Hanford B Reactor
The face of B Reactor during construction.
Location Near junction of WA 24 & WA 240 on the Hanford Site
Nearest city Richland, Washington
Built June 7, 1943[1] to September 1944[2]
Architect E.I. DuPont de Nemours & Co.
Governing body U.S. Department of Energy
NRHP Reference # 92000245
Significant dates
Added to NRHP April 3, 1992
Designated NHL August 19, 2008[3]

The B Reactor at the Hanford Site, near Richland, Washington, USA, was the first large-scale nuclear reactor ever built. The project was commissioned to produce plutonium-239 by neutron activation as part of the Manhattan Project, the United States nuclear weapons development program during World War II. The B reactor was fueled with metallic natural uranium, graphite moderated, and water-cooled. It has been designated a U.S. National Historic Landmark since August 19, 2008[3][4] and in July 2011 the National Park Service recommended that the B Reactor be included in a national historic park commemorating the Manhattan Project.[5]

Reactor design and construction

The reactor was designed and built by E. I. du Pont de Nemours and Company based on experimental designs tested by Enrico Fermi at the University of Chicago, and tests from the X-10 Graphite Reactor at Oak Ridge National Laboratory. It was designed to operate at 250 megawatts.

The reactor occupies a footprint of 46 by 38 ft (14 by 12 m) (about 1,750 sq ft (163 m2) and is 41 ft (12 m) (approximately five stories) tall, occupying a volume of 71,500 cu ft (2,020 m3). The reactor core itself consisted of a 36-foot-tall (11 m) graphite box measuring 28 by 36 ft (8.5 by 11.0 m) occupying a volume of 36,288 cu ft (1,027.6 m3) and weighing 1,200 short tons (1,100 t). It was penetrated horizontally through its entire length by 2,004 aluminum tubes and vertically by channels for the vertical safety rods.[4]

The core is surrounded by a thermal shield of cast iron 8 to 10 inches (20 to 25 cm) thick weighing 1,000 short tons (910 t). Masonite and steel plates enclose the thermal shield on its top and sides, forming a biological shield for radiation protection. The bottom of the thermal shield is supported by a 23-foot-thick (7.0 m) concrete pad topped by cast-iron blocks. The graphite composition was selected to moderate the nuclear reaction fueled by 200 short tons (180 t) of uranium slugs approximately 25 mm (1 in) diameter 70 mm (3 in) long (the approximate size of a roll of quarters[4]), sealed in aluminum cans, and loaded into the aluminum tubes.[4]

The reactor was water-cooled, with cooling water pumped from the Hanford Reach of the Columbia River through the aluminum tubes around the uranium slugs at the rate of 75,000 US gal (280,000 L) per minute. The water was discharged into settling basins, then returned to the river after allowing time for the decay of radioactive materials and the settling out of particulate matter.[6]

Reactor operation

The B Reactor had its first nuclear chain reaction in September, 1944, the D Reactor in December 1944 and the F Reactor in February 1945. The reactor produced plutonium-239 by irradiating uranium-238 with neutrons generated by the nuclear reaction. It was one of three reactors — along with the D and F reactors — built about six miles (10 km) apart on the south bank of the Columbia River. Each reactor had its own auxiliary facilities that included a river pump house, large storage and settling basins, a filtration plant, large motor-driven pumps for delivering water to the face of the pile, and facilities for emergency cooling in case of a power failure.[4]

Emergency shutdown of the reactor, referred to as a SCRAM, was attained either by rapidly fully inserting the vertical safety rods (now called control rods) or, as a backup method, by the injection of borated water into the reactor. In January 1952, the borated water system was replaced by a "Ball-3X" system that injected nickel-plated high-boron steel balls into the channels occupied by the vertical safety rods.[4]

The plutonium for the nuclear bomb used in the Trinity test at Los Alamos in New Mexico and the Fat Man bomb dropped on Nagasaki, Japan was created in the B, D, and F reactors. These first three reactors ran for two decades, and were joined by additional reactors constructed later. The B Reactor was permanently shut down in February 1968.[4]

Current status

B Reactor is now in "interim safe storage" status. The D and F reactors were shut down in June 1967 and June 1965, respectively. In a process called cocooning or entombment, the reactor buildings are demolished up to the 4-foot-thick (1.2 m) concrete shield around the reactor core. Any openings are sealed and a new roof is built. The D and F reactors have already been entombed, as have the C and DR reactors. Most auxiliary buildings at the first three reactors have been demolished, as well. The H, K-East and K-West reactors and the N-Reactor are scheduled to be entombed in that order.

The museum.

Timeline of major events

Year Date Event
1943 October U.S. Army Corps of Engineers breaks ground to build B Reactor [7]
1944 September 13 First Uranium fuel slug loaded into B Reactor[7]
1944 September 26 Initial reactor criticality achieved[7]
1945 February 3 B Reactor Plutonium delivered to Los Alamos[7]
1945 July 16 B Reactor Plutonium used for first nuclear test explosion at Trinity Test Site in Alamagordo, New Mexico[7]
1945 August 9 B Reactor Plutonium used for "Fat Man" bomb dropped on Nagasaki, Japan[7]
1946 March B Reactor operations suspended[7]
1948 June B Reactor operation resumed[7]
1949 March B Reactor begins production of tritium for use in hydrogen bomb[7]
1952 November 1 B Reactor tritium used in first test detonation of a hydrogen bomb at Bikini Atoll[7]
1968 January 29 Atomic Energy Commission directs shutdown of B Reactor[7]
1976 Declared National Historic Mechanical Engineering Landmark by American Society of Mechanical Engineers[7]
2008 Declared National Historic Landmark by U.S. Department of Interior and National Park Service[7]
2009 U.S. Department of Energy announces public tours[8]
2011 July National Park Service recommends B Reactor be included in a national historic park commemorating the Manhattan Project.[5]


  • Project News Volume 1, Issue 04 PDF
  • Hanford Site - Timeline 1943-1990 PDF (168 KB)
  • United States Department of Energy - B Reactor
  • B Reactor a historic Landmark


External links