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Water-cooled

Reactors cooled by ordinary or heavy water, which in most designs is also the neutron moderator.

In the record: 38 companies, 3 laboratories and programmes, 125 reactors and 26 reactor designs. These counts include Pressurised water reactor, Boiling water reactor and Pressurised heavy-water reactor.

Related approaches

Broader: Fission

Narrower:

  • Pressurised water reactor Ordinary (light) water kept under high pressure so it heats without boiling, transferring heat to a separate steam loop; the water is both coolant and moderator. Fuel is low-enriched uranium oxide pellets in zirconium-alloy rods. The most common reactor type in service worldwide.
  • Boiling water reactor Light water boils directly in the core and the steam drives the turbine: one loop instead of two, simpler but with an activated steam circuit. Water is again both coolant and moderator, and fuel is low-enriched uranium oxide, as in a PWR.
  • Pressurised heavy-water reactor Heavy water (deuterium oxide) kept under pressure as both coolant and moderator, which absorbs far fewer neutrons than ordinary water and so lets the reactor run on natural, unenriched uranium. That is the CANDU design's defining trade: heavy water is expensive to produce, but the fuel needs no enrichment plant. Fuel is natural or slightly enriched uranium oxide, usually in horizontal pressure tubes, refuelled online without shutting the reactor down.

Companies 38

Includes companies recorded under a narrower approach, named beside each.

Laboratories and programmes 3

Reactors 125

Operating reactors first, then those being built or planned, then those shut down, suspended or cancelled.

  • Advanced Test Reactor Operating Idaho National Laboratory · US · 1 measurement
  • Advanced Test Reactor Critical Operating Idaho National Laboratory · US · 1 measurement
  • Akademik Lomonosov Operating RU · Pressurised water reactor · 1 measurement
  • Annular Core Research Reactor Operating Sandia National Laboratories · US · 1 measurement
  • Argonauta Operating Instituto de Engenharia Nuclear · BR · 1 measurement
  • BAEC TRIGA Research Reactor Operating Bangladesh Atomic Energy Commission · BD · 1 measurement
  • BME Training Reactor Operating BME Institute of Nuclear Techniques · HU · 1 measurement
  • BR2 Operating SCK CEN · BE · 1 measurement
  • Breazeale Nuclear Reactor Operating Penn State Radiation Science & Engineering Center · US · 1 measurement
  • Budapest Research Reactor Operating HUN-REN Energiatudományi Kutatóközpont · HU · 1 measurement
  • China Advanced Research Reactor Operating China Institute of Atomic Energy · CN · 1 measurement
  • Dalat Nuclear Research Reactor Operating Vietnam Atomic Energy Institute · VN · 1 measurement
  • Dhruva Operating BARC · IN · 1 measurement
  • ETRR-2 Operating Egyptian Atomic Energy Authority · EG · 1 measurement
  • GHARR-1 Operating Ghana Atomic Energy Commission · GH · 1 measurement
  • HANARO Operating KAERI · KR · 1 measurement
  • High Flux Isotope Reactor Operating Oak Ridge National Laboratory · US · 1 measurement
  • High Flux Reactor, Petten Operating NRG PALLAS · NL · 1 measurement
  • HOR Operating Reactor Institute Delft · NL · 1 measurement
  • IAN-R1 Operating Colombian Geological Survey · CO · 1 measurement
  • IEA-R1 Operating Instituto de Pesquisas Energéticas e Nucleares · BR · 1 measurement
  • ILL High-Flux Reactor Operating Institut Laue-Langevin · FR · 1 measurement
  • IPEN/MB-01 Operating Instituto de Pesquisas Energéticas e Nucleares · BR · 1 measurement
  • IPR-R1 Operating Centro de Desenvolvimento da Tecnologia Nuclear · BR · 1 measurement
  • IRR-1 Operating Soreq Nuclear Research Center · IL · 1 measurement
  • IRT-MEPhI Operating National Research Nuclear University MEPhI · RU · 1 measurement
  • IRT-T Operating Tomsk Polytechnic University · RU · 1 measurement
  • IVG.1M Operating National Nuclear Center of the Republic of Kazakhstan · KZ · 1 measurement
  • JRR-3 Operating JAEA · JP · 1 measurement
  • KAMINI Operating Indira Gandhi Centre for Atomic Research · IN · 1 measurement
  • Kansas State University TRIGA Mark II Operating Kansas State University · US · 1 measurement
  • Kyoto University Research Reactor Operating Kyoto University · JP · 1 measurement
  • LR-0 Operating Research Centre Řež · CZ · 1 measurement
  • LVR-15 Operating Research Centre Řež · CZ · 1 measurement
  • MARIA Operating National Centre for Nuclear Research · PL · 1 measurement
  • Maryland University Training Reactor Operating University of Maryland, College Park · US · 1 measurement
  • McClellan TRIGA reactor Operating McClellan Nuclear Research Center · US · 1 measurement
  • McMaster Nuclear Reactor Operating McMaster University · CA · 1 measurement
  • MIR.M1 Operating Research Institute of Atomic Reactors · RU · 1 measurement
  • Missouri S&T Reactor Operating Missouri University of Science and Technology · US · 1 measurement
  • MIT Research Reactor Operating MIT Nuclear Reactor Laboratory · US · 1 measurement
  • NBSR Operating NIST Center for Neutron Research · US · 1 measurement
  • NRAD Operating Idaho National Laboratory · US · 1 measurement
  • NSRR Operating JAEA · JP · 1 measurement
  • Ohio State University Research Reactor Operating Ohio State University · US · 1 measurement
  • OPAL Operating Australian Nuclear Science and Technology Organisation · AU · 1 measurement
  • Oregon State TRIGA Reactor Operating Oregon State University Radiation Center · US · 1 measurement
  • PARR-1 Operating Pakistan Institute of Nuclear Science and Technology · PK · 1 measurement
  • PARR-2 Operating Pakistan Institute of Nuclear Science and Technology · PK · 1 measurement
  • PIK Operating National Research Centre Kurchatov Institute · RU · 1 measurement
  • PULSTAR Operating NC State Nuclear Reactor Program · US · 1 measurement
  • PUR-1 Operating Purdue University School of Nuclear Engineering · US · 1 measurement
  • RA-1 Enrico Fermi Operating CNEA · AR · 1 measurement
  • RA-3 Operating CNEA · AR · 1 measurement
  • RA-6 Operating CNEA · AR · 1 measurement
  • RBT-10/2 Operating Research Institute of Atomic Reactors · RU · 1 measurement
  • RBT-6 Operating Research Institute of Atomic Reactors · RU · 1 measurement
  • RECH-1 Operating Chilean Nuclear Energy Commission · CL · 1 measurement
  • Reed Research Reactor Operating Reed College · US · 1 measurement
  • RP-10 Operating Peruvian Institute of Nuclear Energy · PE · 1 measurement
  • RSG-GAS Operating National Research and Innovation Agency · ID · 1 measurement
  • SAFARI-1 Operating South African Nuclear Energy Corporation · ZA · 1 measurement
  • SLOWPOKE-2, Polytechnique Montréal Operating Polytechnique Montréal · CA · 1 measurement
  • SLOWPOKE-2, Royal Military College of Canada Operating Royal Military College of Canada · CA · 1 measurement
  • SLOWPOKE-2, University of the West Indies Operating International Centre for Environmental and Nuclear Sciences · JM · 1 measurement
  • SM-3 Operating Research Institute of Atomic Reactors · RU · 1 measurement
  • Texas A&M NSC TRIGA reactor Operating Texas A&M Nuclear Engineering and Science Center · US · 1 measurement
  • THOR Operating National Tsing Hua University · TW · 1 measurement
  • TRIGA Mark II reactor, Vienna Operating Atominstitut, TU Wien · AT · 1 measurement
  • TRIGA Mark II, Ljubljana Operating Jožef Stefan Institute · SI · 1 measurement
  • TRIGA Mark III, Salazar Operating National Institute for Nuclear Research (Mexico) · MX · 1 measurement
  • TRIGA PUSPATI Operating Malaysian Nuclear Agency · MY · 1 measurement
  • TRIGA reactor, Pitești Operating Institute for Nuclear Research Pitești · RO · 1 measurement
  • TRR-1/M1 Operating Thailand Institute of Nuclear Technology · TH · 1 measurement
  • UC Irvine TRIGA reactor Operating University of California, Irvine · US · 1 measurement
  • UMass Lowell Research Reactor Operating University of Massachusetts Lowell · US · 1 measurement
  • University of Florida Training Reactor Operating University of Florida · US · 1 measurement
  • University of Missouri Research Reactor Operating University of Missouri Research Reactor · US · 1 measurement
  • University of Utah TRIGA reactor Operating University of Utah Nuclear Engineering Program · US · 1 measurement
  • University of Wisconsin Nuclear Reactor Operating University of Wisconsin-Madison · US · 1 measurement
  • UT Austin TRIGA Mark II Operating University of Texas at Austin · US · 1 measurement
  • UTR-KINKI Operating Kindai University · JP · 1 measurement
  • VK-50 Operating Research Institute of Atomic Reactors · RU · Boiling water reactor · 1 measurement
  • VR-1 Operating Czech Technical University · CZ · 1 measurement
  • Washington State University Reactor Operating Washington State University Nuclear Science Center · US · 1 measurement
  • WWR-K Operating Institute of Nuclear Physics (Kazakhstan) · KZ · 1 measurement
  • ZED-2 Operating Canadian Nuclear Laboratories · CA · 1 measurement
  • Darlington New Nuclear Project Unit 1 Under construction Ontario Power Generation · CA · Boiling water reactor
  • Jules Horowitz Reactor Under construction FR · 1 measurement
  • KJRR Under construction KAERI · KR · 1 measurement
  • Linglong One demonstration unit, Changjiang Under construction CNNC · CN · Pressurised water reactor · 1 measurement
  • PALLAS Under construction NRG PALLAS · NL · 1 measurement
  • RA-10 Under construction CNEA · AR · 1 measurement
  • RMB (Brazilian Multipurpose Reactor) Under construction National Nuclear Energy Commission (Brazil) · BR · 1 measurement
  • Clinch River Nuclear Site Unit 1 Planned Tennessee Valley Authority · US · Boiling water reactor · 1 measurement
  • Pioneer Unit 1 (Palisades SMR-300) Planned Holtec International · US · Pressurised water reactor
  • Pioneer Unit 2 (Palisades SMR-300) Planned Holtec International · US · Pressurised water reactor
  • Halden Reactor Shut down Institute for Energy Technology · NO · 1 measurement
  • HIFAR Shut down Australian Nuclear Science and Technology Organisation · AU · 1 measurement
  • JEEP II Shut down Institute for Energy Technology · NO · 1 measurement
  • JMTR Shut down JAEA · JP · 1 measurement
  • NRU Shut down Canadian Nuclear Laboratories · CA · 1 measurement
  • TRICO I Shut down CREN-K · CD · 1 measurement
  • CIRUS Decommissioned BARC · IN · 1 measurement
  • CP-5 Decommissioned Argonne National Laboratory · US · 1 measurement
  • DIORIT Decommissioned Paul Scherrer Institute · CH · 1 measurement
  • FiR 1 Decommissioned VTT Technical Research Centre of Finland · FI · 1 measurement
  • Ford Nuclear Reactor Decommissioned University of Michigan Nuclear Engineering and Radiological Sciences · US · 1 measurement
  • KRR-1 Decommissioned KAERI · KR · 1 measurement
  • KRR-2 Decommissioned KAERI · KR · 1 measurement
  • Omega West Reactor Decommissioned Los Alamos National Laboratory · US · 1 measurement
  • R1 Decommissioned KTH Royal Institute of Technology · SE
  • RA (Vinča) Decommissioned Vinča Institute of Nuclear Sciences · RS · 1 measurement
  • SAPHIR Decommissioned Paul Scherrer Institute · CH · 1 measurement
  • University of Illinois Advanced TRIGA Decommissioned University of Illinois · US · 1 measurement
  • CAREM-25 Status not recorded CNEA · AR · Pressurised water reactor
  • ETRR-1 Suspended Egyptian Atomic Energy Authority · EG · 1 measurement
  • FRM II Suspended Heinz Maier-Leibnitz Research Neutron Source (FRM II) · DE · 1 measurement
  • GRR-1 (Demokritos) Suspended National Centre for Scientific Research Demokritos · GR · 1 measurement
  • IRT-1 (Tajoura) Suspended Tajoura Nuclear Research Centre · LY · 1 measurement
  • RB (Vinča) Suspended Vinča Institute of Nuclear Sciences · RS
  • RECH-2 Suspended Chilean Nuclear Energy Commission · CL · 1 measurement
  • TR-2 Suspended Turkish Energy, Nuclear and Mineral Research Agency · TR · 1 measurement
  • TRICO II Suspended CREN-K · CD · 1 measurement
  • WWR-M (Gatchina) Suspended National Research Centre Kurchatov Institute · RU · 1 measurement

Reactor designs 26

Size class is worked out from the electrical output of one unit: up to 10 MWe is a microreactor, up to 300 MWe a small modular reactor. A design with no stated output is not classed.

Design Developer Approach Electrical output per unit Size class Licensing stage
ABV-6E OKBM Afrikantov with Rosatom Pressurised water reactor 6 to 9 MWe planned Microreactor No milestone recorded
ACP100 Linglong One CNNC Pressurised water reactor 125 MWe planned Small modular reactor No milestone recorded
ACP100S CNNC Pressurised water reactor 125 MWe planned Small modular reactor No milestone recorded
Advanced Boiling Water Reactor (ABWR) ABWR GE Vernova Hitachi Nuclear Energy Boiling water reactor 1,350 to 1,460 MWe claimed Large reactor No milestone recorded
AP1000 Westinghouse Electric Company Pressurised water reactor 1,110 MWe claimed Large reactor No milestone recorded
AP300 Westinghouse Electric Company Pressurised water reactor 330 MWe planned Large reactor No milestone recorded
BWRX-300 GE Vernova Hitachi Nuclear Energy Boiling water reactor 300 MWe planned Small modular reactor Construction permit issued for one plant: CNSC licence to construct one BWRX-300 at the Darlington New Nuclear Project · Canadian Nuclear Safety Commission · 2025-04-04
CAREM CAREM25 CNEA Pressurised water reactor 30 MWe planned Small modular reactor No milestone recorded
Economic Simplified Boiling Water Reactor (ESBWR) ESBWR GE Vernova Hitachi Nuclear Energy Boiling water reactor 1,520 MWe planned Large reactor No milestone recorded
EPR European Pressurised Reactor, Evolutionary Power Reactor Framatome Pressurised water reactor Output not stated Not classed No milestone recorded
Gravity Nuclear Reactor Gravity reactor, Deep Fission Borehole Reactor Deep Fission Pressurised water reactor 15 MWe planned Small modular reactor No milestone recorded
Hualong One HPR1000 CNNC with CGN Pressurised water reactor Output not stated Not classed No milestone recorded
i-SMR innovative SMR Korea Hydro & Nuclear Power with KAERI Pressurised water reactor 170 MWe planned Small modular reactor No milestone recorded
IPHWR-700 700 MWe PHWR, Indian PHWR-700 NPCIL Pressurised heavy-water reactor 700 MWe claimed Large reactor No milestone recorded
KLT-40S OKBM Afrikantov with Rosatom Pressurised water reactor 35 MWe claimed Small modular reactor No milestone recorded
LDR-50 Steady Energy Water-cooled Output not stated Not classed No milestone recorded
NuScale Power Module (US460) US460, NPM, VOYGR NuScale Power Pressurised water reactor 77 MWe planned Small modular reactor Design approval or certification for the design · US Nuclear Regulatory Commission · 2025-05-29
PWR-20 Last Energy Pressurised water reactor 20 MWe planned Small modular reactor No milestone recorded
RITM-200M OKBM Afrikantov with Rosatom Pressurised water reactor 50 MWe planned Small modular reactor No milestone recorded
RITM-200N OKBM Afrikantov with Rosatom Pressurised water reactor 55 MWe planned Small modular reactor No milestone recorded
Rolls-Royce SMR Rolls-Royce SMR Pressurised water reactor 470 MWe planned Large reactor Accepted for review for the design · Office for Nuclear Regulation · 2022-04
SHELF-M NIKIET with Rosatom Pressurised water reactor 10 MWe planned Microreactor No milestone recorded
SMART System-integrated Modular Advanced Reactor, SMART100 KAERI Pressurised water reactor 107 MWe planned Small modular reactor No milestone recorded
SMR-300 Holtec International Pressurised water reactor 320 MWe planned Large reactor Accepted for review for one plant: Pioneer Units 1 and 2: Part 1 of phased construction permit application accepted for docketing · US Nuclear Regulatory Commission · 2026-02-13
UNITHERM NIKIET with Rosatom Pressurised water reactor 6.6 MWe planned Microreactor No milestone recorded
VBER-300 OKBM Afrikantov with Rosatom Pressurised water reactor 325 MWe planned Large reactor No milestone recorded

Measurements

119 reactors using this approach carry 119 measurements: 112 claimed, 7 planned. The values, each with its status and source, are on the benchmark and on each device's page. Most measured: Advanced Test Reactor (1), Advanced Test Reactor Critical (1), Akademik Lomonosov (1), Annular Core Research Reactor (1), Argonauta (1).

Guides

Includes guides about the narrower approaches.

  • How fission reactors work How a fission reactor sustains a chain reaction, what the moderator, coolant and control rods do, why delayed neutrons make control possible, where decay heat comes from, and what passive safety does and does not mean.
  • Small modular reactors What makes a reactor a small modular reactor, where the IAEA draws the size lines, why size is judged per unit rather than per plant, which ones actually operate, and why their cost claims are not yet proven.
  • Reactor types explained The three questions that classify any fission reactor, and how pressurised water, boiling water, heavy water, gas-cooled, salt-cooled, molten-salt, sodium, lead and heat-pipe reactors each answer them.

Water-cooled in the glossary · Fission overview · All approaches