The AP1000 (Advanced Passive 1000) is a nuclear power plant designed and sold by Westinghouse Electric Company. The plant is a pressurized water reactor with improved use of passive nuclear safety and many design features intended to lower its capital cost and improve its economics.
The design traces its history to the Westinghouse 4-loop SNUPPS design, which was produced in various locations around the world. (Note: System 80 was a similar vintage nuclear steam supply system made by Combustion Engineering.) Further development of the 4-loop reactor and the passively cooled containment initially led to the AP600 concept, with a smaller 600 to 700 MWe output, but this saw limited interest. In order to compete with other designs that were scaling up in size in order to improve capital costs, the design re-emerged as the AP1000 and found a number of design wins at this larger size.
Seventeen AP1000s are currently in operation or under construction. Four are in operation at two sites in China, two at Sanmen Nuclear Power Station and two at Haiyang Nuclear Power Plant. , all four Chinese reactors were completed and connected to the grid, and , eleven more are under construction. Two are in operation at the Vogtle Electric Generating Plant near Augusta, Georgia, in the United States, with Vogtle 3 having come online in July 2023, and Vogtle 4 in April 2024. Construction at Vogtle suffered numerous delays and cost overruns. Construction of two additional reactors at Virgil C. Summer Nuclear Generating Station near Columbia, South Carolina, led to Westinghouse's bankruptcy in 2017 and the cancellation of construction at that site. It was reported in January 2025 by The Wall Street Journal and The State that Santee Cooper, the sole owner of the stored parts and unfinished construction, is exploring construction and financing partners to finish construction these two reactors. The need for large amounts of electricity for data centers is said to be the driving factor for their renewed interest.
Twenty-four more AP1000s are currently being planned, with six in India, nine in Ukraine, three in Poland, two in Bulgaria, and four in the United States.
China is currently developing more advanced versions and owns their patent rights. The first AP1000 began operations in China at Sanmen, where Unit 1 became the first AP1000 to achieve criticality in June 2018, and was connected to the grid the next month. Further builds in China will be based on the modified CAP1000 and CAP1400 designs.
History Previous work The AP1000 design traces its history to two previous designs, the AP600 and the System 80.
The System 80 design was created by Combustion Engineering and featured a two-loop cooling system with a single steam generator paired with two reactor coolant pumps in each loop that makes it simpler and less expensive than systems which pair a single reactor coolant pump with a steam generator in each of two, three, or four loops.The System 80 Three completed reactors in the US and another four in South Korea made it the most successful Generation II+ design.
ABB Group bought Combustion Engineering in 1990 and introduced the System 80+, with a number of design changes and safety improvements. As part of a series of mergers, purchases, and divestitures by ABB, in 2000 the design was purchased by Westinghouse Electric Company, who had itself been purchased in 1999 by British Nuclear Fuels Ltd (BNFL).
Through the 1990s, Westinghouse had been working on a new design known as the AP600 with a design power of about 600 MWe. This was part of the United States Department of Energy's Advanced Light Water Reactor program that worked on a series of Generation III reactor designs. In contrast to Generation II designs, the AP600 was much simpler, with a huge reduction in the total number of parts, and especially pumps. It was also passively safe, a key feature of Gen III designs.
The AP600 was at the small end of the reactor scale. Smaller plants are periodically introduced because they can be used in a wider variety of markets where a larger reactor is simply too powerful to serve the local market. The downside of such designs is that the construction time, and thus cost, does not differ significantly compared to larger designs, so these smaller designs often have less attractive economics. The AP600 addressed this through modular construction and aimed to go from first concrete to fuel load in 36 months. In spite of these attractive features, Westinghouse had no sales of the AP600.
With the purchase of the company by BNFL and its merger with ABB, a design combining the features of the System 80+ with the AP600 started as the AP1000. BNFL in turn sold Westinghouse Electric to Toshiba in 2005.
AP1000 In December 2005, the Nuclear Regulatory Commission (NRC) approved the final design certification for the AP1000. This meant that prospective US builders could apply for a Combined Construction and Operating License before construction starts, the validity of which is conditional upon the plant being built as designed, and that each AP1000 should be identical. Its design is the first Generation III+ reactor to receive final design approval from the NRC. In 2008 China started building four units of the AP1000's 2005-design.
In December 2011, the NRC approved construction of the first US plant to use the design. On February 9, 2012, the NRC approved the construction of two new reactors.
In 2016 and 2017 cost overruns constructing AP1000 plants in the U.S. caused Westinghouse's owner Toshiba to write down its investment in Westinghouse by "several billion" dollars. On February 14, 2017, Toshiba delayed filing financial results, and Toshiba chairman Shigenori Shiga, formerly chairman of Westinghouse, resigned. On March 24, 2017, Toshiba announced that Westinghouse Electric Company will file for Chapter 11 bankruptcy because of US$9 billion of losses from nuclear reactor construction projects, which may impact the future of the AP1000. Westinghouse emerged from bankruptcy in August 2018.
DateMilestoneJanuary 27, 2006NRC issues the final design certification rule (DCR)March 10, 2006NRC issues revised FDA for Revision 15 of the Westinghouse designMay 26, 2007Westinghouse applies to amend the DCR (Revision 16)September 22, 2008Westinghouse updated its application October 14, 2008Westinghouse provides a corrected set for Revision 17 of the designDecember 1, 2010Westinghouse submits Revision 18 of the designJune 13, 2011Westinghouse submits Revision 19 of the designDecember 30, 2011NRC issues the final DC amendment final ruleSeptember 21, 2018Commissioning of the first AP1000 at the Sanmen Nuclear Power Station
Design specifications The AP1000 is a pressurized water reactor with two cooling loops, planned to produce a net power output of 1,117 MWe. It is an evolutionary improvement on the AP600, essentially a more powerful model with roughly the same footprint.
A design objective was to be less expensive to build than other Generation III reactor designs, by both using existing technology, and needing less equipment than competing designs that have three or four cooling loops. The design decreases the number of components, including pipes, wires, and valves. Standardization and type-licensing should also help reduce the time and cost of construction. Because of its simplified design compared to a Westinghouse generation II PWR, the AP1000 has: 50% fewer safety-related valves 35% fewer pumps 80% less safety-related piping 85% less control cable 45% less seismic building volume
The AP1000 design is considerably more compact in land usage than most existing PWRs, and uses under a fifth of the concrete and rebar reinforcing of older designs. Probabilistic risk assessment was used in the design of the plants. This enabled minimization of risks, and calculation of the overall safety of the plant. According to the NRC, the plants will be orders of magnitude safer than those in the last study, NUREG-1150. The AP1000 has a maximum core damage frequency of 5.09 × 10−7 per plant per year. Westinghouse AP 1000 Step 2 PSA Assessment Used fuel produced by the AP1000 can be stored indefinitely in water on the plant site.Westinghouse certain of safety, efficiency of nuclear power , Pittsburgh Post-Gazette, March 29, 2009 Aged used fuel may also be stored in above-ground dry cask storage, in the same manner as the currently operating fleet of US power reactors.
Power reactors of all types continue to produce heat from radioactive decay products even after the main reaction is shut down, so it is necessary to remove this heat to avoid meltdown of the reactor core. In the AP1000, Westinghouse's Passive Core Cooling System uses a tank of water situated above the reactor. When the passive cooling system is activated, the water flows by gravity to the top of the reactor where it evaporates to remove heat. The system uses multiple explosively-operated and DC operated valves which must operate within the first 30 minutes. This is designed to happen even if the reactor operators take no action. The electrical system required for initiating the passive systems doesn't rely on external or diesel power and the valves don't rely on hydraulic or compressed air systems.R.A. and Worrall, A. "The AP1000 Reactor the Nuclear Renaissance Option." Nuclear Energy 2004. The design is intended to passively remove heat for 72 hours, after which its gravity drain water tank must be topped up for as long as cooling is required. The reactor uses canned motor pumps that are hermetically sealed, use no reactor coolant pump seals and are mounted directly on the bottom of the steam generators. This reduces the amount of large diameter primary loop piping.Schulz, T. L. (2006). Westinghouse AP1000 advanced passive plant. Nuclear Engineering and Design, 236(14-16), 1547–1557. doi:10.1016/j.nucengdes.2006.03.049 10.1016/j.nucengdes.2006.03.049
Revision 15 of the AP1000 design has an unusual containment structure which has received approval by the NRC, after a Safety Evaluation Report, and a Design Certification Rule. Revisions 17, 18, and 19 were also approved.
Design disputes
In April 2010, some environmental organizations called on the NRC to investigate possible limitations in the AP1000 reactor design. These groups appealed to three federal agencies to suspend the licensing process because they believed containment in the new design is weaker than existing reactors.
In April 2010, Arnold Gundersen, a nuclear engineer commissioned by several anti-nuclear groups, released a report which explored a hazard associated with the possible rusting through of the containment structure steel liner. In the AP1000 design, the liner and the concrete are separated, and if the steel rusts through, "there is no backup containment behind it" according to Gundersen. If the dome rusted through the design would expel radioactive contaminants and the plant "could deliver a dose of radiation to the public that is 10 times higher than the N.R.C. limit" according to Gundersen. Vaughn Gilbert, a spokesman for Westinghouse, has disputed Gundersen's assessment, stating that the AP1000's steel containment vessel is three-and-a-half to five times thicker than the liners used in current designs, and that corrosion would be readily apparent during routine inspection.Matthew L. Wald. Critics Challenge Safety of New Reactor Design New York Times, April 22, 2010.
Edwin Lyman, a senior staff scientist at the Union of Concerned Scientists, has challenged specific cost-saving design choices made for both the AP1000 and ESBWR, another new design. Lyman is concerned about the strength of the steel containment vessel and the concrete shield building around the AP1000, claiming its containment vessel does not have sufficient safety margins.
John Ma, a senior structural engineer at the NRC was quoted on his stance about the AP1000 nuclear reactor.