What differentiates light water reactors from heavy water reactors?

Heavy water reactors are distinguished from light water reactors primarily by their use of deuterium oxide (D2O) as a neutron moderator and coolant. Deuterium is an isotope of hydrogen that has a neutron in addition to the usual proton. This property allows heavy water reactors to be more efficient in moderating neutrons compared to light water reactors, which use ordinary water (H2O).

The use of deuterium oxide in heavy water reactors allows these systems to effectively utilize natural uranium as fuel, which contains a lower concentration of the fissile isotope Uranium-235. Since heavy water absorbs fewer neutrons than light water, it enables better fission reactions even with the less enriched fuel, making heavy water reactors quite versatile.

In contrast, light water reactors typically require enriched uranium as fuel due to the higher neutron absorption characteristics of regular water, which necessitates a higher concentration of Uranium-235 to maintain a sustained fission reaction. This fundamental difference in the materials used for moderation and cooling is a key factor in their operational parameters and efficiency.

Understanding this distinction is crucial for comprehending the various reactor designs, their fuel requirements, and their efficiency in energy production.