Three Mile Island

Protesters Opposing Give Up Contol of the Canal

On March 28, 1979, a stuck valve at the Three Mile Island nuclear reactor in Pennsylvania released a cloud of radioactive gas in the air. One hundred thousand local residents fled their homes. The accident triggered a thorough reappraisal of nuclear safety, and resulted in a complete halt in the building of nuclear plants. Even plants that were close to completion, like the Shoreham Nuclear Plant on Long Island, had their completion terminated by an invigorated anti-nuclear movement.

Construction began on the Three Mile Island Nuclear plant on May 18, 1968. The plant is located south of Harrisburg Pennsylvania. Unit 1 of the plant opened on September 2, 1974, and the second unit opened December 30, 1978.

On March 28, 1979 reactor #2 was operating at 97% while the reactor one was shut down for refueling. The evening before there was an unsuccessful attempt to clean one of the filters used in the secondary cooling system. This resulted a few hours later for the feedwater turbines to close off. This provides cooling for the reactor. This resulted in the generators no longer receiving water to heat, and this caused the reactor to shut down automatically. With the secondary pumps stopped the auxiliary pumps kicked in, but their valves were closed for maintenance, and they were not able to pump any water — the lack of coolant resultant in the primary loop pressure to increase which resulted in a relief valve on the top of the regulator tank to open automatically. The valve should have closes automatically, but a mechanical failure kept it open. Unfortunately, in the control room, a false indicator showed that the valve was closed. As a result, the containment tank that was filling with radioactive gas and gas began to escape, causing alarms to sound 4:11 AM. The situation, however, was not fully understood and with no coolant circulating there was a partial meltdown of the core. When the new shift of the workers arrived, they realized how bad the situation was and at 6:57 AM an emergency was declared.

Radiation was indeed released into the air, but most of the truly radioactive gas remained in the containment buildings. The amount released in the air was no more than the average person receives when they receive an Xray.

The accident was the worse nuclear accident to occur in the United States. As a result of the accident the growth of nuclear power in the United States came to a complete halt. 51 nuclear plants were canceled between 1980-1984.