Nuclear power
...
explains how nuclear power reactors use a controlled fission reaction to produce
power.
Nuclear reactors have been producing electricity since the 1950s and, in early
2003, there were 441 nuclear reactors operating in 30 countries with a total
installed capacity of 359 GW.
Nuclear reactors
Nuclear reactors depend on a reaction between neutrons and the atomic nuclei
of the fuel for their operation. Uranium, the fuel for almost all reactors, consists
principally of two isotopes, uranium-235 and uranium-238.
In natural uranium,
the fuel for early reactors, those isotopes are in the proportion of 0.7 per
cent and 99.3 per cent, respectively, by weight.
The enriched uranium used in
most currently operating reactors contains
about 2.5 per cent of uranium-235.
Energy is released when a uranium-235 nucleus absorbs a neutron and undergoes
fission, that is, it splits into two large energetic fragments or fission products,
accompanied by the release of several high energy or fast neutrons and some gamma
radiation.
The neutrons are slowed in the reactor so that they induce further
fissions in the uranium-235. Such neutrons are often called thermal neutrons
and the reactors that rely upon them thermal reactors.
