A schematic diagram of a specially designed nuclear power plant is shown in the figure.
92U235 is used as fuel. But the ore of uranium contains 99.3 % of 92U238 and only 0.7 % of 92U235. Hence ore is enriched to contain 3 % of U235. When 92U238 absorbs neutron, it converts into plutonium though the following reactions:
92U238 + 0n1 ® 92U239 ® 93Np239 + e- + n (antineutrino)
93Np239 ® 94Pu239 + e- + n (antineutrino)
Plutonium is highly radioactive and can be fission with slow neutron.
In the reactor shown, ordinary water, used as a moderator and coolant, is circulated through the core of the reactor by means of a pump. Outlet water, at 150 atm and temperature of about 600 K is passed through a steam generator. The steam produced drives the turbine connected to electric generator and the low-pressure outlet steam from the turbine is condensed, cooled and pumped back to the steam generator. Inside the reactor, some safety rods are used in addition to the controlling rods to quickly reduce the multiplication factor, k, below 1 in case of crisis.
In some specially designed reactors, uranium oxide pallets are used as fuel, which are filled in long tubes from one end to another. The tubes through which liquid moderators are circulated surround the tubes. This device forms the core of the reactor.
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