A pressurized heavy-water reactor (PHWR) is a nuclear power reactor, commonly using unenriched natural uranium as its fuel, that uses heavy water (deuterium oxide D2O) as its coolant and moderator. The heavy-water coolant is kept under pressure, allowing it to be heated to higher temperatures without boiling, much as in a PWR. While heavy water is...
(from the article `nuclear reactor`) ...Since light (ordinary) water tends to absorb more neutrons than do other moderators, such enrichment is crucial. The CANDU (Canadian ...
nuclear reactor operated with heavy water as moderator
(HWR) A reactor which uses heavy water as its moderator, eg Canadian CANDU (q.v.) which is a pressurised HWR (PHWR).