Three Mile Island's iconic reactor is moving closer to powering the artificial intelligence boom. The Federal Energy Regulatory Commission (FERC) approved a waiver that allows Constellation Energy to transfer grid interconnection rights from a retiring natural gas plant to Three Mile Island Unit 1, clearing a major regulatory hurdle and moving the project's restart timeline from 2031 to 2027.

Why Is Three Mile Island Restarting Now?

Three Mile Island shut down in 2019 for economic reasons, but the facility never lost its operating license, which remains valid through 2034. Constellation Energy announced plans in 2024 to revive the reactor as the "Crane Clean Energy Center," specifically to meet surging electricity demand from AI and cloud computing infrastructure. The plant will generate 835 megawatts of carbon-free electricity, a significant contribution to regional power supply at a time when data centers are consuming unprecedented amounts of energy.

Constellation Energy

The timing reflects a broader industry shift: as AI models grow larger and more computationally intensive, the power demands of training and running these systems have become a critical bottleneck. Microsoft's partnership with Constellation Energy to supply Three Mile Island's output to its data center network highlights how major technology companies are now directly investing in nuclear power as a solution to their energy needs.

What Was the Regulatory Barrier, and How Was It Solved?

The original challenge was straightforward but significant. Regional transmission operator PJM approved reconnecting Three Mile Island by 2027, but separate grid studies indicated the plant could not deliver its full 835 megawatts of power until after 2030 due to required transmission upgrades. This gap between when the plant could restart and when it could operate at full capacity created a four-year delay.

Constellation's solution was creative: the company requested permission to transfer capacity interconnection rights from two units at its Eddystone natural gas generating station near Philadelphia. FERC approved the transfer, determining that it would improve Three Mile Island's interim deliverability and allow full-capacity operation sooner. Importantly, the regulator concluded the waiver would not harm other market participants or grid users.

The Eddystone units, originally scheduled for retirement, will remain operational under Department of Energy emergency orders that require them to support regional grid reliability. Under the new arrangement, these units can continue producing electricity without retaining their capacity market status, allowing their rights to be reassigned to the restarted nuclear facility.

How to Understand the Licensing Path Forward

• Environmental Review: The Nuclear Regulatory Commission (NRC) released a draft environmental assessment and a draft Finding of No Significant Impact (FONSI) on June 8, 2026, for public review. The NRC's preliminary conclusion is that restarting the reactor would not significantly affect the surrounding environment, meaning a full Environmental Impact Statement may not be necessary.
• License Amendments: Constellation is seeking approval to restart operations under the existing operating license that remains valid through 2034, while also exploring the possibility of extending the plant's operational life to 2054.
• Federal Coordination: The restart effort is progressing through the federal nuclear licensing process, with the NRC's assessment forming part of its review of Constellation's requests for license amendments and exemptions needed to resume commercial operations.

The regulatory momentum is significant. By transferring interconnection rights rather than waiting for new transmission infrastructure, Constellation has effectively compressed a four-year delay into a manageable timeline. The NRC's preliminary environmental assessment suggests the licensing process may move faster than a full Environmental Impact Statement would allow.

What Does This Mean for AI Infrastructure and Power Grids?

Three Mile Island's restart represents a pivotal moment in how the technology industry addresses its energy crisis. AI data centers are among the most power-intensive facilities in the world, and their proliferation has created urgent demand for reliable, carbon-free electricity. Nuclear power offers a solution that coal and natural gas cannot match: continuous, emissions-free baseload power that can run 24/7 without weather dependency.

If approved and completed on schedule, the revived Three Mile Island reactor would become one of the most significant nuclear restart projects in the United States and a major source of emissions-free electricity for decades to come. The project has attracted national attention precisely because it highlights the growing role nuclear power could play in meeting electricity demand from energy-intensive technologies, including AI.

The waiver approval also signals that federal regulators understand the urgency of the situation. Rather than forcing Constellation to wait for transmission upgrades, FERC found a creative solution that balances grid reliability with the need to accelerate clean energy deployment. This pragmatic approach may set a precedent for other nuclear restart projects facing similar interconnection challenges.

For Microsoft and other hyperscalers planning massive AI infrastructure expansions, Three Mile Island's 2027 restart date offers a concrete timeline for securing clean power. The 835 megawatts of carbon-free electricity will be enough to power a substantial portion of a modern AI data center complex, reducing both operational costs and carbon emissions compared to relying on regional grid power sourced from fossil fuels.