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South Texas Nuclear Station

Gulf Coast Nuclear Baseload Anchor and Largest Texas Public-Private Nuclear Operation

The South Texas Project Nuclear Generating Station — known operationally as STP — is a 2,645 MW two-unit Westinghouse pressurized water reactor facility located on a 12,200-acre site west of the Colorado River in Matagorda County, approximately 90 miles southwest of Houston between Bay City and Palacios. STP is one of the newest and largest nuclear power facilities in the United States, with Unit 1 commencing commercial operation in August 1988 and Unit 2 in June 1989 — making STP's reactors the sixth and fourth youngest, respectively, among the nation's currently operating plants. Two units together produce sufficient carbon-free electricity to power approximately two million Texas homes. Approximately 1,200 employees work at the facility, making STP one of the largest single-site employers in the South Texas Gulf Coast region and the largest employer in Matagorda County.

What distinguishes STP at the Texas Nexus level is the three-utility cooperative ownership structure plus its complementary role to Comanche Peak as one of two Texas nuclear baseload anchors. Constellation Energy holds the 44 percent ownership stake (1,100 MW) acquired from NRG Energy in a $1.75 billion transaction completed in 2023; CPS Energy (the municipal utility serving San Antonio) holds 40 percent; and Austin Energy (the municipal utility serving Austin) holds the remaining 16 percent. STP Nuclear Operating Company (STPNOC) operates the plant on behalf of the three owners. The cooperative ownership structure is structurally distinctive — most US nuclear plants operate under single-investor-owned-utility ownership or competitive merchant ownership, while STP combines major-Texas-municipal ownership with merchant operator participation in a way that ties the plant directly to two of the four largest Texas Triangle metros.

Plant Operations and License Status

STP operates two Westinghouse four-loop pressurized water reactors, each holding 193 fuel assemblies. Cooling water comes from the 7,000-acre Main Cooling Reservoir — an off-channel reservoir capable of holding 202,600 acre-feet of cooling water at maximum operating level — eliminating the need for the cooling towers that most US nuclear plants require. The closed-cycle recirculating cooling design draws makeup water from the Colorado River, with the dedicated reservoir providing operational flexibility independent of river flow conditions during drought periods. The reservoir's three-mile by four-mile footprint and 12.4-mile embankment represent one of the largest dedicated nuclear plant cooling reservoirs in the United States.

The 2017 NRC license extensions granted both units 20-year operational life extensions beyond the original 40-year licenses. Unit 1 is now licensed to operate through 2047; Unit 2 through 2048. The extensions allow continued operation through nearly six decades of total operational life — substantially beyond the original 40-year planning horizon. The license extension required STPNOC to demonstrate continued plant safety, reliability, and integrity through the extended operating period; the 2017 approval validated the plant's structural condition and operational practices for two-decade continued service.

Plant performance has been generally strong, with capacity factors consistently above industry averages. STP produced contributions toward Constellation's nuclear fleet output of 45,459 GWh in Q4 2025, comparable to Q4 2024 production. Two unplanned shutdowns in 2024 prompted an NRC special inspection that began in late 2024; the inspection's findings have shaped continued operational improvement work but have not affected the plant's continued operating authorization. Operational stability remains the structural foundation of the plant's continued contribution to ERCOT generation supply and customer commitments.

The Three-Utility Ownership Structure

The cooperative ownership structure has been a defining feature of STP since its origins in the 1971 feasibility study that brought together Houston Lighting & Power, the City of Austin, the City of San Antonio, and Central Power and Light Company to evaluate joint ownership of a nuclear facility. The three-utility structure that operates today reflects the evolution of those original arrangements:

The cooperative structure provides each owner with carbon-free baseload generation supply matched to their capacity allocation. CPS Energy and Austin Energy receive STP power through the underlying ownership arrangement rather than through merchant-market PPAs; the structure provides multi-decade fuel security at fixed-cost economics that competitive market PPAs cannot match for the underlying nuclear baseload. Constellation Energy operates its 44 percent stake commercially within ERCOT, supplying merchant customers and integrating STP output with the broader Constellation nuclear fleet.

The Failed Units 3 and 4 Expansion

STP's history includes a substantial failed expansion that contextualizes the current operational scope. In 2018, Toshiba America Nuclear Energy formally withdrew from the Units 3 and 4 expansion project that would have added two Advanced Boiling Water Reactor units to the STP site, doubling capacity. The economic case for the expansion deteriorated through the 2010s due to substantially lower electricity rates from the shale gas revolution combined with tighter nuclear regulation following the Great East Japan Earthquake. Despite receiving combined NRC operating licenses that would have remained valid for decades without renewal requirements, no investors expressed interest in funding the multi-billion-dollar buildout.

The aborted expansion left a structural opportunity for future redevelopment. The 12,200-acre site retains substantial undeveloped acreage, the cooling reservoir has surplus capacity beyond Units 1 and 2 needs, and the regulatory framework for prospective new construction has been partially de-risked through the original Units 3 and 4 licensing work. Whether and when the expansion case revives depends on the broader nuclear economics that the AI compute infrastructure buildout is reshaping. SMR deployment at the existing STP site could provide an alternative path to expansion at lower capital scale than the original AP1000 or ABWR alternatives, leveraging existing site infrastructure, transmission interconnection, and workforce continuity.

Cross-Anchor Position

STP's most operationally significant cross-anchor relationship is with Comanche Peak Nuclear Power Plant, the other operational Texas nuclear baseload facility. Together STP (2,645 MW) and Comanche Peak (2,400 MW) supply approximately 5,045 MW of Texas nuclear baseload — substantial relative to ERCOT's broader generation mix but small relative to projected continued load growth from AI compute, oil-and-gas electrification, and broader manufacturing buildout. The two plants operate in geographically complementary positions: STP supplying the Gulf Coast and South Texas including direct municipal supply to San Antonio and Austin, Comanche Peak supplying the DFW metro and surrounding North Texas. Project Matador's planned nuclear deployment at Fermi America's HyperGrid Campus in the Panhandle would substantially expand Texas's nuclear baseload but operates on a longer development timeline (first AP1000 grid synchronization 2031-2032).

The relationship with Austin Energy and CPS Energy ties STP directly to two of the four largest Texas Triangle metros. Austin Energy's STP allocation supplies a meaningful share of Austin's baseload generation, complementing the municipal utility's renewable PPA portfolio including the 50 MW Samson Solar commitment, broader West Texas wind generation contracted supply, and adjacent renewable arrangements. CPS Energy's larger STP allocation similarly supplies San Antonio's baseload generation as part of CPS's diversified fuel mix. The two municipal utilities' continued ownership structure provides long-horizon stability for STP that purely merchant nuclear plants face less reliably.

The connection to the broader Texas industrial-and-AI footprint runs through ERCOT generation supply and Constellation's merchant nuclear positioning. Constellation Energy has been one of the most active operators in hyperscaler-coupled nuclear PPA deals, with major arrangements at Three Mile Island Unit 1 (Microsoft 20-year PPA) and adjacent fleet operations. Whether and how Constellation extends similar arrangements to its STP allocation depends on Texas-specific siting and permitting for adjacent data center development, NRC regulatory framework for co-location arrangements, and the broader hyperscaler customer interest in ERCOT-region nuclear baseload coupling. The Comanche Peak Amazon adjacent campus announcement in March 2026 creates precedent that STP-adjacent development could follow if commercial conditions support it.

The Gulf Coast geographic position places STP within direct supply distance of the Houston Ship Channel petrochemical concentration, the Texas LNG export hub at Sabine Pass and Corpus Christi, the Brookshire Megapack Factory in Waller County, the broader Houston metro industrial base, and the prospective adjacent data center development that Texas's behind-the-meter AI infrastructure buildout pattern increasingly favors. Carbon-free baseload supply complements the natural gas generation that dominates Gulf Coast power and provides the structural carbon-free alternative for major industrial and corporate customers seeking renewable supply commitments.

Why Bay City

The original 1971 siting decision reflected the structural fits that drove utility-scale nuclear plant siting in the southern Gulf Coast region. Land availability at scales that the Houston metro could not provide — Matagorda County's rural geography supported the multi-thousand-acre footprint that nuclear plant operations require including reactor units, switchyard, the dedicated cooling reservoir, exclusion area, and emergency planning zones. Cooling water access through the dedicated Main Cooling Reservoir provided the closed-loop cooling system that minimizes river-flow dependencies. Distance from major population centers (90 miles from Houston, 200+ miles from Austin and San Antonio) supported emergency planning requirements while remaining within direct grid-supply distance of the major Texas Triangle metro loads. Texas state-level regulatory environment supported the development trajectory through the long construction period (1975 ground-breaking, 1988 Unit 1 commercial operation).

The continued investment trajectory has compounded over five decades. Original construction completion in the late 1980s, decades of stable operation through the 2010s and 2020s, the 2017 license extensions, the 2023 Constellation acquisition of the NRG stake, and the broader merchant-and-municipal cooperative ownership structure collectively reflect sustained operator and customer commitment to the STP site as a long-horizon strategic asset. Each subsequent commitment makes the next more rational. The site, transmission infrastructure, workforce continuity, and regulatory framework are sunk-cost advantages that no greenfield siting could replicate at comparable timeline or cost.

Constraints and Considerations

Capacity expansion potential is the most material consideration shaping STP's long-term role. The 2,645 MW current nameplate capacity is fixed under existing operational configuration; meaningful expansion requires either uprates (incremental capacity increases at existing units) or new unit construction. The aborted Units 3 and 4 expansion left the site licensed and physically prepared for additional units, but commercial conditions through the late 2010s and early 2020s did not support expansion economics. AI compute infrastructure demand growth, federal critical-infrastructure designation pathways, and prospective hyperscaler customer interest in nuclear-coupled siting could revive the expansion case in different reactor configurations including SMR deployment at lower capital scales or potentially Westinghouse AP1000 or alternative large-reactor options.

Operational reliability is the secondary consideration. The 2024-2025 unplanned shutdowns and resulting NRC special inspection reflect the operational complexity that decades-old nuclear infrastructure faces. Continued license compliance, operational improvement work, and broader STPNOC operating practices shape the plant's continued contribution to Texas baseload supply. The 2047 and 2048 license extensions remain valid; sustained operations through those dates depend on continued NRC compliance and operational excellence.

Workforce continuity is the third consideration. STP's 1,200-person workforce includes specialized nuclear operations, maintenance, and engineering personnel that take years to develop. License extension through 2047/2048 requires sustained workforce build-up across operator generations, with retirements of original commissioning-era personnel offset by new training pipelines. Texas's broader nuclear workforce concentration is small relative to other US states with multiple operating plants; cross-plant workforce mobility between STP and Comanche Peak supports continuity. If Texas adds new nuclear capacity at Project Matador or expansion at either operating plant, broader labor market constraints become more material.

Watching Items

Constellation hyperscaler-coupled nuclear PPA announcements applicable to STP's 44 percent stake validate or rebase the prospective hyperscaler-coupled trajectory at the Gulf Coast nuclear baseload site. SMR deployment exploration at STP, paralleling Vistra's exploration at Comanche Peak, would mark a structural expansion path for the site at lower capital scale than full AP1000 or ABWR alternatives. NRC special inspection findings and continued operational improvement work shape near-term reliability metrics. Adjacent watching items include any Constellation announcements of additional Texas nuclear acquisitions or developments, broader Texas nuclear baseload trajectory through Project Matador AP1000 deployment milestones, and the broader US nuclear renaissance pace through hyperscaler-anchored PPA arrangements at peer plants nationally.

Related Coverage

Gulf Coast | Texas Nexus | Texas Energy Nexus | Comanche Peak Nuclear | Fermi America HyperGrid Campus | Brookshire Megapack | Spotlights Hub