Light water reactor
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- "LWR" redirects here. See also: LWR (disambiguation)
A light water reactor or LWR is a thermal nuclear reactor that uses ordinary water, also called light water, as its neutron moderator. This differentiates it from a heavy water reactor, which uses heavy water as a neutron moderator. In practice all LWRs are also water cooled. While ordinary water has some heavy water molecules in it, it is not enough to be important in most applications.
The most common LWRs are pressurized water reactors and boiling water reactors.
Many other reactors are also (light) water cooled, notably the RBMK and some military plutonium production reactors. These are not regarded as LWRs, as they are moderated by graphite, and as a result their nuclear characteristics are very different.
The light-water reactor uses uranium 235 as a fuel, enriched to approximately 3 percent. Although this is its major fuel, the uranium 238 atoms also contribute to the fission process by converting to plutonium 239 — about one-half of which is consumed in the reactor. Light-water reactors are generally refueled every 12 to 18 months, at which time, about 25 percent of the fuel is replaced.
Light water reactors tend to be simpler and cheaper to build than heavy water reactors. Power-generating capabilities are comparable.
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