Constellation Energy (full disclosure – I work for them) announced plans to restart Three Mile Island Unit 1 after a power purchase deal was signed with Microsoft. This deal is intended to power data centers to support Microsoft’s AI push. The internet reacted with the expected doom and gloom whenever nuclear power is mentioned, with a dash of TMI misunderstanding thrown in.
Here’s the thing though; Three Mile Island Unit 1 ran safely for forty years after the accident at TMI Unit 2 in 1979. Unit 1 is the reactor being restarted. All of the pieces that make a power plant a power plant are still there. All of the systems that keep the reactor safe are still there. This is simply taking something that is still essentially a power plant, checking it out to make sure it still works, and refueling it.
The TMI Unit 2 accident didn’t actually hurt anyone. According to the NRC, the average dose received was 1 mrem. You receive more than that in an hour on an airplane. It was scary and confusing and absolutely not something that should ever happen again, but in the end all the harm was economic and social. If you want to dig into that a little deeper, I wrote about the accident a while ago.
Unit 1 shutdown for economic reasons in 2019, when natural gas was essentially free. I want you to take that in – TMI Unit 1 shutdown because it was cheaper to burn fossil fuels. In the middle of a climate crisis we took 900 MW of clean power off the grid. I don’t care about your stance on building new plants, but dumping that much near-zero CO2 power while the oceans boil seems like it might be self-defeating.
Now, there is a huge demand for power for data centers, and most of the tech companies that are into the AI push want clean power for their data centers. They could easily have chosen to partner with combined-cycle gas turbine power plants, the cleanest fossil fuel powered plants that exist. But, they chose to go nuclear because of the climate benefits. The chart below shows the CO2 emissions by type of power plant. Nuclear is just as clean as wind.
https://energy.utexas.edu/news/nuclear-and-wind-power-estimated-have-lowest-levelized-co2-emissions
Nor is this a first of its kind undertaking. The Palisades nuclear plant in Michigan shutdown in 2020 for similar reasons. It is currently going through the process to restart. There will be items needing repair. There will be major investments to bring the plant up to current safety standards. But, once it is back on the grid, that is another 800 MW of essentially zero CO2 energy back on the grid. They current estimate is for the plant to go back online in 2025.
https://www.technologyreview.com/2024/04/03/1090603/how-to-reopen-a-nuclear-power-plant/
This is not a haphazard process. The inspections that are required are extremely thorough. The NRC takes its responsibility as regulator seriously. They will not approve the restart unless the plant fully meets all current safety requirements. This is similar in scope to the process for obtaining license extensions for plants that are still running. Everything that is needed to make power and keep the plant running safely is inspected by experts and a plan is put in place to repair and maintain that equipment for the life of the plant.
The word current in the last paragraph deserves some emphasis. The NRC is requiring these plants to meet all safety standards that now exist, not simply return to the standards that they met when they shutdown. The NRC issues regulations all the time, updating the requirements to run a nuclear reactor. These restarted plants will meet all of them before returning to operation.
https://www.nrc.gov/reading-rm/doc-collections/fact-sheets/fs-reactor-license-renewal.html
Another concern I have seen is with the words AI being tied to a nuclear power plant. I actually agree that having AI involved in the operation of a nuclear power plant would be a terrible idea. Good thing that is not going to happen. The plant will be restored to its original operating condition, using the same controls and systems it used to operate safely for over forty years following the TMI Unit 2 accident. AI will not in any way be part of the operating systems of the facility.
The NRC takes a very conservative approach to modifications to nuclear plants. Any effort to use AI to run a power plant would require years and years of studies and proof that it met the requirements. Even after all of that happened, I don’t ever see the NRC getting rid of human operators. The ability to process information and make good decisions in a rapidly changing situation is the hallmark of well trained human beings. We are decades away from AI even being close to that level of capability and I don’t ever expect the human licensed operators to go away.
Microsoft will not be using Copilot to control the reactor. Human operators that have gone through one of the most rigorous job training programs on earth will still be in the control room. They will still have a legal mandate to operate safely, which includes shutting the reactors down if they think it is needed. They are legally held to those standards and could very easily end up in prison if they fail to meet them.
So, TMI Unit 1 will be inspected from top to bottom. Once any issues that are identified in these inspections are fixed, and the plant meets all safety standards just like a currently running plant does, the NRC will grant permission to load fuel back into the reactor. The plant will then return to operation under the same rules and regulations that have allowed millions of hours of safe operation by hundreds of reactors in the US.
As always, this is all open source. If you have any questions, please ask.
Sleepy Neutron's Nuclear Knowledge 
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