B Reactor
The B Reactor at the Hanford Site in southeastern Washington state was the world's first full-scale plutonium production reactor, constructed as part of the Manhattan Project during World War II to generate fissile material for nuclear weapons.[1][2] Completed in September 1944 after construction began the previous October, the graphite-moderated, water-cooled reactor achieved criticality on September 26, 1944, and rapidly scaled to full power of 250 megawatts by February 1945.[3][4] It produced plutonium-239 through neutron irradiation of uranium-238, yielding the fissile cores for the Trinity test detonation on July 16, 1945, and the Fat Man implosion-type bomb dropped on Nagasaki on August 9, 1945, which contributed decisively to Japan's surrender.[1][5] Designed and built by the DuPont company under wartime secrecy, the B Reactor exemplified unprecedented engineering feats, including the rapid assembly of over 2,000 process tubes within an 11-month timeline, marking the onset of industrial-scale nuclear technology.[3][4] Decommissioned in 1968 after producing plutonium for subsequent Cold War arsenals, it was designated a National Historic Landmark in 2008 and now forms a core site of the Manhattan Project National Historical Park, offering public tours to illustrate its pivotal role in atomic history.[2][6]Historical Context
Role in the Manhattan Project
The B Reactor served as the cornerstone of plutonium production within the Manhattan Project, the United States' classified program to develop atomic weapons during World War II. Established at the Hanford Site in Washington state, it was engineered to irradiate uranium fuel in a sustained nuclear chain reaction, yielding plutonium-239 as a fissile material alternative to scarce uranium-235. This approach addressed the project's urgent need for bomb-grade material, leveraging graphite-moderated reactor technology scaled from Enrico Fermi's experimental Chicago Pile-1 to industrial levels capable of processing thousands of tons of uranium annually.[2][7] Construction of the B Reactor, the first of three planned plutonium facilities at Hanford's 100 Area, began in October 1943 under the direction of the U.S. Army Corps of Engineers and E.I. du Pont de Nemours & Company, which managed operations to maintain secrecy and efficiency. The reactor's design incorporated a 36-foot aluminum process tube lattice housing 2,004 uranium slugs cooled by the Columbia River, enabling power outputs up to 250 megawatts thermal. It achieved initial criticality on September 26, 1944, just 13 months after groundbreaking, validating the feasibility of continuous, high-volume plutonium breeding essential for weaponizing the element.[3][8][9] In its early operations, the B Reactor supplied the plutonium core for the Trinity test detonation on July 16, 1945—the world's first nuclear explosion—and for the Fat Man implosion-type bomb dropped on Nagasaki, Japan, on August 9, 1945, contributing directly to the war's end. By February 1945, it had reached full production power, yielding approximately 250 grams of plutonium daily and demonstrating the Manhattan Project's capacity to transition from laboratory-scale experiments to wartime industrial output under extreme secrecy constraints.[1][4][10]Hanford Site Selection and Establishment
The selection of the Hanford Site for plutonium production in the Manhattan Project began in spring 1942, driven by the need for a large-scale facility to irradiate uranium fuel in nuclear reactors and separate plutonium chemically.[11] Scientists at the Metallurgical Laboratory in Chicago, led by Arthur Compton, established key criteria including a minimum water supply of 25,000 U.S. gallons per minute for cooling, at least 100,000 kilowatts of electric power, and extensive isolation buffers such as a 4-mile safety radius around chemical separation plants and a 225-square-mile exclusion area to mitigate unknown radiation hazards.[11] These requirements assumed the construction of three to four helium-cooled reactors and two separation plants, prioritizing sites distant from population centers, railroads, and highways to ensure secrecy and safety.[11] By December 14, 1942, a meeting in Wilmington, Delaware, finalized these criteria, leading to Hanford's recommendation on December 31 after evaluating multiple locations.[11] Hanford, a remote desert valley along the Columbia River in southeastern Washington, was favored for its abundant cooling water from the river, reliable hydroelectric power from the nearby Grand Coulee and Bonneville Dams, stable basalt geology suitable for containment, and an uninhabited tract of approximately 500,000 acres with existing railroad access and regional labor availability.[11] [7] It outperformed alternatives like sites near Oak Ridge, Tennessee—deemed too proximate to urban areas for the risks of reactor operations—and other candidates in Indiana or Colorado that lacked comparable water and power resources or sufficient isolation.[11] [12] General Leslie Groves, head of the Manhattan Project, personally inspected the site and endorsed it on January 16, 1943, with final War Department approval on February 9, 1943.[7] [11] Site establishment proceeded rapidly in March 1943, with the U.S. government acquiring about 780 square miles of land for $5.1 million (in 1943 dollars), displacing fewer than 1,500 residents from the small farming communities of Hanford, White Bluffs, and Richland, who received compensation based on appraised property values excluding improvements like crops and equipment.[12] [13] The acquisition, managed by Colonel Franklin T. Matthias of the Army Corps of Engineers, involved 90-day eviction notices, though some residents pursued legal challenges settled out of court; the process also impacted Native American groups like the Wanapum tribe by restricting access to traditional Columbia River fishing grounds.[7] DuPont was contracted to design and construct the Hanford Engineer Works, emphasizing secrecy through compartmentalization and rapid wartime mobilization, which enabled groundbreaking for initial facilities like the B Reactor's water-cooling plant by August 1943.[11] [13] This establishment positioned Hanford as the primary site for full-scale plutonium production, complementing uranium enrichment at Oak Ridge.[12]Design and Engineering
Technical Specifications
The B Reactor was a graphite-moderated, light-water-cooled nuclear reactor designed for large-scale plutonium production as part of the Manhattan Project.[2][14] Its core consisted of a graphite stack measuring 36 feet by 36 feet by 28 feet, comprising approximately 2,200 tons of high-purity graphite arranged in about 75,000 machined blocks.[14][15] The reactor was designed for a thermal power output of 250 megawatts.[2][14] Horizontal process tubes numbering 2,004 pierced the graphite moderator, each 44 feet long with an outer diameter of 1.73 inches and inner diameter of 1.61 inches, fabricated from 2S aluminum alloy coated with 72S zinc.[14][15] These tubes accommodated stacks of 32 to 35 cylindrical uranium fuel slugs per tube, each slug 1.44 inches in diameter and 8.7 inches long, clad in aluminum with a 0.086-inch annular gap for coolant flow.[14] Cooling water from the Columbia River, demineralized and pumped at an initial rate of 30,000 gallons per minute (20 gallons per minute per tube at 200 psi inlet pressure and 18-19.5 feet per second velocity), passed through the tubes in a single pass before discharge.[2][14][15] Control and safety systems included 9 horizontal control rods and 29 vertical safety rods inserted through dedicated channels in the graphite stack.[14] Helium gas circulated through the graphite at 2,600 cubic feet per minute to facilitate heat transfer and remove impurities, with later modifications incorporating CO2 to manage graphite swelling from neutron exposure.[14] The reactor was enclosed in a 105-B building measuring 120 feet by 150 feet by 120 feet high, featuring a 10-inch cast iron thermal shield and additional biological shielding of masonite, steel, and concrete totaling around 10,000 tons.[14][15]| Parameter | Specification |
|---|---|
| Thermal Power (Design) | 250 MW |
| Graphite Mass | ~2,200 tons |
| Process Tubes | 2,004 (aluminum, 44 ft long) |
| Fuel Slugs per Tube | 32–35 (uranium, aluminum-clad) |
| Coolant Flow (Initial) | 30,000 gpm total (20 gpm/tube) |
| Control Rods | 9 horizontal, 29 vertical safety rods |