Facts to Know About Three Mile Island

  • By: David
  • Date: September 13, 2022
  • Time to read: 3 min.

Three Mile Island was the site of one of the most devastating accidents in the history of commercial nuclear power plants. The accident occurred on March 28, 1979, when a partial meltdown occurred in the Unit 2 reactor. This accident is the worst ever at a commercial nuclear power plant in the United States. Learn more about the disaster and how it affected Pennsylvanians.

Unit 2

The nuclear regulatory commission has approved the sale of Unit 2 of Three Mile Island to energy company EnergySolutions, LLC. The deal involves transferring the license from the New Jersey Power Authority to EnergySolutions, which will manage the decommissioning. The company hopes that the plant will be decommissioned by the end 2025.

After an accident in 1979, Unit 2 on Three Mile Island was rendered unusable. The unit suffered a partial meltdown and loss of coolant. The reactor needed extensive repairs and the clean up effort continued until 1990. The unaffected Unit 1 was reopened in 1985, but Unit 2 has been shut down.

The decommissioning of Unit 2 of Three Mile Island will cost more than $1 billion. EnergySolutions is looking to buy the Three Mile Island Unit 2 reactor from First Energy, but it will not take Unit 1, which is still operational. Exelon plans to close the Three Mile Island Unit 1 reactor in the fall.

In 1979, the Three Mile Island reactor underwent a partial core meltdown. Nearly 99 percent of the reactor vessel’s fuel and other core debris were removed and transported to the Idaho National Laboratory in Idaho Falls. The plant is currently in Post Defueling Monitored Storage (PDMS) and is under constant monitoring.

Over a thousand skilled workers developed the clean-up plan and began in August 1979. The first shipments of accident-generated low-level radiological waste were shipped to Richland, Washington, and the final measurements of the fuel in the reactor vessel were taken in 1991. This process removed all remaining fuel and water.

Unit 1

Near Harrisburg, Pennsylvania, is the Three Mile Island power plant. It has two pressurized water reactors. The first unit (TMI-1) entered service in 1974 with an installed capacity of 880 megawatts (MW), or 819 MWe net. The second unit, TMI-2, was damaged in an accident in 1979 and has not been reopened.

In 1967, the General Public Utilities Corporation started construction on Unit 1 of Three Mile Island. The plant was expanded in the 1970s. Metropolitan Edison took over the operation of the reactors and plant while they were being built. Its reactors were pressurized water reactors, which are the most common type of nuclear power reactors in the world.

Exelon estimates that Unit 1 would cost $1.2 billion to decommission over 60 years. However, the plant has been shut down. The company plans to transfer Unit 1 and Unit 2 to other companies in the near future. Both units will be closed by the company before 2024.

The reactors at TMI are still radioactive. TMI units will remain radioactive for decades after their decommissioning. This is because it is a lengthy process. Some radioactive waste will remain onsite, but the company claims minimal environmental impact. The Pennsylvania Department of Environmental Protection will closely monitor the decommissioning process of TMI Unit 1.

In the 1970s, the United States was battling a major oil crisis. According to Smithsonian magazine, gasoline prices had risen by 81% from 1975 to 1988. Nuclear power plants were built across America hoping to find cheaper alternatives to petroleum. Nuclear energy was seen in Middletown as a solution to the problem.

The accident occurred on 28 March 1979, at 4 a.m. A malfunction in the reactor cooling system caused a pilot-operated relief valve to open, a process that should have closed ten seconds later. The valve was left open, which allowed the reactor to leak critical coolant water. This caused the reactor core to suffer catastrophic damage.

The operators mistakenly believed that the reactor’s core would overflow with water. Although the emergency cooling system was shut off, the operators could to restore the reactor to normal temperatures by 8 p.m.

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