That picture above is from what was called the Low-Intensity Test Reactor. It was built around 1950 right in the middle of the Oak Ridge National Lab campus to check out different operational issues and to train operators. That picture appeared on the cover of the Scientific American magazine's October 1951 issue.
ORNL built and operated many reactors over the years (13 of them, I believe), including one designed to power an airplane. If you drive interstate 40 west of Knoxville in the winter time (no leaves on the trees) you can still see the giant towers they used to lift a reactor up in the air to measure radiation doses/shielding studies. Here's a picture of the reactor suspended in the air.. Crazy stuff back then:
