Heavy water reactors use heavy water as a neutron moderator. Heavy water is deuterium oxide, D₂O. Deuterium is an isotope of hydrogen. Most hydrogen atoms have a nucleus that consists of only a single proton, but deuterium has a proton and a neutron, which makes it approximately twice as heavy as a regular hydrogen atom. Heavy water has two atoms of deuterium bonded to an oxygen atom. Neutrons in a nuclear reactor that uses uranium must be slowed down so that they are more likely to split other atoms and get more neutrons released to split other atoms. Light water can be used, as in a Light water reactor, but since it absorbs neutrons the uranium must be enriched for criticality to be possible. The most common Pressurised Heavy Water Reactor is the CANDU reactor. Heavy water is dideuterium oxide, or D2O or 2H2O. It is chemically the same as normal water, H2O, but the hydrogen atoms are of the heavy isotope deuterium, in which the nucleus contains a neutron in addition to the proton found in the nucleus of any hydrogen atom. ... In nuclear engineering, a neutron moderator is a medium which reduces the velocity of fast neutrons, thereby turning them into thermal neutrons capable of sustaining a nuclear chain reaction. ... Deuterium, also called heavy hydrogen, is a stable isotope of hydrogen with a natural abundance in the oceans of planet Earth of approximately one atom in 6500 of hydrogen (~154 PPM). ... An oxide is a chemical compound of oxygen with other chemical elements. ... Isotopes are any of the several different forms of an element each having different atomic mass. ... General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ... Atomic redirects here. ... A semi-accurate depiction of the helium atom. ... // For alternative meanings see proton (disambiguation). ... This article or section does not cite its references or sources. ... General Name, Symbol, Number oxygen, O, 8 Chemical series Nonmetals, chalcogens Group, Period, Block 16, 2, p Appearance colorless (gas) very pale blue (liquid) Atomic mass 15. ... Core of a small nuclear reactor used for research. ... General Name, Symbol, Number uranium, U, 92 Chemical series actinides Group, Period, Block n/a, 7, f Appearance silvery gray metallic; corrodes to a spalling black oxide coat in air Atomic mass 238. ... Light water, in the terminology of nuclear reactors, is ordinary water. ... A light water reactor or LWR is a thermal nuclear reactor that uses ordinary water (as opposed to heavy water) as its neutron moderator. ... A sphere of plutonium surrounded by neutron-reflecting blocks of tungsten carbide. ... A pressurised heavy water reactor is a nuclear power reactor that uses unenriched natural uranium as its fuel and heavy water as a moderator (deuterium oxide D2O). ... The CANDU reactor is a Pressurized Heavy Water Reactor developed initially in the late 1950s and 1960s by a partnership between Atomic Energy of Canada Limited (AECL), the Hydro-Electric Power Commission of Ontario (now known as Ontario Power Generation), Canadian General Electric (now known as GE Canada), as well...