26 July 1959. A partial core meltdown took place when the Sodium Reactor Experiment (SRE) experienced a power excursion that caused severe overheating of the reactor core, resulting in the melting of one-third of the nuclear fuel and significant release of radioactive gases. The amount of radioactivity released is disputed, with it ranging from 28 Curies to as much as 240 to 260 times worse than Three Mile Island. Over the succeeding years, the site was cleaned up and all buildings and contamination removed.