Three Mile Island nuclear power plant
Three Mile Island nuclear power plant is a nuclear site in United States with 3 units on record. None is currently operating.
Units
| Unit | Status | Type | Model | Gross MW | Online |
|---|---|---|---|---|---|
| Unit 1 | Retired | PWR | B&W LLP (DRYAMB) | 880 | 1974 |
| Unit 2 | Retired | PWR | - | 959 | 1978 |
| Unit Unit 1 Repower | Pre-construction | PWR | B&W LLP (DRYAMB) | 880 | 2027 |
Unit by unit
Each unit's rating, type and milestone dates as recorded by the Global Nuclear Power Tracker, with any correction we made to it. A dash or "not disclosed" means the source does not give the value.
Three Mile Island nuclear power plant 1 Retired
| Reactor type | Pressurised water reactor (PWR) |
|---|---|
| Model | B&W 177-FA |
| Size class | Large |
| Gross capacity | 880MW |
| Net capacity | 819MW |
| Thermal output | 2,568MWt |
| Enrichment | 3–5% U-235 |
| NSSS vendor | Babcock & Wilcox |
| Owner | Exelon Corp100% |
| Operator | Exelon Generation |
| Construction start | 18 May 1968 |
|---|---|
| First criticality | 5 Jun 1974 |
| Grid connection | 19 Jun 1974 |
| Commercial operation | 2 Sep 1974 |
| Permanent shutdown | 20 Sep 2019 |
Three Mile Island nuclear power plant 2 Retired
| Reactor type | Pressurised water reactor (PWR) |
|---|---|
| Model | not disclosed |
| Size class | Large |
| Gross capacity | 959MW |
| Net capacity | 880MW |
| Thermal output | 2,772MWt |
| Enrichment | 3–5% U-235 |
| NSSS vendor | not on record |
| Operator | General Public Utilities |
| Construction start | 1 Nov 1969 |
|---|---|
| First criticality | 27 Mar 1978 |
| Grid connection | 21 Apr 1978 |
| Commercial operation | 30 Dec 1978 |
| Permanent shutdown | 28 Mar 1979 |
Accident on record: Three Mile Island Unit 2, 1979-03-28, INES level 5, accident with wider consequences.
Three Mile Island nuclear power plant Unit 1 Repower Pre-construction
| Reactor type | Pressurised water reactor (PWR) |
|---|---|
| Model | B&W 177-FA |
| Size class | Large |
| Gross capacity | 880MW |
| Net capacity | 819MW |
| Thermal output | 2,568MWt |
| Enrichment | 3–5% U-235 |
| NSSS vendor | Babcock & Wilcox |
| Owner | Constellation Energy Corp100% |
| Commercial operation | 1 Jan 2027 |
|---|
Three Mile Island nuclear power plant in context
The 2 units with both construction and grid dates on record took 6.1 to 8.5 years (median 7.3) from construction start to grid connection; the median across all reactors connected in the 1970s is 5.4 years.
The nearest other tracked nuclear sites are Peach Bottom nuclear power plant (59 km), Limerick nuclear power plant (97 km) and Susquehanna nuclear power plant (115 km).
Build time by unit
| Unit | Construction start | Grid connection | Years | Fleet median, same decade |
|---|---|---|---|---|
| Unit 1 | 1968 | 1974 | 6.1 | 5.4 (1970s) |
| Unit 2 | 1969 | 1978 | 8.5 | 5.4 (1970s) |
Nearest tracked nuclear sites
| Site | Country | Distance | Operating GW gross |
|---|---|---|---|
| Peach Bottom nuclear power plant | United States | 59 km | 2.8 |
| Limerick nuclear power plant | United States | 97 km | 2.4 |
| Susquehanna nuclear power plant | United States | 115 km | 2.7 |
How these are worked out: ranks use gross operating capacity; ages count from the start-up year on record, as on the age page; build times run from construction start to grid connection, as on the build-times page; ratings are the tracker's net and design net capacity, as on the uprates page. Distances are straight-line between exact positions, so a site with only an approximate position gets none. A unit missing a date or a rating is left out of the figure that needs it.
| Location | Pennsylvania, United States |
|---|---|
| Coordinates | 40.1539, -76.7248 |
| Elevation | about 100 mabove sea level |
| Setting | About 90 km from the sea |
| Region | Northern America |
| Units by status | Retired: 2 Pre-construction: 1 |
Elevation is read at the listed coordinates from a 30 m terrain model (SRTM 30 m). Two independent models differ by a median of 6 m across our plants and by up to about 40 m on steep or coastal ground, and a point on a shoreline can read as sea level. Distance to the water is measured to a generalised 1:10 million coastline, so a few kilometres or less is not resolved. This is context, not a design-basis or flood-risk figure.
| Owners | Exelon Corp Constellation Energy Corp |
|---|---|
| Operators | Exelon Generation General Public Utilities |
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Sources
- Global Nuclear Power Tracker, Global Energy Monitor, August 2026 release , CC BY 4.0 · retrieved 2026-09-06
- GEM.wiki entry (further reading) , CC BY-SA 4.0, linked, not quoted
How these sources are used, including the corrections applied on top of them and what is deliberately left blank · download the underlying data