Light water graphite reactor

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] The Soviet Union also developed civilian power prototypes eventually into the RBMK design, the only widespread use of LWGRs for commercial nuclear power plants.^[3] RBMKs use slightly enriched uranium (<2% ²³⁵U). China's nuclear weapons program also developed two military plutonium production LWGRs.^[4] 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]}

Selected examples of LWGRs

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	[4]
Guangyan reactor	China	1973	~250	Third Front facility, military use	[4]

See also

• RBMK
• Hanford Engineer Works
• Hanford Site
• Void coefficient