NUCLEAR POWER PLANT:
Nuclear power is the
use of sustained Nuclear fission to generate heat and do useful
work. Nuclear Electric Plants, Nuclear Ships and Submarines use controlled
nuclear energy to heat water and produce steam, while in
space, nuclear energy decays naturally in a radioisotope thermoelectric
generator. Scientists are experimenting with fusion
energy for future generation, but these experiments do not currently generate
useful energy.
Nuclear power provides about 6%
of the world's energy and 13–14% of the world's electricity, with the U.S., France, and Japan together accounting for about 50% of
nuclear generated electricity. Also, more than 150 naval vessels using nuclear propulsion have been built.
Just as many conventional thermal power stations generate electricity
by harnessing the thermal energy released from burning fossil
fuels, nuclear power plants convert the energy released from the nucleus of
an atom, typically via nuclear fission.
Nuclear reactor technology
When a relatively large fissile atomic
nucleus (usually uranium-235 or plutonium-239)
absorbs a neutron,
a fission of the atom often results. Fission splits the atom into two or more
smaller nuclei with kinetic
energy (known as fission products) and also releases gamma
radiation and free neutrons.[59]
A portion of these neutrons may later be absorbed by other fissile atoms and
create more fissions, which release more neutrons, and so on.
This nuclear chain reaction can be controlled by
using neutron poisons and neutron moderators to change the portion of
neutrons that will go on to cause more fissions.[60]
Nuclear reactors generally have automatic and manual systems to shut the
fission reaction down if unsafe conditions are detected.
Three nuclear
powered ships, (top to bottom) nuclear cruisers USS Bainbridge and USS Long Beach with USS Enterprise the first nuclear
powered aircraft carrier in 1964. Crew members are spelling out Einstein's
mass-energy equivalence formula E = mc2
on the flight deck.
There are many different reactor
designs, utilizing different fuels and coolants and incorporating different
control schemes. Some of these designs have been engineered to meet a specific
need. Reactors for nuclear submarines and large naval ships, for
example, commonly use highly enriched uranium as a fuel. This
fuel choice increases the reactor's power density and extends the usable life
of the nuclear fuel load, but is more expensive and a greater risk to nuclear
proliferation than some of the other nuclear fuels.
A number of new designs
for nuclear power generation, collectively known as the Generation IV reactors, are the subject of
active research and may be used for practical power generation in the future.
Many of these new designs specifically attempt to make fission reactors
cleaner, safer and/or less of a risk to the proliferation of nuclear weapons. Passively safe plants (such as the ESBWR) are available to
be builtand other designs that are believed to be nearly fool-proof are being
pursued. Fusion reactors, which may be viable in the future,
diminish or eliminate many of the risks associated with nuclear fission. There
are trades to be made between safety, economic and technical properties of
different reactor designs for particular applications. Historically these
decisions were often made in private by scientists, regulators and engineers,
but this may be considered problematic, and since Chernobyl and Three Mile
Island, many involved now consider informed consent and morality should be
primary considerations.
Cooling system
A cooling system removes
heat from the reactor core and transports it to another area of the plant,
where the thermal energy can be harnessed to produce electricity or to do other
useful work. Typically the hot coolant will be used as a heat source for a boiler, and the
pressurized steam from that boiler will power one or more steam
turbine driven electrical generators.
Flexibility of nuclear power plants
It is often claimed that
nuclear stations are inflexible in their output, implying that other forms of
energy would be required to meet peak demand. While that is true for the vast
majority of reactors, this is no longer true of at least some modern designs.
Nuclear plants are routinely used in load following mode on a large scale in
France. Unit A at the German Biblis Nuclear Power Plant is designed
to in- and decrease his output 15 % per minute between 40 and 100 %
of it's nominal power. Boiling water reactors normally have load-following
capability, implemented by varying the recirculation water flow.
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