Three Mile Island accident

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Tmi-2 schematic

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Graphic TMI-2 Core End-State Configuration

Three Mile Island accident sign

Harrisburg Int Airport with Pennsylvania ANG aircraft 1979

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Nuclear power history

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TMI cleanup-2

Three Mile Island accident was a significant event in the history of nuclear power in the United States, occurring on March 28, 1979. It was the most serious accident in U.S. commercial nuclear power plant history. The incident took place at the Three Mile Island Nuclear Generating Station in Dauphin County, Pennsylvania, near Harrisburg. It was a partial meltdown of reactor number 2 (TMI-2) of the plant. Despite the significant release of radioactive gases, there were no immediate deaths or injuries due to the accident, but the event had lasting impacts on nuclear policy, safety regulations, and public perception of nuclear energy.

Background

The Three Mile Island Nuclear Generating Station, located on a small island in the Susquehanna River, consisted of two separate nuclear reactors, TMI-1 and TMI-2. At the time of the accident, TMI-2 was relatively new, having been in operation for only about three months.

The Accident

The accident began in the early morning hours of March 28, 1979, when a failure in the non-nuclear secondary system led to a malfunction in the primary cooling system of the TMI-2 reactor. This caused the reactor core to overheat due to a lack of cooling water. A series of operator errors and equipment failures exacerbated the situation, leading to a partial meltdown of the reactor core. The most critical moment occurred when a relief valve failed to close, but indicators in the control room mistakenly showed that the valve was closed, leading operators to reduce cooling water flow when it was critically needed.

Response and Aftermath

Immediate efforts to stabilize the reactor and contain the release of radioactive materials were successful to a degree, but small amounts of radioactive gases were released into the environment. The incident prompted widespread public fear and mistrust of nuclear power. In response, the Nuclear Regulatory Commission (NRC) tightened its regulatory oversight, and many new safety protocols and emergency response procedures were implemented across the industry.

The cleanup of the TMI-2 reactor took nearly 12 years and cost approximately $1 billion. The reactor was permanently shut down, but TMI-1 continued to operate until September 20, 2019.

Impact

The Three Mile Island accident had a profound impact on nuclear power development in the United States. It led to a halt in the construction of new nuclear plants, as public concern and regulatory requirements increased. The accident also fueled anti-nuclear movements and led to significant changes in how nuclear plants were regulated and operated. It highlighted the need for improved safety measures, better operator training, and more stringent regulatory oversight.

Legacy

Today, the Three Mile Island accident serves as a case study in the importance of nuclear safety and the potential consequences of human and mechanical error in the operation of nuclear power plants. It also remains a pivotal moment in the debate over the role of nuclear energy in the United States and around the world.