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 wat

After an anxious month, on April 27th operators established natural convection circulation of coolant. The reactor core was being cooled by the natural movement of water rather than by mechanical pumping. The plant was in "cold shutdown".

er 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).

By late afternoon, operators began high-pressure injection of water into the reactor cooling system to increase pressure and to collapse steam bubbles. By 7:50 pm on 28 March, they restored forced cooling of the reactor when they were able to restart one reactor coolant pump. They had condensed steam so that the pump could run without severe vibrations. Radioactive gases from the reactor cooling system built up in the makeup tank in the auxiliary building. During March 29 and 30, operators used a system of pipes and compressors to move the gas to waste gas decay tanks. The compressors leaked, and some radioactive gas was released to the environment (Three Mile Island, 2001).

More than 2,000 lawsuits, claiming that leaked radiation caused cancer, and birth defects such as clubfeet and Down Syndrome, were dismissed in 1996 but now are on appeal. Although studies done after the incident showed that increased radiation in the air did not pose threats to humans, a 1997 study revealed an increase in cancer in areas surrounding Three Mile Island (Three Mile Island, 1997).

From March 30

Some common words found in the essay are:
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Approximate Word count = 1117
Approximate Pages = 4 (250 words per page double spaced)