Uranium is the most widely used nuclear fuel in nuclear fission reactions. It is a natural element that can be found in nature. In any case, in order to use uranium in a nuclear reactor you must undergo some treatment.
To know the particularities that makes uranium so different from the other substances, we must first consider some basic nuclear physics.
Basic physical considerations of uranium
The positive charges of the protons try to push violently outward. What prevents them from separating is a new kind of force: an immensely powerful short-range attraction force acts interchangeably between protons and neutrons (which, from this point of view, are all nucleons). The short-range nuclear force holds them together, opposing the repulsive effect of the positive charges of the protons. In this way, neutrons act as "nuclear cement."
Characteristics of uranium, an unstable element
The nucleus of a uranium atom contains 92 protons. Under these conditions the repulsive force between the protons is about to defeat the nuclear force.
If there are 146 neutrons in the nucleus of the uranium atom, it is in an unstable situation. This form of uranium that contains a total of 238 nucleons (92 protons and 146 neutrons), is called uranium-238.
The next most likely provision is a uranium nucleus that contains three fewer neutrons: uranium-235. Atoms with these lighter nuclei account for about 0.7% of the uranium that appears naturally.
Both cases are the same element, uranium, since they have 92 protons. However, they belong to different isotopes because one has 238 neutrons and the other 235.
The uranium-235 nucleus is already under a tension close to the internal rupture; a misguided neutron that approaches it can break it completely.
For nuclear fission reactions we are interested in this combination between protons and neutrons that is so close to beating nuclear force. Thus, just adding a neutron to the atom it explodes and divides generating other neutrons that can collide with other uranium atoms that are also at the limit.
Enriched uranium and depleted uranium
Uranium is almost as hard as steel and much denser than lead. This feature makes depleted uranium an optimal element for what applications such as:
- Counterweight in helicopter rotors and aircraft parts
- Protective shield against ionizing radiation
- Ammunition component so that they more easily penetrate the enemy's armored vehicles.
- Armor in military vehicles.
Uranium can occur in different compositions in its nucleus, that is, in different isotopes. Although uranium can be found in nature, most of it is found in a configuration that is not the most suitable for generating nuclear reactions. For this reason, uranium atoms are artificially altered to turn them into other more unstable isotopes. These new uranium isotopes will favor the generation of nuclear fission chain reactions.
Uranium-235 (235U) is the only fissile isotope, that is, capable of causing a nuclear fission chain reaction, present in nature. It is a characteristic that not even uranium-238, the most common of this element, possesses.
Other uranium isotopes are as follows
- Uranium-232 of synthetic origin.
- Uranium-233 of synthetic origin.
- Uranium-234 present in 0.0054% in nature.
- Uranium-235 present in 0.7204% in nature.
- Uranium-236 of synthetic origin.
- Uranium-238 present in 99.2742% in nature.