The worst nuclear accident in US history occurred on March 28, 1979. The nuclear power plant on Three Mile Island had two pressurized water reactors. A malfunction in the cooling system of reactor number two resulted in a meltdown of the reactor core. The radioactive gases released by the core meltdown accumulated in a tank in the secondary building. Two days after the accident, the accumulated radioactive waste gas was transferred to the decay tank. At this stage, low levels of gases leaked into the environment, but a significant portion was captured by filters. According to the report produced as a result of the accident, the leaked radiation was claimed to be lower than the level of radiation considered to affect health. However, INES designated this accident as level 5. Following the accident, almost all nuclear power plant projects in the US were canceled.
