Plum Brook was built to research atomic airplanes.
It is located in Sandusky Ohio on the site of the Plumb Brook Station - land given to veterans of war of 1812. Subsequently Plumb Brook Station was converted to handle US Government ordinance and later in the 1950's converted into a nuclear research facility.
Atomic airplanes were abandon before the Plumb Brook facility and its reactor were completed but President JFK reinvigorated the program with his atomic rocket program in 1961.
The Plumb Brook reactor was taken "critical" in June of 1961 for the first time.
The program continued into January of 1973 when the site was "temporarily closed." The site never reopened and today the site has been mostly "decommissioned" (as documented here by NASA).
Nuclear aircraft research ended with the Convair X-6 program (from Wikipedia):
The idea was to use the General Electric HTRE-3 jet nuclear-powered get engines to propel the aircraft. At the bottom are two traditional jet engines. Air is taken in the front, passed into the reactor (above the two engines) to cool it, and the heated air passed back into the jet engines to drive the turbines (from Wikipedia):
Test versions of this engine still exist at the Idaho National Laboratory (from Wikipedia):
In September of 1951 project MX-1589 became the first and only flight test of a nuclear reactor in the US. The reactor did not power the plane but instead was used to evaluate shielding for the crew. There some 47 flights over southwest Texas and New Mexico.
The program was canceled in 1961.
Recently I watched the original Japanese ゴジラ Gojira (Godzilla) movie.
Key to the plot is the fact that Gojira (Godzilla) is unleashed on Tokyo by a nuclear explosion.
While the US was developing these atomic flight systems the Japanese, the first victim of US atomic energy, were developing a voice to protest against nuclear weapons. I find it fascinating that the Japanese, while recent victims of the atomic bomb, apparently had little problem fully embracing nuclear energy for power a few decades later.
There is a scene in Gojira where the "dangers" of atomic weapons are discussed. There is sort of an eerie (and ironic) predictive aspect to the scene where the same fears could be applied to the Japanese themselves and Fukushima some 55 years later.