In the first nine months of operation, the B reactor produced fissionable plutonium for the world's first atomic bomb (the Trinity test on July 16, 1945), and for the atomic bomb that was dropped on Nagasaki, Japan, on August 9, 1945, killing 35,000 people.  This, and similar destruction at Hiroshima caused by the atomic bomb dropped three days earlier, hastened the end of World War II.

The B Reactor (Building 105-B at the Hanford Site) was the world's first production-scale plutonium nuclear reactor. It was rushed into construction during the height of WW II as part of the Manhattan Project, the urgent effort by the U.S. to create an atomic bomb before one could be built by Nazi Germany.

The design for the reactor came from an extremely slender volume of research, most of which was barely a year old. Construction started June 7, 1943 and the reactor was taken to criticality with complete success on September 26, 1944 - an unprecedented engineering and construction feat, particularly considering wartime procurement conditions and the tight security needed to protect the secret plutonium production methods.

Facts  

• Located near the Columbia River, with an ample electric power supply from the Bonneville Dam and Grand Coulee Dam, the Hanford B Reactor was a graphite-moderated, water-cooled reactor, designed to operate at 250 million watts. 
• At the peak of Hanford construction in mid-1944, there were some 45,000 workers on the payroll. An average force of 22,000 worked throughout the life of the project. To achieve these numbers and maintain the workforce, recruiters interviewed some 262,040 applicants throughout the United States and hired 94,307. 
• The job of simply preparing to build the production facilities at Hanford was a monumental undertaking in itself. Hanford Camp was a sprawling complex of barracks, trailers, hutments (later called Quonset huts), and other temporary buildings that housed the majority of the Hanford workers during the construction phase.
• Every aspect of design and construction was scrutinized and then structured to maintain security. The general rule was that employees or visitors should know only as much as necessary to complete their jobs, and as few people as possible would know the entire scope of the project and its inner workings.
• Over 2000 aluminum-lined nuclear fuel channels and many control rod channels pierce the core of B Reactor, roughly a 30-foot cube of high-purity graphite. Construction tolerances were extremely demanding for the reactor foundation, concrete shielding, walls, and control rod structures.
• Because B Reactor operated at very high thermal power levels (for the time) and was cooled by once-through flow of cooling water, a very large water treatment plant was built to provide water of high purity and minimum solids. Water was pumped from the Columbia River by ten 10,500-gallon- per-minute pumps working at 180 feet of head.