Heavy water reactor
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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.
Proponents of heavy water reactors will cite the fact that because such reactors can be fueled with unenriched uranium, there is less of a nuclear proliferation risk in marketing such technology to other nations as such nations will have no legitimate use for uranium enrichment facilities. On the other hand, light water reactors produce steady but small amounts of plutonium, which is suitable for nuclear weaponry. It is widely suspected that India obtained the fissile material it required for its nuclear weapons from plutonium generated from nuclear power plants built from a CANDU-derived design.
