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Home > Publications > Research Papers > > The History of Reactor Generations
Nuclear Reactors: Generation to Generation

The History of Reactor Generations

Three generations of nuclear power systems, derived from designs originally developed for naval use beginning in the late 1940s, are operating worldwide today (Figure 1).

Figure 1. The Evolution of Nuclear Power

Figure 1

Reprinted from U.S. Department of Energy, Office of NuclearEnergy, “Generation IV Nuclear Energy Systems:Program Overview” (Department of Energy, n.d.), http://nuclear.energy.gov/genIV/neGenIV1.html.

Generation I

Gen I refers to the prototype and power reactors that launched civil nuclear power. This generation consists of early prototype reactors from the 1950s and 1960s, such as Shippingport (1957–1982) in Pennsylvania, Dresden-1 (1960–1978) in Illinois, and Calder Hall-1 (1956–2003) in the United Kingdom. This kind of reactor typically ran at power levels that were “proof-of-concept.” In the United States, Gen I reactors are regulated by the Nuclear Regulatory Commission (NRC) pursuant to Title 10, Code of Federal Regulations, Part 50 (10 CFR Part 50).

The only remaining commercial Gen I plant, the Wylfa Nuclear Power Station in Wales, was scheduled for closure in 2010. However, the UK Nuclear Decommissioning Authority announced in October 2010 that the Wylfa Nuclear Power Station will operate up to December 2012.

Generation II

Gen II refers to a class of commercial reactors designed to be economical and reliable. Designed for a typical operational lifetime of 40 years,2 prototypical Gen II reactors include pressurized water reactors (PWR), CANada Deuterium Uranium reactors (CANDU), boiling water reactors (BWR), advanced gas-cooled reactors (AGR), and Vodo-Vodyanoi Energetichesky Reactors (VVER). Gen II reactors in the United States are regulated by the NRC pursuant to 10 CFR Part 50.

Gen II systems began operation in the late 1960s and comprise the bulk of the world’s 400+ commercial PWRs and BWRs. These reactors, typically referred to as light water reactors (LWRs), use traditional active safety features involving electrical or mechanical operations that are initiated automatically and, in many cases, can be initiated by the operators of the nuclear reactors. Some engineered systems still operate passively (for example, using pressure relief valves) and function without operator control or loss of auxiliary power. Most of the Gen II plants still in operation in the West were manufactured by one of three companies: Westinghouse,3 Framatome4 (now part of AREVA5), and General Electric (GE).

The Korean Standard Nuclear Power Plant (KSNP), which is based on Gen II technology developed by Combustion Engineering (now Westinghouse) and Framatome (now AREVA), is now recognized as a Gen II design and has evolved to become the KSNP+. In 2005 the KSNP/KSNP+ was re-branded as the OPR-1000 (Optimized Power Reactor) for Asian markets, particularly Indonesia and Vietnam. Six OPR-1000 units are in operation, and four are under construction. China’s existing and planned civilian power fleet is based on the PWR. Two important designs used in China are the improved Chinese PWR 1000 (the CPR-1000), which is based on Framatome’s 900 megawatt (MW) three-loop Gen II design, and the standard PWR 600 MW and 1,000 MW designs (the CNP series).

These designs require relatively large electrical grids, have a defined safety envelope based on Western safety standards, and produce significant quantities of used fuel that require ultimate disposition in a high-level waste repository or reprocessing as part of a partially or fully closed fuel cycle. The economics of existing Gen II plants and of those under construction or in the planning stage are generally favorable, particularly in Asia (Table 1 shows a schedule of plants under construction as of November 2010).6

Table 1. Global Nuclear Power Plant Construction

Reactor designs China France Japan Republic
of Korea
Russia Other
Gen II
CPR-1000 (Gen II) 18 19.4
CNP series (Gen II) 3 2.0
OPR-1000 (Gen II) 4 4.0
VVER series (Gen II) 7 4 12.3
APR-1400 (Gen III)* 2 2.7
ABWR (Gen III) 2 2 5.4
APWR (Gen III) 2 3.1
Gen III +
AP-1000 (Gen III+)† 4 4.8
EPR (Gen III+) 2 1 1 6.6
Sub-total 27 1 4 6 7 7
Total 60.3

* The United Arab Emirates has ordered four APR-1400 reactors.
† The table does not include four U.S. AP-1000 reactor projects. Construction is underway in the United States at the Vogtle sites, and preparation is underway at the Virgil C Summer sites.
Modified from: S&P Credit Research, Global Nuclear Power Development Offers Lessons for New U.S. Construction (New York: Standard & Poor’s, 2010).

The extraordinary events unfolding at the Fukushima Daiichi and Daini nuclear power plants are being assessed by the technical and regulatory experts both in the United States and across the world. At press time, a full assessment is not possible. We have learned that an increased safety focus will likely be required and, at a minimum, will focus on four safety systems: 1) Mark I BWR containment structures; 2) common-mode emergency core cooling capability resulting from loss of emergency backup power; 3) the performance of mixed-oxide fuel in Gen II reactor designs; and 4) critical safety analyses of the various extant used fuel cooling pool designs.

Generation III

Gen III nuclear reactors are essentially Gen II reactors with evolutionary, state-of-the-art design improvements.7 These improvements are in the areas of fuel technology, thermal efficiency, modularized construction, safety systems (especially the use of passive rather than active systems), and standardized design.8 Improvements in Gen III reactor technology have aimed at a longer operational life, typically 60 years of operation, potentially to greatly exceed 60 years, prior to complete overhaul and reactor pressure vessel replacement. Confirmatory research to investigate nuclear plant aging beyond 60 years is needed to allow these reactors to operate over such extended lifetimes. Unlike Gen I and Gen II reactors, Gen III reactors are regulated by NRC regulations based on 10 CFR Part 52.9

The Westinghouse 600 MW advanced PWR (AP-600) was one of the first Gen III reactor designs. On a parallel track, GE Nuclear Energy designed the Advanced Boiling Water Reactor (ABWR) and obtained a design certification from the NRC. The first of these units went online in Japan in 1996. Other Gen III reactor designs include the Enhanced CANDU 6, which was developed by Atomic Energy of Canada Limited (AECL); and System 80+, a Combustion Engineering design.10

Only four Gen III reactors, all ABWRs, are in operation today. No Gen III plants are in service in the United States.

Hitachi carefully honed its construction processes during the building of the Japanese ABWRs. For example, the company broke ground on Kashiwazaki-Kariwa Unit 7 on July 1, 1993. The unit went critical on November 1, 1996, and began commercial operation on July 2, 1997—four years and a day after the first shovel of dirt was turned. If the U.S. nuclear power industry can learn from Hitachi’s construction techniques, many billions of dollars and years of time might be saved.11 The Shaw Group and Westinghouse have adopted modular construction practices in launching a joint venture for a Lake Charles, Louisiana, facility that will manufacture modules for the AP-1000.

Generation III+

Gen III+ reactor designs are an evolutionary development of Gen III reactors, offering significant improvements in safety over Gen III reactor designs certified by the NRC in the 1990s. In the United States, Gen III+ designs must be certified by the NRC pursuant to 10 CFR Part 52.

Examples of Gen III+ designs include:

  • VVER-1200/392M Reactor of the AES-2006 type
  • Advanced CANDU Reactor (ACR-1000)
  • AP1000: based on the AP600, with increased power output
  • European Pressurized Reactor (EPR): evolutionary descendant of the Framatome N4 and Siemens Power Generation Division KONVOI reactors
  • Economic Simplified Boiling Water Reactor (ESBWR): based on the ABWR
  • APR-1400: an advanced PWR design evolved from the U.S. System 80+, originally known as the Korean Next Generation Reactor (KNGR)
  • EU-ABWR: based on the ABWR, with increased power output and compliance with EU safety standards
  • Advanced PWR (APWR): designed by Mitsubishi Heavy Industries (MHI)12
  • ATMEA I: a 1,000–1,160 MW PWR, the result of a collaboration between MHI and AREVA.13
  • Manufacturers began development of Gen III+ systems in the 1990s by building on the operating experience of the American, Japanese, and Western European LWR fleets. Perhaps the most significant improvement of Gen III+ systems over second-generation designs is the incorporation in some designs of passive safety features that do not require active controls or operator intervention but instead rely on gravity or natural convection to mitigate the impact of abnormal events. The inclusion of passive safety features, among other improvements, may help expedite the reactor certification review process and thus shorten construction schedules.14 These reactors, once on line, are expected to achieve higher fuel burnup than their evolutionary predecessors (thus reducing fuel consumption and waste production). More than two dozen Gen III+ reactors based on five technologies are planned for the United States (Table 2 lists applications and their status as of November 2010).

    Table 2. New Nuclear Power Plant Applications

    Company Design Site under Construction Existing Unit(s) Existing Plant Design Operating Plant Design15 State Status
    Applications accepted and docketed
    Ameren UE US-EPR Callaway
    (1 unit)
    1 Operating PWR Westing-house 4 loop, 1,235 MWe MO Vendor change to AREVA from Westinghouse for new unit. The company suspended its plan to build a new reactor on April 23, 2009. The NRC suspended review of the combined operating license in June 2009.
    Detroit Edison Co. ESBWR Enrico Fermi
    (1 unit)
    1 Operating BWR GE, Type 4,
    1,039 MWe
    MI The only ESBWR application currently open.
    Dominion Resources Inc. APWR North Anna
    (1 unit)
    2 Operating PWR Westing-house, 3 loop, 925 MWe and 917MWe VA Originally chose the ESBWR design. On May 7, 2010, Dominion said that it had selected Mitsubishi’s US-APWR design and will decide over the next year whether to build the 1,700 MW APWR unit.
    Duke Energy Corp AP-1000 William States Lee III Nuclear Station
    (2 units)
    Greenfield16 NA SC
    Entergy Corp. ESBWR River Bend
    (1 unit)
    1 Operating BWR GE, Type 6, 936 MWe LA On Jan. 9, 2009, Entergy requested the NRC to suspend the review of its combined operating license because the company is considering alternate reactor technologies.
    Florida Power & Light Co. AP-1000 Turkey Point
    (2 units)
    2 Operating PWR Westing-house, 3 loop, 693 MWe each FL New units delayed from 2018–2020 to 2023. Uprating existing nuclear units
    Luminant Power US-APWR Comanche Peak
    (2 units)
    2 Operating PWR Westing-house, 4 loop, 1,150 MWe each TX PWR technology. Vendor changed from Westinghouse to MHI.
    NRG Energy Inc. ABWR South Texas Project (STP)
    (2 units)
    2 Operating PWR Westing-house, 4 loop, 1,168 MWeeach TX Existing site has a PWR. The new unit is an ABWR.
    NuStart Energy17 (Tennessee Valley Authority [TVA]) AP-1000 Bellefonte
    (2 units)
    Greenfield NA AL TVA staff has said that completing the 1,260 MW Bellefonte Unit 1 is preferable to building an AP-1000 unit. When stopped in 1988, Unit 1 was 88% complete, and Unit 2 was 58% complete. Over the years, equipment from these sites has been used elsewhere; therefore the percentage complete needs to be revised downward.
    NuStart Energy ESBWR Grand Gulf
    (1 unit)
    1 Operating BWR GE, Type 6, 1,204 MWe MS On Jan. 9, 2009, NRC was requested to suspend the review of its combined operating license because the company is considering alternate reactor technologies.
    PP&L Generation US-EPR Bell Bend18
    (1 unit)
    2 Operating BWR GE, Type 4, 1,100 MWe and 1,103 MWe PA The original units are BWRs. The EPR is a PWR. Vendor changed to AREVA from GE. Although the application is open, the company will decide in 2011–2012 whether it plans to pursue construction of a new plant.
    Progress Energy Inc. AP-1000 Levy County
    (2 units)
    Greenfield NA FL In May 2010, Progress announced plans to slow work at Levy to reduce capital spending and avoid short-term rate increases and because of a delay in the licensing timeline for its combined operating license, as well as the current economic climate and uncertainty about U.S. energy policy.
    Progress Energy Inc. AP-1000 Shearon Harris
    (2 units)
    1 Operating PWR Westing-house 3 loop, 860 MWe NC
    South Carolina Electric & Gas Co. AP-1000 Virgil C Summer
    (2 units)
    1 Operating PWR Westing-house, 3 loop, 885 MWe SC
    Southern Nuclear Operating Co. AP-1000 Vogtle
    (2 units)
    2 Operating PWR Westing-house, 4 loop, 1,150 MWe each GA An $8.3 billion conditional loan guarantee was received Feb. 16, 2010.
    Tennessee Valley Authority mPower Clinch River Greenfield TN TVA has announced its intention to submit a Construction Permit Application in 2012. As many as 6 mPower units are planned.
    Unistar US-EPR Calvert Cliffs
    (1 unit)
    2 Operating PWR Combustion Engineering, 825 MWe each MD Vendor change to AREVA (Combustion Engineering was acquired by Westinghouse in 2000).
    Unistar US-EPR Nile Mile Point
    (1 unit)
    2 Operating BWR GE, Type 2: 610MWe and Type 5:1143 MWe NY On Dec. 7, 2009, Unistar requested the NRC to temporarily suspend Nile Mile Point’s combined operating license application.
    Unannounced technology (not submitted)
    Alternate Energy Holdings Undecided Payette
    (1 unit)
    Greenfield NA ID
    Blue Castle Project Undecided Blue Castle Greenfield UT
    Exelon Corp. ABWR Victoria County
    (2 units)
    Greenfield NA TX Exelon originally selected the ESBWR design and then switched to ABWR. In July 2009, the company changed its combined operating license to an early site permit application that was submitted to the NRC on March 25, 2010.
    PSEG Inc. Undecided Salem County 3 operating BWR & PWR Westing-house PWR (Salem): 1,106 MWe each BWR (Hope Creek): 1,031 MWe NJ On May 25, 2010, PSEG filed an early site permit with the NRC. Location will be contiguous to the Salem and Hope Creek units in Salem County.

    Based upon Aneesh Prabhu, “The Expansion of Nuclear Power Plants in the U.S.: What Could Get in the Way?” in S&P’s Special Reports: Can the U.S. Nuclear Power Industry Hold Its Spot as the World Leader? (New York: Standard & Poor’s, 2010). Modified and updated with information found at http://world-nuclear.org/NuclearDatabase/Default.aspx?id=27232 (accessed on February 11, 2011).

    Gen III and III+ designs have a defined safety envelope based on Western safety standards and set the worldwide standards for safeguards and security. However, they have also produced a legacy of significant quantities of used fuel, require relatively large electric grids, and present public-acceptance challenges.


    2. The frequency of core damage to Gen II reactors is reported to be as high as one core damage event for every 100,000 years of operation (10 −5 core damage events per reactor year for the BWR(4)). In light of the ongoing events at the nuclear power plants in Fukushima, Yamato Province, Japan, the authors strongly suggest that the core damage frequencies be reanalyzed.

    3. Combustion Engineering is now part of Westinghouse. Toshiba is the majority owner of Westinghouse.

    4. BSW’s 177 class reactors were sold to Framatome.

    5. The parent company, incorporated under French law, is a Société Anonyme (S.A.).

    6. In the United States, early movers will need government assistance, particularly loan guarantees.

    7. Core damage frequencies for Gen III and Gen III+ reactors are reported to be lower than those of Gen II reactors, in the range of one core damage event for every 15–20 million years of operation (6 × 10−7 core damage events per reactor year) for the EPR and one core damage event for every 300–350 million years of operation (3 × 10 −8 core damage events per reactor year) for the ESBWR. In light of the ongoing events at the nuclear power plants in Fukushima, Yamoto Province, Japan, the authors strongly suggest that these core damage frequencies be reanalyzed.

    8. These standardized designs are intended to reduce maintenance and capital costs. The capital cost requirements are highly dependent on country and international material, labor, and other considerations.

    9. Following passage of the Energy Policy Act of 1992, the NRC adopted an additional licensing pathway option: the combined construction and operating license (COL). Except for the licensing of Brown’s Ferry I and, potentially, a small modular reactor construction application at the TVA Clinch River site, all recent licensing applicants have chosen this pathway, which is seen as a streamlined approach (see Table 2).

    10. ABB Group’s nuclear power business, formerly Combustion Engineering (CE), was purchased by BNFL and merged into Westinghouse Electric Company.

    11. Institutional and regulatory differences between the Japanese and U.S. systems may mitigate some of these savings.

    12. The US-APWR is designed to be 1,700 MW because of longer (4.3m) fuel assemblies, higher thermal efficiency (39 percent), and a 24-month refueling cycle. In March 2008, MHI submitted the same design for EUR certification and partnered with Iberdrola Engineering and Construction to build these plants in the EU.

    13. ATMEA I is one of the three technologies Jordan is considering for its next power plant.

    14. Because no COL has been issued to date, this is an opinion of the authors and might not be shared by nuclear manufacturers of active nuclear safety systems. COL, as defined by the Code of Federal Regulations, means a combined construction permit and operating license with conditions for a nuclear power facility.

    15. Net Capacity (MWe) is electricity generated and sold.

    16. Undeveloped (virgin) site earmarked for potential new nuclear reactor.

    17. NuStart Energy is a limited liability corporation comprised of ten power companies, created in 2004 for the dual purposes of: 1) obtaining a Construction and Operating License (COL) from the Nuclear Regulatory Commission (NRC), using the never before used, streamlined licensing process developed in 1992 and 2) completing the design engineering for the selected reactor technologies.

    18. New site adjacent to PPL’s Susquehanna Steam Electric Station, Luzerne County, PA.