They're both nuclear reactions (i.e., they change the
structure of an atomic nucleus) and they both represent what happens when
Einstein's famous E = mc(squared) is acted out. In fission, which is
behind atomic bombs, nuclear reactors, and radioactivity, the nucleus of a big uranium atom
is split into smaller parts when struck by a free neutron. Uranium is the fuel
of choice because it "splinters" readily, releasing two or three more
neutrons, which in turn strike and splinter neighboring uranium nuclei in a chain
reaction. The result: energy; also, Chernobyl.
In fusion, which is behind starlight, sunshine, and the
hydrogen (aka. thermonuclear) bomb, and which scientists hope someday to adapt
to nuclear-energy production, the nuclei of two little hydrogen atoms are
joined together, or fused, at temperatures approaching 50,000,000 Celsius, to
form a single, heavy helium nucleus, ejecting high-speed neutrons (and
impressively little pollution) in the process. In both fission and fusion, the
atoms resulting from the splitting and the joining, respectively, weigh
slightly less than the ones that went into the process. It's this difference in
mass that has been converted into energy.
So why not forget dangerous, dirty fission and get behind
controllable, clean fusion? Because fusion, while it works nicely on the sun,
requires temperatures higher than we've in general been able to achieve here on
earth except, so far, in the hydrogen bomb, which is triggered by fission -- in
the form of an atomic bomb -- at its core anyway. It's true that in late 1993
an experimental fusion reactor at Princeton produced a few megawatts of power
for a fraction of a second; while doing so, though, it used up more power than
it produced. Nevertheless, a number of countries, including Japan, China, the
United States, Russia, and members of the European Union [later joined by India
and South Korea] started collaborating on an International Thermonuclear
Experimental Reactor (ITER).
ITER (originally an acronym
of International Thermonuclear
Experimental Reactor and Latin for "the way" or "the
road") is an international nuclear fusion research and engineering
project, which is currently building the world's largest experimental tokamak nuclear
fusion reactor at the Cadarache facility in the south of France. The ITER
project aims to make the long-awaited transition from experimental studies of plasma
physics to full-scale electricity-producing fusion power plants. The project is
funded and run by seven member entities — the European Union (EU), India, Japan,
China, Russia, South Korea and the United States. The EU, as host party for the
ITER complex, is contributing 45% of the cost, with the other six parties
contributing 9% each.
The ITER fusion
reactor itself has been designed to produce 500 megawatts of output power for
50 megawatts of input power, or ten times the amount of energy put in. The
machine is expected to demonstrate the principle of producing more energy from
the fusion process than is used to initiate it, something that has not yet been
achieved with previous fusion reactors. Construction of the facility began in
2007, and the first plasma is expected to be produced in 2020. When ITER
becomes operational, it will become the largest magnetic confinement plasma
physics experiment in use, surpassing the Joint European Torus. The first
commercial demonstration fusion power plant, named DEMO, is proposed to follow
on from the ITER project to bring fusion energy to the commercial market. (From
‘An Incomplete Education’, by Judy Jones and William Wilson; and ‘Wikipedia’)