Three Mile Island is best known for the worst U.S. nuclear event ever. Now it's coming back to power Microsoft's AI.
Constellation signed a 20-year deal with Microsoft in September 2024. The deal restarts Unit 1 of the plant.
That's a different reactor than the one that broke down in 1979. Unit 1 was shut in 2019 to save costs.
Microsoft will buy the full 835 megawatts of output. That power will match its data center use.
The sites are in Pennsylvania, Chicago, Virginia, and Ohio.
The deal is the biggest power deal Constellation has ever signed.
AI data centers need power that runs all day. Solar and wind can't do that.
Nuclear can.
It also has zero carbon. That fits the climate goals Microsoft has set.
The firm will spend about $1.6 billion to fix up the plant. That covers new turbines and other parts.
The Trump team gave the firm a $1 billion loan in November 2025. That pulled the restart up from 2028 to 2027.
The plant's license got pushed out to 2054.
Microsoft's deal kicked off a wave across the field. Amazon signed deals with the the Susquehanna nuclear plant in Pennsylvania and the Clinton plant in Illinois.
Google and Meta have signed with firms making smaller next-gen reactors.
Constellation (CEG) is the biggest U.S. nuclear name. It runs 21 reactors.
They put out 22.1 gigawatts. That can power about 40 million homes.
The firm cleared 17,950 megawatts in PJM's December 2025 auction. That locks in about $2.2 billion in 2027/28 revenue.
The 20-year deal length is unusual. Microsoft's solar and wind deals are much shorter.
That length tells you how baseline this kind of power has become for big tech.
For investors, the nuclear names tied to AI demand have all run hard on this story. The list includes Constellation (CEG), Vistra (VST), and Talen Energy (TLN).
Each owns big nuclear sites that can be tapped for cloud giant deals.
The trend isn't just about new power. It's about new long-term cash flow.
The plants were once seen as too costly to run.
Bobby Hollis runs energy at Microsoft. He's called it a "once-in-a-lifetime" chance.
He says nuclear is the only way to match AI's growth.
The reactor that started a nuclear safety debate is now one of the most-watched power deals in the country.
The 2027 startup date is the key checkpoint. If Constellation hits the date, more reactor restarts will follow.
The deal becomes a model.
The question is whether the restarts come in on time.
The 2027 date matters for a different reason too. Power deals signed today need a clear delivery path.
If the plant starts on time, more restarts will follow. The next sites for restart are already lined up.
That's the longer-term path. For now, all eyes are on the 2027 startup date.
Investors are watching for any sign of slip-ups.
