Unlocking the Energy of the Atom
Nuclear energy is the energy released from the nucleus of an atom. There are two primary ways to release this energy: fission and fusion.
Mass-Energy Equivalence: E=mc²
The energy released in nuclear reactions comes from the conversion of a small amount of mass into a large amount of energy, as described by Albert Einstein's famous equation.
E is energy, m is mass, and c is the speed of light (a very large constant).
In both fission and fusion, the total mass of the products is slightly less than the total mass of the reactants. This 'missing' mass, called the mass defect, has been converted into a tremendous amount of energy.
Nuclear Fission
Fission is the process of splitting a large, unstable atomic nucleus into two or more smaller nuclei.
This process is typically initiated by bombarding a heavy nucleus, like Uranium-235, with a neutron.
The nucleus absorbs the neutron, becomes highly unstable, and splits, releasing smaller nuclei (fission products), several more neutrons, and a large amount of energy.
Chain Reaction: The neutrons released from the initial fission event can go on to strike other U-235 nuclei, causing them to split and release even more neutrons. If this process is controlled, it can be used to generate power. If it is uncontrolled, it results in an atomic explosion.
Fission Reactors:
Fuel Rods: Contain the fissile material (e.g., U-235).
Control Rods: Made of neutron-absorbing material (like cadmium or boron). They are raised or lowered to control the rate of the chain reaction.
Moderator: A substance (like water or graphite) that slows down the fast neutrons produced by fission, making them more likely to be captured by other U-235 nuclei.
Coolant: A fluid (usually water) that transfers the heat generated by the fission reaction to a steam generator, which then turns a turbine to produce electricity.
Nuclear Fusion
Fusion is the process of combining two light atomic nuclei to form a single, heavier nucleus.
This is the process that powers the Sun and other stars.
The most common fusion reaction in stars combines hydrogen nuclei (protons) to form helium.
Fusion releases even more energy per nucleon than fission.
It requires extremely high temperatures and pressures to overcome the electrostatic repulsion between the positively charged nuclei.
Sustaining a controlled fusion reaction on Earth for power generation is a major scientific and engineering challenge.