Why Is Uranium, Not Iron, Used in Nuclear Reactors?

Even though everything in the world is made of atoms, nuclear reactors use only a very narrow set of elements as fuel. Why do they rely on Uranium that is in short supply instead of using, say, Iron that is in plenty?

Nuclear reactors work on the foundation that when atoms are split, they will release enormous amount of energy, which can be harnessed to heat water or other fluids and ultimately produce electricity.

In theory, the atoms in anything can be split, but science is not that advanced yet. Present day nuclear reactors split atoms by bombarding the nucleus of the atom with high-speed particles called neutrons. 

However, slamming neutrons at high speeds can only do so much, so it is complemented with fuel material that meets certain characteristics: 

·         The atomic structure of the fuel material is relatively unstable (in other words, radioactive). The stability is measured using a metric known as Binding Energy per Nucleon; the lower the value, the better. Uranium has a lower binding energy of 7.59 MeV (million electron volts) compared to 8.79 MeV for Iron.

·         The fuel has high energy density. Uranium has energy density of over 80 million Joules per kilogram, and Iron has a fractional 5 million Joules. This roughly translates to one kilogram of Uranium producing 22 million KWH of power and one kilogram of Iron producing one million KWH.

·         Have a reasonably long half-life, so it does not get destroyed quickly in a reactor. The half-life of Uranium is several times longer than Iron.

·         Be available in suitable quantities. Current estimates peg Uranium to be available for another 200 years at the current consumption rate.

Note: There are several types of Uranium, also known as Isotopes. Nuclear reactors usually use Uranium-235.