Introduction to nuclear energy

Nuclear energy is the energy from nuclear reactions or from the disintegration of the nuclei of some atoms. It comes from the release of energy stored in their nucleus.

A nuclear power plant is a thermoelectric plant, that is, a facility that uses a heat source to convert a liquid that circulates through a set of ducts into high-temperature steam; and that uses said steam to drive a turbine-alternator group, thus producing electrical energy.

The main difference between conventional thermoelectric plants and nuclear thermoelectric plants is the reaction that releases the energy necessary to obtain the heat source for steam production. In the case of conventional plants, it is the carbon combustion reaction (coal, gas or fuel oil), in the second, the nuclear fission reaction of uranium nuclei. In the latter case, the energy released by reaction is in the order of millions of times higher than in the first case, which explains the lower consumption of fuel and production of waste, the latter of a different nature, in a nuclear power plant compared to a conventional power plant, with equal production powers.

Fission is a reaction in which a heavy nucleus, being bombarded with neutrons, decomposes into two nuclei, whose sizes are of the same order of magnitude, with a large release of energy and the emission of two or three neutrons. These, in turn, can cause more fissions by interacting with new fissile nuclei that will emit new neutrons and so on.

This multiplier effect is known as a chain reaction. In a small fraction of a second, the number of nuclei that have fissioned releases energy 106 times greater than that obtained by burning a block of coal or exploding a stick of dynamite of the same mass. Because of the speed at which a nuclear reaction takes place, energy is released much more quickly than in a chemical reaction.

If, on the contrary, it is achieved that only one of the released neutrons produces a subsequent fission, the number of fissions that take place per second is constant and the reaction is controlled. This is the principle of operation on which nuclear reactors, which are controllable sources of nuclear fission energy, are based.

Fission reactions were discovered by Otto Hahn and Fritz Strassman in 1939, and the architect in charge of putting the idea of developing the chain reaction into practice was Enrico Fermi, who had the double condition of being a magnificent theoretician and a skilful experimenter. On December 2, 1942 he achieved, with his team, the self-sustaining fission chain reaction in the famous Chicago Pile 1, built on a squash court under the bleachers of the University of Chicago football stadium. It was a stack of approximately 7m × 7m made up of blocks of graphite (neutron moderator), crossed from side to side by bars of natural uranium (nuclear fuel) one inch in diameter.

Nuclear energy is a good solution to reduce CO2 emissions into the atmosphere, since it does not emit this polluting gas in power generation, the only thing that goes outside is water vapor through the cooling tower.