Crane Clean Energy Center (TMI-1 Restart) by Constellation Energy: status and timeline

Crane Clean Energy Center (TMI-1 Restart)

Constellation is restarting Three Mile Island Unit 1, a 835 MW pressurized water reactor shut down in 1999, to supply power to Microsoft data centers under a 20-year power purchase agreement.

DeployStage 4 of 5

NRC fuel license amendment approved. Restart targeted for 2027, pending transmission upgrades.

Checked 10 Oct0 updates this week

Milestones

Next · Reactor restart and grid connection

Three Mile Island Unit 1 shut down1999Complete.
NRC fuel license amendment approvedQ3 2026Complete.
Reactor restart and grid connectionTarget 2027Not yet reached.
Full commercial operationTarget Q4 2027Not yet reached.

Upcoming

2027Reactor restart and grid connection (next)
Q4 2027Full commercial operation

Current obstacles

Transmission bottleneckPJM estimates grid upgrades could take until 2031, potentially delaying grid connection after reactor startup.
Public perception of Three Mile IslandThe 1979 accident at Unit 2 created lasting safety concerns, requiring careful communication and regulatory confidence.

Physics limits

Physics and reactor safetyPressurized water reactors operate near the limits of water's pressure tolerance and heat transfer capacity. Neutron irradiation of reactor vessel materials sets an effective lifetime of 60–80 years.
Fuel enrichmentPWRs require uranium enriched to 3–5%, which depends on geopolitical fuel supply chains and U.S. enrichment capacity.

How it works

2 parts

Nuclear heat

PWR design

The pressurized water reactor uses uranium fuel to heat water under high pressure, which generates steam. Steam drives turbines for electricity.

Supply

Data center power

Constellation delivers the power to Microsoft under a long-term PPA for AI computing workloads.

Spec sheet

Spec	Crane Clean Energy Center (TMI-1 Restart)
Electrical output	835 MW^R (reported)
Reactor type	Pressurized water reactor (PWR)^R (reported)

^R reported by the company

About Constellation Energy

The team behind Crane Clean Energy Center (TMI-1 Restart)

Constellation Energy

Nuclear power, grid reliability, data center power

Constellation Energy is the largest private-sector power producer in the United States, operating 55 GW of generating capacity with over 16,500 employees. The company is restarting closed nuclear reactors and building new nuclear capacity to power data centers and support the AI boom.

Constellation operates 55 GW of generating capacity from nuclear, natural gas, and renewables.
Recent partnerships include Google (890 MW new nuclear capacity) and Amazon (190 MW expansion at Calvert Cliffs).
The company operates the largest fleet of nuclear power plants in the United States and supplies data centers seeking 24/7 clean power.

constellationenergy.com (opens constellationenergy.com)Company profile →

Founded: 199333 yrs
Headquarters: United States
Status: Public
Valuation: public
Staff: ~16,500Jan 2026
Works in: EnergyFission
Coverage: 1 program · 2 updateslatest 10d agochecked 10 Oct
Customers: MicrosoftGoogleAmazon
People: Joseph DominguezPresident and CEO

Spec

Crane Clean Energy Center (TMI-1 Restart)

Electrical output

835 MW^R (reported)

Reactor type

Pressurized water reactor (PWR)^R (reported)