انرژی ها نو

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to keep radioactive gases or liquids from getting out. The
core and moderator lie inside a strong steel container called a
pressure vessel. The vessel is usually located in a solid, airtight
building known as a containment structure. The containment

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ENRICO FERMI
Enrico Fermi was responsible
for the fi rst controlled chain
reaction. Fermi was born in
Rome, Italy, in 1901. He became
a physics professor at the
University of Rome at the age
of 26. In 1938, he won the
Nobel Prize—which is awarded
each year for achievements in
different branches of science
and other areas—for his work
on radioactivity and nuclear
reactions involving neutrons.
That same year, he moved to the
United States.
During World War II, the
U.S. government began a secret
program called the Manhattan
Project to develop the atomic
bomb. Fermi played an important
role in the program. As part
of the project, the world’s fi rst
controlled fi ssion chain reaction
took place in a reactor. Fermi headed the effort to achieve the chain
reaction, which occurred on December 2, 1942. Fermi died of
cancer in 1954. The element fermium was named in his honor

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structure is typically made of concrete and steel. Its walls may
be 3 to 6 feet (1 to 2 meters) thick. If an accident occurs in the
reactor, the containment structure helps keep radioactivity from
escaping into the environment.
Pressurized water reactors have two water systems. One
pumps water through the reactor core under high pressure,
to keep the water from boiling. The fl owing water acts as a

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coolant. It picks up heat from the core and carries the heat to a
device called a heat exchanger. There, the heat is transferred
to the second water system. This causes the water in the second
system to boil, forming steam. The steam is used to make a
turbine turn, which causes a generator to produce electricity.
Boiling water reactors have just one water system. The same
water that passes through the core forms the steam that drives
the turbine.
Scientists in Canada invented another type of reactor known
as the CANDU reactor. (The name comes from CANada

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Deuterium Uranium.) This type of reactor is now used in
Canada as well as some other countries. It is a special kind of
pressurized water reactor that uses so-called heavy water as
a moderator and coolant. All water is made of hydrogen and
oxygen. Ordinary water, or “light” water, uses mainly the most
common hydrogen isotope. Heavy water, however, has a high
percentage of a heavier hydrogen isotope called deuterium.
As a result, heavy water is about 10 percent heavier than light
water. Also, heavy water is a fine moderator because it is very
good at slowing neutrons down for use in fission. It is so good
that the CANDU reactor can use natural, unenriched uranium
as fuel

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The Case for
Nuclear Power


An ideal source of energy would be
low in cost and readily available. It
would be safe and would not harm the
environment. It would provide as much energy
as people need at any time of day and on any day
of the year. In addition, the energy source would continue to
be reliable in the future. No current power source can satisfy all
these requirements. Modern nuclear plants, however, make a
reasonably good attempt.
Environment and Safety Issues
Nuclear power plants do not produce the emissions that
come from burning fossil fuels. Thus, nuclear power does not
contribute to the climate change or some of the other problems
that have been associated with fossil fuels.
Uranium mining and related work can release polluting
substances. With modern methods, however, the amount of
pollutants released is small. Radioactivity is another concern
about mining. Uranium ore gives off radiation, but not very
much. Most of the uranium contained in the ore is U-238,
which is not very radioactive.
Workers in underground mines face an extra risk. Uranium
ore gives off a radioactive gas called radon. Radon is released
naturally from the ground in small amounts in many parts of
the world and typically disperses (scatters) in the air. In the

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closed-in space of an underground mine, however, radon may
accumulate to a dangerous level. A good ventilation system is
needed. Today, uranium mining is often done in a different way
that helps avoid the danger of radon. Uranium is taken from an
open pit at the surface of the ground. This allows the radon to
disperse in the air.
People concerned about the safety of nuclear plants
often point to the dangerous radioactivity contained in the
plants. Modern plants are specially designed to prevent the
radioactivity from leaking out. In addition, plant workers
follow strict safety rules. Thus, while the plants do produce
radioactive waste, much is done to keep the radioactivity
away from the general environment. In addition, in many ways,
the nuclear power industry has been safer and cleaner than the
industries associated with other power sources, such as coal.
Power Galore
The number of people in the world keeps growing. So does the
demand for electricity. The world has to find ways to supply

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more electricity. Nuclear power could be a big help since
nuclear plants are capable of producing a large amount of
electricity. In 2008, the world had only a few hundred nuclear
plants, but they accounted for 15 percent of its electricity. There
are both large and small nuclear plants. An average plant may
have a capacity of 1,000 megawatts (a megawatt is a unit of
measurement for the rate at which electrical energy is used).
That is enough to provide electricity for hundreds of thousands
of homes.
The Palo Verde nuclear power plant in Arizona has three
reactors, each with a capacity about 1,200 to 1,300 megawatts.
The small Fort Calhoun plant in Nebraska has a single reactor
with a capacity of less than 500 megawatts. Power plants in
the United States that use coal vary in capacity from a few
megawatts to more than 2,000 megawatts.
People worry about running out of fossil fuels, but they do
not need to worry about running out of nuclear fuels. Earth

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does not have an endless amount of uranium, but it has a great
deal. In 2007, experts believed there was enough uranium to
last at least another 100 years. Building more effi cient reactors
will probably make the supply last much longer. Additional
nuclear fuel can be gotten from the reprocessing of spent fuel
and nuclear material from decommissioned weapons. Still
more fuel can be obtained from breeder reactors.

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Considering the Alternatives
Solar power, wind power, geothermal power, and water power
are clean and renewable. Currently, the fi rst three supply only a
tiny portion of the world’s electricity—approximately 2 percent
in the year 2005. Water power supplies slightly more than the
amount produced by nuclear power. Water power, however, is
available only in certain areas.
Many people would like to see solar and wind power largely
replace fossil fuels as primary sources for electricity. For that to
happen, solar and wind power would have to become cheaper