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>Like nuclear
fission, nuclear fusion releases some of the energy normally contained in
an atom's nucleus by converting some of the mass to energy in the form of
fast-moving neutrons. While energy release in fission involves splitting
nuclei, the opposite is true in fusion, where joining two nuclei produces
energy.
Starting and
sustaining the fusion process requires temperatures three times hotter
than the sun's interior. The sun itself is a large, nuclear-fusion reactor
operating on a continuous basis, and the solar energy we receive is a
byproduct of nuclear fusion.
The first controlled
fusion reactions probably will use an isotope of hydrogen – known as
tritium –bred from the element lithium.
Despite years of
research, no one yet has been able to sustain a fusion reaction in the
laboratory. But researchers believe they are progressing in several
different approaches.
One is a MAGNETIC
CONFINEMENT FUSION DEVICE WITH TORUS. The deuterium-tritium plasma whirls
around the torus, a doughnut-shaped vacuum chamber, where the magnetic
field confines and compresses the plasma. causing it to heat up, A strong
electric current from outside augments the heat. To achieve a fusion
reaction, the device must keep this plasma at 180 million degrees
Fahrenheit for about one second. The lithium blanket in the torus
transfers heat to an exchanger to produce steam and drive a
turbine-generator to produce electricity.
An alternative is
called the LASER FUSION DEVICE. Here laser beams strike the
deuterium-tritium fuel pellets as they fall into the vessel. Each
resulting fusion reaction is a small explosion that releases kinetic
energy. When this kinetic energy becomes heat, it can power a conventional
steam-turbine generator to make electricity.
Nuclear fusion has
the potential for producing great quantities of electricity from cheap and
virtually inexhaustible fuel but development is still in its infancy. Even
if scientists can solve fusion's problems, they do not expect an operating
demonstration plant before 2020. |
