70 years ago

Nov. 4 is the 70th anniversary of the historic Graphite Reactor's first fission reaction.


X-10 Reactor project leaders, including Enrico Fermi, were awakened in the early morning of Nov. 4, 1943, with the news that the reactor was reaching criticality.X-10 Reactor project leaders, including Enrico Fermi, were awakened in the early morning of Nov. 4, 1943, with the news that the reactor was reaching criticality. (hi-res image)

Monday, Nov. 4, is the 70th anniversary of the morning the Graphite Reactor -- then known as the "Clinton Pile" or "X-10 Pile" -- achieved a nuclear chain reaction for the first time. It was the initial major milestone for the facility, built to demonstrate the production of plutonium in a nuclear reactor.

The Department of Energy's Oak Ridge National Laboratory is still sometimes referred to as X-10, although no one really knows what the designation stood for, if anything.

The reactor was constructed with remarkable speed -- work had begun the previous February -- and cloaked in the now legendary secrecy of the Manhattan Project. The project was led by Enrico Fermi, who directed a staff that was small by Manhattan Project standards but stacked with brain power, including Nobel laureates Arthur Compton and Eugene Wigner, as well as future ORNL director Alvin Weinberg.

ORNL staff member Tim Gawne, who occasionally combs the archives looking for historical records related to his work, recently came across documents about Nov. 4, 1943, relating to "critical reached," as that morning's accomplishment was noted in the logbook.

The chain reaction happened sooner than expected.

"There are theories surrounding why it went critical early. One is that the person on duty wanted it to go critical when they were there. There may be a more simple explanation -- a miscalculation,” Gawne says.

"It was calculated long before the pile was finished that it would take in excess of 70 tons of fuel to bring the reactor to criticality. However, closer to the moment it was surmised that it would take 35 tons of material. It actually only took 30.5 tons.

"The reactor suddenly at 5 a.m. came to life showing signs of a self-sustaining chain reaction. As the story goes, a staff member was dispatched to wake Fermi to come and verify that they had reached criticality," Gawne says.

The pile was eventually renamed the Graphite Reactor -- the fission reaction is moderated by tons of graphite -- and after World War II had a historic peacetime mission that included the first deliveries of radioisotopes for medical uses and some of the earliest neutron scattering studies. It is now preserved as the Graphite Reactor Museum on the ORNL campus and draws thousands of visitors annually.

An account of Nov. 4, 1943, and the early history of ORNL, is given at this link: /ornl/news/communications/graphite-reactor


 -  Bill Cabage,  865.576.1946,  November 01, 2013

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