Why Constellation is Restarting a Reactor for Microsoft

In September 2024, Constellation Energy announced the signing of a 20 year power purchase agreement with Microsoft that set up the launch of the restart of Three Mile Island Unit 1, to be known as the Crane Clean Energy Center. 

Constellation now says that the nuclear power plant is on track to restart ahead of schedule and will add US$16bn to Pennsylvania’s GDP. 

Three Mile Island Unit 2 was the site of what the US Nuclear Regulatory Commission describes as the “most serious accident” in US nuclear power plant history in 1979, and the reopening of Unit 1 faces some opposition. 

“As Microsoft continues its path to become a carbon negative company, this agreement brings a significant supply of new, reliable, carbon-free electricity back to the PJM power grid,” says Bobby Hollis, VP of Energy at Microsoft. 

“This will help address the grids’ capacity and reliability needs in the regions we operate.”

Why Microsoft wants nuclear power

By 2033, the UN Trade and Development predicts the AI market will reach US$4.8tn.

Nearly 80% of organisations surveyed by McKinsey already use AI in at least one business function, and generative AI has seen use grow from 33% in 2023 to 71% in 2024. 

Usage of generative AI has skyrocketed from 33% in 2023 to 71% in 2024.

As artificial intelligence and cloud computing depend heavily on data centers, they necessitate a large energy supply.

The growth of AI and cloud computing, both of which require data centres, need a significant amount of power. 

This has caused Microsoft’s emissions to rise despite its 2020 goal of becoming carbon negative by 2030. 

In the 2024 fiscal year, its total emissions rose by 23.4%. 

The company’s Chief Sustainability Officer, Melanie Nakagawa, implied this may be the case in February 2025, as Microsoft announced it was readjusting its focus on sustainability.

"In 2020, Microsoft leaders referred to our sustainability goals as a 'moonshot', and nearly five years later, we have had to acknowledge that the moon has gotten further away," she wrote in a blog post at the time.

The operational aspect of nuclear power plants promises zero greenhouse gas emissions, making them an excellent candidate for catering to energy-intensive data centre requirements without increasing their environmental impact.

In addition to nuclear power, Microsoft is investing in renewable resources.

However, the intermittent nature of wind and solar power presents limitations for the need for uninterrupted, 24/7 energy, which data centres require.

About the Crane Clean Energy Center

What is now known as the Crane Clean Energy Center was once Unit 1 of the Three Mile Island Nuclear Generating Station. 

A partial meltdown occurred in Unit 2 after a cooling malfunction led to overheating and damage to the fuel. 

Some radioactive gas was released a few days after the accident, but the World Nuclear Association says it was “not enough to cause any dose above background levels to local residents” and that there were no injuries or adverse health effects. 

The accident was rated Level 5 on the International Nuclear Event Scale (INES), indicating an incident with “wider consequences”, and Unit 2 is in the process of being decommissioned.

Unit 1 went offline for refuelling in 1979 around a month before the accident in Unit 2 and was brought back online in 1985.

It was shut down in 2019 due to financial issues, but the reactor remains in “excellent shape” according to Constellation. 

Ahead of schedule

With the power purchase agreement signed by Microsoft in 2020, the Crane Clean Energy Center was initially planned for activation in 2028.

Constellation now says the facility could restart as early as 2027 with the approval of an early interconnection request by grid operator PJM. 

“My Administration has worked closely with Constellation and PJM on the Crane Clean Energy Center since 2023 in order to get this new generation online as quickly as possible, ensure the reliability of our grid, and cement the Commonwealth’s energy future,” explains Pennsylvania Governor Josh Shapiro. 

“This restart will safely take advantage of existing infrastructure while creating thousands of energy jobs and strengthening Pennsylvania’s legacy as a national energy leader.”

“Today we begin a new chapter for reliable, emissions-free nuclear energy, returning thousands of good jobs and billions in economic opportunities for Pennsylvania families and businesses,” adds Joe Dominguez, Constellation’s President and CEO. 

“With PJM’s action, Microsoft’s historic investment and strong support from Governor Shapiro, elected officials and members of this community, we’re on track to make history ahead of schedule, helping America achieve energy independence, supercharge economic growth and win the global AI race.”

The facility is now more than 65% staffed and several technical milestones have been reached, including the successful operation of major systems including the main generator and turbines. 

“We congratulate Constellation, Microsoft and the state of Pennsylvania for doing something that seemed impossible just a few years ago: restarting a shuttered nuclear plant,” says Maria Korsnick, President and CEO of the Nuclear Energy Institute. 

“The US nuclear industry is uniquely positioned to meet the rising demand for clean, reliable, and affordable energy. The Crane Clean Energy Center is a powerful example of how our industry is rising to the challenge.”