Info: Light-water reactors

The difference between the various reactor types is in the coolant used (water, gas or liquid metal) and the moderator used (a substance that slows down fast neutrons, thus enabling and maintaining the chain reaction – thermal fission). Water or carbon in the form of graphite can be used as moderators.

Light-water reactors

Today, light-water reactors are used in Germany, which are the most common types of reactors used world-wide. Among light-water reactors are pressurised water reactors and boiling water reactors. In light-water reactors, normal water (light water) is used as coolant. At the same time the water serves as moderator.

One molecule of water (H₂O) consists of two hydrogen atoms and one oxygen atom. If both hydrogen atoms (H) do have only one proton (positively charged module) in the core but no neutron (uncharged module of the nucleus), the combination with oxygen is termed "light water".

In the case of "heavy water", on the other hand, both hydrogen atoms in the core have one proton and one neutron each. These hydrogen atoms are also termed deuterium – an isotope of hydrogen.

The number of protons and neutrons in the core determine the mass number of a nucleus. The hydrogen atoms of heavy water show a larger mass (u≈2) than the hydrogen atoms in light water (u≈1).