Microsoft nuke power deal for Three Mile Island appears to be ahead of schedule

837 megawatt reactor now expected in 2027, energy CEO says

A revamped Three Mile Island nuclear plant could be fueling Microsoft's AI datacenters sooner than first thought, according to Constellation Energy executives.

In September 2024, Microsoft signed a 20-year power purchase agreement (PPA) with Constellation Energy to bring the shuttered TMI Unit-1 reactor — not to be confused with the Unit-2 reactor that had a partial meltdown back in 1979 — online in 2028.

But now, the CEO is making noises about being ready early. "Two years from now… when PJM gets this thing interconnected, we're going to be ready," Constellation Energy CEO Joe Dominguez said during a press conference [Video] on Wednesday. PJM, which stands for Pennsylvania-New Jersey-Maryland, is the local grid operator for the portion of Pennsylvania where the plant is located.

Constellation retired the 837-megawatt reactor back in 2019 after it failed to get subsidies it said were necessary for the plant to compete with cheaper fossil fuels. 

"We made a mistake in shutting down this plant. But we're not here to dwell on that mistake. We're here to look to the future," Dominguez said. 

As we previously reported, bringing the reactor back online won't be as simple as flipping a switch. While TMI Unit 1 has only been inactive for six years, the reactor itself is more than 50 years old, and the turbine, generator, transformers, and cooling and control systems will all need to be overhauled before it starts churning out electricity.

The reopening will also need approval from the US Nuclear Regulatory Commission — although that should be a known quantity for Constellation considering it already operates a fleet of 21 nuclear reactors across the United States.

Faced with AI's seemingly insatiable thirst for power, Microsoft is one of several hyperscalers that have thrown their weight behind nuclear, and more specifically Constellation, over the past year.

In June, Meta signed a 20-year PPA with Constellation to extend operations at its 1.1 gigawatt nuclear plant in DeWitt County, Illinois. The Clinton Clean Energy Center faced a similar fate as Three Mile Island's Unit 1 reactor once the state's zero-emission credit program expired in 2027.

Prior to the deal, Meta had solicited proposals for between one and four gigawatts of nuclear energy deliverable by 2030.

Amazon Web Services (AWS) has also sought refuge in the power of the atom, dropping $650 million to acquire Cumulus Data's nuclear bit barns, located alongside Talen Energy's 2.5 gigawatt Susquehanna nuclear power plant in northeast Pennsylvania. The original deal ensured Amazon access to a minimum of 480 megawatts of clean behind-the-meter energy, but was revised this spring after opposition from local utilities concerned about grid stability.

So, rather than getting its energy directly from the nuclear plant, Talen will now provide AWS's datacenters in the region with up to 1.92 gigawatts of grid power through the end of 2042, with the potential for small modular reactors (SMRs) to boost the plant's output further.

Alongside existing nuclear plants, SMRs have garnered considerable attention from hyperscalers, including Microsoft, Google, Amazon, and Oracle as a source of datacenter power. That said, most of these miniaturized reactors aren't expected to come online until the early 2030s. ®