The South Texas Project Electric Generating Station (also known as STP, STPEGS, South Texas Project), is a nuclear power station southwest of Bay City, Texas, United States. STP occupies a 12,200-acre (4,900 ha) site west of the Colorado River about 90 miles (140 km) southwest of Houston. It consists of two Westinghouse Pressurized Water Reactors and is cooled by a 7,000-acre (2,800 ha) reservoir, which eliminates the need for cooling towers.

On December 6, 1971, Houston Lighting & Power Co. (HL&P), the City of Austin, the City of San Antonio, and the Central Power and Light Co. (CPL) initiated a feasibility study of constructing a jointly-owned nuclear plant. The initial cost estimate for the plant was $974 million (equivalent to approximately $5,700,741,167 in 2015 dollars).

By mid-1973, HL&P and CPL had chosen Bay City as the site for the project and San Antonio had signed on as a partner in the project. Brown and Root was selected as the architect and construction company. On November 17, 1973 voters in Austin narrowly approved their city's participation and the city signed onto the project on December 1. Austin held several more referendums through the years on whether to stay in the project or not.

An application for plant construction permits was submitted to the Atomic Energy Commission, now the Nuclear Regulatory Commission (NRC), in May 1974 and the NRC issued the permits on December 22, 1975. Construction started on December 22, 1975.

By 1978, the South Texas Project was two years behind schedule and had substantial cost overruns. A new management team had been put in place by HL&P in late 1978 to deal with the cost overruns, schedule delays and other challenges. However, events at Three Mile Island in March 1979 had a substantial impact on the nuclear industry including STNP. The new team again moved forward with developing a new budget and schedule. Brown and Root revised their completion schedule to June 1989 and the cost estimate to $4.4–$4.8 billion. HL&P executives consulted with its own project manager and concluded that Brown and Root was not making satisfactory progress and a decision was reached to terminate their role as architect/engineer but retain them as constructor. Brown and Root was relieved as architect/engineer in September 1981 and Bechtel Corporation contracted to replace them. Less than two months later, Brown and Root withdrew as the construction contractor and Ebasco Constructors was hired to replace them in February 1982 as constructor.

Austin voters authorized the city council on November 3, 1981 to sell the city's 16 percent interest in the STP. No buyers were found.

Unit 1 reached initial criticality on March 8, 1988 and went into commercial operation on August 25. Unit 2 reached initial criticality on March 12, 1989 and went into commercial operation on June 19.

In February 1993, both units had to be taken offline to resolve issues with the steam-driven auxiliary feedwater pumps. They were not back in service until March (Unit 1) and May (Unit 2) of 1994. The history of STNP is somewhat unusual since most nuclear plants that were in the early stages of engineering construction at the time of the Three Mile Island event were never completed.

On June 19, 2006, NRG Energy filed a letter of intent with the NRC to build two 1,358-MWe advanced boiling water reactors (ABWRs) at the South Texas Nuclear Project site. South Texas Nuclear Project Partners CPS Energy and Austin Energy were not involved in the initial letter of intent and development plans.

On September 24, 2007, NRG Energy filed an application with the NRC to build two Toshiba ABWRs at the South Texas Nuclear Project site. It was the first application for a nuclear reactor submitted to the NRC since 1979. The proposed expansion would generate an additional 2700 MW of electrical generating capacity, which would double the capacity of the site. The total estimated cost of constructing the two reactors is $10 billion, or $13 billion with financing, according to Steve Bartley, interim general manager at CPS Energy.

In October 2009, main contractor Toshiba had informed CPS Energy that the cost would be "substantially greater," possibly up to $4 billion more. As a result of the escalating cost estimates for units 3 and 4, in 2010 CPS Energy reached an agreement with NRG Energy to reduce CPS's stake in the new units from 50% to 7.625%. To that point, CPS Energy had invested $370 million in the expanded plant. CPS Energy's withdrawal from the project put the expansion into jeopardy.

In October 2010, the South Texas Project announced that the Tokyo Electric Power Company (TEPCO) had entered into an agreement with Nuclear Innovation North America (a joint venture between the reactor manufacturer, Toshiba, and plant partner NRG Energy) which was the largest of the two stakeholders in the proposed reactors, to purchase an initial 9.2375% stake in the expansion for $125 million, and $30 million for an option to purchase an additional stake in the new units for $125 million more (resulting in approximately 18% ownership by TEPCO, or 500 MW of generation capacity). The agreement was made conditional upon STNP securing construction loan guarantees from the United States Department of Energy.

On 19 April 2011, NRG announced in a conference call with shareholders, that they had decided to abandon the permitting process on the two new units due to the ongoing expense of planning and slow permitting process. Anti-nuclear campaigners alleged that the financial situation of new partner TEPCO, combined with the ongoing Fukushima nuclear accident were also key factors in the decision. NRG has written off its investment of $331 million in the project.

Despite the April 2011 NRG announcement of the reactor's cancellation, the NRC continued the combined licensing process for the new reactors in October 2011. It was unclear at the time why the reactor license application was proceeding. During early 2015 some pre-construction activities were performed on site and initial NRC documents listed the original targeted commercial operational dates as March 2015 for unit 3 and a year later for the other unit. On February 9, 2016 the NRC approved the combined license. Due to market conditions, no construction events occurred at that time. The two planned units do not currently have a planned construction date.

On February 15, 2021 during a major power outage that impacted much of the state of Texas, an automatic reactor trip shut South Texas Nuclear Generation Station Unit 1 due to low steam generator levels. According to a Nuclear Regulatory Commission report, the low steam generator levels were due to loss of feedwater pumps 11 and 13. However, Unit 2 and both units at the Comanche Peak Nuclear Power Plant remained online during the power outage.

South Texas Project Electric Generating Station generated 21,920 GWh in 2022.

Generation (MWh) of South Texas Project Electric Generating Station

Year	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec	Total
2001	1,886,321	1,525,367	1,023,965	1,693,902	1,749,601	1,803,826	1,862,368	1,861,391	1,784,413	948,097	1,821,433	1,879,914	19,840,598
2002	1,877,631	1,694,952	1,874,294	1,802,364	1,853,569	1,651,816	1,804,722	1,863,231	1,809,080	961,912	648,839	1,207,192	19,049,602
2003	993,000	858,234	1,167,859	906,020	926,323	897,961	924,414	1,550,300	1,826,511	1,901,587	1,835,032	1,901,300	15,688,541
2004	1,794,208	1,783,984	1,866,066	967,940	1,898,881	1,833,986	1,888,035	1,886,885	1,832,462	1,898,705	1,846,256	1,874,559	21,371,967
2005	1,910,104	1,425,909	1,145,000	1,347,849	1,899,476	1,827,979	1,882,165	1,865,460	1,793,374	961,783	1,812,505	1,917,689	19,789,293
2006	1,918,500	1,734,226	1,916,180	1,848,924	1,902,066	1,835,603	1,894,140	1,889,118	1,754,581	949,107	1,751,295	1,974,529	21,368,269
2007	1,978,523	1,769,752	1,631,719	1,020,990	1,997,207	1,913,083	1,974,291	1,945,127	1,911,186	1,994,784	1,951,698	2,020,923	22,109,283
2008	2,027,749	1,894,252	1,857,380	1,059,644	1,996,808	1,911,071	1,970,008	1,968,743	1,883,018	1,091,075	1,804,680	2,028,321	21,492,749
2009	2,026,109	1,816,781	2,001,913	1,933,642	1,976,442	1,893,260	1,945,400	1,945,673	1,491,904	987,917	1,314,044	2,023,063	21,356,148
2010	1,901,689	1,616,544	1,878,021	959,782	1,894,264	1,905,405	1,965,866	1,889,669	1,908,067	2,000,442	1,180,689	2,026,343	21,126,781
2011	2,019,203	1,831,865	2,010,915	1,022,733	1,722,511	1,919,280	1,972,583	1,862,971	1,922,238	1,926,927	1,161,050	993,620	20,365,896
2012	1,000,676	932,122	954,597	1,191,768	1,996,956	1,916,509	1,972,364	1,968,957	1,917,986	1,618,514	1,046,510	2,027,134	18,544,093
2013	1,129,541	907,783	1,001,457	1,214,363	1,800,887	1,909,913	1,972,700	1,929,852	1,755,607	1,457,708	1,482,475	1,265,570	17,827,856
2014	1,996,545	1,803,728	1,467,789	949,590	965,031	1,819,148	1,938,482	1,937,255	1,886,353	1,964,871	1,929,852	1,993,023	20,651,667
2015	1,994,899	1,798,046	1,876,998	944,816	1,633,328	1,873,563	1,924,005	1,921,588	1,870,805	1,474,997	931,979	1,155,529	19,400,553
2016	1,867,890	1,853,605	1,971,083	1,899,518	1,791,929	1,869,512	1,921,476	1,921,320	1,863,053	1,199,327	1,551,143	1,984,447	21,694,303
2017	1,982,755	1,781,424	1,496,196	941,003	1,947,349	1,872,796	1,915,879	1,922,021	1,874,558	1,951,826	1,911,553	1,984,116	21,581,476
2018	1,990,840	1,791,895	1,716,130	1,026,669	1,948,056	1,862,498	1,926,877	1,926,702	1,862,974	1,104,073	1,542,275	1,988,643	20,687,632
2019	1,989,139	1,794,419	1,977,848	1,907,580	1,952,400	1,865,069	1,923,822	1,916,348	1,861,164	1,076,425	1,746,675	1,982,408	21,993,297
2020	1,981,132	1,854,898	1,386,851	1,267,605	1,965,407	1,887,512	1,941,500	1,925,033	1,879,619	1,963,043	1,910,507	1,995,650	21,958,757
2021	1,991,790	1,680,259	1,600,163	1,269,956	1,955,134	1,730,291	1,933,495	1,927,320	1,879,819	1,211,341	1,688,551	1,986,885	20,855,004
2022	1,996,621	1,804,682	1,990,353	1,908,367	1,953,488	1,870,425	1,924,485	1,927,102	1,859,877	1,164,373	1,533,211	1,986,901	21,919,885
2023	1,981,393	1,794,205	1,496,119	1,181,761	1,941,365	1,862,343	1,911,690	1,904,511	1,853,615	1,953,564	1,917,848	1,988,730	21,787,144
2024	1,634,136	1,833,846	1,517,587	913,191	1,292,316

Nuclear whistleblower Ronald J. Goldstein was a supervisor employed by EBASCO, which was a major contractor for the construction of the South Texas plants. In the summer of 1985, Goldstein identified safety problems to SAFETEAM, an internal compliance program established by EBASCO and Houston Lighting, including noncompliance with safety procedures, the failure to issue safety compliance reports, and quality control violations affecting the safety of the plant.

SAFETEAM was promoted as an independent safe haven for employees to voice their safety concerns. The two companies did not inform their employees that they did not believe complaints reported to SAFETEAM had any legal protection. After he filed his report to SAFETEAM, Goldstein was fired. Subsequently, Goldstein filed suit under federal nuclear whistleblower statutes.

The U.S. Department of Labor ruled that his submissions to SAFETEAM were protected and his dismissal was invalid, a finding upheld by Labor Secretary Lynn Martin. The ruling was appealed and overturned by the Fifth Circuit Court of Appeals, which ruled that private programs offered no protection to whistleblowers. After Goldstein lost his case, Congress amended the federal nuclear whistleblower law to provide protection for reports made to internal systems and prevent retaliation against whistleblowers.

The STPEGS reactors are operated by the STP Nuclear Operating Company (STPNOC). Ownership is divided among Constellation Energy at 44 percent, San Antonio municipal utility CPS Energy at 40 percent and Austin Energy at 16 percent.

The Nuclear Regulatory Commission defines two emergency planning zones around nuclear power plants: a plume exposure pathway zone with a radius of 10 miles (16 km), concerned primarily with exposure to, and inhalation of, airborne radioactive contamination, and an ingestion pathway zone of about 50 miles (80 km), concerned primarily with ingestion of food and liquid contaminated by radioactivity.

In 2010, the population within 50 miles (80 km) of the station was 254,049, an increase of 10.2 percent since 2000; the population within 10 miles (16 km) was 5,651, a 2.4 percent decrease. Cities within 50 miles include Lake Jackson (40 miles to the city center) and Bay City.

The Nuclear Regulatory Commission's estimate of the risk each year of an earthquake intense enough to cause core damage to the reactor at South Texas was 1 in 158,730, according to an NRC study published in August 2010.

The South Texas Generating Station consists of two operational reactors. A two reactor expansion (Unit 3 and Unit 4) was planned but later cancelled.

Reactor unit	Reactor plant type	Capacity (MW)		Construction started	Electricity grid connection	Commercial operation	Current license expiration
		Net	Gross
South Texas-1	Westinghouse 4-loop PWR	1280	1354	22 December 1975	30 March 1988	25 August 1988	20 August 2047
South Texas-2					11 April 1989	19 June 1989	15 December 2048
South Texas-3 (cancelled)	ABWR	1350	1400	License terminated (2018)
South Texas-4 (cancelled)

• List of largest power stations in the United States
• Largest nuclear power plants in the United States
• List of power stations in Texas

• "Milestones". South Texas Project Nuclear Operating Company. Retrieved Jul. 14, 2005.
• "CenterPoint Energy Historical Timeline". CenterPoint Energy. Retrieved Jul. 14, 2005.

• Energy Information Administration page