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. This reactor was of vital importance to 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 at the site's T Plant, as an alternative to the Project's uranium enrichment plants in Tennessee. 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 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. Visitors can take a tour of the reactor by advance reservation.
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 (thermal).
The purpose of the reactor was to breed plutonium from natural uranium metal. Enriching fissionable <sup>235</sup>U from <sup>238</sup>U, the dominant natural isotope, was extremely complex; plutonium's distinct chemistry made separation trivial by comparison. For example, the Y12 uranium enrichment plant in Tennessee required 14,700 tons of silver loaned by the Treasury Department for the windings in its calutrons, employed 22,000 people and consumed more electrical power than most states. Reactor B on the other hand needed only a few dozen employees and far fewer exotic materials required in much smaller quantities. The most important special material needed were the 1,200 tons of purified graphite for neutron moderation, and only enough electricity to run the cooling pumps.
The reactor has a footprint of (about and is tall, giving a volume of . The reactor core itself consists of a graphite box measuring occupying a volume of and weighing . It is penetrated horizontally through its entire length by 2,004 aluminum tubes containing fuel and vertically by channels housing the control rods.
thumb|right|Map of the [[Hanford site with the B/C reactor site shown at the upper left.]]
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 initial operation was halted by a problem identified as neutron absorption by the fission product Xenon-135, first identified in a research paper of Chien-Shiung Wu that was shared with Fermi. It was overcome by increasing the amount of uranium charged. 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.
Current status
thumb|right|Exterior of the Hanford B Reactor as of 2018
thumb|right|Hanford B Reactor Control Station as of 2018
thumb|right|Hanford B Reactor Tubes and Elevator as of 2018
The United States Department of Energy has administered the site since 1977 and offers public tours on set dates during the spring, summer, and fall of the year, as well as special tours for visiting officials.
six of the nine production reactors at Hanford were considered to be in "interim safe storage" status, and two more were to receive similar treatment. The exception was the B Reactor, which was given special status for its historical significance.
In a process called cocooning or entombment, the reactor buildings are demolished up to the concrete shield around the reactor core. Any openings are sealed and a new roof is built. It was cocooned as of 1998.
The D reactor operated from 1944 to June 1967, and was cocooned in 2004. The DR Reactor went online in October 1950, and was shut down in 1964. It was cocooned in 2002.
The F reactor was shut down in June 1965 and cocooned in 2003.
The H Reactor became operational as of October 1949 and was shut down as of April 1965. It was cocooned as of 2005.
Cocooning of the N-Reactor, which operated from 1963 to 1987, was completed as of 14 June 2012.
The decommissioned reactors are inspected every five years by the Department of Energy.
Preliminary plans for interim stabilizing of the K-East and K-West reactors were underway as of 30 January 2018.
The B Reactor was added to the National Register of Historic Places (#) on 3 April 1992. A Record of Decision (ROD) was issued in 1999, and an EPA Action Memorandum in 2001 authorized hazards mitigation in the reactor with the intention of allowing public tours of the reactor. It was named a National Historic Landmark on 19 August 2008. The park was formally established by a Memorandum of Agreement on November 10, 2015, which was signed by the National Park Service and the Department of Energy. Museum development at Hanford may include the B Reactor, Bruggemann's Warehouse, Hanford High School, Pump House, and White Bluffs Bank.
Timeline of major events
{|class="wikitable"
|-
!Year
!Date
!Event
|-
|1943
|October
| U.S. Army Corps of Engineers breaks ground to build B Reactor
|-
|1944
|13 September
| First uranium fuel slug loaded into B Reactor
|-
|2011
|July
|National Park Service recommends B Reactor be included in a national historic park commemorating the Manhattan Project.