Nuclear power plants

Summary: Nuclear power plants, which rely on nuclear fission to produce electricity, have been promoted as a solution to energy problems and as a way to reduce greenhouse gas emissions. However, concerns persist over the production of radioactive waste and possibility of dangerous nuclear meltdowns.

Soon after the discovery of nuclear fission in 1938, scientists started working on producing electricity using nuclear fission. The first nuclear power station, known as APS-1 Obninsk (Atomic Power Station 1 Obninsk), was built in 1954 about 110 kilometers southwest of Moscow, Russia. The power plant had a capacity of about 6 megawatts (MW) and functioned until 2002. In the United States, the Shippingport Reactor in Pennsylvania was the first commercial nuclear power plant to become operational in 1957. This reactor provided about 60 MW of energy and was located about 25 miles from Pittsburgh. It remained operational until 1982.

By the mid-2020s, there were about 440 nuclear power plants located in dozens of countries worldwide, providing about 9 percent of the world's energy. France and Slovakia produced about two-thirds of their electricity from nuclear power. Belgium, Bulgaria, Czech Republic, Finland, Hungary, Slovenia, Switzerland, and Ukraine generated one-third or more of their electricity from nuclear power.

In the United States, fifty-three nuclear power plants, with a total of ninety-four nuclear reactors, remained active in the mid-2020s. These facilities were spread out across twenty-eight states and, according to the US Department of Energy, generated about 18 percent of the electricity produced in the US. This fell short of twentieth-century predictions that expected nuclear power to gain a larger foothold in the US energy sector; for example, in the mid-1970s, new nuclear power plants were being constructed in the United States and experts predicted that the country would have approximately one thousand nuclear power plants in operation by the year 2000. However, for a number of reasons, the country did not embrace nuclear power to the extent some experts predicted, and the US did not construct any new nuclear power plants for nearly three decades.

The US Nuclear Regulatory Commission (NRC) approved licenses to construct two nuclear reactors in Waynesboro, Georgia, about 170 miles east of Atlanta, in 2012, the first such issuance of licenses since 1979. The Obama administration allocated $8.3 billion in federal loan guarantees to build these two reactors. This was the first loan guarantee to a nuclear power plant under the Energy Policy Act of 2005. The effort was made to promote the nuclear technologies in use in the Westinghouse AP1000 reactor, which make reactors more efficient and safer. The years-long construction of these reactors, the Vogtle 3 and 4, concluded in late 2022, and the reactors became fully operational in 2023 and 2024, respectively.

Nuclear Power Generation

In traditional power plants, coal, natural gas, or petroleum are commonly used to heat water. Similarly, in the case of a nuclear power plant, the nuclear fission process is used to produce heat to boil water, and using a turbine, electricity is produced. Nuclear power is derived by splitting uranium-235 with neutrons. This reaction produces two or three neutrons that can further be used to split other uranium nuclei and produce a “self-sustaining” chain reaction. This chain reaction produces an enormous amount of energy with each fission—about 200 milli-electron volts (meV) per fission.

The first self-sustaining chain reaction was successfully carried out at the University of Chicago’s Amos Alonso Stagg Field on December 2, 1942. Neutrons with a 0.4 electron volt (eV) of energy or less are most effective in the fission of U-235. Neutrons ejected during fission have energies that are comparable to millions of electron volts. These neutrons simply escape and do not produce another reaction. A medium is required to slow down the neutrons, known as a moderator, which dampens the energies of neutrons without absorbing them.

Graphite and water are two common moderators. The hydrogen nuclei in water play a key role in the slowing of neutrons. In a collision process, for example, when a moving tennis ball strikes another stationary tennis ball it will lose more energy than a tennis ball striking a bowling ball. It takes about 10^-5 seconds for a 2-MeV neutron to slow down to 0.025 eV in a mere 18 collisions with hydrogen nuclei.

To maintain a steady state, it is essential that the flux of neutrons that produce fission remain constant. Since more neutrons are produced than consumed in U-235 fission reaction, it is imperative to remove some neutrons. This is accomplished by using control rods that are made of either boron or cadmium. Both elements are quite efficient in absorbing neutrons. The rate of absorption is controlled by the movement of these rods in and out of the reactor core. If the control rods do not absorb neutrons, the neutron density increases and causes a rapid release of energy. However, since nuclear fuel used in a reactor contains about 3–4 percent pure ²³⁵U versus about 95 percent purity in an atomic bomb, a nuclear reactor cannot explode like a nuclear bomb even in the event of a meltdown.

By the end of the twentieth century, the idea of nuclear fusion had attracted renewed attention from scientists and advocates of nuclear power. As opposed to nuclear fission, which involves splitting atomic nuclei in order to generate energy, nuclear fusion involves combining atomic nuclei in order to generate energy. As a power source, nuclear fusion has a number of advantages over fission—namely, it does not produce radioactive waste and also cannot result in a meltdown. While fusion occurs in nature, it requires a precise set of conditions in order to occur, which makes it challenging for humans to use nuclear fusion as a way to generate electricity. To overcome these obstacles, a number of countries and organizations, including the US, Japan, China, and Russia, invested in nuclear fusion research during the 2010s and 2020s. A major breakthrough came in 2022 when, for the first time in history, US scientists were able to achieve fusion ignition. This was considered a breakthrough because, for the first time ever, scientists were able to create a fusion reaction that produced a net gain of energy, meaning it produced more energy than it used.

Types of Reactors

There is no single design to produce the fission process: most reactors in the world are light-water reactors, implying that the moderation and cooling is done by regular water; about 10 percent are moderated and cooled by heavy water; and even smaller percentages are either gas-cooled reactors or graphite and water-cooled reactors. The term light-water is used to distinguish it from heavy-water reactors. Water is used as a moderator, as a coolant to remove heat from the reactor, and as a source to produce steam for the turbine.

Thirty-five percent of light-water reactors are boiling-water reactors (BWRs), while 65 percent are pressurized water reactors (PWRs). In PWRs, the water in the reactor core is kept at a high pressure of about 2,200 lbs/in² (psi) and the reactor core water temperature is kept at about 600 degrees Fahrenheit.

Even at this high temperature, the water remains in liquid form due to high pressure. This hot water gives off its heat to the water in the steam generator through a heat exchanger. In BWRs, water in the primary core turns into steam and hits the turbine blades to produce electricity. Afterward, it is condensed and pumped back to the reactor core. Radioactivity is better contained in PWRs than in BWRs.

Both types of reactors have more or less the same efficiency rate of about 33 percent and consume the same amount of water. The remaining 67 percent of the energy is released into the environment. Most nuclear power plants use somewhere between 400 and 720 gallons of water per 1MW.h production of electricity. Thus, the water consumption of nuclear power plants is relatively high. Ocean water is usually avoided for use as a coolant due to the corrosive nature of salt water.

Heavy-water reactors use deuterium oxide rather than hydrogen oxide as a moderator. The method has several benefits: it does not absorb neutrons and it effectively slows down fast neutrons. It also can achieve a sustainable chain reaction with naturally occurring uranium. This type of reactor is common in Canada.

A different reactor design involves uranium fuel being placed inside a 2.5-inch-deep bed of pyrolytic graphite pebbles. These pebbles are covered with silicon carbide ceramic. Both materials are highly resistant to high heat and the chance of radioactive release is minimal. With this design, if a reactor becomes hotter than desired, the uranium-238 in the pebbles absorbs high-energy neutrons in a nonchain reaction and slows the fission process. Thus, this type of reactor protects the public more effectively from accidental meltdown or fires. Instead, any damage generally affects one pebble at a time. Another advantage to pebble-bed reactors is higher efficiency. Traditional nuclear power plants produce electricity at about a 35 percent efficiency rate, while pebble-bed reactors range from 40 to 50 percent efficiency.

Environmental Impact

Nuclear power plants do not generate greenhouse gases like power plants that rely on fossil fuels such as coal or natural gas. They do release trace amounts of radioactive gases; namely krypton, xenon, and iodine vapor. However, these power plants do indirectly cause greenhouse gas emissions. In a typical reactor, about 1.6 million tons of steel and about 14 million tons of concrete are manufactured, transported to the site, and used in construction. This process consumes millions of gallons of fossil fuel. For example, for every ton of Portland cement manufactured, about a ton of carbon dioxide is released into the atmosphere. This indirect emission is prominent only during the construction phase.

Nuclear reactors generate both high-level and low-level radioactive waste. High-level waste is waste generated in the nuclear reactor fuel cycle. Low-level waste includes gloves, clothing, tools, machine parts, and other items that may be contaminated with radioactivity. Extreme care needs to be taken in handling and storing these wastes.

A typical 1,000-MW nuclear power plant produces about 30 metric tons of high-level waste. This waste includes uranium, plutonium, cesium, strontium, and neptunium. The plutonium in this spent fuel is a major concern as it can be separated into dangerous and valuable materials using chemical techniques. Smuggling of radioactive waste is a major concern for nuclear power plants in several developing countries and in eastern Europe, where security measures may be inadequate.

In the United States, consumers end up paying about 1 cent per kilowatt-hour of electricity used toward nuclear waste management, although the US lacked a dedicated permanent dump for nuclear waste well into the 2020s. Additionally, the half-life of uranium-238, uranium-235, and plutonium-239 is quite high; 24,000 years for plutonium, 713,000,000 years for uranium-235, and 4,500,000,000 for uranium-238. The half-life of strontium and cesium are twenty-nine and thirty years, respectively. These wastes will need to be secured for extremely long periods of time.

By the 2020s, the world had seen two major nuclear power accidents: the first at the Chernobyl reactor in Ukraine (then a part of the Soviet Union) on April 26, 1986, and the second on March 11, 2011, at the Fukushima Daiichi Nuclear Power Station in Japan after an earthquake-triggered tsunami. In both disasters, radioactive debris spread to the soil that produces food, groundwater used for drinking, and the air.

In the United States, the most severe nuclear accident up to that point occurred at the Three Mile Island power plant in Pennsylvania on March 28, 1979. Due to a valve malfunction, a large amount of radioactive coolant escaped. In an emergency measure, some radioactive wastewater was dumped into the Susquehanna River. The cleanup cost related to the disaster was around $1 billion and was completed in 1993, over fourteen years later.

Major Issues

In the United States, nuclear power has encountered much public opposition, turning many politicians against its proliferation. The International Atomic Energy Agency (IAEA) acknowledges the task of “achieving and retaining public confidence in nuclear power” as a challenge in many parts of the world. If nuclear power is to continue to develop, public acceptance of its importance as an energy resource needs to improve. This is true for the United States as well as for many other nations.

The IAEA acknowledges that there is a shortage of nuclear reactor design, architecture, engineering, and project management organizations internationally. Nuclear proliferation in developing countries is another major concern, where the safety of used fuel for short- or long-term storage is an issue. Since most nuclear power plants are large, producing more than 1,000 MW, proper grids for power transmission are also essential. Such grids are not widely available in many countries.

The life span of a typical nuclear reactor is about fifty to sixty years. Reactors need to be decommissioned and sealed for thousands of years after their use period. The decommissioning cost alone can cost $500 million or more for each reactor.

In public perception, the nuclear industry functions under a veil of secrecy. For example, the IAEA prohibited the World Health Organization from releasing information about the adverse health impacts of Chernobyl without getting prior clearance from the IAEA. For this reason, some information has never been released to the public. In Japan, the Japanese government and the Tokyo Electric Power Company (Tepco), the owner of the nuclear reactors, have admitted there was a lack of communication to the general public about the magnitude of the problem in the early stages of the disaster. As a result of the Chernobyl and Fukushima Daiichi fallout, German officials abandoned plans to build new nuclear power plants, and Italy became a nuclear-free country. However, China still planned to proceed with the construction of about twenty-five new nuclear power plants.

Nuclear power remained a divisive issue throughout the first decades of the twenty-first century; while some promoted nuclear energy as a generally safe, renewable alternative to fossil fuels, others remained concerned over issues related to radioactive waste and potential nuclear disasters. Meanwhile, developments in nuclear fusion had the potential to completely reshape the industry in subsequent decades.

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