South Texas Project Nuclear Generating Station

STP Nuclear Operating Co. · Bay City · Matagorda County

The South Texas Project (STP) near Bay City runs two Westinghouse reactors of about 2,560 MW net, owned by Constellation Energy, San Antonio's CPS Energy and Austin Energy. Two Texas city utilities own 56 percent of the plant, so most of its output serves San Antonio and Austin through ownership rather than purchase contracts.

Who owns and runs the South Texas Project WHO HOLDS EACH LAYER CONSTELLATION ENERGY 44%, bought from NRG for $1.75B in 2023 CPS ENERGY (SAN ANTONIO) 40%, rising to 42% on a pending transfer AUSTIN ENERGY 16%, city-owned utility share STP NUCLEAR OPERATING CO. Runs the plant for the three owners ERCOT Grid that carries the output
Capacity
2,560 MW net
Units
Two PWRs
Owners
Constellation, CPS, Austin
Licensed to
2047 and 2048
County
Matagorda
Sector
Energy

Overview

Two Reactors on a 12,200-Acre Gulf Coast Site

STP sits on a 12,200-acre site west of the Colorado River in Matagorda County, about 90 miles southwest of Houston between Bay City and Palacios. STP Nuclear Operating Company (STPNOC) runs two Westinghouse four-loop pressurized water reactors (PWRs) totaling about 2,560 MW net. Construction began in December 1975; Unit 1 entered commercial operation in August 1988 and Unit 2 in June 1989. The plant supplies about two million Texas homes on the grid run by the Electric Reliability Council of Texas (ERCOT) and employs about 1,200 people.

A 7,000-acre Main Cooling Reservoir, holding up to 202,600 acre-feet and filled with makeup water from the Colorado River, cools both units without cooling towers. The Nuclear Regulatory Commission (NRC) renewed both licenses in 2017, to August 2047 for Unit 1 and December 2048 for Unit 2. With Comanche Peak in Somervell County, STP is one of two operating nuclear plants in Texas, together above 5,000 MW.

Profile
OperatorSTP Nuclear Operating Company
OwnersConstellation 44%, CPS Energy 40%, Austin Energy 16%
LocationNear Bay City, Matagorda County
ReactorsTwo Westinghouse four-loop PWRs
Net capacityAbout 2,560 MW
Commercial operation1988 and 1989
License expiration2047 and 2048
Cooling7,000-acre Main Cooling Reservoir
WorkforceAbout 1,200

Ownership

Two City Utilities and Constellation Split the Output

Constellation Energy bought NRG Energy's 44 percent stake for $1.75 billion, closing in November 2023, and sells its share into ERCOT as merchant power. CPS Energy, San Antonio's city-owned utility, holds 40 percent. Austin Energy holds 16 percent. The two city utilities take their shares of STP output directly as owners.

The NRC approved a transfer of two percent of the plant from Constellation to CPS Energy in December 2024, which would leave each at 42 percent. The deal has not closed: the parties are waiting on an Internal Revenue Service ruling on the tax treatment of decommissioning trust funds, and the NRC has extended the closing deadline twice, most recently to December 11, 2026.

STP ownership and approximate share of net capacity
OwnerStakeApprox. MWType
Constellation Energy44%1,130Merchant generator
CPS Energy40%1,020San Antonio city utility
Austin Energy16%410Austin city utility

History

The Units 3 and 4 Expansion Ended in 2018

NRG Energy applied to the NRC in September 2007 for two Advanced Boiling Water Reactors (ABWRs) of about 2,700 MW combined, the first new US reactor application since 1979. Tokyo Electric Power agreed in 2010 to buy into the project, but in April 2011, weeks after the Fukushima accident, NRG abandoned it and wrote off its $331 million investment. The NRC issued combined licenses in February 2016, and the licenses were terminated in 2018 without construction.

The site acreage and reservoir remain. Any new reactor at STP, whether a large unit or a small modular reactor (SMR), would need a new license. None has been announced.

Constraints

NRC Oversight Follows 2024 Unplanned Shutdowns

A transformer failure tripped Unit 2 in May 2024 and a switchyard fire tripped Unit 1 in July 2024; the NRC opened a special inspection that September. In April 2026 the NRC issued a Severity Level III violation for a plant modification made without a required license amendment that led to a reactor trip, and in May 2026 it scheduled a public meeting on STP's 2025 performance. Both units remain licensed into the late 2040s.

STP has no announced data center supply deal. Constellation supplies Microsoft from the Crane Clean Energy Center, the former Three Mile Island Unit 1 in Pennsylvania, and Vistra's 1,200 MW Amazon contract at Comanche Peak is the first Texas nuclear deal of that kind.

Record

Dataset Record

Sources
Nuclear Regulatory Commission, Federal Register, Constellation Energy, Texas Comptroller of Public Accounts, American Nuclear Society Nuclear News, Bay City Tribune, Power Engineering, Wikipedia (plant data)
Last verified
October 2026