X-10 Graphite Reactor

A large wall face with dozens of holes. Two mannequins are present at bottom.
X-10 Graphite Reactor began operating on November 4, 1943


Quick Facts
Oak Ridge, TN

Historical/Interpretive Information/Exhibits, Restroom, Wheelchair Accessible

The X-10 Graphite Reactor is on Oak Ridge National Laboratory property. During the 2023 Public Bus Tour Season, no access to the reactor is offered by the US Department of Energy.

On February 2, 1943, only two months after the first experimental nuclear reactor was constructed by Enrico Fermi's team at the Chicago Metallurgical Laboratory, design work began on the X-10 Graphite Reactor. The Chicago reactor, known as CP-1, had only operated for a few minutes; X-10, by contrast, was designed for continuous operation so that Manhattan Project personnel could develop the necessary skills and technologies for the production-scale reactors and plutonium separation plants at Hanford, WA. 

Inside the X-10 reactor, neutrons released from uranium fission transformed uranium 238 into plutonium, another element altogether. In 2018, former Oak Ridge National Laboratory Director, Alvin Weinberg described the fantastical nature of this process: “It is hard for us old timers to convey the wonderment of the time -- and it was wonderment -- that we could use uranium to produce energy. It was an unreal aspect to us." 

Designed and built in ten months, the X-10 Graphite Reactor began operating on November 4, 1943. The reactor consisted of a large block of graphite surrounded by concrete and pierced by 1,248 horizontal channels. Workers inserted uranium control rods into the channels, and cooling air circulated around the control rod channels. After a period of time, scientist/workers inserted fresh rods into the face of the reactor as irradiated rods fell from the back through a chute and into a water-cooled bucket. 

Though the reactor never produced fissionable quantities of plutonium, it did supply Los Alamos scientists with experimental quantities of plutonium necessary to design Fat Man, the world’s first plutonium-fueled atomic bomb used in war. In addition, X-10 paved the way for the design and development of Hanford’s large-scale reactors and chemical separation facilities, including the B Reactor and T Plant, which ultimately provided plutonium for use in Fat Man. 

The X-10 Graphite Reactor ceased operating on November 4, 1963, exactly twenty years after it first went critical. X-10 was designated a National Historic Landmark in 1965.

Continue Your Journey

The X-10 Graphite Reactor is located within present-day Oak Ridge National Laboratory (ORNL). ORNL is a highly-secured facility.  During the 2023 Public Bus Tour Season, no access to the reactor is offered by the US Department of Energy. In prior seasons, access to X-10 was only granted to US citizens aged 10 and above, and only on guided tours. To get a better understanding of X-10's role during the Manhattan Project, please visit the American Museum of Science and Energy.



Manhattan Project National Historical Park

Last updated: May 10, 2023