Three Mile Island: The Controversy Continues

On March 28, 1979, a cooling circuit pump in the non-nuclear section of Three Mile Island's second station (TMI-2) malfunctioned, causing the reactor's primary coolant to heat and internal pressure to rise. Within seconds, the automated response mechanism thrust control rods into the reactor and shut down the core. An escape valve opened to release pressure but failed to close properly. Control room operators only saw that a "close" command was sent to the relief valve, but nothing displayed the valve's actual position.[1] With the valve open, coolant escaped through the pressurizer, sending misinformation to operators that there was too much pressure in the coolant system. Operators then shut down the water pumps to relieve the "pressure......."