The story of Three Mile Island, located near Harrisburg, Pennsylvania, is a tale of technological failure and crisis management that gripped the nation in the late 1970s. On March 28, 1979, the worst accident in the history of American commercial nuclear power unfolded at the Three Mile Island Nuclear Generating Station, specifically at the Unit 2 reactor.
In the early hours of that day, a minor malfunction occurred in the secondary, non-nuclear section of the plant. This triggered the shutdown of the main feedwater pumps, which were responsible for sending water to the steam generators that remove heat from the reactor core. Without the water supply, the reactor began to overheat.
As the pressure in the primary coolant system rose, a relief valve opened to relieve the pressure but failed to close as it should have, allowing large amounts of coolant to escape. This malfunction went unnoticed by the plant operators, who misinterpreted the readings from their instruments. They assumed the valve had closed and that the core was still properly cooled, leading to a series of incorrect decisions.
The plant's control room was filled with confusing and sometimes contradictory information. The operators shut down the emergency cooling pumps because they believed the core was overfilled with coolant, while in reality, the reactor was losing coolant and overheating. This misjudgment exacerbated the situation, causing the reactor core to be partially uncovered and leading to the core's meltdown.
The first signs of a serious problem emerged when the temperature of the reactor coolant system continued to rise despite efforts to control it. By mid-morning, radiation levels inside the plant were significantly elevated. The plant operators were uncertain about the extent of the damage and the amount of radioactive material that might be released. The lack of clear information and the complexity of the situation led to delays in providing accurate information to the public and authorities.
As news of the incident spread, public fear and confusion grew. The governor of Pennsylvania, Dick Thornburgh, was advised to evacuate the area, but initial uncertainty about the severity of the situation led to mixed messages. On March 30, with concerns mounting, he advised pregnant women and young children within a five-mile radius to leave the area as a precautionary measure.
During the next few days, efforts to stabilize the reactor continued amid widespread fear of a major radiation release. On April 1, a hydrogen bubble was discovered in the reactor vessel, raising fears of a potential explosion. However, experts concluded that the bubble would not ignite, and by April 4, the crisis was considered under control as the hydrogen was dissipated and the reactor cooled.
In the aftermath, detailed investigations revealed that although some radioactive gases had been released, the overall radiation exposure to the public was low and not expected to cause adverse health effects. However, the incident exposed serious flaws in the design, operation, and emergency response systems of nuclear power plants.
The Three Mile Island accident had profound impacts on the nuclear power industry. It led to widespread public opposition to nuclear energy, significant regulatory changes, and the eventual shutdown of many planned nuclear projects. The incident highlighted the need for improved safety measures, better operator training, and more effective communication protocols during emergencies.