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Pennsylvania's Three Mile Island Nuclear Generating Station opens its second nuclear reactor 4 years after Reactor-1. -
Less than 2 weeks before the TMI Reactor-2 accident, a movie called “The China Syndrome” depicts a meltdown at a fictional nuclear plant. -
Helicopters hired by GPU Nuclear (the company which operated the TMI facility at the time) and the U.S. Department of Energy sample radioactivity in the atmosphere above the power plant. A team from the Brookhaven National Laboratory is sent to assist in radiation monitoring. -
Problems start in 1 of 3 water loops in Reactor-2's pressurized water reactor: a small amount of water breaches a stuck-open valve and enters an air line. -
An operator saw that the emergency pumps were on, but did not notice a block valve was closed in both emergency lines. Valve position lights for one block valve were covered by a yellow maintenance tag. The reason why the operator missed the light for the 2nd valve is unknown.
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With block valves closed, the system was unable to pump water. The closure of these valves was a violation of a federal Nuclear Regulatory Commission (NRC) rule which requires reactors to be shut down if all auxiliary feed pumps are closed. Less than a minute after the start of the event, the water level in the pressurizer began to rise, forcing the pilot-operated relief valve open.
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With the pilot-operated relief valve stuck open due to pressure, coolant levels dropped in the reactor coolant system. This causes 50% of Reactor-2's core to melt down, though the extent of the damage wasn't known to the public for years.
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The containment features of the reactor worked, holding in an estimated 18 billion Curies of radioactivity, more than 100 times the amount that was estimated to be released in the 1986 Chernobyl disaster. No one died as an immediate result of the Reactor-2 meltdown.
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Water in the instrument air line causes feedwater pumps (which cool Reactor-2's core) to shut down. 3 emergency feedwater pumps start automatically, but they would fail to increase water flow.
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Residents who didn't evacuate report a "metallic taste" in their mouths immediately after the accident. Some complained of skin rashes, nausea, and respiratory problems.
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Venting of radioactive steam is performed to relieve pressure on the primary system and avoid blockages in the flow of coolant to the core. Pennsylvania Governor Dick Thornburgh advises pregnant women and preschool-age children within a 5-mile radius to evacuate.
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President Jimmy Carter and First Lady arrive at Three Mile Island several days after the accident to reassure the public. Carter was also a trained nuclear engineer. -
Immediate cleanup efforts started in August 1979 and officially ended in December 1993, with a total cost of about $1 billion. Efforts focused on defueling the damaged reactor. Additional efforts to contain radioactive waste from the Reactor-2 accident continue to this day. -
The Three Mile Island accident inspired nationwide protests against nuclear energy, including a protest of 200,000 people in NYC. It is considered the largest anti-nuclear protest to date. Public support for nuclear energy fell from 69% in 1977 to 46% in 1979. -
The Kemeny Commission was a research group established by President Carter to publish a health impact report within 6 months of the TMI Reactor-2 accident. They concluded that mental distress was the only health threat the accident posed to residents. The commission consisted of a panel of 12 researchers chosen for their lack of strong pro- or anti-nuclear views, headed by John G. Kemeny, president of Dartmouth College.
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PA Health Secretary Gordon MacLeod publicly stated the # of babies born with hypothyroidism in 3 counties surrounding TMI jumped from 9 in the 9 months before the accident to 20 in the 9 months after. In the county where TMI is located, the 1979 death rate of infants 1 year old increased 28% from 1978; among infants 1 month, an increase of 54%.
MacLeod was fired by the governor within 6 months. Epidemiology officials in 1981 claimed the accident caused "no significant physical health effects." -
The U.S. Supreme Court denied citizen activist group TMI Alert's request to halt the restart of Three Mile Island's undamaged Reactor-1 by an 8-1 vote.
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Information gathered by the PA Department of Health from residents within a 5-mile radius of the TMI accident was compared with decades of mortality data for the area. The number of deaths from cancer among the "exposed" population was not significantly different from the general population. There was a small rise in the number of lymphatic and blood cancer deaths among women in the exposed group.
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After a series of legal challenges, a federal appeals court dismisses consolidated cases of 2,000 plaintiffs who sought damages for illnesses related to the Three-Mile Island accident. The court says the plaintiffs failed to present evidence that they received a radiation dose large enough to cause health effects.
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Due to financial struggles in the energy industry overall, the TMI Generating Station shuts down. The nuclear industry generally struggles to compete with less expensive energy generated from natural gas, solar, and wind. -
TMI-2 Solutions announces they are moving into a cleanup phase they call DECON, involving removing contaminated materials with remotely-operated robots and sending them to a specialized disposal site. This phase will last until 2029.
TMI-2 Solutions plans to finish all cleanup by 2052. The company originally planned to be done by 2037, but said "current market conditions are creating a delay." -
Constellation Energy plans to sell Reactor-1 to Microsoft, which wants to dedicate its energy to AI data centers. Reactor-1 is expected to restart in 2028, subject to approval by the Nuclear Regulatory Commission. Its control room still looks largely the same as it did in the 1980s. -
Over 100 people attended a public meeting held by the federal Nuclear Regulatory Commission (NRC) on what it would mean to restart Reactor-1 for Microsoft. More people provided statements virtually in August.
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Constellation Energy says Reactor-1 could generate power again by 2027, a year earlier than initially projected.