B Reactor

B Reactor
U.S. National Register of Historic Places
U.S. National Historic Landmark
The face of B Reactor during construction.
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Location	About 5.3 miles (8.5 km) northeast of junction of State Route 24 and State Route 240 on the Hanford Site
Nearest city	Richland, Washington
Coordinates	46°37′49″N 119°38′50″W / 46.63028°N 119.64722°W / 46.63028; -119.64722
Area	9.5 acres (3.8 ha)
Built	7 June 1943[1] to September 1944[2]
Architect	E.I. DuPont de Nemours & Company
NRHP reference No.	92000245
Significant dates
Added to NRHP	3 April 1992
Designated NHL	19 August 2008[3]

The B Reactor at the Hanford Site, near Richland, Washington, was the first large-scale nuclear reactor ever built, at 250 MW. It achieved criticality on September 26, 1944. The project was a key part of the Manhattan Project, the United States nuclear weapons development program during World War II. Its purpose was to convert part of its natural uranium fuel into plutonium-239 by neutron activation, for use in nuclear weapons. Pure plutonium was then chemically separated in the site's T Plant, as an alternative to the Project's uranium enrichment plants. The B reactor was graphite moderated and water-cooled, via a contaminating open cycle with the Columbia River.

It was preceded by Clinton Laboratory's X-10 Graphite Reactor, a pilot plant for reactor production and chemical separation of plutonium, which by mid-1944 had reached a capacity of 4 MW. The B reactor thus represented a massive leap of two orders of magnitude in reactor design. Primarily constructed by DuPont, the operation was assisted by scientists including Enrico Fermi, John Archibald Wheeler, and Chien-Shiung Wu. Two identical reactors, the D Reactor and F Reactor, were launched in December 1944 and February 1945. The plutonium from the site was used in the Trinity test, the Fat Man bomb detonated above Nagasaki, the demon core, and thousands of US warheads during the Cold War. By the early 1960s, the reactors had been upgraded to capacities of 2000 MW. It is historically significant as the world's first large-scale reactor, the first to use water cooling, the first to experience xenon poisoning, the first employed for thermonuclear weapon tritium production, and the seventh critical assembly in total.

The reactor was permanently shut down in February 1968. It has been designated a U.S. National Historic Landmark since 19 August 2008^[3][4] and in July 2011 the National Park Service recommended that the B Reactor be included in the Manhattan Project National Historical Park commemorating the Manhattan Project.^[5] Visitors can take a tour of the reactor by advance reservation.^[6]