Nuclear Fusion Energy

By David Arez, 12ºD
Escola Secundária de Loulé

Nuclear energy can be obtained from the fission of heavy nuclei with formation of smaller nuclei or by nuclear fusion where the energy the released when two nuclei come together to form a new nucleus of a greater number of mass.

At this moment, major research is trying to build a nuclear reactor that could be used in future to produce nuclear fusion using the conversion of hydrogen into helium, usually from using deuterium as fuel.

The reactions of formation of helium by fusion only occur spontaneously at temperatures of about 10⁸ K. This creates great difficulties regarding the confinement of the material in a reaction chamber, since its not possible to have any solid material at this temperature. In fact, at these temperatures atoms are totally ionized into free electrons and nuclei, forming a state of matter called plasma.

To confine the nuclear reaction site several tests have been conducted in special reactors, and there are two common techniques for confinement.
The first is by magnetic confinement applying magnetic fields to trap the particles in the plasma.

Tokamak. A reactor of magnetic confinement. (Image credit: General Atomics)

The second is by inertial confinement, bombarding small amounts of nuclear fuel with nuclei that will induce the reaction and using laser beams coming from many directions in order to maintain the plasma confined in a region away from the walls of the reactor.

Inertial confinement using laser beam

The usual reaction is the deuterium-tritium fusion

The neutrons released in the reaction are received by the walls of the reactor and because they aren’t charged they can not be confined. These neutrons carry much of the energy released in nuclear reaction as kinetic energy.

Usually the material used to capture this energy is merged lithium. Lithium suffers neutron capture through the reaction

To confine a nucleus reaction occurs where trials have been conducted in which the kinetic energy of tritium and of the alpha particles is converted into energy inside the lithium merged which will then serve to heat the water connected to a turbine. Another advantage of using lithium is that the tritium is then easily separated once again be used as fuel, and therefore only catalytic amounts would be necessary under ideal conditions.

The advantages of nuclear fission consist of three fundamental aspects:

1. Abundant and cheap fuel (typically deuterium);
2. Impossibility of accidents due to leakage (when temperature gets lower the reaction stops);
3. It is clean and does not produce radioactive waste. The biggest drawback is the shortage of lithium and that therefore new ways of converting the kinetic energy of neutrons are required.

Presently huge efforts are being made to solve the engineering problems that need to be solved in order to make this source of energy a cost-effective and safe source that will hopefully be used in the second half of the twenty-first century.