Neha Patil

AP1000

Updated on
Share on FacebookTweet on TwitterShare on LinkedIn
AP1000

The AP1000 is a nuclear power plant designed and sold by Westinghouse Electric Company, now majority owned by Toshiba. The plant is a pressurized water reactor with improved use of passive nuclear safety. The first AP1000 is expected to start operations in 2017 in China.

Contents

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.

Aspects of the AP1000 design have been questioned and disputed by senior scientists and engineers including John Ma (of the NRC), Edwin Lyman, and Arnold Gundersen. 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.

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 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. Used fuel produced by the AP1000 can be stored indefinitely in water on the plant site. 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 this general type 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. 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.

    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.

    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.

    In 2009, the NRC made a safety change related to the events of September 11, ruling that all plants be designed to withstand the direct hit from a plane. To meet the new requirement, Westinghouse encased the AP1000 buildings concrete walls in steel plates. Last year Ma, a member of the NRC since it was formed in 1974, filed the first "non-concurrence" dissent of his career after the NRC granted the design approval. In it Ma argues that some parts of the steel skin are so brittle that the "impact energy" from a plane strike or storm driven projectile could shatter the wall. A team of engineering experts hired by Westinghouse disagreed...

    In 2010, following Ma's initial concerns, the NRC questioned the durability of the AP1000 reactor's original shield building in the face of severe external events such as earthquakes, hurricanes, and airplane collisions. In response to these concerns Westinghouse prepared a modified design. This modified design satisfied the NRC, with the exception of Ma, hence the "non-concurrence". In contrast to the NRC's decision, Ma believed that computer codes used to analyze the modified design were not precise enough and some of the materials used were too brittle.

    A US consultant engineer has also criticized the AP1000 containment design arguing that, in the case of a design-basis accident, it could release radiation; Westinghouse has denied the claim. The NRC completed the overall design certification review for the amended AP1000 in September 2011.

    In May 2011, US government regulators found additional problems with the design of the shield building of the new reactors. The chairman of the Nuclear Regulatory Commission said that: computations submitted by Westinghouse about the building's design appeared to be wrong and "had led to more questions."; the company had not used a range of possible temperatures for calculating potential seismic stresses on the shield building in the event of, for example, an earthquake; and that the commission was asking Westinghouse not only to fix its calculations but also to explain why it submitted flawed information in the first place. Westinghouse said that the items the commission was asking for were not "safety significant".

    In November 2011, Arnold Gundersen published a further report on behalf of the AP1000 Oversight Group, which includes Friends of the Earth and Mothers against Tennessee River Radiation. The report highlighted six areas of major concern and unreviewed safety questions requiring immediate technical review by the NRC. The report concluded that certification of the AP1000 should be delayed until the original and current “unanswered safety questions” raised by the AP1000 Oversight Group are resolved.

    In 2012, Ellen Vancko, from the Union of Concerned Scientists, said that "the Westinghouse AP1000 has a weaker containment, less redundancy in safety systems, and fewer safety features than current reactors". In response to Ms. Vancko's concerns, climate policies author and retired nuclear engineer Zvi J. Doron, replied that the AP1000's safety is enhanced by fewer active components, not compromised as Ms. Vancko suggests. As in direct contrast to currently operating reactors, the AP1000 has been designed around the concept of passive nuclear safety. In October 2013, Li Yulun, a former vice-president of China National Nuclear Corporation (CNNC), raised concerns over the safety standards of the delayed AP1000 third-generation nuclear power plant being built in Sanmen, due to the constantly changing, and consequently untested, design. Citing a lack of operating history, he also questioned the manufacturer's assertion that the AP1000 reactor's "primary system canned motor pumps" were "maintenance-free" over 60 years, the assumed life of the reactor and noted that the expansion from 600 to 1,000 megawatts has not yet been commercially proven and Westinghouse has yet to receive approval from British authorities on an improved version of AP1000.

    Chinese CAP1400 design extension

    In 2008 and 2009, Westinghouse made agreements to work with the Chinese State Nuclear Power Technology Corporation (SNPTC) and other institutes to develop a larger design, the CAP1400 of 1,400 MWe capacity, possibly followed by a 1,700 MWe design. China will own the intellectual property rights for these larger designs. Exporting the new larger units may be possible with Westinghouse's cooperation.

    In September 2014 the Chinese nuclear regulator approved the design safety analysis following a 17-month review. In May 2015 the CAP1400 design passed an International Atomic Energy Agency's Generic Reactor Safety Review.

    In December 2009, a Chinese joint venture was set up to build an initial CAP1400 near the HTR-10 Shidaowan site. In 2015 site preparation started, and approval to progress was expected by the end of the year.

    China

    Four AP1000 reactors are under construction in China, at Sanmen Nuclear Power Plant in Zhejiang, and Haiyang Nuclear Power Plant in Shandong. The Sanmen unit 1 is expected to be the first AP1000 to begin operating in 2017, more than three years after the original plan date. All four Chinese AP1000s were scheduled to be operational by 2016, but are reported to be running over two years late mainly due to key component delays and project management issues. The first four AP1000s to be built are to an earlier revision of the design without a strengthened containment structure to provide improved protection against an aircraft crash.

    China has officially adopted the AP1000 as a standard for inland nuclear projects. The National Development and Reform Commission (NDRC) has already approved several nuclear projects, including the Dafan plant in Hubei province, Taohuajiang in Hunan, and Pengze in Jiangxi. The NDRC is studying additional projects in Anhui, Jilin and Gansu provinces.

    In 2014, China First Heavy Industries manufactured the first domestically produced AP1000 reactor pressure vessel, for the second AP1000 unit of Sanmen Nuclear Power Station.

    United States

    Four AP1000 reactors are being built in the United States: two at Vogtle (units 3&4) and two at VC Summer (units 2&3). All four reactors are identical and the two projects run in parallel, with the first two reactors (Vogtle 3 and Summer 2) planned to be commissioned in 2019 and the remaining two (Vogtle 4 and Summer 3) in 2020. Both projects are running approximately three years behind schedule. On April 9, 2008, Georgia Power Company reached a contract agreement with Westinghouse and Shaw for two AP1000 reactors to be built at Vogtle. The contract represents the first agreement for new nuclear development since the Three Mile Island accident in 1979. The COL for the Vogtle site is to be based on the revision 18 to the AP1000 design. On February 16, 2010, President Obama announced $8.33 billion in federal loan guarantees to construct the two AP1000 units at the Vogtle plant. The cost of building the two reactors is expected to be $14 billion.

    Environmental groups opposed to the licensing of the two new AP1000 reactors to be built at Vogtle filed a new petition in April 2011 asking the Nuclear Regulatory Commission's commission to suspend the licensing process until more is known about the evolving Fukushima I nuclear accidents. In February 2012, nine environmental groups filed a collective challenge to the certification of the Vogtle reactor design and in March they filed a challenge to the Vogtle license. In May 2013, the U.S. Court of Appeals ruled in favor of the Nuclear Regulatory Commission (NRC).

    As of February 2012, the US Nuclear Regulatory Commission has approved the two proposed reactors at the Vogtle plant.

    For VC Summer a delay of at least one year and extra costs of $1.2 billion were announced in October 2014, largely due to fabrication delays. Unit 2 was expected to be substantially complete in late 2018 or early 2019, with unit 3 about a year later.

    In October 2013, US energy secretary Ernest Moniz announced that China was to supply components to the US nuclear power plants under construction as part of a bilateral co-operation agreement between the two countries. Since China’s State Nuclear Power Technology Co (SNPTC) acquired Westinghouses's AP1000 technology in 2006, it has developed a manufacturing supply chain capable of supplying international power projects. But industry analysts have highlighted a number of problems facing China’s expansion in the nuclear market including continued gaps in their supply chain, coupled with Western fears of political interference and Chinese inexperience in the economics of nuclear power.

    Bulgaria

    On November 22, 2013, the Bulgarian economy and energy minister Dragomir Stoynev announced during a visit to the United States, that Bulgaria wants to build an AP1000 nuclear reactor as the seventh unit of the Kozloduy Nuclear Power Plant. On December 11, the Bulgarian government gave its approval to Bulgarian Energy Holding (BEH) to start talks with Toshiba and Westinghouse on the new unit. Toshiba will hold a 30% share of the new unit. As of December 2013, the overall costs of the unit were estimated to be about $8 billion. On December 13, talks between BEH and Westinghouse started. As of December 2013, Westinghouse planned to complete preparatory work in nine months for technical, financial and economic parameters of the new unit, so that construction can begin in 2016. In 2013 the Austrian Environment Agency's report on the Bulgarian Ministry for the Environment's Environmental Impact Assessment (EIA) on the proposed 7th unit of the Kozloduy Nuclear Power Plant found a number unsubstantiated claims and some serious failings in the Bulgarian EIA report. On July 30, 2014 a shareholder agreement has been signed by Westinghouse Electric Company LLC and the state-owned Kozloduy NPP for the construction of the Kozloduy-7 nuclear reactor and reactor block, for an estimated total price of $5 billion.

    United Kingdom

    In December 2013, Toshiba, through its Westinghouse subsidiary, purchased a 60% share of NuGeneration, with the intention of building 3 AP1000s at Moorside near the Sellafield nuclear reprocessing site in Cumbria, England, with a target first operation date of 2024. In December 2011, the UK’s Office for Nuclear Regulation (ONR) published a design assessment report on the Westinghouse AP1000 reactor which highlighted 51 Generic Design Assessment (GDA) issues remaining which must be addressed before the assessment process would be completed. Now that a UK customer have been found for the AP1000, Toshiba intends to complete the Generic Design Assessment by addressing each of these issues.

    India

    In June 2016, the US and India agreed to build six AP-1000 in India as part of civil nuclear deal signed by both countries. Negotiations are being conducted with the commercial contract expected to be signed by June 2017. The proposed locations for the six-unit nuclear power plant is the coastal district of Gujarat, however, the site may be moved to the southeastern state of Andhra Pradesh, due to opposition from the local community. Following Westinghouse's parent company Toshiba deciding in 2017 to withdraw from the construction of nuclear power plants, following financial difficulties, the proposed agreement is in doubt.

    References

    AP1000 Wikipedia


    Similar Topics
    THX 1138
    Pat Brassington
    Cheng Ding An
    Topics