October 8, 2018, marks the fiftieth anniversary of the operation of the Molten-Salt Reactor Experiment (MSRE) using uranium-233 as a fuel. U-233 does not occur naturally; it is formed when thorium absorbs a neutron undergoes a double beta decay to form U-233. U-233 is a superior nuclear fuel, producing enough neutrons through its fission (whether by a fast or thermal neutron) to allow sufficient conversion of thorium to U-233 to replace its consumption. That makes it very unique and very valuable.

Alvin Weinberg and the other researchers on the Molten-Salt Reactor Program (MSRP) at Oak Ridge National Laboratory (ORNL) recognized this property of U-233 and sought to demonstrate its actual use in a real nuclear reactor. The MSRE was designed for this purpose. When the MSRE was first brought to criticality in June 1965, this was a great accomplishment, but the MSRP researchers had something more in mind. Therefore, after a few years of operation, they removed the initial uranium inventory from the reactor by fluorination and replaced it with uranium-233.

To commemorate this accomplishment, they invited Dr. Glenn Seaborg to ORNL to be the one to first take the MSRE to a significant power level on uranium-233 fuel. Seaborg’s participation was significant on several levels. At that time, Seaborg was the chairman of the Atomic Energy Commission (AEC) which had funded the development of the MSRE. But even more importantly, it was Seaborg who had a led of team of chemists at the University of California, Berkeley, to discover uranium-233 in the early days of the Manhattan Project. Seaborg was the first person to grasp the potential of thorium as an energy source when he received information about the performance of uranium-233 in the ORNL Graphite Reactor in late 1944.