Nuclear physics and nuclear engineering have been the most sensitive and sophisticated fields in science for half a century.

 The fuel used by nuclear power plants is uranium,  a metallic element that is found in nature under the form of oxides as a component of several minerals.  These oxides (general formula U₃O₈) can be separated from the minerals, obtaining what is known as “yellow cake”. Further processes allow the obtaining of Uranium Dioxide (UO₂), with which the fuel rods are made.

 The most abundant isotope of the uranium, ²³⁸U, is not fissionable, whereas the fissionable isotope ²³⁵U represents only 0.7% of the element’s total mass.

 In order for the fission process to take place, the energy of the neutrons has to be reduced by means of a moderator, making it impossible for a chain reaction to occur in natural conditions.

 This problem has two solutions, and each gives birth to a line of reactors: the natural uranium reactors and the enriched uranium reactors.

 The natural uranium reactors use a moderator in order to slow the neutrons down to the energy required (“thermal neutrons”) for their absorption by the ²³⁵U nuclei, starting and maintaining the chain reaction. Water would be a good moderator but it has the disadvantage of absorbing neutrons. On the other hand, heavy water (D₂O) and graphite are suitable moderators.

 The other line of reactors relies on the process of “enrichment” of uranium, that is to say, to increase the percentage of the fissionable ²³⁵U in the fuel’s total mass. The most commonly used technologies are gaseous diffusion and centrifuging. This high percentage of  ²³⁵U makes it possible for the chain reaction to be maintained by the un-moderated, fast neutrons.

 The heat produced by the nuclear reaction is used to boil water into steam and drive an electricity generating turbine.

 The world’s known uranium reserves are large. The mineral is economically classified in groups according to the uranium extraction cost. The cost of the fuel at a nuclear power plant approximately amounts to only 1% of the revenue of the generated electricity, thus making its operation not very dependable on the fuel prices.