Microsoft and Three Mile Island: Why a 20-Year Buyer Matters

In 2024, Constellation estimated it would spend about $1.6 billion to restart Three Mile Island Unit 1 in Pennsylvania, a reactor it had retired in 2019 for economic reasons. What changed was a buyer. In September 2024, Constellation announced a 20-year power purchase agreement under which Microsoft will purchase the output of the renewed plant.

The plant is now called the Crane Clean Energy Center. The 1979 accident happened at the separate Unit 2, and Constellation says Unit 1’s long-term operation was not affected by it. The business question is what makes a restart worth attempting, and what could still get in the way.

Why a working plant can lose money

A power plant can work technically and still fail commercially. Staff, maintenance and fuel have to be paid for, and electricity sales have to cover the bills. A restart means committing money before the plant earns anything from renewed operations.

Constellation’s investor presentation describes the Microsoft deal as a 20-year fixed-price agreement for the plant’s full output. That makes future revenue easier to plan around. The restart has a committed buyer instead of relying entirely on future market prices.

Keep the two numbers separate

In November 2025, the Department of Energy closed a $1 billion loan to Constellation to help finance the restart. The two figures answer different questions. $1.6 billion was Constellation’s announced restart estimate. $1 billion is loan financing for the project, and it has to be repaid. Adding them together would double count part of the funding story.

Neither figure is what Microsoft pays for the electricity, and that price has not been disclosed. The size of the investment is visible. Its profit or payback cannot be calculated from these figures alone.

What Microsoft is buying

For Microsoft, the attraction is a large supply of carbon-free electricity over a long period. Constellation says the purchases are part of Microsoft’s goal to match the power its data centers in PJM, the regional grid, use with carbon-free energy. Those data centers run cloud services as well as AI, so the agreement concerns electricity for a broad computing business. Crane’s planned capacity is about 835 megawatts.

That power enters a shared grid through transformers, substations and transmission connections. Microsoft is the customer and Constellation owns the plant. The arrangement is regional, not a private line into one AI service.

A contract is not yet electricity

Buying future power and having power available are different milestones. A contract can be signed while the physical work is years from finished, and a data center expansion has to be planned around when the electricity can actually reach the grid.

Constellation says the restart includes restoring the turbine, generator, main power transformer, and cooling and control systems. Returning the plant to operation also requires Nuclear Regulatory Commission approval, including inspections and licensing work.

Approvals and the 2027 target

In August 2026, Constellation reported that the NRC had approved a fuel license amendment and that federal regulators had approved moving grid interconnection rights from another Constellation plant to Crane. It was targeting a restart in 2027, earlier than the 2028 date it gave in 2024.

Those are milestones, not final permission to operate. As of October 2026, the NRC’s record still lists the restart license changes as under review, and 2027 remains a company target. A delay would postpone the power the agreement is meant to bring back.

A wider strategy

On October 6, 2026, Google and Constellation announced a separate 20-year power purchase agreement supporting upgrades intended to add 890 megawatts across 11 existing Constellation nuclear units, with the first upgrade expected by 2028. It is a different project from Crane.

The shared idea is a large technology customer committing to purchases that help support investment in generating capacity. It suggests that access to electricity can become a competitive advantage in the AI build-out. A company planning more computing needs a credible plan for the power behind it.

What still has to go right

Unit 1 is not a new kind of reactor. A long-term buyer helped change the business case for bringing an existing one back. The test is whether Constellation can deliver safely, on schedule and at a cost that makes the deal work. It is the same execution test that decides whether Intel’s factories turn a design into a product.

When the next AI expansion is announced, look for the power agreement, the grid connection and the delivery date. Does reliable power become a competitive advantage in the AI race?