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_Nuclear Energy © _
By: April Catchings
Nuclear energy © By: April R. Catchings © 28 page term paper Nuclear energy,
also called atomic energy, is the powerful energy released by changes in the
nucleus (core) of atoms. The heat and light of the sun result from nuclear
energy. Scientists and engineers have found many uses for this energy,
including the production of electric energy and the explosion of nuclear
weapons. Scientists knew nothing about nuclear energy until the early 1900's,
though they knew that all matter consists of atoms. Scientists then further
learned that a nucleus makes up most of the mass of every atom and that this
nucleus is held together by an extremely strong force. A huge amount of energy
is concentrated in the nucleus because of this force. The next step was to
make nuclei let go of much of that energy. Scientists first released nuclear
energy on a large scale at the University of Chicago in 1942, three years
after World War II began. This achievement led to the development of the
atomic bomb. The first atomic bomb was exploded in the desert near Alamogordo,
New Mexico, on July 16, 1945. In August, United States planes dropped bombs on
Hiroshima and Nagasaki, Japan. The bombs largely destroyed both cities and
helped end World War II. Since 1945, peaceful uses of nuclear energy have been
developed. The energy released by nuclei creates large amounts of heat. This
heat can be used to make steam, and the steam can be used to generate electric
energy. Engineers have built devices called nuclear reactors to produce and
control nuclear energy. A nuclear reactor operates somewhat like a furnace.
But instead of using such fuels as coal or oil, almost all reactors use
uranium. And instead of burning in the reactor, the uranium fiss power
production is by far the most important peaceful use of nuclear energy.
Nuclear energy also powers some submarines and other ships. In addition, the
fission that produces nuclear energy is valuable because it releases particles
and rays called nuclear radiation that have uses in medicine, industry, and
science. However, nuclear radiation can be extremely dangerous. Exposure to
too much radiation can result in a condition called radiation sickness. Almost
all the world's electric energy is produced by hydroelectric and thermal power
plants. Hydroelectric plants use the force of rushing water from a dam or
waterfall to generate electricity. Thermal plants use the force of steam from
boiling water. The great majority of thermal plants burn fossil fuels--coal,
oil, and natural gas--to produce heat to boil water. The remaining thermal
plants fission uranium. Few countries have enough water power to generate
large amounts of hydroelectricity. Most countries depend mainly on fossil
fuels. But fossil fuels are a non-renewable resource. Therefore, many experts
predict that nuclear power will become increasingly important. Worldwide
distribution of nuclear energy. In the mid-1990's, about 425 nuclear power
reactors operated in about 30 countries. Nuclear power plants produced less
than 20 percent of the world's electric energy. The United States had about
110 nuclear reactors and was the world's largest producer of nuclear energy.
Reactors produced about 20 percent of the country's electricity. Canada had 22
reactors, which produced about 15 percent of Canada's electricity. Other
countries, notably France and Japan, have a large nuclear power generating
capacity. Advantages and disadvantages of nuclear energy. Nuclear power plants
have two main advantages over fossil-fuel plants. (1) Once built, a nuclear
plant can be less expensive to operate than a fossil-fuel plant, mainly
because a nuclear plant uses a much smaller volume of fuel. (2) Uranium,
unlike fossil fuels, releases no chemical or solid pollutants into the air
during use. However, nuclear power plants have three major disadvantages.
These drawbacks have slowed the development of nuclear energy in the United
States. (1) Nuclear plants cost more to build than fossil-fuel plants. (2)
Because of the need to assure that hazardous amounts of radioactive materials
are not released, nuclear plants must meet certain government regulations that
fossil-fuel plants do not have to meet. For example, a nuclear plant must
satisfy the government that it can quickly and automatically deal with any
kind of emergency. (3) Used nuclear fuel produces dangerous radiation long
after it has been removed from the reactor. The full development of nuclear
energy. Many experts believe that the benefits of nuclear energy outweigh any
problems involved in its production. According to these experts, oil may be so
scarce by the mid-2000's that it will be too expensive to drill. Canada,
Germany, Russia, the United States, and some other countries have enough coal
to meet their energy requirements for hundreds of years at present rates of
use. However, coal releases large amounts of sulfur and other pollutants into
the air when it is burned. If nuclear energy were fully developed, it could
completely replace oil and coal as a source of electric power. But a number of
problems must be solved before nuclear energy can be fully developed. For
example, almost all today's power reactors use a scarce type of uranium known
as U-235. If U-235 continues to be used at its present rate, the world's
supply of it will become so small that it will be too expensive to mine and
process by about 2050. Therefore, for nuclear energy to replace other energy
sources, it must be based on fuel that is much more plentiful than U-235.
NUCLEAR ENERGY/The science of nuclear energy The process by which a nucleus
releases energy is called a nuclear reaction. To understand the various types
of nuclear reactions, a person must know something about the nature of matter.
The composition of matter All the matter that makes up all solids, liquids,
and gases is composed of chemical elements. The chemical elements, in turn,
are composed of atoms. A chemical element consists of a substance that cannot
be broken down chemically into simpler substances. There are 112 known
chemical elements. Ninety-one of them are found on or in the earth. The other
21 elements are artificially created. Scientists rank the elements according
to mass, a measure of the quantity of matter in an object. An object's mass is
proportional to its weight. Hydrogen is the lightest natural element, and
uranium is the heaviest. Most of the artificially created elements are heavier
than uranium. Atoms and nuclei. An atom consists of a positively charged
nucleus and one or more electrons, which are negatively charged. The nucleus
makes up almost all of an atom's mass. The electrons, which are almost
massless, revolve about the nucleus. Electrons determine the various chemical
combinations that an atom enters into with other kinds of atoms . However,
electrons do not play an active part in nuclear reactions. The nuclei of every
chemical element except hydrogen consist of particles called protons and
neutrons. An ordinary nucleus of hydrogen, the lightest element, has one
proton and no neutrons. The heaviest elements, such as uranium and thorium,
have the largest number of protons and neutrons. Protons carry a positive
charge. Neutrons have no net charge. Extremely strong forces, called nuclear
forces, hold the protons and neutrons together in the nucleus. The nuclear
forces of each type of nucleus determine the amount of energy that would be
required to release its neutrons and protons. Isotopes. Most chemical elements
have more than one form. These different forms are called the isotopes of an
element. The atoms that make up each of the different forms have different
masses and are also called isotopes. Scientists identify an isotope by its
mass number--that is, the total number of protons and neutrons in each of its
nuclei. All the isotopes of a given element have the same number of protons in
every nucleus. Every hydrogen nucleus, for example, has just 1 proton. Every
uranium nucleus has 92 protons. However, each isotope of an element has a
different number of neutrons in its nuclei and so has a different mass number.
For example, the most plentiful isotope of uranium has 146 neutrons. Its mass
number is therefore 238 (the sum of 92 and 146). Scientists call this isotope
uranium 238 or U-238. The uranium isotope that almost all nuclear reactors use
as fuel has 143 neutrons, and so its mass number is 235. This isotope is
called uranium 235 or U-235. No two elements have the same number of protons
in their atoms. However, if an atom gains or loses one or more protons, it
becomes an atom of a different element. However, if an atom gains or loses one
or more neutrons, it becomes another isotope of the same element. Nuclear
reactions A nuclear reaction changes the structure of a nucleus. The nucleus
gains or loses one or more neutrons or protons. It thus changes into the
nucleus of a different isotope or element. If the nucleus changes into the
nucleus of a different element, the change is called a transmutation . Three
types of nuclear reactions release useful amounts of energy. These reactions
are (1) radioactive decay, (2) nuclear fission, and (3) nuclear fusion. During
each reaction, the matter involved loses mass. The mass is lost because it
changes into energy. Radioactive decay, or radioactivity, is the process by
which a nucleus changes into the nucleus of another isotope or element. The
process releases energy chiefly in the form of particles and rays called
nuclear radiation. Uranium, thorium, and several other elements decay
naturally and so contribute to the natural, or background, radiation that is
always present on the earth. Nuclear reactors produce radioactive isotopes
artificially. Nuclear radiation accounts for about 10 percent of the energy
produced in a reactor. Nuclear radiation consists largely of alpha and beta
particles and gamma rays. An alpha particle, which is made up of two protons
and two neutrons, is identical with a helium nucleus. A beta particle is
identical with an electron. It results from the breakdown of a neutron in a
radioactive nucleus. The breakdown also produces a proton, which remains in
the nucleus. Gamma rays are electromagnetic waves similar to X rays.
Scientists measure the rate of radioactive decay in units of time called
half-lives. A half-life equals the time required for half the atoms of a
particular radioactive element or isotope to decay. Half-lives range from a
fraction of a second to billions of years. Nuclear fission is the splitting of
heavy nuclei to release energy. All commercial nuclear reactors produce energy
in this way. To produce fission, a reactor requires a bombarding particle,
such as a neutron, and a target material, such as U-235. Nuclear fission
occurs when the bombarding particle splits a nucleus in the target material
into two parts called fission fragments. Each fragment consists of a nucleus
with about half the neutrons and protons of the original nucleus. The energy
is released in many forms. But most of the energy released by fission
eventually takes the form of heat. The bombarding particle must first be
captured by a nucleus for fission to occur. Reactors use neutrons as
bombarding particles because they are the only atomic particles that are both
easily captured and able to cause fission. Neutrons can also pass through most
kinds of matter, including uranium. The target material. Commercial power
reactors use uranium as their target material, or fuel. A uranium nucleus is
the easiest of all natural nuclei to split because it has a large number of
protons. Protons naturally repel one another, and so a nucleus with many
protons has a tendency to "fly apart" and can be split with little difficulty.
Uranium also makes a good nuclear reactor fuel because it can sustain a
continuous series of fission reactions. As a result, uranium can produce a
steady supply of energy. To create a series of reactions, each fissioned
nucleus must give off neutrons. Each of these neutrons can split still another
uranium nucleus, thus releasing still more neutrons. As this process is
repeated over and over, it becomes a self-sustaining chain reaction. Chain
reactions can produce an enormous amount of energy. Only nuclei that have many
more neutrons than protons, such as uranium nuclei, can produce a nuclear
chain reaction. The scarce uranium isotope U-235 is the only natural material
that nuclear reactors can use to produce a chain reaction. Nuclei of the much
more abundant U-238 isotope usually absorb neutrons without fissioning. An
absorbed neutron simply becomes part of the U-238 nucleus. Neutrons released
in fission travel too rapidly to be absorbed by U-235 nuclei in numbers large
enough to sustain a chain reaction. Reactors can use U-235 as a fuel because
they utilize other materials called moderators to slow the neutrons down. Some
reactors use water as a moderator, while others use graphite. The slowed
neutrons travel at a velocity of about 2.2 kilometers per second and are known
as thermal neutrons. Reactors that use moderators are called thermal reactors.
Most of today's reactors are thermal reactors. Thermal neutrons are highly
effective in causing fission in U-235. Therefore, the uranium in a thermal
reactor can have a low percentage of U-235 content. Depending on their design,
today's power reactors use a U-235 content ranging from 0.71 percent--the
percentage in natural uranium--to about 4 percent. Special purpose reactors
may use fuel with a higher percentage of U-235. Scientists have also developed
fast reactors, in which high-velocity neutrons cause the fissions. These
reactors use plutonium or uranium 233 fuel. Fast breeder reactors produce more
fuel material than they consume. A fast breeder reactor that converts U-238 to
plutonium can greatly extend the use of uranium as an energy resource. In
addition, a fast reactor can be designed to consume certain radioactive
elements that have long-lives and are present in used fuel. Such a reactor
would reduce the amount of certain radioactive wastes that must be disposed
of. The section Research on new types of reactors in this article discusses
fast reactors in more detail. Nuclear fusion occurs when two lightweight
nuclei fuse (combine) and form a nucleus of a heavier element. The products of
the fusion have less mass than the original nuclei had. The lost mass has
therefore been changed into energy. Fusion reactions that produce large
amounts of energy can be created by means of extremely intense heat. Such
reactions are called thermonuclear reactions. Thermonuclear reactions produce
the energy of both the sun and the hydrogen bomb. A thermonuclear reaction can
occur in only a form of matter called plasma. Plasma is a gaslike substance
made up of free electrons and free nuclei (nuclei that have no electrons
revolving about them). Normally, nuclei repel one another because of the
positive charges of their protons. However, if a plasma containing lightweight
atomic nuclei is heated many millions of degrees, the nuclei begin moving so
fast that they overcome the force of repulsion and fuse. Problems of
controlling fusion. Scientists have not yet succeeded in harnessing the energy
of fusion to produce electric energy. In their fusion experiments, scientists
generally work with plasmas that are made from isotopes of hydrogen. Hydrogen
has three isotopes. A mixture of deuterium and tritium is an excellent
thermonuclear fuel because ordinary seawater contains plentiful stocks of
deuterium and lithium. One barrel of seawater contains enough of these
substances to produce as much energy as the burning of about one-fifth of a
barrel of oil. To produce a controlled thermonuclear reaction, a plasma of one
or more hydrogen isotopes must be heated many millions of degrees. But
scientists have yet to develop a container that can hold plasma this hot. The
plasma expands quickly. In addition, the walls of the container must be kept
at low temperatures to prevent them from melting. But if the plasma touches
the walls, it becomes too cool to produce fusion. The plasma must therefore be
kept away from the walls of the container long enough for its nuclei to fuse
and produce usable amounts of energy. Fusion devices. Most experimental fusion
reactors are designed to contain hot plasma in "magnetic bottles" twisted into
various shapes. The walls of the bottles are made of copper or some other
metal and are surrounded by electromagnets. An electric current is passed
through the electromagnets, creating a magnetic field on the inside of the
walls. The magnetism pushes the plasma away from the walls. All the fusion
devices thus far developed, however, use much more energy than they create.
The section Research on new types of reactors discusses experimental fusion
reactors in greater detail. NUCLEAR ENERGY/How nuclear energy is produced All
large commercial nuclear power plants produce energy by fissioning U-235. But
U-235 makes up about 0.71 percent of the uranium found in nature. About 99.28
percent of all natural uranium is U-238. The two types occur together in
uranium ores, such as carnotite and pitchblende. Separating the U-235 from the
U-238 in these ores is difficult and costly. For this reason, the fuel used in
reactors consists largely of U-238. But the fuel has enough U-235 to produce a
chain reaction. Nuclear fuel requires special processing before and after it
is used. The processing begins with the mining of uranium ore and ends with
the disposal of fuel wastes. This section deals chiefly with the methods used
in the U.S. nuclear power industry. These methods resemble those used in other
countries. Power plant design. Most nuclear power plants cover 200 to 300
acres (80 to 120 hectares). The majority are built near a large river or lake
because nuclear plants require enormous quantities of water for cooling
purposes. A nuclear plant consists of several main buildings, one of which
houses the reactor and its related parts. Another main building houses the
plant's turbines and electric generators. Every plant also has facilities for
storing unused and used fuel. Many plants are largely automated. Each of these
plants has a main control room, which may be in a separate building or in one
of the main buildings. The reactor building, or containment building, has a
thick concrete floor and thick walls of steel or of concrete lined with steel.
The concrete and steel guard against the escape of radioactive material from
an accidental leak in the nuclear reactor. Power reactors that are used in
nuclear power plants in the United States consist of three main parts: (1) a
reactor, or pressure, vessel; (2) a core; and (3) a set of control rods. In
addition, reactor operations depend upon two substances--moderators and
coolants. The reactor, or pressure, vessel is a tanklike structure that
encloses the other main parts of the reactor. The vessel has steel walls that
are typically up to least 6 inches (15 centimeters) thick and capable of
containing the high pressure exerted in a reactor. The core contains the
nuclear fuel, in which the fission chain reaction occurs. The core sits in the
lower half of the reactor vessel. A great many fuel assemblies stand upright
in the core between an upper and lower support plate. Each fuel assembly
contains a bundle of fuel rods. A fuel rod consists of pellets of fuel inside
a metal tube. The pellet material is usually a powder called uranium dioxide.
The tubing material is typically zircalloy, a mixture of the metal zirconium
and one or more other metals. Neutrons can pass from the fuel through the tube
walls, but most other nuclear particles cannot. The control rods are long
metal rods that are used to regulate fission in the fuel. The control rods
contain such neutron-absorbing materials as boron or cadmium. A mechanism
outside the reactor vessel is attached to the rods. This mechanism inserts the
rods into the core and withdraws them when necessary. When inserted fully into
the core, the control rods absorb many neutrons and so prevent a fission chain
reaction from occurring. To begin operation of the reactor, the control rods
are partially withdrawn until a chain reaction occurs at a constant rate. To
increase power in the reactor, the rods are withdrawn slightly more. Thus,
fewer neutrons are absorbed, and more are available to cause fission. To stop
the chain reaction, the rods are inserted all the way into the core to absorb
most of the neutrons. The moderator is a substance that slows down neutrons as
they pass through it. Slow neutrons are needed for fission. The moderator
fills the space between the fuel rods in the fuel assemblies. It slows down
neutrons as they pass from one fuel rod to another. The coolant is a liquid or
gas that carries off the heat created by the fission chain reaction. The
coolant circulates throughout the core. It carries the heat from the reactor
to an energy conversion system. Thus, the coolant keeps the fuel and cladding
from getting too hot, and it transfers energy to a place where electricity can
be generated. All commercial power reactors in the United States are light
water reactors. In these devices, light (ordinary) water serves as the
moderator and the coolant. Canadian reactors are heavy water reactors. They
use heavy water as the moderator and the coolant. Heavy water contains
deuterium in place of ordinary hydrogen. For more information on reactors, see
the section Research on new types of reactors in this article. Fuel
preparation. After uranium ore has been mined, it goes through a long milling
and refining process to separate the uranium from other elements in the ore.
Light water absorbs more neutrons than do other types of moderators. The
uranium used in light water reactors must therefore be enriched--that is, the
percentage of U-235 must be increased. Neutrons then have a better chance of
striking a U-235 nucleus. In the United States, uranium that has been
separated from the ore is sent to an enrichment plant. Enrichment plants
increase the proportion of U-235 in the uranium, depending on the intended use
of the uranium. Most light water reactors use fuel with about 2 to 4 percent
U-235. Each tube measures about 1/2 inch (13 millimeters) in diameter and 10
to 14 feet (3 to 5 meters) long. After a tube has been filled with uranium
dioxide pellets, its ends are welded shut. These fuel rods are then fastened
together into bundles of 30 to 300 each. Each bundle, or fuel assembly, weighs
300 to 1,500 pounds (140 to 680 kilograms). Commercial power reactors need 50
to 150 short tons (45 to 136 metric tons) of uranium dioxide. The amount
depends on the size of the reactor. Chain reactions. A reactor requires a
certain minimum amount of fuel to keep up a chain reaction. This amount,
called the critical mass, varies according to the design and size of the
reactor. Reactors are designed to hold more than a critical mass of fuel to
allow for fuel use during operation. The position of the control rods
determines the effective mass of the fuel, the amount of fuel taking part in
the chain reaction. If the effective mass is decreased below the critical
mass, the chain reaction will die out and reactor power will decrease. If the
effective mass is increased above the critical mass, the chain reaction will
become more rapid and reactor power will increase. In an emergency, if the
chain reaction became too rapid, the reactor could overheat. However, the
control rods are available to slow down the chain reaction if it becomes too
rapid. To prepare a reactor for operation, the fuel assemblies are loaded into
the core with the control rods completely inserted. In a light water reactor,
the water used as a moderator to slow down the neutrons fills the spaces
between the fuel assemblies. The control rods are then slowly withdrawn, and a
chain reaction begins. The farther the rods are withdrawn, the greater the
rate of the reaction because fewer neutrons are absorbed. More neutrons thus
are available to cause fission. When the desired power is reached, the control
rods are positioned so that the effective mass is equal to the critical mass.
The water in the core carries off the heat created by the chain reaction. To
stop the reaction, the rods are again inserted all the way into the core to
absorb most neutrons. Steam production. The light water reactors used by
almost all U.S. nuclear plants are of two main types. One type, the
pressurized water reactor, produces steam outside the reactor vessel. The
other type, the boiling water reactor, makes steam inside the vessel. Most
nuclear plants in the United States use pressurized water reactors. These
reactors heat the moderator water in the core under extremely high pressure.
The pressure allows the water to heat past its normal boiling point of 212 °F
(100 °C) without actually boiling. The chain reaction heats the water to about
600 °F (316 °C). Pipes carry this extremely hot, though not boiling, water to
steam generators outside the reactor. The steam generators transfer heat from
the pressurized water to a separate supply of water that boils and so produces
steam. In a boiling water reactor, the chain reaction boils the
moderator-water in the core. Steam is therefore produced inside the reactor
vessel. Pipes carry the steam from the reactor to the plant's turbines. In
producing electric energy, a nuclear plant's steam turbines and electric
generators work like those in a fossil-fuel plant. The steam produced by a
reactor spins the blades of the plant's turbines, which drive the generators.
Many plants have combination turbines and generators called turbo generators.
After steam has passed through a plant's turbines, it is piped to a condenser.
The condenser changes the steam back into water. A reactor can thus use the
same water over and over. But a condenser requires a constant supply of fresh
water to cool the steam. Most plants pump this water from a nearby river or
lake. The water, which becomes warm as it passes through the condenser, is
then pumped back into the river or lake. This warm wastewater may heat the
water in the river or lake enough to endanger plants and animals that live
there. For this reason, the discharge of the wastewater is sometimes called
thermal pollution. To help solve the problem of thermal pollution, most new
nuclear plants have cooling towers. Hot water from the steam condensers is
moved through the towers in such a way that the heat passes into the
atmosphere. The cooled water is returned to the steam condenser for reuse.
Hazards and safeguards. An ordinary power reactor cannot explode like an
atomic bomb. Only a greatly supercritical mass of plutonium 239 or of highly
enriched uranium 235 can explode in this way. A supercritical mass contains
more than the amount of plutonium or uranium required to sustain a chain
reaction. The chief hazards of nuclear power production result from the great
quantities of radioactive material that a reactor produces. These materials
give off radiation in the form of alpha and beta particles and gamma rays. The
reactor vessel is surrounded by thick concrete blocks called a shield, which
normally prevents almost all radiation from escaping. Federal regulations
limit the amount of radiation allowed from U.S. nuclear plants. Every plant
has instruments that continually measure the radioactivity in and around the
plant. They automatically set off an alarm if the radioactivity rises above a
predetermined level. If necessary, the reactor is shut down. A plant's routine
safety measures greatly reduce the possibility of a serious accident.
Nevertheless, every plant has emergency safety systems. Possible emergencies
range from a break in a reactor water pipe to a leak of radiation from the
reactor vessel. Any such emergency automatically activates a system that
instantly shuts down the reactor, a process called scramming. The usual method
of scramming is to insert the control rods rapidly into the core. A leak or
break in a reactor water pipe could have dangerous consequences if it results
in a loss of coolant. Even after a reactor has been shut down, the radioactive
materials remaining in the reactor core can become so hot without sufficient
coolant that the core melts. This condition, called a meltdown, could result
in the release of dangerous amounts of radiation. In most cases, the large
containment structure that houses a reactor would prevent radioactive material
from escaping into the atmosphere. To prevent such an accident from occurring,
all reactors are equipped with an emergency core cooling system, which
automatically floods the core with water in case of a loss of coolant. Wastes
and waste disposal. The fissioning of U-235 produces more neutrons than are
needed to continue a chain reaction. Some of them combine with U-238 nuclei,
which far outnumber U-235 nuclei in the reactor fuel. When U-238 captures a
neutron, it is changed into U-239. The U-239 then decays into neptunium 239
(Np-239), which decays into plutonium 239 (Pu-239). This same process forms
Pu-239 in a breeder reactor. Slow neutrons can fission Pu-239, as well as
U-235. Some of the newly formed Pu-239 is thus fissioned during the fissioning
of U-235. Even in small amounts, plutonium can cause cancer or genetic damage
in human beings. Larger amounts can cause radiation sickness and death. Safe
disposal of these wastes is one of the most difficult problems involved in
nuclear power. Most nuclear plants need to replace their fuel assemblies only
about once a year. The radioactive wastes generate heat, and so used fuel
assemblies must be cooled after removal from a reactor. Nuclear plants cool
the assemblies by storing them underwater in specially designed storage pools.
In the United States, the federal government is working on guidelines for the
safe and permanent disposal of nuclear wastes. The current U.S. plan calls for
isolating long-lived radioactive waste from the environment in underground
storage sites. A law passed by Congress in 1982 required the federal
government to build two sites for nuclear wastes from commercial power plants.
In 1987, the law was changed to require a single site. A storage site for
nuclear waste must lie in a highly stable area that is free of earthquakes,
faulting, and other geologic activity. The site must be dry so that the waste
containers cannot be corroded and water supplies cannot be contaminated. The
site also must be constructed so that future generations do not dig into it
and release radioactivity. The government is studying the suitability of a
location in Nevada. In the meantime, commercial nuclear power plants in the
United States continue to store used fuel assemblies and other wastes in pools
of water on the plant grounds. Other countries, including Japan, Russia, and
the United Kingdom, are pursuing a reprocessing plan. Under this plan, nuclear
plants would ship their used fuel assemblies to the reprocessing plants for
removal of Pu-239 and unused U-235. These radioactive isotopes would then be
recycled into fuel for nuclear reactors. However, this method would leave
radioactive isotopes in the chemical solutions used for reprocessing. These
solutions would have to be changed into a solid form that could be safely
stored. In every country that has a nuclear energy industry, the government
plays a role in the industry. But the government's role varies greatly among
countries. This section deals mainly with the U.S. and Canadian nuclear energy
industries. Organization of the industry. Private utility companies own most
of the nuclear power plants in the United States. The rest are publicly owned.
Private companies also manufacture reactors, mine uranium, and handle most
other aspects of U.S. nuclear power production. Canada's nuclear power plants
are all publicly owned. Atomic Energy of Canada Limited (AECL), a government
corporation, has overall responsibility for the country's nuclear research and
development program. AECL also designs the CANDU (CANada Deuterium
oxide-Uranium) heavy water reactors used by all Canadian nuclear plants.
Private companies make the various reactor parts and mine and process the
country's uranium. Canada has no uranium enrichment plants because CANDU
reactors operate with unenriched uranium fuel. The industry and the economy.
The main economic advantage of nuclear power plants is that this fuel is less
expensive than fossil fuels. But nuclear plants cost somewhat more to build
than do fossil-fuel plants. Under normal economic conditions, a nuclear
plant's savings in fuel eventually make up for its higher construction
expenses. At first, these expenses add to the cost of producing electricity.
But after some years, a plant will have paid off its construction costs. It
can then produce electricity more cheaply than a fossil-fuel plant can. But
two main problems--sharply higher costs and equipment failures--have somewhat
lessened this long-run economic advantage of nuclear power plants. Many
nuclear plants in the United States have had to shut down for months at a time
because of equipment failures. Such losses of operating time further add to
the cost of producing electricity. The industry and the environment. Unlike
fossil-fuel plants, nuclear plants do not release solid or chemical pollutants
into the atmosphere. A nuclear plant releases small amounts of radioactive gas
into the air. In addition, the cooling water used in pressurized water plants
picks up a small amount of radioactive tritium in the steam condenser. The
tritium remains in this water when it is returned to a river or lake. But
these small amounts of radiation released into the environment are not
believed to be harmful. Thermal pollution remains a problem at some nuclear
plants. But cooling towers help correct this problem. In a small number of
nuclear accidents, hazardous amounts of radiation have been released into the
atmosphere. Accidental releases of radioactive substances have occurred in
Russia, the United States, and the United Kingdom; and an especially serious
accident occurred in 1986 at the Chernobyl nuclear power plant in Ukraine
(then part of the Soviet Union). The subsection Hazards and safeguards that
appears earlier in this article discusses the main methods of guarding against
accidents. Critics of nuclear power also fear another danger to the
environment. As power production increases, the creation of high-level
radioactive wastes also increases. The United States has no permanent storage
place for such wastes. The problem of storing radioactive wastes is discussed
in the subsection Wastes and waste disposal. Government regulation. The
Nuclear Regulatory Commission (NRC), an agency of the federal government,
regulates nonmilitary nuclear power production in the United States. One of
the NRC's main duties is to ensure that nuclear power plants operate safely,
and it makes and enforces a variety of safety standards. Every nuclear reactor
and power plant must be inspected and licensed by the NRC before it may begin
operations. The NRC also supervises the manufacture and distribution of
nuclear fuels, and controls the disposal of radioactive wastes from commercial
production. The Atomic Energy Control Board, a Canadian government agency,
regulates Canada's nuclear energy industry. The board's duties resemble those
of the Nuclear Regulatory Commission. Careers in nuclear energy cover a wide
range of occupations and require widely varying amounts of training. A high
percentage of the jobs require a college degree or extensive technical
education. Many of these jobs are in large research laboratories, which work
to improve nuclear processes and to lessen their hazards. Other careers
requiring advanced training are in such areas as uranium mining and
processing, reactor manufacturing and inspection, power plant operation, and
government regulation. In 1972, scientists discovered that a natural chain
reaction had released nuclear energy nearly 2 billion years ago in a uranium
deposit in west-central Africa. Two billion years ago, there had been so
little radioactive decay that the ore contained enough U-235 for a chain
reaction. An accumulation of ground water acted as a moderator to begin the
reaction. As heat from the reaction changed the water into steam, less and
less water was available to serve as a moderator and the reaction died out.
Except for such rare natural occurrences, nuclear energy was not released on a
large scale on the earth until 1942. That year, scientists produced the first
artificially created chain reaction. Scientific discoveries that took place
within the last 100 years led to the large-scale release of nuclear energy.
Early developments Before the late 1800's, scientists did not suspect that
atoms could release nuclear energy. Then in 1896, the French physicist Antoine
Henri Becquerel found that uranium constantly gives off energy in the form of
invisible rays. He thus became the discoverer of radioactivity. Other
scientists soon began experiments to learn more about this mysterious
phenomenon. The beginning of nuclear physics. In 1898, the great British
physicist Ernest Rutherford identified two kinds of radioactive "rays," which
he called alpha rays and beta rays. He and other researchers later showed that
these rays are actually high-energy particles, which became known as alpha and
beta particles. Experiments with these particles then led Rutherford to
discover the atom's nucleus. This achievement, which Rutherford announced in
1911, marked the beginning of a new science--nuclear physics. About 1914,
scientists began doing experiments to see what happens when nuclear particles
collide. The experimenters used alpha particles from naturally radioactive
materials to bombard the nuclei of light atoms. Light nuclei do not repel
positively charged particles, such as alpha particles, as strongly as heavy
nuclei do. Rutherford used this method to produce the first artificial
transmutations in a series of experiments from 1917 to 1919. He bombarded
nitrogen atoms with alpha particles. In rare collisions, a nitrogen 14 nucleus
absorbed an alpha particle (a helium 4 nucleus). At the same time, the alpha
particle pushed a proton out of the nitrogen nucleus. The nucleus thereby
became an oxygen 17 nucleus. Artificial fission. To produce nuclear reactions
in heavy nuclei, scientists needed a particle that heavy nuclei would not
repel. In 1932, the British physicist James Chadwick discovered such a
particle--the neutron. In 1938, two German radiochemists, Otto Hahn and Fritz
Strassmann, reported they had produced the element barium by bombarding
uranium with neutrons. At first, scientists could not explain how uranium had
produced barium, which is much lighter than uranium. All previous
transmutations had resulted in an element about as heavy as the original one.
Then in 1939, the Austrian physicist Lise Meitner and her nephew Otto Frisch
showed that Hahn and Strassman had in fact produced the first known artificial
fission reaction. A uranium nucleus had split into two nearly equal fragments,
one of which consisted of a barium nucleus. Two neutrons were also emitted.
The other fragment consisted of a nucleus of krypton, a somewhat lighter
element than barium. These two nuclei, together with the emitted neutrons, are
lighter than a uranium nucleus and a neutron. The reaction had therefore
produced more energy than it consumed. Scientists soon realized that if many
uranium nuclei could be made to fission, a tremendous amount of energy would
be released. The amount of energy could be calculated from a theory developed
by the great German-born physicist Albert Einstein in 1905. The theory shows
that matter can change into energy and that matter and energy are related by
the equation E equals m times c-squared. This equation states that the energy
(E) into which a given amount of matter can change equals the mass (m) of that
matter multiplied by the speed of light squared (c-squared). The speed of
light squared is obtained by multiplying the speed of light by itself. Using
this equation, scientists determined that the fissioning of 1 pound (0.45
kilogram) of uranium would release as much energy as 8,000 short tons (7,300
metric tons) of TNT. Uranium could therefore be used to make a powerful bomb.
The beginning of the nuclear age The development of nuclear weapons. World War
II broke out in Europe in September 1939. The month before, Einstein had
written to U.S. President Franklin D. Roosevelt urging him to commit the
United States to developing an atomic bomb. Einstein had fled to the United
States from Germany to escape Nazi persecution. He warned Roosevelt that
German scientists might already be working on a nuclear bomb. Roosevelt acted
on Einstein's urging, and early in 1940 scientists received the first funds
for uranium research in the United States. The United States entered World War
II in 1941. The government then ordered an all-out effort to build an atomic
bomb and in 1942 established the top-secret Manhattan Project to achieve this
goal. A group of scientists at the University of Chicago had charge of
producing plutonium for the Manhattan Project. The group included such noted
physicists as Enrico Fermi, Leo Szilard, and Eugene Wigner, all of whom had
been born in Europe and had settled in the United States. Fermi headed the
group. Under the scientists' direction, workers built an atomic pile, or
reactor, beneath the stands of the university athletic field. The pile
consisted of 50 short tons (45 metric tons) of natural uranium oxide and
uranium embedded in 500 short tons (450 metric tons) of graphite. The graphite
served as a moderator. The pile was designed to demonstrate a controlled
nuclear chain reaction in the uranium. Cadmium rods controlled the reaction.
On Dec. 2, 1942, this reactor produced the first artificial chain reaction.
The success of the University of Chicago project led the U.S. government to
build a plutonium-producing plant in Hanford, Wash. The government also built
a uranium enrichment plant in Oak Ridge, Tenn. Plutonium and greatly enriched
uranium from these plants were used in the two atomic bombs that the United
States dropped on Japan in August 1945. After World War II, scientists began
work on developing a hydrogen bomb. The United States exploded the first
hydrogen bomb in 1952 and so achieved the world's first large-scale
thermonuclear reaction But the AEC became responsible for regulating the
nuclear energy industry. It also kept control in such areas as uranium
enrichment and waste disposal. The United States made the world's first
full-scale use of controlled nuclear energy in 1954. That year, the U.S. Navy
launched the first nuclear-powered vessel, the submarine Nautilus. The world's
first full-scale nuclear power plant began operations in 1956 at Calder Hall
in northwestern England. In 1957, the first large-scale nuclear plant in the
United States opened in Shippingport, Pa. It supplied electricity to the
Pittsburgh area until 1982, when the plant was closed. Canada opened its first
full-scale plant in 1962 at Rolphton, Ont. The successful start of the nuclear
power industry convinced world leaders of the need for international
cooperation in the field. In 1957, the United Nations (UN) established the
International Atomic Energy Agency to promote the peaceful uses of nuclear
energy. Also in 1957, Belgium, France, Italy, Luxembourg, the Netherlands, and
West Germany formed the European Atomic Energy Community (Euratom). The
organization encourages the development of nuclear power among its member
countries. Denmark, the United Kingdom, and Ireland joined Euratom in 1973.
The spread of nuclear capability During the 1960's and early 1970's, a number
of countries acquired reactors and used them to start nuclear power
development. Progress was also made during this period toward limiting nuclear
weapons tests and stopping the spread of nuclear weapons. In 1970, for
example, a nuclear nonproliferation treaty went into effect. The treaty
prohibits the nuclear powers that have agreed to abide by the document from
giving nuclear weapons to nations that do not already have them. The
nonproliferation treaty also prohibits nations without nuclear weapons from
acquiring them. But the nonproliferation treaty does not prohibit nations from
selling or buying nuclear reactors. A reactor can be used not only for
peaceful purposes but also to produce plutonium for nuclear weapons. India
used a research reactor for this purpose and in 1974 exploded its first atomic
bomb. Canada had supplied the reactor to India with the understanding it would
be used for peaceful purposes only. Canada has signed the nonproliferation
treaty, but India has not. Critics of India's action question the wisdom of
supplying reactors to countries that do not already have them. Meanwhile, the
United States had been greatly increasing its nuclear power capacity. But
opposition to nuclear power development also increased in the United States
during the late 1960's and early 1970's. Critics began to question nearly
every aspect of nuclear power production, from the cost of uranium enrichment
to the problems of waste disposal. Many critics of the United States nuclear
program charged that the government overlooked various safety risks at nuclear
plants to promote nuclear power development. Partly as a result of such
criticism, Congress disbanded the Atomic Energy Commission (AEC) in 1974 and
divided its functions between two newly formed agencies. The Energy Research
and Development Administration (ERDA) took over the AEC's development
programs. The Nuclear Regulatory Commission (NRC) took over its regulatory
duties. The NRC, it was believed, could better regulate the industry if it was
not also responsible for the industry's growth and development. In 1977,
Congress abolished ERDA and transferred its responsibilities to the newly
created Department of Energy. Safety concerns There have been a number of
accidents at nuclear power plants. Most of them have not been serious.
However, in 1957, a fire at the Windscale plutonium production plant in
northern England resulted in the release of a large quantity of radioactivity.
The British government banned the sale of milk from cows in that part of
England for more than a month after the fire. In the United States, concerns
about the safety of nuclear reactors increased after a serious accident in
1979 at the Three Mile Island nuclear power plant near Harrisburg,
Pennsylvania. Mechanical and human failures resulted in a breakdown of the
reactor's cooling system and the destruction of the reactor core. Scientists
and technicians prevented a failure of the reactor vessel that might have
released large amounts of radioactive isotopes into the reactor containment
building. Cleanup of the plant was completed in the early 1990's. The worst
nuclear accident in history occurred in 1986 at the Chernobyl nuclear power
plant near Kiev in Ukraine, which was then part of the Soviet Union. An
explosion and fire ripped apart the reactor and released large amounts of
radioactive isotopes into the atmosphere. Unlike most Western reactors, the
Chernobyl reactors lacked an enclosure to prevent radioactive isotopes from
escaping. Soviet officials reported that 31 people died from radiation
sickness or burns and more than 200 others were seriously injured. The
radioactive substances spread over parts of what are now Ukraine, Russia, and
Belarus, and were carried by wind into northern and central Europe. Experts
expected a significant increase in the number of cancer deaths among those
near the reactor. But they predicted that the health effects outside the
Chernobyl area would be slight. As a result of the accidents at Three Mile
Island and Chernobyl, opposition to nuclear power increased in many countries
during the late 1980's. In the United States, the NRC tightened its control of
nuclear plants. Experts have expressed particular concern over the safety of
older Soviet-designed reactors now operating in Russia, Ukraine, and several
countries of the former Soviet bloc. Western scientists and engineers are
helping to remedy some of the most urgent safety problems in these reactors.
As the nuclear power industry has continued to develop, many improvements in
plant equipment and operation have increased safety. Nonetheless, some experts
insist that the next generation of reactors should take greater advantage of
design features that rely less--or not at all--on mechanical equipment such as
pumps and valves to remove heat if an accident occurs. Some of these reactors
are known as passively safe reactors.
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