1979 Three Mile Island Nuclear Reactor Incident
Three Mile Island is a nuclear power station located in Middletown, Pennsylvania, along the Susquehanna River, just ten miles south of the Pennsylvania state capital Harrisburg, and is also the site of the worst commercial nuclear disaster in United States history that took place on March 28, 1979 (Nuclear Disaster, 1997).
The pilot-operated relief valve (PORV) on the reactor cooling system opened like it was supposed to and then about ten seconds later it should have closed but it remained open, leaking very important reactor coolant water to the reactor coolant drain tank. The operators believed the PORV had shut because instruments showed them that a signal was sent to the valve but they did not have an instrument indicating the valve’s actual position. High-pressure injection pumps automatically pushed replacement water into the reactor system (Three Mile Island, 2001). As water and steam escaped through the relief valve, cooling water surged into the pressuriser, raising the water level in it. Operators responded by reducing the flow of replacement water. Their training told them that the pressuriser water level was the only dependable indication of the amount of cooling water in the system. Because the pressuriser level was increasing, they thought the reactor system was too full of water. Their training told them to do all they could to keep the pressuriser from filling with water. If it filled, they could not control pressure in the cooling system and it might rupture (Three Mile Island, 2001).
Steam then formed in the reactor cooling system. Pumping a mixture of steam and water caused the reactor cooling pumps to vibrate. Because the severe vibrations could have damaged the pumps and made them unusable, operators shut down the pumps. This ended forced cooling of the reactor.However, as reactor coolant water boiled away, the reactor’s fuel core was uncovered and became ev…