Constellation, an energy company that provides electricity and natural gas to customers in 16 states and Washington, announced on September 20, 2024, that it plans to restore and restart Unit 1 at Three Mile Island, a nuclear plant near Middletown, Pennsylvania, that was shut down in 2019. Microsoft has signed a 20-year agreement to purchase electricity generated by the facility to reduce electricity demand for its data centers in the mid-Atlantic region.
Three Mile Island became the site of the 1979 Unit 2 reactor plant meltdown. The Nuclear Regulatory Commission called the incident “the worst accident in the history of US nuclear power plant operations,” although only small amounts of radiation were released, and no health effects to plant workers or the public were found. Unit 1 was not affected by the accident. University of Michigan nuclear engineering professor Todd Allen explains what restarting Unit 1 will entail, and why other shuttered nuclear plants may get a new lease on life.
What is the history of TMI-1?
Three Mile Island Unit 1 is a large nuclear power station with a capacity to generate 837 megawatts of electricity – enough to power about 800,000 homes. It began commercial operations in 1974 and operated until September 2019.
After the Unit 2 accident in 1979, Unit 1 was shut down for six years, until the operator at the time, Metropolitan Edison, demonstrated to the Nuclear Regulatory Commission that it could operate the reactor safely.
Constellation shut Unit 1 down in 2019, although the facility’s operating license had been extended to 2034 and had no operational or safety issues. TMI-1 could not compete economically at the time with natural gas-fired power plants because gas was so cheap.
Pennsylvania also has a policy preference for increasing electricity production from solar and wind power. The state legislature chose not to reclassify the plant as a carbon-free power source, which would have been eligible for government support.
What is the current state of the reactor?
Since its closure in 2019, the plant has remained idle. The NRC calls this secure storage condition, or SAFSTOR. The facility is shut down, the uranium fuel is removed from the reactor, and the facility is kept in a safe, stable environment. Spent fuel is stored in large steel and concrete boxes in a physically protected part of the site, known as the Independent Spent Fuel Storage Facility.
Besides the fuel, other things in the plant are radioactive, such as the structural channels that direct the cooling water during operation and the main vessel where the reactor is kept. Radioactive decay occurs during SAFSTOR, reducing the radiation output of the plant and making it easier to dismantle the plant later.
What will Constellation need to prepare the reactor for restart?
Constellation will need to ensure that it has enough fuel and an adequately trained crew. It will also have to ensure that the reactor components are still in a condition that allows for safe operation.
This will require detailed testing and mandatory maintenance actions to ensure that all components are working properly. In some cases, the company may need to install new equipment.
The exact work will depend on the results of the tests but could include upgrading or replacing major parts of the reactor, such as the turbine and associated power generator; large transformers that move electricity from the reactor to the grid; equipment used to cool the reactor during operation; and plant control systems during startup, shutdown and power generation.
As an illustration, imagine you move to a city and stop driving your car for five years. When you decide to start driving again, you’ll need to make sure you have gas, that your driver’s license is still valid and that all parts of the car are still working properly. It will probably need new oil, air in the tires, new filters and other replacement parts to keep it running smoothly.
A nuclear plant is more complex than a car, so the amount of testing and verification will take longer and cost more. Constellation expects to bring the restored plant online in 2028 at an estimated cost of US $1.6 billion.
What will the NRC consider as it decides whether to decommission the reactor?
The agency needs to independently verify that Constellation has sufficient fuel and trained personnel, and that the plant can operate safely. These checks must be approved by the commission before the facility can operate.
In my view, Constellation will need to demonstrate that the plant is in a position to operate at the same safety levels as it was in September 2019 when the company ceased operations.
Do you expect other utilities to attempt this type of recovery in closed reactors?
Constellation is not the only utility considering restarting a nuclear plant. Holtec International, an energy technology company, bought the closed Palisades nuclear plant in southwest Michigan with the intention of decommissioning it in 2022, but the company then decided to restore and reopen the plant.
That work is now underway. Recently, in its first major inspection of the industry, NRC found a number of parts that it says require additional testing and repair work.
Wolverine Power Cooperative, a non-profit energy provider to rural communities across Michigan, plans to purchase electricity from the restored Palisades plant, with the help of the US Department of Agriculture’s Rural Empowerment Program. Holtec is receiving support for the Palisades restoration from the US Department of Energy and the state of Michigan.
A third company, NextEra Energy, is considering restarting its Duane Arnold nuclear plant in Palo, Iowa. And others could follow. In the last decade, a dozen nuclear plants were shut down before the end of their licensed operating life because they were struggling to compete economically. But as demand for electricity increases, particularly to power data centers and electric vehicles, some of those plants may be candidates for reopening.
Todd Allen is a professor of nuclear engineering and radiological science at the University of Michigan.
This article has been republished from The conversation under a Creative Commons license. Read the first article.
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