The Three Mile Island Nuclear Generating Station is a commercial nuclear power plant. It is located on Three Mile Island in the Susquehanna River. The island is three miles downriver from the town of Middletown, Pennsylvania which is near the city of Harrisburg, Pennsylvania. There are two nuclear reactors referred to as Three Mile Island Unit 1(TMI-1) and Three Mile Island Unit 2 (TMI-2) at the station.
TMI-1 is a pressurized water reactor with two cooling towers that draws water from the Susquehanna River. It has a net generating capacity of eight hundred megawatts of electrical energy. It began generating electricity in 1974 and was licensed to operate for fourty years. In 2009, its license was extended for another twenty years.
TMI-2 is a pressurized water reactor with two cooling towers that draws water from the Susquehanna River and is similar to TMI-2 It has a net generating capacity of nine hundred megawatts of electrical energy. It began generating electricity in at the end of 1978 and was licensed to operate for fourty years.
On March 28, 1979 TMI-2 suffered the worst accident to ever happen at a commercial nuclear reactor in the United States. At 4 A.M. there were failures in the secondary cooling system which is separate from the reactor core. Then a relief valve stuck in the open position in the primary cooling system which resulted in the release of large amounts of the steam from the reactor.
The operators failed to recognize that the problem was a loss of coolant. The indicators in the control room had been poorly designed and the operators were not well trained. One of the operators mistakenly believed that there was too much water in the reactor causing the steam release. He prevented the automatic emergency cooling system from switching on.
The employees of Met Ed, the company that operated the TMI power station and the Nuclear Regulatory Commission (NRC) spent the next five days trying to understand the full scope and cause of the accident. During that time, they worked with the media to communication the evolving situation to public, especially those who lived around the plant. One hundred and fourty thousand pregnant women and pre-school children were evacuated from the surrounding area. The NRC ultimately authorized the release of fourty thousand gallons of radioactive waste water into the Susquehanna River. This led to a public outcry and loss of credibility for the NRC. The full complexity of the accident was not well understood until much later.
Although there were radioactive gases and iodine-131released into the environment, the authorities claimed that subsequent epidemiological studies indicate that there was no impact on public health. This finding has been disputed up to the present day with claims that some people were made ill by the accident.
Clean up started in the summer of 1979 and officially ended in December of 1993, nearly fifteen years later, and cost around one billion dollars. The seven level International Nuclear Event Scale rated the accident as an "Accident with Wider Consequences" known as a level five incident.
Public reaction to the accident galvanized the anti-nuclear activists. New regulations were imposed on the nuclear industry and there was a decline in the construction of new power plants.
