total of $2 billion for six new nuclear plants.
US nuclear power plants, highlighting recently and soon-to-be retired plants, as of 2018 (US EIA).

The low price of natural gas in the US since 2008 has spurred construction of gas-fired power plants as an alternative to nuclear plants. In August 2011, the head of America's largest nuclear utility said that this was not the time to build new nuclear plants, not because of political opposition or the threat of cost overruns, but because of the low price of natural gas. John Rowe, head of Exelon, said “Shale [gas] is good for the country, bad for new nuclear development".

In 2013, four older reactors were permanently closed: San Onofre 2 and 3 in California, Crystal River 3 in Florida, and Kewaunee in Wisconsin. The state of Vermont tried to shut Vermont Yankee, in Vermont, but the plant was closed by the parent corporation for economic reasons in December 2014. New York State is seeking to close Indian Point Nuclear Power Plant, in Buchanan, 30 miles from New York City, despite this reactor being the primary contributor to Vermont's green energy fund.

The additional cancellation of five large reactor upgrades (Prairie Island, 1 reactor, LaSalle, 2 reactors, and Limerick, 2 reactors), four by the largest nuclear company in the U.S., suggest that the nuclear industry faces "a broad range of operational and economic problems".

In July 2013, economist Mark Cooper named some nuclear power plants that face particularly intense challenges to their continued operation. Cooper said that the lesson for policy makers and economists is clear: "nuclear reactors are simply not competitive".

In December 2010, The Economist reported that the demand for nuclear power was softening in America. In recent years, utilities have shown an interest in about 30 new reactors, but the number with any serious prospect of being built as of the end of 2010 was about a dozen, as some companies had withdrawn their applications for licenses to build. Exelon has withdrawn its application for a license for a twin-unit nuclear plant in Victoria County, Texas, citing lower electricity demand projections. The decision has left the country's largest nuclear operator without a direct role in what the nuclear industry hopes is a nuclear renaissance. Ground has been broken on two new nuclear plants with a total of four reactors. The Obama administration was seeking the expansion of a loan guarantee program but as of December 2010 had been unable to commit all the loan guarantee money already approved by Congress. Since talk a few years ago of a “nuclear renaissance”, gas prices have fallen and old reactors are getting license extensions. The only reactor to finish construction after 1996 was at Watts Bar, Tennessee, is an old unit, begun in 1973, whose construction was suspended in 1988, and was resumed in 2007. It became operational in October 2016. Of the 100 reactors operating in the U.S., ground was broken on all of them in 1974 or earlier.

In August 2012, Exelon stated that economic and market conditions, especially low natural gas prices, made the "construction of new merchant nuclear power plants in competitive markets uneconomical now and for the foreseeable future". In early 2013, UBS noted that some smaller reactors operating in deregulated markets may become uneconomic to operate and maintain, due to competition from generators using low priced natural gas, and may be retired early. The 556 MWe Kewaunee Power Station is being closed 20 years before license expiry for these economic reasons. In February 2014, the Financial Times identified Pilgrim, Indian Point, Clinton, and Quad Cities power stations as potentially at risk of premature closure for economic reasons.

Timeline of state subsidies for nuclear power as of 2019

As of 2017, the U.S. shale gas boom has lowered electricity generation costs placing severe pressure on the economics of operating older existing nuclear power plants. Analysis by Bloomberg shows that over half of U.S. nuclear plants are running at a loss. The Nuclear Energy Institute has estimated that 15 to 20 reactors are at risk of early closure for economic reasons. Nuclear operators in Illinois and New York have obtained financial support from regulators, and operators in Connecticut, New Jersey, Ohio and Pennsylvania are seeking similar support. Some non-nuclear power generating companies have filed unfair competition lawsuits against these subsidies, and have raised the issue with the Federal Energy Regulatory Commission.

Statistics

 

Eye tracking

From Wikipedia, the free encyclopedia
Eye tracking device

Eye tracking is the process of measuring either the point of gaze (where one is looking) or the motion of an eye relative to the head. An eye tracker is a device for measuring eye positions and eye movement. Eye trackers are used in research on the visual system, in psychology, in psycholinguistics, marketing, as an input device for human-computer interaction, and in product design. In addition, eye trackers are increasingly being used for assistive and rehabilitative applications such as controlling wheelchairs, robotic arms, and prostheses. There are several methods for measuring eye movement, with the most popular variant using video images to extract eye position. Other methods use search coils or are based on the electrooculogram.

History

Yarbus eye tracker from the 1960s

In the 1800s, studies of eye movement were made using direct observations. For example, Louis Émile Javal observed in 1879 that reading does not involve a smooth sweeping of the eyes along the text, as previously assumed, but a series of short stops (called fixations) and quick saccades. This observation raised important questions about reading, questions which were explored during the 1900s: On which words do the eyes stop? For how long? When do they regress to already seen words?

An example of fixations and saccades over text. This is the typical pattern of eye movement during reading. The eyes never move smoothly over still text.

Edmund Huey built an early eye tracker, using a sort of contact lens with a hole for the pupil. The lens was connected to an aluminum pointer that moved in response to the movement of the eye. Huey studied and quantified regressions (only a small proportion of saccades are regressions), and he showed that some words in a sentence are not fixated.

The first non-intrusive eye-trackers were built by Guy Thomas Buswell in Chicago, using beams of light that were reflected on the eye, then recording on film. Buswell made systematic studies into reading and picture viewing.

In the 1950s, Alfred L. Yarbus performed eye tracking research, and his 1967 book is often quoted. He showed that the task given to a subject has a very large influence on the subject's eye movement. He also wrote about the relation between fixations and interest:

All the records ... show conclusively that the character of the eye movement is either completely independent of or only very slightly dependent on the material of the picture and how it was made, provided that it is flat or nearly flat."

The cyclical pattern in the examination of pictures "is dependent on not only what is shown on the picture, but also the problem facing the observer and the information that he hopes to gain from the picture."

This study by Yarbus (1967) is often referred to as evidence on how the task given to a person influences his or her eye movement.

Records of eye movements show that the observer's attention is usually held only by certain elements of the picture.... Eye movement reflects the human thought processes; so the observer's thought may be followed to some extent from records of eye movement (the thought accompanying the examination of the particular object). It is easy to determine from these records which elements attract the observer's eye (and, consequently, his thought), in what order, and how often.

The observer's attention is frequently drawn to elements which do not give important information but which, in his opinion, may do so. Often an observer will focus his attention on elements that are unusual in the particular circumstances, unfamiliar, incomprehensible, and so on.

... when changing its points of fixation, the observer's eye repeatedly returns to the same elements of the picture. Additional time spent on perception is not used to examine the secondary elements, but to reexamine the most important elements.

This study by Hunziker (1970) on eye tracking in problem solving used simple 8 mm film to track eye movement by filming the subject through a glass plate on which the visual problem was displayed.

In the 1970s, eye-tracking research expanded rapidly, particularly reading research. A good overview of the research in this period is given by Rayner.

In 1980, Just and Carpenter formulated the influential Strong eye-mind hypothesis, that "there is no appreciable lag between what is fixated and what is processed". If this hypothesis is correct, then when a subject looks at a word or object, he or she also thinks about it (process cognitively), and for exactly as long as the recorded fixation. The hypothesis is often taken for granted by researchers using eye-tracking. However, gaze-contingent techniques offer an interesting option in order to disentangle overt and covert attentions, to differentiate what is fixated and what is processed.

During the 1980s, the eye-mind hypothesis was often questioned in light of covert attention, the attention to something that one is not looking at, which people often do. If covert attention is common during eye-tracking recordings, the resulting scan-path and fixation patterns would often show not where attention has been, but only where the eye has been looking, failing to indicate cognitive processing.

The 1980s also saw the birth of using eye-tracking to answer questions related to human-computer interaction. Specifically, researchers investigated how users search for commands in computer menus. Additionally, computers allowed researchers to use eye-tracking results in real time, primarily to help disabled users.

More recently, there has been growth in using eye tracking to study how users interact with different computer interfaces. Specific questions researchers ask are related to how easy different interfaces are for users. The results of the eye tracking research can lead to changes in design of the interface. Another recent area of research focuses on Web development. This can include how users react to drop-down menus or where they focus their attention on a website so the developer knows where to place an advertisement.

According to Hoffman, current consensus is that visual attention is always slightly (100 to 250 ms) ahead of the eye. But as soon as attention moves to a new position, the eyes will want to follow.

Specific cognitive processes still cannot be inferred directly from a fixation on a particular object in a scene. For instance, a fixation on a face in a picture may indicate recognition, liking, dislike, puzzlement etc. Therefore, eye tracking is often coupled with other methodologies, such as introspective verbal protocols.

Thanks to advancement in portable electronic devices, portable head-mounted eye trackers currently can achieve excellent performance and are being increasingly used in research and market applications targeting daily life settings. These same advances have led to increases in the study of small eye movements that occur during fixation, both in the lab and in applied settings.

The use of convolutional neural networks in eye-tracking allow for new information to be identified by artificial intelligence.

In the 21st century, the use of artificial intelligence (AI) and artificial neural networks has become a viable way to complete eye-tracking tasks and analysis. In particular, the convolutional neural network lends itself to eye-tracking, as it is designed for image-centric tasks. With AI, eye-tracking tasks and studies can yield additional information that may not have been detected by human observers. The practice of deep learning also allows for a given neural network to improve at a given task when given enough sample data. This requires a relatively large supply of training data, however.

The potential use cases for AI in eye-tracking cover a wide range of topics from medical applications to driver safety to game theory and even education and training applications.

Tracker types

Eye-trackers measure rotations of the eye in one of several ways, but principally they fall into one of three categories:

  1. measurement of the movement of an object (normally, a special contact lens) attached to the eye
  2. optical tracking without direct contact to the eye
  3. measurement of electric potentials using electrodes placed around the eyes.

Eye-attached tracking

The first type uses an attachment to the eye, such as a special contact lens with an embedded mirror or magnetic field sensor, and the movement of the attachment is measured with the assumption that it does not slip significantly as the eye rotates. Measurements with tight-fitting contact lenses have provided extremely sensitive recordings of eye movement, and magnetic search coils are the method of choice for researchers studying the dynamics and underlying physiology of eye movement. This method allows the measurement of eye movement in horizontal, vertical and torsion directions.

Optical tracking

An eye-tracking head-mounted display. Each eye has an LED light source (gold-color metal) on the side of the display lens, and a camera under the display lens.

The second broad category uses some non-contact, optical method for measuring eye motion. Light, typically infrared, is reflected from the eye and sensed by a video camera or some other specially designed optical sensor. The information is then analyzed to extract eye rotation from changes in reflections. Video-based eye trackers typically use the corneal reflection (the first Purkinje image) and the center of the pupil as features to track over time. A more sensitive type of eye-tracker, the dual-Purkinje eye tracker, uses reflections from the front of the cornea (first Purkinje image) and the back of the lens (fourth Purkinje image) as features to track. A still more sensitive method of tracking is to image features from inside the eye, such as the retinal blood vessels, and follow these features as the eye rotates. Optical methods, particularly those based on video recording, are widely used for gaze-tracking and are favored for being non-invasive and inexpensive.

Electric potential measurement

The third category uses electric potentials measured with electrodes placed around the eyes. The eyes are the origin of a steady electric potential field which can also be detected in total darkness and if the eyes are closed. It can be modelled to be generated by a dipole with its positive pole at the cornea and its negative pole at the retina. The electric signal that can be derived using two pairs of contact electrodes placed on the skin around one eye is called Electrooculogram (EOG). If the eyes move from the centre position towards the periphery, the retina approaches one electrode while the cornea approaches the opposing one. This change in the orientation of the dipole and consequently the electric potential field results in a change in the measured EOG signal. Inversely, by analysing these changes in eye movement can be tracked. Due to the discretisation given by the common electrode setup, two separate movement components – a horizontal and a vertical – can be identified. A third EOG component is the radial EOG channel, which is the average of the EOG channels referenced to some posterior scalp electrode. This radial EOG channel is sensitive to the saccadic spike potentials stemming from the extra-ocular muscles at the onset of saccades, and allows reliable detection of even miniature saccades.

Due to potential drifts and variable relations between the EOG signal amplitudes and the saccade sizes, it is challenging to use EOG for measuring slow eye movement and detecting gaze direction. EOG is, however, a very robust technique for measuring saccadic eye movement associated with gaze shifts and detecting blinks. Contrary to video-based eye-trackers, EOG allows recording of eye movements even with eyes closed, and can thus be used in sleep research. It is a very light-weight approach that, in contrast to current video-based eye-trackers, requires low computational power, works under different lighting conditions and can be implemented as an embedded, self-contained wearable system. It is thus the method of choice for measuring eye movement in mobile daily-life situations and REM phases during sleep. The major disadvantage of EOG is its relatively poor gaze-direction accuracy compared to a video tracker. That is, it is difficult to determine with good accuracy exactly where a subject is looking, though the time of eye movements can be determined.

Technologies and techniques

The most widely used current designs are video-based eye-trackers. A camera focuses on one or both eyes and records eye movement as the viewer looks at some kind of stimulus. Most modern eye-trackers use the center of the pupil and infrared / near-infrared non-collimated light to create corneal reflections (CR). The vector between the pupil center and the corneal reflections can be used to compute the point of regard on surface or the gaze direction. A simple calibration procedure of the individual is usually needed before using the eye tracker.

Two general types of infrared / near-infrared (also known as active light) eye-tracking techniques are used: bright-pupil and dark-pupil. Their difference is based on the location of the illumination source with respect to the optics. If the illumination is coaxial with the optical path, then the eye acts as a retroreflector as the light reflects off the retina creating a bright pupil effect similar to red eye. If the illumination source is offset from the optical path, then the pupil appears dark because the retroreflection from the retina is directed away from the camera.

Bright-pupil tracking creates greater iris/pupil contrast, allowing more robust eye-tracking with all iris pigmentation, and greatly reduces interference caused by eyelashes and other obscuring features. It also allows tracking in lighting conditions ranging from total darkness to very bright.

Another, less used, method is known as passive light. It uses visible light to illuminate, something which may cause some distractions to users. Another challenge with this method is that the contrast of the pupil is less than in the active light methods, therefore, the center of iris is used for calculating the vector instead. This calculation needs to detect the boundary of the iris and the white sclera (limbus tracking). It presents another challenge for vertical eye movements due to obstruction of eyelids.

Eye-tracking setups vary greatly. Some are head-mounted, some require the head to be stable (for example, with a chin rest), and some function remotely and automatically track the head during motion. Most use a sampling rate of at least 30 Hz. Although 50/60 Hz is more common, today many video-based eye trackers run at 240, 350 or even 1000/1250 Hz, speeds needed to capture fixational eye movements or correctly measure saccade dynamics.

Eye movements are typically divided into fixations and saccades – when the eye gaze pauses in a certain position, and when it moves to another position, respectively. The resulting series of fixations and saccades is called a scanpath. Smooth pursuit describes the eye following a moving object. Fixational eye movements include microsaccades: small, involuntary saccades that occur during attempted fixation. Most information from the eye is made available during a fixation or smooth pursuit, but not during a saccade.

Scanpaths are useful for analyzing cognitive intent, interest, and salience. Other biological factors (some as simple as gender) may affect the scanpath as well. Eye tracking in human–computer interaction (HCI) typically investigates the scanpath for usability purposes, or as a method of input in gaze-contingent displays, also known as gaze-based interfaces.

Data presentation

Interpretation of the data that is recorded by the various types of eye-trackers employs a variety of software that animates or visually represents it, so that the visual behavior of one or more users can be graphically resumed. The video is generally manually coded to identify the AOIs (areas of interest) or recently using artificial intelligence. Graphical presentation is rarely the basis of research results, since they are limited in terms of what can be analysed - research relying on eye-tracking, for example, usually requires quantitative measures of the eye movement events and their parameters, The following visualisations are the most commonly used:

Animated representations of a point on the interface This method is used when the visual behavior is examined individually indicating where the user focused their gaze in each moment, complemented with a small path that indicates the previous saccade movements, as seen in the image.

Static representations of the saccade path This is fairly similar to the one described above, with the difference that this is static method. A higher level of expertise than with the animated ones is required to interpret this.

Heat maps An alternative static representation, used mainly for the agglomerated analysis of the visual exploration patterns in a group of users. In these representations, the ‘hot’ zones or zones with higher density designate where the users focused their gaze (not their attention) with a higher frequency. Heat maps are the best known visualization technique for eyetracking studies.

Blind zones maps, or focus maps This method is a simplified version of the heat maps where the visually less attended zones by the users are displayed clearly, thus allowing for an easier understanding of the most relevant information, that is to say, it provides more information about which zones were not seen by the users.

Saliency maps Similar to heat maps, a saliency map illustrates areas of focus by brightly displaying the attention-grabbing objects over an initially black canvas. The more focus is given to a particular object, the brighter it will appear.

Eye-tracking vs. gaze-tracking

Eye-trackers necessarily measure the rotation of the eye with respect to some frame of reference. This is usually tied to the measuring system. Thus, if the measuring system is head-mounted, as with EOG or a video-based system mounted to a helmet, then eye-in-head angles are measured. To deduce the line of sight in world coordinates, the head must be kept in a constant position or its movements must be tracked as well. In these cases, head direction is added to eye-in-head direction to determine gaze direction. However, if the motion of the head is minor, the eye remains in constant position.

If the measuring system is table-mounted, as with scleral search coils or table-mounted camera (remote) systems, then gaze angles are measured directly in world coordinates. Typically, in these situations head movements are prohibited. For example, the head position is fixed using a bite bar or a forehead support. Then a head-centered reference frame is identical to a world-centered reference frame. Or colloquially, the eye-in-head position directly determines the gaze direction.

Some results are available on human eye movements under natural conditions where head movements are allowed as well. The relative position of eye and head, even with constant gaze direction, influences neuronal activity in higher visual areas.

Practice

A great deal of research has gone into studies of the mechanisms and dynamics of eye rotation, but the goal of eye tracking is most often to estimate gaze direction. Users may be interested in what features of an image draw the eye, for example. It is important to realize that the eye tracker does not provide absolute gaze direction, but rather can measure only changes in gaze direction. To determine precisely what a subject is looking at, some calibration procedure is required in which the subject looks at a point or series of points, while the eye tracker records the value that corresponds to each gaze position. (Even those techniques that track features of the retina cannot provide exact gaze direction because there is no specific anatomical feature that marks the exact point where the visual axis meets the retina, if indeed there is such a single, stable point.) An accurate and reliable calibration is essential for obtaining valid and repeatable eye movement data, and this can be a significant challenge for non-verbal subjects or those who have unstable gaze.

Each method of eye-tracking has advantages and disadvantages, and the choice of an eye-tracking system depends on considerations of cost and application. There are offline methods and online procedures like AttentionTracking. There is a trade-off between cost and sensitivity, with the most sensitive systems costing many tens of thousands of dollars and requiring considerable expertise to operate properly. Advances in computer and video technology have led to the development of relatively low-cost systems that are useful for many applications and fairly easy to use. Interpretation of the results still requires some level of expertise, however, because a misaligned or poorly calibrated system can produce wildly erroneous data.

Eye-tracking while driving a car in a difficult situation

Frames from narrow road eye tracking described in this section

The eye movement of two groups of drivers have been filmed with a special head camera by a team of the Swiss Federal Institute of Technology: Novice and experienced drivers had their eye-movement recorded while approaching a bend of a narrow road. The series of images has been condensed from the original film frames to show 2 eye fixations per image for better comprehension.

Each of these stills corresponds to approximately 0.5 seconds in real time.

The series of images shows an example of eye fixations #9 to #14 of a typical novice and of an experienced driver.

Comparison of the top images shows that the experienced driver checks the curve and even has Fixation No. 9 left to look aside while the novice driver needs to check the road and estimate his distance to the parked car.

In the middle images, the experienced driver is now fully concentrating on the location where an oncoming car could be seen. The novice driver concentrates his view on the parked car.

In the bottom image the novice is busy estimating the distance between the left wall and the parked car, while the experienced driver can use their peripheral vision for that and still concentrate vision on the dangerous point of the curve: If a car appears there, the driver has to give way, i.e. stop to the right instead of passing the parked car.

More recent studies have also used head-mounted eye tracking to measure eye movements during real-world driving conditions.

Eye-tracking of younger and elderly people while walking

While walking, elderly subjects depend more on foveal vision than do younger subjects. Their walking speed is decreased by a limited visual field, probably caused by a deteriorated peripheral vision.

Younger subjects make use of both their central and peripheral vision while walking. Their peripheral vision allows faster control over the process of walking.

Applications

A wide variety of disciplines use eye-tracking techniques, including cognitive science; psychology (notably psycholinguistics; the visual world paradigm); human-computer interaction (HCI); human factors and ergonomics; marketing research and medical research (neurological diagnosis). Specific applications include the tracking eye movement in language reading, music reading, human activity recognition, the perception of advertising, playing of sports, distraction detection and cognitive load estimation of drivers and pilots and as a means of operating computers by people with severe motor impairment. In the field of virtual reality, eye tracking is used in head mounted displays for a variety of purposes including to reduce processing load by only rendering the graphical area within the user's gaze.

Commercial applications

In recent years, the increased sophistication and accessibility of eye-tracking technologies have generated a great deal of interest in the commercial sector. Applications include web usability, advertising, sponsorship, package design and automotive engineering. In general, commercial eye-tracking studies function by presenting a target stimulus to a sample of consumers while an eye tracker records eye activity. Examples of target stimuli may include websites, television programs, sporting events, films and commercials, magazines and newspapers, packages, shelf displays, consumer systems (ATMs, checkout systems, kiosks) and software. The resulting data can be statistically analyzed and graphically rendered to provide evidence of specific visual patterns. By examining fixations, saccades, pupil dilation, blinks and a variety of other behaviors, researchers can determine a great deal about the effectiveness of a given medium or product. While some companies complete this type of research internally, there are many private companies that offer eye-tracking services and analysis.

One field of commercial eye-tracking research is web usability. While traditional usability techniques are often quite powerful in providing information on clicking and scrolling patterns, eye-tracking offers the ability to analyze user interaction between the clicks and how much time a user spends between clicks, thereby providing valuable insight into which features are the most eye-catching, which features cause confusion and which are ignored altogether. Specifically, eye-tracking can be used to assess search efficiency, branding, online advertisements, navigation usability, overall design and many other site components. Analyses may target a prototype or competitor site in addition to the main client site.

Eye-tracking is commonly used in a variety of different advertising media. Commercials, print ads, online ads and sponsored programs are all conducive to analysis with current eye-tracking technology. One example is the analysis of eye movements over advertisements in the Yellow Pages. One study focused on what particular features caused people to notice an ad, whether they viewed ads in a particular order and how viewing times varied. The study revealed that ad size, graphics, color, and copy all influence attention to advertisements. Knowing this allows researchers to assess in great detail how often a sample of consumers fixates on the target logo, product or ad. Hence an advertiser can quantify the success of a given campaign in terms of actual visual attention. Another example of this is a study that found that in a search engine results page, authorship snippets received more attention than the paid ads or even the first organic result.

Yet another example of commercial eye-tracking research comes from the field of recruitment. A study analyzed how recruiters screen LinkedIn profiles and presented results as heat maps.

Safety applications

Scientists in 2017 constructed a Deep Integrated Neural Network (DINN) out of a Deep Neural Network and a convolutional neural network. The goal was to use deep learning to examine images of drivers and determine their level of drowsiness by "classify[ing] eye states." With enough images, the proposed DINN could ideally determine when drivers blink, how often they blink, and for how long. From there, it could judge how tired a given driver appears to be, effectively conducting an eye-tracking exercise. The DINN was trained on data from over 2,400 subjects and correctly diagnosed their states 96%-99.5% of the time. Most other artificial intelligence models performed at rates above 90%. This technology could ideally provide another avenue for driver drowsiness detection.

Game theory applications

In a 2019 study, a Convolutional Neural Network (CNN) was constructed with the ability to identify individual chess pieces the same way other CNNs can identify facial features. It was then fed eye-tracking input data from 30 chess players of various skill levels. With this data, the CNN used gaze estimation to determine parts of the chess board to which a player was paying close attention. It then generated a saliency map to illustrate those parts of the board. Ultimately, the CNN would combine its knowledge of the board and pieces with its saliency map to predict the players' next move. Regardless of the training dataset the neural network system was trained upon, it predicted the next move more accurately than if it had selected any possible move at random, and the saliency maps drawn for any given player and situation were more than 54% similar.

Assistive technology

People with severe motor impairment can use eye tracking for interacting with computers as it is faster than single switch scanning techniques and intuitive to operate. Motor impairment caused by Cerebral Palsy or Amyotrophic lateral sclerosis often affects speech, and users with Severe Speech and Motor Impairment (SSMI) use a type of software known as Augmentative and Alternative Communication (AAC) aid, that displays icons, words and letters on screen and uses text-to-speech software to generate spoken output. In recent times, researchers also explored eye tracking to control robotic arms and powered wheelchairs. Eye tracking is also helpful in analysing visual search patterns, detecting presence of Nystagmus and detecting early signs of learning disability by analysing eye gaze movement during reading.

Aviation applications

Eye tracking has already been studied for flight safety by comparing scan paths and fixation duration to evaluate the progress of pilot trainees, for estimating pilots’ skills, for analyzing crew's joint attention and shared situational awareness. Eye tracking technology was also explored to interact with helmet mounted display systems and multi-functional displays in military aircraft. Studies were conducted to investigate the utility of eye tracker for Head-up target locking and Head-up target acquisition in Helmet mounted display systems (HMDS). Pilots' feedback suggested that even though the technology is promising, its hardware and software components are yet to be matured. Research on interacting with multi-functional displays in simulator environment showed that eye tracking can improve the response times and perceived cognitive load significantly over existing systems. Further, research also investigated utilizing measurements of fixation and pupillary responses to estimate pilot's cognitive load. Estimating cognitive load can help to design next generation adaptive cockpits with improved flight safety. Eye tracking is also useful for detecting pilot fatigue.

Automotive applications

In recent time, eye tracking technology is investigated in automotive domain in both passive and active ways. National Highway Traffic Safety Administration measured glance duration for undertaking secondary tasks while driving and used it to promote safety by discouraging the introduction of excessively distracting devices in vehicles In addition to distraction detection, eye tracking is also used to interact with IVIS. Though initial research investigated the efficacy of eye tracking system for interaction with HDD (Head Down Display), it still required drivers to take their eyes off the road while performing a secondary task. Recent studies investigated eye gaze controlled interaction with HUD (Head Up Display) that eliminates eyes-off-road distraction. Eye tracking is also used to monitor cognitive load of drivers to detect potential distraction. Though researchers explored different methods to estimate cognitive load of drivers from different physiological parameters, usage of ocular parameters explored a new way to use the existing eye trackers to monitor cognitive load of drivers in addition to interaction with IVIS.

Entertainment applications

The 2021 video game Before Your Eyes registers and reads the player's blinking, and uses it as the main way of interacting with the game.

Engineering applications

The widespread use of eye-tracking technology has shed light to its use in empirical software engineering in the most recent years. The eye-tracking technology and data analysis techniques are used to investigate the understandability of software engineering concepts by the researchers. These include the understandability of business process models, and diagrams used in software engineering such as UML activity diagrams and EER diagrams. Eye-tracking metrics such as fixation, scan-path, scan-path precision, scan-path recall, fixations on area of interest/relevant region are computed, analyzed and interpreted in terms of model and diagram understandability. The findings are used to enhance the understandability of diagrams and models with proper model related solutions and by improving personal related factors such as working-memory capacity, cognitive-load, learning style and strategy of the software engineers and modelers.

Privacy concerns

With eye tracking projected to become a common feature in various consumer electronics, including smartphones, laptops and virtual reality headsets, concerns have been raised about the technology's impact on consumer privacy. With the aid of machine learning techniques, eye tracking data may indirectly reveal information about a user's ethnicity, personality traits, fears, emotions, interests, skills, and physical and mental health condition. If such inferences are drawn without a user's awareness or approval, this can be classified as an inference attack. Eye activities are not always under volitional control, e.g., "stimulus-driven glances, pupil dilation, ocular tremor, and spontaneous blinks mostly occur without conscious effort, similar to digestion and breathing”. Therefore, it can be difficult for eye tracking users to estimate or control the amount of information they reveal about themselves.

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