Nuclear Energy: Understanding Power from Atomic Reactions

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Nuclear Energy

Nuclear Energy, energy released in large amounts by the splitting or formation of atomic nuclei. The light and heat of the sun and other stars is an example of naturally occurring nuclear energy. Artificially produced nuclear energy can be released either in a steady, controllable manner, as in devices called nuclear reactors, or in the form of a violent explosion, as in nuclear weapons. Properly speaking, the energy released by the process of radioactive decay is also a form of nuclear energy. In radioactive decay, elements such as uranium produce radiation when the nucleus of the element loses protons or neutrons, thus changing into a different kind of nucleus. However, this type of energy is generally not included in discussions of nuclear energy. This article deals with nuclear energy in the usual sense.

Nuclear energy is sometimes called atomic energy. However, atoms can be the source of both nuclear and chemical energy. Nuclear energy involves the atom's nucleus; chemical energy involves the atom's electrons—subatomic particles that surround the nucleus. Pound for pound, a nuclear fuel (a material used as a source of nuclear energy) will produce several million times as much energy as a chemical fuel such as gasoline. Nuclear fuels yield so much energy that even a heavy ship such as an aircraft carrier powered by nuclear energy can operate many years without refueling.

Basic Principles

Nuclear Forces

The particles that make up an atom's nucleus are protons, which carry a positive charge of electricity, and neutrons, which are uncharged (electrically neutral). Protons and neutrons collectively are often called nucleons.

A fundamental law of electricity states that like charges repel each other. In a large nucleus there are many nucleons close to one another, held together by forces much stronger than the electrical forces that tend to push the protons apart. The forces that hold the nucleus together act only at extremely short range, and can thus be overcome if the shape of the nucleus is significantly distorted (which may happen, for example, when the nucleus captures a neutron). When these strong forces, as they are called, are overcome, the repulsion between the like-charged protons becomes the effective force, and the particles fly apart with tremendous energy. Some elements such as uranium have isotopes. While every nucleus of uranium has 92 protons, the different isotopes of uranium have 146 and 143 neutrons respectively. Based on their atomic mass numbers, these isotopes have been named U-238 and U-235 respectively.

Mass and Energy

The equivalence of mass and energy, stated in 1905 by Albert Einstein as part of his special theory of relativity, is an important concept in nuclear physics. Einstein's mass-energy relation, the formula E = mc², shows why nuclear reactions yield so much energy from the conversion of a small amount of matter. In this formula E represents energy, m mass, and c the speed of light. If the mass is measured in kilograms and the speed of light in meters per second, the result is energy in joules. The conversion of 1 kilogram (2.2 pounds) of matter into energy would produce 1 X (3 X 108)2 = 9 X 1016 joules of energy. This is equivalent to 25 billion kilowatt-hours, enough energy to keep 25 billion 100-watt bulbs burning for 10 hours.

Binding Energy

Except for the nucleus of the most common type of hydrogen atom, which consists of just one proton, the mass of an atom's nucleus is always less than the sum of the masses of the individual nucleons it contains. This difference in mass is sometimes called the mass defect; more commonly, however, it is expressed in units of energy, and is then called the binding energy of the nucleus.

For example, the mass of the nucleus of helium 4, the most common type of helium atom, is less than the combined masses of the two protons and two neutrons that make up this nucleus. (In terms such as "helium 4" and "uranium 235" the number indicates the total number of nucleons in the nucleus.) The difference amounts to 5.042582 X 10-29 kilogram, or

0.00000000000000000000000000005042582 kg.

Mass defects are usually stated in terms of the unified atomic mass unit (u). The u is defined as 1/12 the mass of an atom of carbon 12 and is equal to approximately 1.66 X 10-27 kilogram. (The term atomic mass unit, or amu, is sometimes used to mean u, but this term properly refers to a unit of slightly different value based on the mass of an atom of oxygen 16.)

The mass of a free proton is 1.0072766 u; that of a free neutron, 1.0086654 u. The mass of the helium 4 nucleus, however, is not 4.0318840, but 4.0015028 u. The mass defect, therefore, is 0.0303812 u; the binding energy, according to the relation 1 u = 931 MeV, is about 28.3 MeV. (MeV is the abbreviation for "million electron volts"; one electron volt is the amount of energy acquired by an electron as it moves between two points that have a difference of potential of one volt. One MeV equals about 1.6 X 10-3 joule.)

The binding energy of a nucleus is a measure of the amount of mass converted into energy during the formation of the nucleus. It is equal to the amount of energy that would have to be supplied to the nucleus to cause it to break up completely into separate nucleons. The average binding energy per nucleon (the binding energy of the nucleus divided by the number of nucleons) is a measure of the stability of the nucleus; the higher the average binding energy, the more difficult it is to break up the nucleus.

How Nuclear Energy Is Released

Fission

The fission of a heavy atom usually results in the formation of two lighter nuclei of approximately equal mass and in the release of several neutrons. The total mass of the fission products is less than the mass of the original nucleus; the "lost" mass has been converted into energy. The fissioning of a single uranium atom releases about 200 MeV of energy; about 177 MeV of this total is the kinetic energy (energy of motion) of the fission products, the remainder is radiant energy in the form of gamma rays. The average binding energy of the two lighter nuclei formed by fission is higher than the average binding energy of the original nucleus.

Although several types of heavy nuclei can be made to fission by bombarding them with neutrons, only three—those of uranium 235, uranium 233, and plutonium 239—are relatively easy to split and can be produced in quantity. The fission of all the nuclei contained in one kilogram of uranium 235 would yield about 23,000,000 kilowatt-hours of energy.

Uranium 235 occurs in nature, but forms less than one per cent of naturally occurring uranium. For commercial use, the uranium 235 content of natural uranium is usually increased, a process called uranium enrichment. Plutonium 239 and uranium 233, which do not occur in nature, are created in nuclear reactors. When the nucleus of one element changes into the nucleus of another element, it is known as transmutation.

Chain Reactions

On the average, two or three neutrons are released in each individual fission reaction. In a given quantity of matter containing fissionable material, some of the neutrons will cause the splitting of other fissionable nuclei, some will escape, and some will be captured (absorbed) by nuclei that do not undergo fission. If, on the average, at least one neutron from each fission reaction causes one other nucleus to undergo fission, the sequence of fission reactions is self-sustaining and is called a chain reaction.

The quantity of material required for a chain reaction to occur is called the critical mass. It varies with the nature and shape of the fissionable material. The bombarding particle causes the fission material to undergo fission. In most nuclear reactors, neutrons are used as bombarding particles. The target material is the substance that is bombarded; in most cases it is uranium. This is because uranium can release neutrons constantly, keeping up a flow of energy.

In a fission weapon, a quantity of fissionable material in excess of the critical mass is brought together very rapidly, and almost every neutron released in each fission reaction causes another nucleus to fission. As a result, the number of fission reactions increases so rapidly that within a fraction of a second most of the nuclei have undergone fission and a vast quantity of energy is released.

In a nuclear reactor, on the other hand, the fissionable material is dispersed within other matter so that such a rapid, explosive reaction will not occur. The chain reaction in a nuclear reactor is controlled so that, on the average, just one neutron from each fission reaction causes another nucleus to undergo fission.

Moderators

Slow-moving neutrons are captured by fissionable nuclei several hundred times more easily than are fast-moving neutrons. The neutrons that are released when fission occurs move very fast, but a moderator may be used to slow them down. Typical moderators are ordinary water, heavy water (water that contains deuterium, a rare and heavy form of hydrogen, in place of ordinary hydrogen), beryllium, paraffin, or graphite.

When a fast neutron passes through a moderator, it collides with the moderator's atoms. Each collision reduces the neutron's speed. By the time the neutron has passed through the moderator and reached the fissionable material, its speed has been reduced enough so that it can be readily captured. Moderators must be able to reduce the speed of fast neutrons rapidly without an excessive number of collisions, and must be poor absorbers of slow neutrons.

Fusion

Although a large amount of energy can be obtained by fission, an even greater amount can be obtained by fusion. The percentage of total mass that is converted into energy in both fission and fusion is small—less than 1 per cent—but the percentage is about seven times as great for a fusion reaction as for a fission reaction. The fusion of two protons and two neutrons into a helium-4 nucleus, for example, would result in the "loss" of 0.0303812 u of mass and the release of about 28.3 MeV of energy.

For fusion reactions to be readily produced in large numbers, there must be a very high temperature. For this reason, fusion reactions are often termed thermonuclear reactions. (The prefix "thermo" means "heat.")

Fusion In the Sun

The temperature in the interior of the sun is about 30,000,000 F. (16,700,000 C.), high enough to permit several types of fusion reactions to occur. The most important type of fusion believed to take place in the sun and other hydrogen-rich stars is a three-step process, the net result of which is the conversion of four nuclei of ordinary hydrogen into a nucleus of helium 4. During each of the three steps, energy is released. The sun radiates this energy in the form of light and heat.

Man-made Fusion

No furnace that has ever been built can produce the heat necessary to initiate large numbers of fusion reactions; however, a fission explosion creates a temperature of many millions of degrees and such explosions have been used as "triggers" to initiate fusion explosions.

The most promising materials (fuels) for controlled fusion reactions are deuterium, or hydrogen 2, a type of hydrogen atom whose nucleus consists of one proton and one neutron; and tritium, or hydrogen 3, a type of hydrogen atom with a nucleus consisting of one proton and two neutrons. (The fusion of ordinary hydrogen nuclei, or protons, which occurs in the sun, requires too much time—several million years to convert even a single gram of hydrogen into helium—to be practical for use on Earth.)

At sufficiently high temperatures, deuterium and tritium nuclei will readily come together to form a larger nucleus. For example, two deuterium nuclei can combine to form a helium-3 nucleus and a free neutron, while a deuterium nucleus can combine with a tritium nucleus to form a helium-4 nucleus and a free neutron. When these helium nuclei are formed, energy is simultaneously released. In order for fusion reactions to occur at a useful rate, the fuel must be heated to a temperature of more than 100 million degrees.

In one type of fusion reactor, called a tokamak, fuel in the form of a plasma (a very hot, ionized gas) is held within a doughnut-shaped vacuum chamber by a strong magnetic field. The magnetic field prevents the plasma from touching the walls of the chamber, which would vaporize on contact with the plasma. Development of this type of fusion reactor has been hindered by difficulties in simultaneously heating the plasma to sufficiently high temperatures and containing the plasma long enough to produce more power than is used to start the reaction.

In an inertial-confinement reactor, fuel in the form of small pellets is used. The pellets are dropped individually into a vacuum chamber. In one type of such reactor, each pellet is struck by beams of intense light from a laser; in another, by beams of charged particles. The beams are timed to strike the pellet from different directions simultaneously, causing the pellet to implode (collapse in upon itself) and undergo fusion.

Thus far, controlled and continuous fusion reactions have not been attained. This is because plasma must be heated to a very high temperature for the reaction to occur. So far, no chamber has been found that can withstand such heat. If an efficient working fusion reactor is ultimately developed, mankind will have a great new source of power at its disposal. The advantages of fusion over fission for producing power are several: as a source of energy, fusion is considerably more efficient than fission; deuterium, the principal fuel component, can be obtained relatively easily and cheaply from ordinary seawater; finally, a fusion reactor would produce less radioactivity and radioactive waste than a fission reactor does.

In early 1989, evidence from experiments using a simple electrolytic cell with palladium electrodes indicated that the cell had produced heat-releasing fusion at room temperature. However, after intensive efforts by scientists worldwide failed to verify the results satisfactorily, most scientists dismissed the experiment as flawed.

Nuclear energy is released by three processes—fission, fusion, and radioactive decay. Fission is the splitting of a large nucleus to form two or more smaller nuclei; the splitting is usually achieved by bombarding the large nucleus with neutrons. Fusion is the building up of a nucleus by combining smaller nuclei or individual protons and neutrons. Radioactive decay, which releases much smaller amounts of energy than fission and fusion, is discussed in the article Radioactivity.

Nuclear Reactors

Power Reactors

Power reactors use the heat produced by nuclear fission to form steam. In a nuclear power plant (as opposed to power plants that burn coal or petroleum), the steam is used to drive turbines that generate electricity. Many large nuclear plants generate more than 1,000 megawatts (1,000 million watts) of electricity. In a nuclear ship, the steam is used to drive a turbine that turns the ship's propellers.The different parts of a nuclear reactor are housed in different parts of the nuclear plant. One building contains the nuclear reactor proper, while other structures contain the turbines and other parts. Within the plant grounds are storage facilities for spent fuel.

Most power reactors use ordinary water as the coolant. They are called light-water reactors to distinguish them from reactors that use heavy water as a moderator. In light-water reactors, the reactor core is surrounded by the coolant under pressure within a container called the pressure vessel. The nuclear fuel is enriched uranium containing 2 to 4 per cent uranium 235. For use in the fuel rods, the uranium is converted into uranium dioxide.

There are two major types of light-water reactors.

In boiling-water reactors, the water heated in the core boils, forming steam. The steam is fed through pipes from the pressure vessel to the turbine. It is then cooled, condensing into water, which is pumped back to the core.

In pressurized-water reactors, the water is kept under very high pressure so that it cannot turn into steam as it is heated in the core. The heated water is pumped from the pressure vessel to a heat exchanger, where it flows through a system of narrow pipes surrounded by water. The hot, pressurized water gives up its heat to the water outside the pipes. As it is heated, this water boils, forming steam that is fed to the turbine. The steam is then condensed into water and returned to the heat exchanger. Meanwhile, the pressurized water circulates back to the pressure vessel, where it picks up more heat from the core.

Several other types of power reactors are used in certain countries. These reactors include the CANDU reactor, developed in Canada, and gas-cooled types, such as the advanced gas reactor (AGR) developed in Great Britain.

The CANDU uses natural uranium—that is, uranium that has not been enriched—as the fuel and heavy water as the coolant and moderator. The AGR uses enriched uranium as the fuel, graphite as the moderator, and carbon dioxide as the coolant.

Breeder Reactors

Power reactors called breeder reactors produce more nuclear fuel than they consume. The core of a breeder reactor produces excess neutrons that are used to convert uranium 238 or thorium 232 into fissionable materials—plutonium 239 and uranium 233, respectively.

The most important type of breeder reactor is the liquid metal fast breeder reactor. It uses liquid sodium as a coolant and plutonium as a fuel. As in a pressurized-water reactor, heated coolant is passed through a heat exchanger to produce steam to generate electricity. In a fast reactor no moderator is used to slow down the neutrons produced in the core.

The core is surrounded by a blanket (layer) of uranium 238. As fast-moving neutrons from the core pass through the blanket, some of the neutrons strike uranium 238 nuclei and are absorbed. When a neutron is absorbed, uranium 238 becomes uranium 239, which then decays, becoming plutonium 239. The plutonium is then separated from the rest of the blanket for use as a fuel in other breeder reactors.

France currently has the breeder reactor that produces the most energy. Many other countries too have built breeder reactors.

Production Reactors

Production reactors are used chiefly to produce plutonium 239 for use in nuclear weapons. In the most important type of production reactor, fuel rods containing both uranium 235 and uranium 238 are placed in horizontal channels in a large cube of graphite, which serves as the moderator. Water circulates through the channels, removing the heat produced by the fuel rods. Neutrons emitted by the fission of uranium 235 are absorbed by the uranium 238, forming uranium 239, which decays into plutonium 239. After a certain percentage of the uranium has been converted into plutonium, the bars are removed from the reactor and the plutonium is chemically separated from the rest of the material in the bars.

Research Reactors

These reactors are usually designed to provide large quantities of free neutrons and relatively little heat. When nonradioactive materials are bombarded by the free neutrons within the research reactor, their atoms are made radioactive—that is, they are transformed into radioisotopes. Hundreds of different radioisotopes have been produced in research reactors. Research reactors are also used to determine the effects of neutrons and gamma rays on various structural materials, and to test design features of proposed new reactors.

Advanced Light Water Reactor

This reactor is an advancement over the Light Water Reactor. These reactors have safety features based on gravitation. This reactor is in use in Japan.

High Temperature Gas-Cooled Reactor

This fission reactor uses uranium oxycarbide as fuel and helium as coolant. The fuel is sealed in ceramic containers. This safety feature ensures that the fission of uranium inside the container does not rupture the container, in case the coolant escaped. As long as the ceramic containers are not damaged due to heat released during the reaction, the fuel remains safely inside.

Preparation of Nuclear Fuel

Between the stages of mining and fission, uranium undergoes a series of processes to purify it. The percentage of U-235 in the fuel should be around 5 per cent. After uranium is mined, it is processed in an enrichment plant for increasing the percentage of U-235. Next, the uranium is oxidized. The uranium dioxide is put into small tubes, which are then sealed at the ends. The tubes are shipped to nuclear reaction plants for further use.

Nuclear energy has many advantages. A nuclear power facility uses less fuel than plants that use traditional fuels such as coal and gasoline. If properly handled, fission materials do not release air contaminants during reaction process. However, nuclear power facilities are more expensive to build compared to traditional plants. The spent fuel remains radioactive for years, posing problems in storage.

Nuclear Reactor Safety

Nuclear fission produces various kinds of nuclear radiation, chiefly gamma rays and high-speed neutrons. The radiation is very harmful to the human body when absorbed in sufficient quantities. For this reason, heavy shielding is placed around the core and pressure vessel.

In addition to the immediate radiation produced by fission, the fission process and the bombardment of materials by neutrons create a variety of both gaseous and solid radioactive materials. Some of these materials emit intense radiation and some remain radioactive for a very long time. A nuclear reactor is built with certain features designed to prevent these materials from escaping into the environment. These features include metal cladding on fuel rods to confine the radioactive materials produced in the fuel, and filters to remove impurities in the water that may have become radioactive as they passed through the core. Most reactors are housed in a steel-lined concrete structure called the containment building whose purpose is to contain radioactive materials should an accident release them from the reactor.

When a serious accident occurs, the chain reaction in the reactor can be stopped immediately by rapidly inserting the control rods into the core, an action called scramming. One of the most serious accidents that could occur in a commercial reactor is the loss of coolant around the core. In a light-water reactor, such an accident could occur with the rupture of the pressure vessel or the failure of one or more valves. Even when the chain reaction in the core is immediately stopped, the loss of coolant would let the core overheat. The ensuing meltdown would result in the formation of an extremely hot mass that could melt its way through the floor of the containment building, a situation sometimes referred to as the "China Syndrome." Although the mass would not sink far into the earth, the ground would become contaminated with large amounts of radioactive material. The hot mass would turn water in the ground into steam, which could carry a portion of the radioactive materials into the air. To prevent the possibility of a meltdown, nuclear reactors are built with one or more emergency cooling systems to provide extra coolant in case it is needed. The effectiveness of these systems has been debated, however, because the conditions that would be produced following the loss of coolant in the core are uncertain.

Disposal of Radioactive Wastes

A serious problem associated with the use of nuclear energy is the handling, treatment, and disposal of the radioactive waste products—liquid, solid, and gaseous—it creates. These wastes, such as liquids used in the chemical processing of reactor fuels or as coolants, spent (used-up) solid fuel elements, and gases used as reactor coolants, contain dangerous radioactive materials. These materials can remain radioactive for more than 500 years, making them a health hazard. Some materials, such as plutonium, retain radioactivity for more than a thousand years.

Several methods for the long-term disposal of highly radioactive wastes have been developed and studied. The most widely accepted plan consists of binding the wastes in a glasslike or ceramic substance that is very resistant to corrosion. This waste material would be placed deep underground in very stable geological formations where it would remain undisturbed. Long-range plans of several countries include disposal of highly radioactive wastes in granite formations underground or under the sea floor, in frozen clay, and in salt domes. In the United States no long-term plan has been agreed upon. Radioactive wastes are being held in temporary storage, typically in containers held in pools of water near nuclear plants. The water carries away the heat produced by radioactive decay and serves as a shield against the radiation they emit.

Another method, used on a limited scale, involves recycling of spent fuel. The radioactive plutonium and uranium is removed from the used fuel and used in reactors again.

Nuclear Regulatory Commission

The regulation and safety of nuclear power in the United States is the responsibility of the Nuclear Regulatory Commission (NRC), an independent agency of the federal government. The commission carries out its work through a number of offices. The most important are:

Office of Nuclear Reactor Regulation,

which is in charge of licensing and regulating the development and use of nuclear reactors. The office is also responsible for the inspection of nuclear facilities and the enforcement of federal safety and licensing provisions.

Office of Nuclear Material Safety and Safeguards,

which is concerned with ensuring the safe processing, transportation, and handling of nuclear materials. It is also involved in the maintenance of safeguards against the theft of nuclear materials and the sabotage of nuclear facilities.

Office of Nuclear Regulatory Research,

which is responsible for devising procedures and policies regarding nuclear regulation.

The NRC is headed by five commissioners, appointed by the President with the advice and approval of the Senate. Commissioners serve five-year terms. The commission was established under the Energy Reorganization Act of 1974. It took over the regulatory functions of the disbanded Atomic Energy Commission.

A nuclear reactor is a device in which a controlled chain reaction is maintained. This section discusses only fission reactors; fusion reactors are still in the developmental stage.

The nuclear fuel used in virtually all fission reactors is shaped into pellets that are loaded and sealed in metal tubes. The tubes of nuclear fuel, called fuel rods, are assembled to form an array known as the reactor core. The core is contained within a reactor vessel, which is generally made of steel and can be up to 8 inches thick. The core of a large nuclear reactor holds several thousand fuel rods placed in such a way that they support a chain reaction. As the nuclear fuel undergoes fission, many new substances are continually formed. These substances include radioactive elements formed during fission reactions and other elements formed as the radioactive elements decay. Many of these substances absorb neutrons that are needed to help continue the chain reaction in the core. For this reason, the fuel rods must be periodically replaced before all the nuclear fuel they contain has been used up.

The chain reaction in a nuclear reactor is regulated with control rods made of boron or some other material that readily absorbs neutrons. The control rods can be moved into or out of the core; when they are fully inserted into the core, they absorb so many neutrons that the chain reaction immediately stops.

A liquid called a coolant is used to absorb and remove the treat produced in the core. The coolant used in most nuclear reactors is ordinary water, which also serves as the moderator.

Most nuclear reactors are used to generate electricity commercially. Other nuclear reactors are used to propel submarines or other ships; to produce plutonium 239; or to create radioactive isotopes (radioisotopes) for science, medicine, or industry.

Research and Development

Important Installations

The Department of Energy has its own production and research and development facilities. They are operated by academic institutions and private firms, through contracts with the government. Major facilities include:

Argonne National Laboratory,

Argonne, Illinois, concentrates on nonmilitary applications of nuclear power, especially the design and development of nuclear reactors. It also conducts extensive biological and environmental research, particularly on the effects of nuclear radiation.

Ernesto Orlando Lawrence Berkeley National Laboratory,

Berkeley, California, conducts research in a wide variety of fields, including high-energy particle physics, nuclear fusion, computer-aided engineering, earth sciences, chemical sciences, and biological sciences.

Fermi National Accelerator Laboratory,

Batavia, Illinois, conducts research in high-energy physics.

Hanford Site,

Richland, Washington, was built during World War II. It was the world's first full-scale nuclear energy plant. Its 105-B reactor permanently ceased plutonium-production operations in 1968, and the reactor building is now a controlled-access museum. The reactor building was entered into the National Register of Historic Places in 1992.

Idaho National Engineering and Environmental Laboratory,

Idaho Falls, Idaho, is primarily involved in nuclear waste management, environmental restoration, materials and fuel testing, and research in nuclear and renewable energy.

Lawrence Livermore National Laboratory,

Livermore, California, conducts research in such areas as nuclear energy, lasers, chemistry, biomedicine, weaponry, and materials science.

Los Alamos National Laboratory,

Los Alamos, New Mexico, conducts research in nuclear weaponry and energy, cryogenic physics, space sciences, molecular biology, and metallurgy.

Nevada Test Site,

Mercury, Nevada. Nuclear weapons are tested here.

Oak Ridge National Laboratory,

Oak Ridge, Tennessee, includes among the many research facilities the Center for Global Environmental Studies, Bioprocessing Research and Development Facility, Collaborative Technologies Research Center, and Oak Ridge National Laboratory (for nuclear energy research).

Portsmouth Gaseous Diffusion Plant,

Piketon, Ohio, is a plant that uses gaseous diffusion to enrich uranium.

Sandia National Laboratories,

Albuquerque, New Mexico, and Livermore, California,build nuclear weapons. Its primary mission is to ensure the safety, security, and reliability of the nation's nuclear weapons stockpile. There are also facilities for research on combustion, hydrogen, and computational modeling and simulation.

Savannah River Site and Laboratory,

Aiken, South Carolina, is a plant that produces plutonium-238 for deep space probes.

In the United States, nuclear energy research and development is a responsibility of the United States Department of Energy and its various subdepartments. The department's nuclear energy programs include the production of nuclear materials and the design, construction, and testing of nuclear weapons and nuclear reactors. A prime objective of the department is to develop the use of nuclear energy. A person who wants to work in this field needs undergraduate and graduate degrees in physics or nuclear technology. Related industries such as mining and regulation have jobs for geology, chemistry, and life sciences graduates.

History

Nuclear Fission

In 1932, James Chadwick, working in Rutherford's Cavendish Laboratory at Cambridge University, discovered a previously unknown particle, the neutron. In 1934, Irne and Frdric Joliot-Curie discovered that by bombarding certain elements with alpha particles they were able to produce nuclei that decayed spontaneously, emitting nuclear radiation. Enrico Fermi, a young Italian physicist, read the Joliot-Curies' report on this work and decided to try similar experiments on uranium, using the neutron as a bombarding particle. An important result of Fermi's experiments was the discovery that slowing down neutrons makes them much more effective in causing uranium to decay spontaneously.

However, one result of the experiments was misinterpreted. After attempting unsuccessfully to determine the atomic numbers of the atoms formed by the neutron bombardment, Fermi concluded that he had created several transuranium elements (elements with atomic numbers larger than that of uranium).

In 1938, the German scientists Otto Hahn and Fritz Strassmann repeated Fermi's experiments. Among the products resulting from the bombardment of uranium nuclei with neutrons they identified barium, which has an atomic weight only slightly more than half that of uranium. Hahn notified Lise Meitner, a former associate, of the results of the experiments. She realized that Fermi had not created new elements in his 1934 experiments; instead, he had split the uranium nucleus into two smaller nuclei of approximately equal mass.

This news spread rapidly throughout the scientific world. Within a few months, Frdric Joliot-Curie with Hans von Halban and Lew Kowarski proved that, in the process of splitting, the uranium nucleus gives off free neutrons. This finding suggested that a self-sustaining fission reaction might be possible if the freed neutrons would, in turn, cause other uranium atoms to split. Albert Einstein in 1905 proved that matter was changed into energy during the reaction.

World War II began in 1939, and these advances in nuclear physics assumed military and political importance as it was realized that a fission reaction could be used for a devastating new weapon—an atomic bomb. Both the United States and Germany set to work in developing such a weapon, but only the United States succeeded. On December 2, 1942, the world's first nuclear reactor (built under Fermi's direction at the University of Chicago) produced a controlled chain reaction, marking the beginning of the nuclear age. On July 16, 1945, the United States detonated the first atomic bomb at a test site in the desert near Alamogordo, New Mexico.

Even before the end of World War II, scientists and political leaders in the United States began to plan the development of atomic energy for nonmilitary purposes. Control of atomic energy in the United States was passed from a military to a civilian agency by the Atomic Energy Act of 1946, which created the Atomic Energy Commission (AEC).

President Dwight D. Eisenhower proposed international sharing of the benefits of atomic energy with his Atoms-for-Peace program, presented to the United Nations in 1953. This program led to the formation, in 1957, of the International Atomic Energy Agency. In 1958 Belgium, France, West Germany, Italy, Luxembourg, and the Netherlands organized the European Atomic Community (EURATOM). Other international organizations to promote the peaceful uses of nuclear energy have since been formed.

In 1946, the United States government for the first time released for private use radioisotopes produced in government-owned nuclear reactors. In 1951 an experimental nuclear reactor at the AEC testing station at Idaho Falls, Idaho, produced the first useful amounts of electricity derived from nuclear energy.

In 1954, Congress passed legislation aimed at encouraging private industry to build nuclear reactors and to use reactor-produced electricity. An important military advance was also made in 1954 when the United States launched the world's first nuclear powered vehicle, the submarine USS Nautilus. The first nuclear-powered surface vessel, the Soviet icebreaker Lenin, was launched in 1957.

In the early 1960s, several demonstration nuclear power plants for the commercial production of electrical power went into operation in the United States. By the late 1960s, electric utilities, perceiving nuclear power as economically attractive, began to order large numbers of nuclear power plants.

In 1974, the Atomic Energy Commission was abolished and replaced by the Nuclear Regulatory Commission (NRC) and the energy Research and Development Administration (ERDA). The NRC assumed the regulatory functions of the AEC; the ERDA, its research and development functions. In 1977, the ERDA became part of the newly created Department of Energy.

The cost of power from nuclear plants increased rapidly through the early 1970s. Factors contributing to this increase included rising construction costs, high interest rates, and construction delays caused by licensing procedures and environmental lawsuits. By the late 1970s, few orders were being placed for nuclear power plants in the United States.

In May, 1979, a major accident occurred in a pressurized-water nuclear reactor at the Three Mile Island nuclear power plant near Harrisburg, Pennsylvania. There were no casualties, but residents in the area were exposed to radiation by a leakage of radioactive contaminants. The reactor was left crippled, and lengthy and expensive clean-up operations were required. The accident greatly raised public concern over the safety of nuclear reactors.

In 1986, a major accident at a nuclear power plant in Chernobyl, Ukraine, resulted in the release of a dangerous amount of radioactive material, causing a number of deaths and contaminating a large area. The reactor had no containment building, and the explosion tore through the roof of the reactor building. The accident again raised concerns over the safety of nuclear reactors.

By the mid-1990s, the building of new nuclear power plants in the United States and in many western European countries had largely ceased. Many older ones were being dismantled. There were several reasons for abandoning nuclear energy. In the wake of several nuclear accidents, such as the one at Chernobyl, many nuclear plants were investigated and found to be unsafe. Also, the cost of producing energy from nuclear reactors had risen higher than the cost of producing energy from fossil fuels. The disposal of nuclear waste materials also became a growing and increasingly costly problem.

In certain countries—particularly Japan, France, and those of eastern Europe—new nuclear energy plants continued to be built. Other nuclear capable countries include China, India, South Africa, United Kingdom, and Pakistan.

Nuclear energy today is used for powering ships and submarines, apart from producing electricity. Nuclear radiation is used in scientific studies and medicine. Around 29 countries use electricity generated through nuclear energy produced in 440 reactors.

The Fusion Process

During the 1920s and 1930s physicists, in experiments using high-energy particles, were able to fuse nuclei of hydrogen and other light atoms. In 1938, the German-American physicist Hans Bethe and the German physicist Carl von Weizscker, working independently, calculated the details of fusion processes that occur in stars.

The development of the atomic bomb led some scientists, including the United States physicist Edward Teller, to believe that a similar weapon could be made that would utilize the fusion process. Such a weapon—the hydrogen bomb—was developed by Teller and other U.S. scientists, and the first one was detonated in 1952. Since that time physicists have experimented with various techniques for making nuclear fusion a source of energy for commercial use, but the controlled and continuous fusion reactions required for such use have yet to be achieved.

Antoine Henri Becquerel, a French physicist, discovered the radioactivity of uranium in 1896. In 1898, two other French physicists, Marie and Pierre Curie, discovered two previously unknown radioactive elements, radium and polonium. Soon scientists all over the world were studying radioactivity. Among them was a British physicist, Ernest Rutherford. In the early twentieth century he helped establish that radioactive substances gave off three kinds of radiation—alpha particles, beta particles, and gamma rays. He showed that alpha particles were essentially atoms of helium without electrons. To account for the scattering behavior of alpha particles in passing through a metal foil, Rutherford theorized that an atom consists of a relatively heavy nucleus surrounded by tiny electrons. This theory was published in 1911. The studies of radioactivity made by Rutherford and other scientists showed that the nucleus is not indivisible, and that the nucleus of an atom of one element can be changed into that of another element.