goingcritical:crane-tmi-1United States · Restart

Crane Clean Energy Center (Three Mile Island Unit 1)

Status: Under construction target criticality 2027 (confidence: medium) ? Reactor status full glossary → Announced Publicly announced — a site and design are proposed, but construction has not begun. Site preparation Early site and civil works are under way; the first safety-related ("nuclear") concrete has not yet been poured. Under construction Formal construction has begun, marked by the first nuclear concrete. Fuel loaded Nuclear fuel has been loaded into the core. The reactor is fuelled but has not yet gone critical. Critical Has reached first criticality — a self-sustaining chain reaction, usually at low power — but is not yet connected to the grid. Grid connected Synchronised to the electrical grid and exporting power for the first time, but still in commissioning and power-ascension testing — not yet in commercial service. Operating In commercial operation — the operator has formally declared the unit in regular commercial service. Shut down Permanently shut down and no longer generating; may be defuelled, undergoing decommissioning, or preserved in place. Canceled Abandoned before completion.

Developer: Constellation Energy

Site: Londonderry Township, Pennsylvania

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Constellation accelerated the restart target from 2028 to 2027 and says the project is ahead of schedule; NRC restart approval still pending (draft environmental assessment issued June 2026)

Details

Design	Babcock & Wilcox PWR
Electrical output	835 MWe

Milestone history

1. Announced September 20, 2024
2. Construction start —
3. Fuel load —
4. First criticality target 2027
5. Grid connection —
6. Commercial operation —