Light water graphite reactor
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The light water graphite reactor (LWGR) is a design of nuclear reactor that uses purified graphite as a neutron moderator and light water (H2O) as a liquid coolant. Due to the superior moderating properties of graphite, natural uranium can be used as a fuel, avoiding enrichment.
The design was developed during the Manhattan Project, in a horizontal layout, first used in the 1944 B Reactor, also the world's first large-scale reactor. The Project's Hanford Site constructed nine LWGRs in total for plutonium production, used throughout the Cold War.[1] The Soviet Union subsequently developed a vertical design for use in military plutonium production reactors, constructed at Mayak, the Siberian Chemical Combine in Seversk, and the Mining and Chemical Combine in Zhelenogorsk.[2] China's nuclear weapons program also developed two military plutonium production LWGRs.[3] Reactors used for plutonium production in the nuclear weapons programs of the United Kingdom, France, and North Korea used gas-cooled reactors (GCRs) moderated by graphite, while those used by Israel, India, and Pakistan were believed to be heavy water reactors (HWRs).[citation needed]
The Soviet Union also developed civilian power prototypes eventually into the RBMK design, the only widespread use of LWGRs for commercial nuclear power plants.[4] RBMKs use slightly enriched uranium (<2% 235U).
| Reactor | Country | Criticality date | Initial power
(MWth) |
Notes | Refs. |
|---|---|---|---|---|---|
| B Reactor |  United States |
26 September 1944 | 250 | First LWGR, twin D and F reactors built under Manhattan Project | [1] |
| A-1 |  Soviet Union |
10 June 1948 | 100 | First Soviet plutonium production reactor; in Mayak | [2] |
| AM-1 | Soviet Union |
6 May 1954 | 30 | First LWGR to generate electricity | [5] |
| AMB-100 | Soviet Union |
1 September 1963 | 286 | SCWR test? | [6] |
| N Reactor | United States |
8 December 1963 | 4000 | Also Hanford Site, shutdown following Chernobyl disaster | [1] |
| AMB-200 | Soviet Union |
10 October 1967 | 530 | SCWR test? | [7] |
| Chernobyl Reactor 4 | Soviet Union |
26 November 1983 | 3200 | Reactor exploded in 1986, worst nuclear accident in history | [8] |
| Jiuquan reactor |  China |
1966 | ~250 | China's first plutonium production reactor, military use | [3] |
| Guangyan reactor | China |
1973 | ~250 | Third Front facility, military use | [3] |