The SL-1 , or Stationary Low-Power Reactor Number One , was a United States Army experimental nuclear power reactor which underwent a steam explosion and meltdown on January 3 , 1961 , killing its three operators ; John Byrnes , Richard McKinley , and Richard Legg . The direct cause was the improper manual withdrawal of the central control rod , responsible for absorbing neutrons in the reactor core . This caused the reactor power to surge to about 20,000 MW and in turn , an explosion occurred . The event is the only known fatal reactor accident in the United States and the first to occur in the world . The accident released about of iodine-131 , which was not considered significant due to its location in a remote desert of Idaho . About of fission products were released into the atmosphere
SL-1
SL-1
Environmental impact of nuclear power