Spent nuclear fuel pool



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

An atom of a nucleus and of electrons surrounding this nucleus. In turn, a nucleus consists of protons and neutrons. A proton has a positive charge. A neutron has no electrical charge and is neutral.

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.

Atoms of the same element can belong to different isotopes depending on the number of neutrons they contain.

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

Depleted uranium is a mixture of the same three uranium isotopes except that it has very little 234U and 235U. It is less radioactive than natural uranium.

Enriched uranium is another mixture of isotopes that has more 234U and 235U than natural uranium. Enriched uranium is more radioactive than natural uranium.

Natural uranium is used to make enriched uranium; The remaining product is depleted uranium.

Uranium Applications

Uranium is very important in the nuclear energy industry as a nuclear fuel. Specifically, nuclear ractures often use enriched uranium. Still, there are other applications of 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 Isotopes

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.




    Published: April 8, 2014
    Last review: November 19, 2019