B Reactor

Color photograph of a very large industrial building composed of stacked concrete cubes
The B Reactor was the world's first full scale nuclear reactor.


Quick Facts
Richland, WA
World's First Full-Scale Nuclear Reactor
National Historical Landmark

Historical/Interpretive Information/Exhibits, Restroom

The Manhattan Project launched the Atomic Age. This imposing building opened the door to this new reality. At Hanford, and specifically in the B Reactor, the first full-scale nuclear reactor ever constructed, scientists and engineers harnessed the power of the atom and pioneered the processes to produce plutonium on an industrial scale.   

In 1942, Physicist Enrico Fermi and his team designed Chicago Pile-1 (CP-1), the world’s first artificial nuclear reactor. CP-1 went critical for the first time on December 2, 1942. Scientists further refined nuclear reactor technology for plutonium production at the X-10 Graphite Reactor in Oak Ridge, Tennessee. X-10 went into operation on November 4, 1943. 

Less than two years after Fermi’s successful CP-1 experiment, DuPont Company contractors and Manhattan Project scientists, used Fermi’s CP-1 reactor designs to begin the construction of the B Reactor on June 7, 1943. Despite not having precise blueprints or a firm understanding of the nuclear physics critical to B Reactor’s success, the reactor went critical for the first time on September 26, 1944. 

Some of the earliest workers at the B Reactor were African American laborers who poured the 23-foot (7 meters) thick concrete foundation for the reactor. High wages enticed African American workers to move to the Tri-Cities. Their job site was rigidly segregated, with African Americans working under all black crews with white foremen and residing either in segregated barracks at the Hanford Construction Camp or in East Pasco, the only community in the Tri-Cities without rigid racial restrictions.  
The B Reactor is the centerpiece of a global and local story that required tremendous effort and ingenuity from many people. The uranium that fueled the B Reactor was mined primarily in the Belgian Congo and refined in northern Canada. Several processing plants in the US further refined and milled uranium into billets. The billets were then shipped to Hanford’s fuel-fabrication area Machines shaped the billets into fuel slugs and sealed the uranium slugs in aluminum jackets.  
Transported across the Hanford Site by truck, the fuel slugs, which are roughly the size of two Snickers bars stacked end to end, arrived at the B Reactor ready for irradiation. Workers individually loaded sixty-four thousand fuel slugs weighing approximately 500,000 pounds (226 metric tons) by hand into the 2004 process tubes on the front face of the reactor. Fuel spent several weeks to a year in the reactor. Every four to six weeks, workers pushed 10-20% of the irradiated uranium out of the back of the reactor into the water-filled fuel-storage basin. Here, the fuel slugs would thermally and radiologically cool off for approximately two to three months underwater before being shipped to the T Plant to chemically separate the plutonium from the uranium and other radioactive byproducts. This plutonium was shipped to Los Alamos and formed into the core of an atomic weapon.  
Hanford’s plutonium powered the first man-made atomic explosion at the Trinity test on July 16, 1945 and the Fat Man atomic bomb dropped on Nagasaki, Japan, on August 9, 1945. Japan surrendered on August 14, 1945, bringing World War II, the deadliest conflict in human history, to an end. By the end of 1945, over 200,000 people had died as a result of the atomic bombings of Hiroshima and Nagasaki.

Continue Your Journey

You may only visit the B Reactor on a Department of Energy B Reactor Tour ,which are typically offered spring through fall. The Department of Energy also offers Pre-War Historic Sites Tours which show visitors where indigenous people and white settlers lived prior to the Manhattan Project. 

Manhattan Project National Historical Park

Last updated: January 17, 2023