Three Mile Island
Risks and major accidents

At 4 a.m. on March 28, 1979, an accident sequence began at the Three Mile Island nuclear power plant that would lead to a partial meltdown of the fuel in the reactor core within ten hours.

This reactor is of the PWR (Pressurized Water Reactor) type. It comprises a primary circuit in which the fuel is immersed, and a secondary circuit (figure 6). The primary circuit comprises the reactor, four primary pumps to circulate the water, two heat exchangers or steam generators and a pressurizer. The nuclear reaction produces heat. The pumps circulate the heat transfer fluid (pressurized water) between the reactor and the heat exchanger. Through the steam generator, the heat is transmitted to a secondary...