08 September 2009

Nuclear power plant




The invention: 

The first full-scale commercial nuclear power plant, which gave birth to the nuclear power industry.  



The people behind the invention:

Enrico Fermi (1901-1954), an Italian American physicist who
won the 1938 Nobel Prize in Physics
Otto Hahn (1879-1968), a German physical chemist who won the
1944 Nobel Prize in Chemistry
Lise Meitner (1878-1968), an Austrian Swedish physicist
Hyman G. Rickover (1898-1986), a Polish American naval officer




Discovering Fission

Nuclear fission involves the splitting of an atomic nucleus, leading
to the release of large amounts of energy. Nuclear fission was
discovered in Germany in 1938 by Otto Hahn after he had bombarded
uranium with neutrons and observed traces of radioactive
barium. When Hahn’s former associate, Lise Meitner, heard of this,
she realized that the neutrons may have split the uranium nuclei
(each of which holds 92 protons) into two smaller nuclei to produce
barium (56 protons) and krypton (36 protons). Meitner and her
nephew, Otto Robert Frisch, were able to calculate the enormous energy
that would be released in this type of reaction. They published
their results early in 1939.
Nuclear fission was quickly verified in several laboratories, and
the Danish physicist Niels Bohr soon demonstrated that the rare uranium
235 (U-235) isotope is much more likely to fission than the common
uranium 238 (U-238) isotope, which makes up 99.3 percent of
natural uranium. It was also recognized that fission would produce
additional neutrons that could cause new fissions, producing even
more neutrons and thus creating a self-sustaining chain reaction. In
this process, the fissioning of one gram of U-235 would release about
as much energy as the burning of three million tons of coal.
The first controlled chain reaction was demonstrated on December
2, 1942, in a nuclear reactor at the University of Chicago, under
 the leadership of Enrico Fermi. He used a graphite moderator to
slow the neutrons by collisions with carbon atoms. “Critical mass”
was achieved when the mass of graphite and uranium assembled
was large enough that the number of neutrons not escaping from
the pile would be sufficient to sustain a U-235 chain reaction. Cadmium
control rods could be inserted to absorb neutrons and slow
the reaction.
It was also recognized that the U-238 in the reactor would absorb
accelerated neutrons to produce the new element plutonium, which
is also fissionable. During World War II (1939-1945), large reactors
were built to “breed” plutonium, which was easier to separate than
U-235. An experimental breeder reactor at Arco, Idaho, was the first
to use the energy of nuclear fission to produce a small amount of
electricity (about 100 watts) on December 20, 1951.


Nuclear Electricity

Power reactors designed to produce substantial amounts of
electricity use the heat generated by fission to produce steam or
hot gas to drive a turbine connected to an ordinary electric generator.
The first power reactor design to be developed in the United
States was the pressurized water reactor (PWR). In the PWR, water
under high pressure is used both as the moderator and as the coolant.
After circulating through the reactor core, the hot pressurized
water flows through a heat exchanger to produce steam. Reactors
moderated by “heavy water” (in which the hydrogen in the water
is replaced with deuterium, which contains an extra neutron) can
operate with natural uranium.
The pressurized water system was used in the first reactor to
produce substantial amounts of power, the experimental Mark I
reactor. It was started up on May 31, 1953, at the Idaho National
Engineering Laboratory. The Mark I became the prototype for the
reactor used in the first nuclear-powered submarine. Under the
leadership of Hyman G. Rickover, who was head of the Division of
Naval Reactors of the Atomic Energy Commission (AEC), Westinghouse
Electric Corporation was engaged to build a PWR system
to power the submarine USS Nautilus. It began sea trials in January
of 1955 and ran for two years before refueling.
In the meantime, the first experimental nuclear power plant for
generating electricity was completed in the Soviet Union in June of
1954, under the direction of the Soviet physicist Igor Kurchatov. It
produced 5 megawatts of electric power. The first full-scale nuclear
power plant was built in England under the direction of the British
nuclear engineer Sir Christopher Hinton. It began producing about
90 megawatts of electric power in October, 1956.
 On December 2, 1957, on the fifteenth anniversary of the first controlled
nuclear chain reaction, the Shippingport Atomic Power Station
in Shippingport, Pennsylvania, became the first full-scale commercial
nuclear power plant in the United States. It produced about
60 megawatts of electric power for the Duquesne Light Company until
1964, when its reactor core was replaced, increasing its power to
100 megawatts with a maximum capacity of 150 megawatts.


Consequences

The opening of the Shippingport Atomic Power Station marked
the beginning of the nuclear power industry in the United States,
with all of its glowing promise and eventual problems. It was predicted
that electrical energy would become too cheap to meter. The
AEC hoped to encourage the participation of industry, with government
support limited to research and development. They encouraged
a variety of reactor types in the hope of extending technical
knowledge.
The Dresden Nuclear Power Station, completed by Commonwealth
Edison in September, 1959, at Morris, Illinois, near Chicago,
was the first full-scale privately financed nuclear power station in
the United States. By 1973, forty-two plants were in operation producing
26,000 megawatts, fifty more were under construction, and
about one hundred were on order. Industry officials predicted that
50 percent of the nation’s electric power would be nuclear by the
end of the twentieth century.
The promise of nuclear energy has not been completely fulfilled.
Growing concerns about safety and waste disposal have led to increased
efforts to delay or block the construction of new plants. The
cost of nuclear plants rose as legal delays and inflation pushed costs
higher, so that many in the planning stages could no longer be competitive.
The 1979 Three Mile Island accident in Pennsylvania and
the much more serious 1986 Chernobyl accident in the Soviet Union
increased concerns about the safety of nuclear power. Nevertheless,
by 1986, more than one hundred nuclear power plants were operating
in the United States, producing about 60,000 megawatts of
power. More than three hundred reactors in twenty-five countries
provide about 200,000 megawatts of electric power worldwide.
 Many believe that, properly controlled, nuclear energy offers a
clean-energy solution to the problem of environmental pollution.


See also : Breeder reactor; Compressed-air-accumulating power
plant; Fuel cell; Geothermal power; Nuclear reactor; Solar thermal
engine; Nuclear power plant

 Further Reading :


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