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mw-ui-icon-wikimedia-expand"></span> <span>Toggle Reactor design subsection</span> </button> <ul id="toc-Reactor_design-sublist" class="vector-toc-list"> <li id="toc-Control" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Control"> <div class="vector-toc-text"> <span class="vector-toc-numb">3.1</span> <span>Control</span> </div> </a> <ul id="toc-Control-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Coolant" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Coolant"> <div class="vector-toc-text"> <span class="vector-toc-numb">3.2</span> <span>Coolant</span> </div> </a> <ul id="toc-Coolant-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Fuel" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Fuel"> <div class="vector-toc-text"> <span class="vector-toc-numb">3.3</span> <span>Fuel</span> </div> </a> <ul id="toc-Fuel-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Moderator" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Moderator"> <div class="vector-toc-text"> <span class="vector-toc-numb">3.4</span> <span>Moderator</span> </div> </a> <ul id="toc-Moderator-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-See_also" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#See_also"> <div class="vector-toc-text"> <span class="vector-toc-numb">4</span> <span>See also</span> </div> </a> <ul id="toc-See_also-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-References" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#References"> <div class="vector-toc-text"> <span class="vector-toc-numb">5</span> <span>References</span> </div> </a> <ul id="toc-References-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-External_links" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#External_links"> <div class="vector-toc-text"> <span class="vector-toc-numb">6</span> <span>External links</span> </div> </a> <ul id="toc-External_links-sublist" class="vector-toc-list"> </ul> </li> </ul> </div> </div> </nav> </div> </div> <div class="mw-content-container"> <main id="content" class="mw-body"> <header class="mw-body-header vector-page-titlebar"> <nav aria-label="Contents" class="vector-toc-landmark"> <div id="vector-page-titlebar-toc" class="vector-dropdown vector-page-titlebar-toc vector-button-flush-left" title="Table of Contents" > <input type="checkbox" id="vector-page-titlebar-toc-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-vector-page-titlebar-toc" class="vector-dropdown-checkbox " aria-label="Toggle the table of contents" > <label id="vector-page-titlebar-toc-label" for="vector-page-titlebar-toc-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--icon-only " aria-hidden="true" ><span class="vector-icon mw-ui-icon-listBullet mw-ui-icon-wikimedia-listBullet"></span> <span class="vector-dropdown-label-text">Toggle the table of contents</span> </label> <div class="vector-dropdown-content"> <div id="vector-page-titlebar-toc-unpinned-container" class="vector-unpinned-container"> </div> </div> </div> </nav> <h1 id="firstHeading" class="firstHeading mw-first-heading"><span class="mw-page-title-main">Light-water reactor</span></h1> <div id="p-lang-btn" class="vector-dropdown mw-portlet mw-portlet-lang" > <input type="checkbox" id="p-lang-btn-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-p-lang-btn" class="vector-dropdown-checkbox mw-interlanguage-selector" aria-label="Go to an article in another language. Available in 25 languages" > <label id="p-lang-btn-label" for="p-lang-btn-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--action-progressive mw-portlet-lang-heading-25" aria-hidden="true" ><span class="vector-icon mw-ui-icon-language-progressive mw-ui-icon-wikimedia-language-progressive"></span> <span class="vector-dropdown-label-text">25 languages</span> </label> <div class="vector-dropdown-content"> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li class="interlanguage-link interwiki-ar mw-list-item"><a href="https://ar.wikipedia.org/wiki/%D9%85%D9%81%D8%A7%D8%B9%D9%84_%D8%A7%D9%84%D9%85%D8%A7%D8%A1_%D8%A7%D9%84%D8%AE%D9%81%D9%8A%D9%81" title="مفاعل الماء الخفيف – Arabic" lang="ar" hreflang="ar" data-title="مفاعل الماء الخفيف" data-language-autonym="العربية" data-language-local-name="Arabic" class="interlanguage-link-target"><span>العربية</span></a></li><li class="interlanguage-link interwiki-bn mw-list-item"><a href="https://bn.wikipedia.org/wiki/%E0%A6%B9%E0%A6%BE%E0%A6%B2%E0%A6%95%E0%A6%BE-%E0%A6%9C%E0%A6%B2_%E0%A6%9A%E0%A7%81%E0%A6%B2%E0%A7%8D%E0%A6%B2%E0%A7%80" title="হালকা-জল চুল্লী – Bangla" lang="bn" hreflang="bn" data-title="হালকা-জল চুল্লী" data-language-autonym="বাংলা" data-language-local-name="Bangla" class="interlanguage-link-target"><span>বাংলা</span></a></li><li class="interlanguage-link interwiki-ca mw-list-item"><a href="https://ca.wikipedia.org/wiki/Reactor_d%27aigua_lleugera" title="Reactor d'aigua lleugera – Catalan" lang="ca" hreflang="ca" data-title="Reactor d'aigua lleugera" data-language-autonym="Català" data-language-local-name="Catalan" class="interlanguage-link-target"><span>Català</span></a></li><li class="interlanguage-link interwiki-cs mw-list-item"><a href="https://cs.wikipedia.org/wiki/Lehkovodn%C3%AD_reaktor" title="Lehkovodní reaktor – Czech" lang="cs" hreflang="cs" data-title="Lehkovodní reaktor" data-language-autonym="Čeština" data-language-local-name="Czech" class="interlanguage-link-target"><span>Čeština</span></a></li><li class="interlanguage-link interwiki-de mw-list-item"><a href="https://de.wikipedia.org/wiki/Leichtwasserreaktor" title="Leichtwasserreaktor – German" lang="de" hreflang="de" data-title="Leichtwasserreaktor" data-language-autonym="Deutsch" data-language-local-name="German" class="interlanguage-link-target"><span>Deutsch</span></a></li><li class="interlanguage-link interwiki-es mw-list-item"><a href="https://es.wikipedia.org/wiki/Reactor_de_agua_ligera" title="Reactor de agua ligera – Spanish" lang="es" hreflang="es" data-title="Reactor de agua ligera" data-language-autonym="Español" data-language-local-name="Spanish" class="interlanguage-link-target"><span>Español</span></a></li><li class="interlanguage-link interwiki-fa mw-list-item"><a href="https://fa.wikipedia.org/wiki/%D9%88%D8%A7%DA%A9%D9%86%D8%B4%DA%AF%D8%A7%D9%87_%D8%A2%D8%A8%E2%80%8C%D8%B3%D8%A8%DA%A9" title="واکنشگاه آب‌سبک – Persian" lang="fa" hreflang="fa" data-title="واکنشگاه آب‌سبک" data-language-autonym="فارسی" data-language-local-name="Persian" class="interlanguage-link-target"><span>فارسی</span></a></li><li class="interlanguage-link interwiki-fr mw-list-item"><a href="https://fr.wikipedia.org/wiki/R%C3%A9acteur_%C3%A0_eau_l%C3%A9g%C3%A8re" title="Réacteur à eau légère – French" lang="fr" hreflang="fr" data-title="Réacteur à eau légère" data-language-autonym="Français" data-language-local-name="French" class="interlanguage-link-target"><span>Français</span></a></li><li class="interlanguage-link interwiki-ko mw-list-item"><a href="https://ko.wikipedia.org/wiki/%EA%B2%BD%EC%88%98%EB%A1%9C" title="경수로 – Korean" lang="ko" hreflang="ko" data-title="경수로" data-language-autonym="한국어" data-language-local-name="Korean" class="interlanguage-link-target"><span>한국어</span></a></li><li class="interlanguage-link interwiki-hr mw-list-item"><a href="https://hr.wikipedia.org/wiki/Lakovodni_reaktor" title="Lakovodni reaktor – Croatian" lang="hr" hreflang="hr" data-title="Lakovodni reaktor" data-language-autonym="Hrvatski" data-language-local-name="Croatian" class="interlanguage-link-target"><span>Hrvatski</span></a></li><li class="interlanguage-link interwiki-id mw-list-item"><a href="https://id.wikipedia.org/wiki/Reaktor_air_ringan" title="Reaktor air ringan – Indonesian" lang="id" hreflang="id" data-title="Reaktor air ringan" data-language-autonym="Bahasa Indonesia" data-language-local-name="Indonesian" class="interlanguage-link-target"><span>Bahasa Indonesia</span></a></li><li class="interlanguage-link interwiki-it mw-list-item"><a href="https://it.wikipedia.org/wiki/Reattore_nucleare_ad_acqua_leggera" title="Reattore nucleare ad acqua leggera – Italian" lang="it" hreflang="it" data-title="Reattore nucleare ad acqua leggera" data-language-autonym="Italiano" data-language-local-name="Italian" class="interlanguage-link-target"><span>Italiano</span></a></li><li class="interlanguage-link interwiki-nl mw-list-item"><a href="https://nl.wikipedia.org/wiki/Lichtwaterreactor" title="Lichtwaterreactor – Dutch" lang="nl" hreflang="nl" data-title="Lichtwaterreactor" data-language-autonym="Nederlands" data-language-local-name="Dutch" class="interlanguage-link-target"><span>Nederlands</span></a></li><li class="interlanguage-link interwiki-ja mw-list-item"><a href="https://ja.wikipedia.org/wiki/%E8%BB%BD%E6%B0%B4%E7%82%89" title="軽水炉 – Japanese" lang="ja" hreflang="ja" data-title="軽水炉" data-language-autonym="日本語" data-language-local-name="Japanese" class="interlanguage-link-target"><span>日本語</span></a></li><li class="interlanguage-link interwiki-pt badge-Q70893996 mw-list-item" title=""><a href="https://pt.wikipedia.org/wiki/Reatores_de_%C3%A1gua_leve" title="Reatores de água leve – Portuguese" lang="pt" hreflang="pt" data-title="Reatores de água leve" data-language-autonym="Português" data-language-local-name="Portuguese" class="interlanguage-link-target"><span>Português</span></a></li><li class="interlanguage-link interwiki-ru mw-list-item"><a href="https://ru.wikipedia.org/wiki/%D0%9B%D0%B5%D0%B3%D0%BA%D0%BE%D0%B2%D0%BE%D0%B4%D0%BD%D1%8B%D0%B9_%D1%80%D0%B5%D0%B0%D0%BA%D1%82%D0%BE%D1%80" title="Легководный реактор – Russian" lang="ru" hreflang="ru" data-title="Легководный реактор" data-language-autonym="Русский" data-language-local-name="Russian" class="interlanguage-link-target"><span>Русский</span></a></li><li class="interlanguage-link interwiki-sl mw-list-item"><a href="https://sl.wikipedia.org/wiki/Lahkovodni_reaktor" title="Lahkovodni reaktor – Slovenian" lang="sl" hreflang="sl" data-title="Lahkovodni reaktor" data-language-autonym="Slovenščina" data-language-local-name="Slovenian" class="interlanguage-link-target"><span>Slovenščina</span></a></li><li class="interlanguage-link interwiki-sh mw-list-item"><a href="https://sh.wikipedia.org/wiki/Lakovodni_reaktor" title="Lakovodni reaktor – Serbo-Croatian" lang="sh" hreflang="sh" data-title="Lakovodni reaktor" data-language-autonym="Srpskohrvatski / српскохрватски" data-language-local-name="Serbo-Croatian" class="interlanguage-link-target"><span>Srpskohrvatski / српскохрватски</span></a></li><li class="interlanguage-link interwiki-fi mw-list-item"><a href="https://fi.wikipedia.org/wiki/Kevytvesireaktori" title="Kevytvesireaktori – Finnish" lang="fi" hreflang="fi" data-title="Kevytvesireaktori" data-language-autonym="Suomi" data-language-local-name="Finnish" class="interlanguage-link-target"><span>Suomi</span></a></li><li class="interlanguage-link interwiki-sv mw-list-item"><a href="https://sv.wikipedia.org/wiki/L%C3%A4ttvattenreaktor" title="Lättvattenreaktor – Swedish" lang="sv" hreflang="sv" data-title="Lättvattenreaktor" data-language-autonym="Svenska" data-language-local-name="Swedish" class="interlanguage-link-target"><span>Svenska</span></a></li><li class="interlanguage-link interwiki-ta mw-list-item"><a href="https://ta.wikipedia.org/wiki/%E0%AE%AE%E0%AF%86%E0%AE%A9%E0%AF%8D%E0%AE%A9%E0%AF%80%E0%AE%B0%E0%AF%8D_%E0%AE%85%E0%AE%A3%E0%AF%81_%E0%AE%89%E0%AE%B2%E0%AF%88" title="மென்னீர் அணு உலை – Tamil" lang="ta" hreflang="ta" data-title="மென்னீர் அணு உலை" data-language-autonym="தமிழ்" data-language-local-name="Tamil" class="interlanguage-link-target"><span>தமிழ்</span></a></li><li class="interlanguage-link interwiki-tr mw-list-item"><a href="https://tr.wikipedia.org/wiki/Hafif_su_reakt%C3%B6r%C3%BC" title="Hafif su reaktörü – Turkish" lang="tr" hreflang="tr" data-title="Hafif su reaktörü" data-language-autonym="Türkçe" data-language-local-name="Turkish" class="interlanguage-link-target"><span>Türkçe</span></a></li><li class="interlanguage-link interwiki-uk mw-list-item"><a href="https://uk.wikipedia.org/wiki/%D0%A0%D0%B5%D0%B0%D0%BA%D1%82%D0%BE%D1%80_%D0%BD%D0%B0_%D0%BB%D0%B5%D0%B3%D0%BA%D1%96%D0%B9_%D0%B2%D0%BE%D0%B4%D1%96" title="Реактор на легкій воді – Ukrainian" lang="uk" hreflang="uk" data-title="Реактор на легкій воді" data-language-autonym="Українська" data-language-local-name="Ukrainian" class="interlanguage-link-target"><span>Українська</span></a></li><li class="interlanguage-link interwiki-vi mw-list-item"><a href="https://vi.wikipedia.org/wiki/L%C3%B2_ph%E1%BA%A3n_%E1%BB%A9ng_n%C6%B0%E1%BB%9Bc_nh%E1%BA%B9" title="Lò phản ứng nước nhẹ – Vietnamese" lang="vi" hreflang="vi" data-title="Lò phản ứng nước nhẹ" data-language-autonym="Tiếng Việt" data-language-local-name="Vietnamese" class="interlanguage-link-target"><span>Tiếng Việt</span></a></li><li class="interlanguage-link interwiki-zh mw-list-item"><a href="https://zh.wikipedia.org/wiki/%E8%BD%BB%E6%B0%B4%E5%8F%8D%E5%BA%94%E5%A0%86" title="轻水反应堆 – Chinese" lang="zh" hreflang="zh" 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id="mw-content-subtitle"></div></div> <div id="mw-content-text" class="mw-body-content"><div class="mw-content-ltr mw-parser-output" lang="en" dir="ltr"><div class="shortdescription nomobile noexcerpt noprint searchaux" style="display:none">Type of nuclear reactor that uses normal water</div> <style data-mw-deduplicate="TemplateStyles:r1236090951">.mw-parser-output .hatnote{font-style:italic}.mw-parser-output div.hatnote{padding-left:1.6em;margin-bottom:0.5em}.mw-parser-output .hatnote i{font-style:normal}.mw-parser-output .hatnote+link+.hatnote{margin-top:-0.5em}@media print{body.ns-0 .mw-parser-output .hatnote{display:none!important}}</style><div role="note" class="hatnote navigation-not-searchable">"LWR" redirects here. For other uses, see <a href="/wiki/LWR_(disambiguation)" class="mw-disambig" title="LWR (disambiguation)">LWR (disambiguation)</a>.</div> <figure class="mw-halign-right" typeof="mw:File/Thumb"><a href="/wiki/File:Pumpless_light_water_reactor.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/7/78/Pumpless_light_water_reactor.jpg/200px-Pumpless_light_water_reactor.jpg" decoding="async" width="200" height="256" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/7/78/Pumpless_light_water_reactor.jpg/300px-Pumpless_light_water_reactor.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/7/78/Pumpless_light_water_reactor.jpg/400px-Pumpless_light_water_reactor.jpg 2x" data-file-width="440" data-file-height="563" /></a><figcaption>A simple light-water reactor</figcaption></figure> <p>The <b>light-water reactor</b> (<b>LWR</b>) is a type of <a href="/wiki/Thermal-neutron_reactor" title="Thermal-neutron reactor">thermal-neutron reactor</a> that uses normal water, as opposed to <a href="/wiki/Pressurized_heavy-water_reactor" title="Pressurized heavy-water reactor">heavy water</a>, as both its coolant and <a href="/wiki/Neutron_moderator" title="Neutron moderator">neutron moderator</a>; furthermore a solid form of fissile elements is used as fuel. Thermal-neutron reactors are the most common type of <a href="/wiki/Nuclear_reactor" title="Nuclear reactor">nuclear reactor</a>, and light-water reactors are the most common type of thermal-neutron reactor. </p><p>There are three varieties of light-water reactors: the <a href="/wiki/Pressurized_water_reactor" title="Pressurized water reactor">pressurized water reactor</a> (PWR), the <a href="/wiki/Boiling_water_reactor" title="Boiling water reactor">boiling water reactor</a> (BWR), and (most designs of) the <a href="/wiki/Supercritical_water_reactor" title="Supercritical water reactor">supercritical water reactor</a> (SCWR). </p> <meta property="mw:PageProp/toc" /> <div class="mw-heading mw-heading2"><h2 id="History">History</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Light-water_reactor&action=edit&section=1" title="Edit section: History"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <div class="mw-heading mw-heading3"><h3 id="Early_concepts_and_experiments">Early concepts and experiments</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Light-water_reactor&action=edit&section=2" title="Edit section: Early concepts and experiments"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>After the discoveries of <a href="/wiki/Nuclear_fission" title="Nuclear fission">fission</a>, <a href="/wiki/Neutron_moderator" title="Neutron moderator">moderation</a> and of the theoretical possibility of a <a href="/wiki/Nuclear_chain_reaction" title="Nuclear chain reaction">nuclear chain reaction</a>, early experimental results rapidly showed that natural uranium could only undergo a sustained chain reaction using graphite or <a href="/wiki/Heavy_water" title="Heavy water">heavy water</a> as a moderator. While the world's first reactors (<a href="/wiki/Chicago_Pile-1" title="Chicago Pile-1">CP-1</a>, <a href="/wiki/X-10_Graphite_Reactor" title="X-10 Graphite Reactor">X10</a> etc.) were successfully reaching <a href="/wiki/Critical_mass" title="Critical mass">criticality</a>, <a href="/wiki/Uranium_enrichment" class="mw-redirect" title="Uranium enrichment">uranium enrichment</a> began to develop from theoretical concept to practical applications in order to meet the goal of the <a href="/wiki/Manhattan_Project" title="Manhattan Project">Manhattan Project</a>, to build a <a href="/wiki/Nuclear_weapon" title="Nuclear weapon">nuclear explosive</a>. </p><p>In May 1944, the first grams of enriched uranium ever produced reached criticality in the <a href="/wiki/Aqueous_homogeneous_reactor#History" title="Aqueous homogeneous reactor">low power (LOPO)</a> reactor at <a href="/wiki/Los_Alamos_National_Laboratory" title="Los Alamos National Laboratory">Los Alamos</a>, which was used to estimate the <a href="/wiki/Critical_mass" title="Critical mass">critical mass</a> of U235 to produce the atomic bomb.<sup id="cite_ref-Federation_of_American_Scientists_-_Early_Reactors_1-0" class="reference"><a href="#cite_note-Federation_of_American_Scientists_-_Early_Reactors-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> LOPO cannot be considered as the first light-water reactor because its fuel was not a solid uranium compound cladded with corrosion-resistant material, but was composed of <a href="/wiki/Uranyl_sulfate" title="Uranyl sulfate">uranyl sulfate</a> salt dissolved in water.<sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup> It is however the first <a href="/wiki/Aqueous_homogeneous_reactor" title="Aqueous homogeneous reactor">aqueous homogeneous reactor</a> and the first reactor using enriched uranium as fuel and ordinary water as a moderator.<sup id="cite_ref-Federation_of_American_Scientists_-_Early_Reactors_1-1" class="reference"><a href="#cite_note-Federation_of_American_Scientists_-_Early_Reactors-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> </p><p>By the end of <a href="/wiki/World_War_II" title="World War II">the war</a>, following an idea of <a href="/wiki/Alvin_M._Weinberg" title="Alvin M. Weinberg">Alvin Weinberg</a>, natural uranium fuel elements were arranged in a lattice in ordinary water at the top of the <a href="/wiki/X-10_Graphite_Reactor" title="X-10 Graphite Reactor">X10 reactor</a> to evaluate the neutron multiplication factor.<sup id="cite_ref-Oak_Ridge_National_Laboratory_3-0" class="reference"><a href="#cite_note-Oak_Ridge_National_Laboratory-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> The purpose of this experiment was to determine the feasibility of a nuclear reactor using light water as a moderator and coolant, and clad solid uranium as fuel. The results showed that, with a lightly enriched uranium, criticality could be reached.<sup id="cite_ref-Oak_Ridge_National_Laboratory_-_X10_4-0" class="reference"><a href="#cite_note-Oak_Ridge_National_Laboratory_-_X10-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup> This experiment was the first practical step toward the light-water reactor. </p><p>After <a href="/wiki/World_War_II" title="World War II">World War II</a> and with the availability of enriched uranium, new reactor concepts became feasible. In 1946, <a href="/wiki/Eugene_Wigner" title="Eugene Wigner">Eugene Wigner</a> and Alvin Weinberg proposed and developed the concept of a reactor using enriched uranium as a fuel, and light water as a moderator and coolant.<sup id="cite_ref-Oak_Ridge_National_Laboratory_3-1" class="reference"><a href="#cite_note-Oak_Ridge_National_Laboratory-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> This concept was proposed for a reactor whose purpose was to test the behavior of materials under <a href="/wiki/Neutron_flux" title="Neutron flux">neutron flux</a>. This reactor, the <a href="/wiki/Materials_testing_reactor" title="Materials testing reactor">Material Testing Reactor (MTR)</a>, was built in Idaho at <a href="/wiki/Idaho_National_Laboratory" title="Idaho National Laboratory">INL</a> and reached criticality on March 31, 1952.<sup id="cite_ref-Idaho_National_Laboratory_-_Proving_the_principle_5-0" class="reference"><a href="#cite_note-Idaho_National_Laboratory_-_Proving_the_principle-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> For the design of this reactor, experiments were necessary, so a mock-up of the MTR was built at <a href="/wiki/Oak_Ridge_National_Laboratory" title="Oak Ridge National Laboratory">ORNL</a>, to assess the hydraulic performances of the primary circuit and then to test its neutronic characteristics. This MTR mock-up, later called the Low Intensity Test Reactor (LITR), reached criticality on February 4, 1950<sup id="cite_ref-INEL_-_History_6-0" class="reference"><a href="#cite_note-INEL_-_History-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup> and was the world's first light-water reactor.<sup id="cite_ref-FirstReactor_7-0" class="reference"><a href="#cite_note-FirstReactor-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Pressurized_water_reactors">Pressurized water reactors</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Light-water_reactor&action=edit&section=3" title="Edit section: Pressurized water reactors"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Immediately after the end of <a href="/wiki/World_War_II" title="World War II">World War II</a> the <a href="/wiki/United_States_Navy" title="United States Navy">United States Navy</a> started a program under the direction of Captain (later Admiral) <a href="/wiki/Hyman_Rickover" class="mw-redirect" title="Hyman Rickover">Hyman Rickover</a>, with the goal of <a href="/wiki/Nuclear_propulsion" title="Nuclear propulsion">nuclear propulsion</a> for ships. It developed the first pressurized water reactors in the early 1950s, and led to the successful deployment of the first nuclear submarine, the <a href="/wiki/USS_Nautilus_(SSN-571)" title="USS Nautilus (SSN-571)">USS <i>Nautilus</i> (SSN-571)</a>. </p><p>The <a href="/wiki/Soviet_Union" title="Soviet Union">Soviet Union</a> independently developed a version of the PWR in the late 1950s, under the name of <a href="/wiki/VVER" title="VVER">VVER</a>. While functionally very similar to the American effort, it also has certain design distinctions from Western PWRs. </p> <div class="mw-heading mw-heading3"><h3 id="Boiling_water_reactor">Boiling water reactor</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Light-water_reactor&action=edit&section=4" title="Edit section: Boiling water reactor"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Researcher <a href="/wiki/Samuel_Untermyer_II" title="Samuel Untermyer II">Samuel Untermyer II</a> led the effort to develop the BWR at the US <a href="/wiki/National_Reactor_Testing_Station" class="mw-redirect" title="National Reactor Testing Station">National Reactor Testing Station</a> (now the <a href="/wiki/Idaho_National_Laboratory" title="Idaho National Laboratory">Idaho National Laboratory</a>) in a series of tests called the <a href="/wiki/BORAX_experiments" title="BORAX experiments">BORAX experiments</a>. </p> <div class="mw-heading mw-heading3"><h3 id="PIUS_reactor">PIUS reactor</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Light-water_reactor&action=edit&section=5" title="Edit section: PIUS reactor"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>PIUS, standing for <i>Process Inherent Ultimate Safety</i>, was a Swedish design designed by ASEA-ATOM. It is a concept for a light-water reactor system.<sup id="cite_ref-8" class="reference"><a href="#cite_note-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup> Along with the SECURE reactor,<sup id="cite_ref-9" class="reference"><a href="#cite_note-9"><span class="cite-bracket">[</span>9<span class="cite-bracket">]</span></a></sup> it relied on passive measures, not requiring operator actions or external energy supplies, to provide safe operation. No units were ever built. </p> <div class="mw-heading mw-heading3"><h3 id="OPEN100">OPEN100</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Light-water_reactor&action=edit&section=6" title="Edit section: OPEN100"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>In 2020, the <a href="/wiki/Energy_Impact_Center" title="Energy Impact Center">Energy Impact Center</a> announced publication of an open-sourced engineering design of a pressurized water reactor capable of producing 300 MWth/100 MWe of energy called <a href="/wiki/OPEN100" title="OPEN100">OPEN100</a>.<sup id="cite_ref-10" class="reference"><a href="#cite_note-10"><span class="cite-bracket">[</span>10<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="Overview">Overview</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Light-water_reactor&action=edit&section=7" title="Edit section: Overview"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure typeof="mw:File/Thumb"><a href="/wiki/File:Koebergnps.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/7/7d/Koebergnps.jpg/300px-Koebergnps.jpg" decoding="async" width="300" height="148" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/7/7d/Koebergnps.jpg/450px-Koebergnps.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/7/7d/Koebergnps.jpg/600px-Koebergnps.jpg 2x" data-file-width="3728" data-file-height="1840" /></a><figcaption>The <a href="/wiki/Koeberg" class="mw-redirect" title="Koeberg">Koeberg</a> nuclear power station, consisting of two <a href="/wiki/Pressurized_water_reactors" class="mw-redirect" title="Pressurized water reactors">pressurized water reactors</a> fueled with <a href="/wiki/Uranium" title="Uranium">uranium</a></figcaption></figure> <p>The family of nuclear reactors known as light-water reactors (LWR), cooled and moderated using ordinary water, tend to be simpler and cheaper to build than other types of nuclear reactors<sup class="noprint Inline-Template Template-Fact" style="white-space:nowrap;">[<i><a href="/wiki/Wikipedia:Citation_needed" title="Wikipedia:Citation needed"><span title="This claim needs references to reliable sources. (June 2014)">citation needed</span></a></i>]</sup>; due to these factors, they make up the vast majority of civil nuclear reactors and naval propulsion reactors in service throughout the world as of 2009. LWRs can be subdivided into three categories – pressurized water reactors (PWRs), boiling water reactors (BWRs), and supercritical water reactors (<a href="/wiki/SCWR" class="mw-redirect" title="SCWR">SCWRs</a>). The <a href="/wiki/SCWR" class="mw-redirect" title="SCWR">SCWR</a> remains hypothetical as of 2009; it is a <a href="/wiki/Generation_IV_reactor" title="Generation IV reactor">Generation IV</a> design that is still a light-water reactor, but it is only partially moderated by light water and exhibits certain characteristics of a <a href="/wiki/Fast_neutron_reactor" class="mw-redirect" title="Fast neutron reactor">fast neutron reactor</a>. </p><p>The leaders in national experience with PWRs, offering reactors for export, are the United States (which offers the passively safe <a href="/wiki/AP1000" title="AP1000">AP1000</a>, a <a href="/wiki/Westinghouse_Electric_Company" title="Westinghouse Electric Company">Westinghouse</a> design, as well as several smaller, modular, passively safe PWRs, such as the <a href="/wiki/Babcock_%26_Wilcox" title="Babcock & Wilcox">Babcock & Wilcox</a> <a href="/wiki/B%26W_mPower" title="B&W mPower">MPower</a>, and the <a href="/wiki/NuScale" class="mw-redirect" title="NuScale">NuScale</a> MASLWR), the Russian Federation (offering both the VVER-1000 and the VVER-1200 for export), the Republic of France (offering the <a href="/wiki/AREVA" class="mw-redirect" title="AREVA">AREVA</a> <a href="/wiki/EPR_(nuclear_reactor)" title="EPR (nuclear reactor)">EPR</a> for export), and Japan (offering the <a href="/wiki/Mitsubishi" title="Mitsubishi">Mitsubishi</a> <a href="/wiki/Advanced_Pressurized_Water_Reactor" class="mw-redirect" title="Advanced Pressurized Water Reactor">Advanced Pressurized Water Reactor</a> for export); in addition, both the People's Republic of China and the <a href="/wiki/South_Korea" title="South Korea">Republic of Korea</a> are both noted to be rapidly ascending into the front rank of PWR-constructing nations as well, with the Chinese being engaged in a massive program of nuclear power expansion, and the Koreans currently designing and constructing their second generation of indigenous designs. The leaders in national experience with BWRs, offering reactors for export, are the United States and Japan, with the alliance of <a href="/wiki/General_Electric" title="General Electric">General Electric</a> (of the US) and <a href="/wiki/Hitachi" title="Hitachi">Hitachi</a> (of Japan), offering both the <a href="/wiki/ABWR" class="mw-redirect" title="ABWR">Advanced Boiling Water Reactor (ABWR)</a> and the <a href="/wiki/ESBWR" class="mw-redirect" title="ESBWR">Economic Simplified Boiling Water Reactor (ESBWR)</a> for construction and export; in addition, <a href="/wiki/Toshiba" title="Toshiba">Toshiba</a> offers an <a href="/wiki/ABWR" class="mw-redirect" title="ABWR">ABWR</a> variant for construction in Japan, as well. <a href="/wiki/West_Germany" title="West Germany">West Germany</a> was also once a major player with BWRs. The other types of nuclear reactor in use for power generation are the <a href="/wiki/Heavy_water_moderated_reactor" class="mw-redirect" title="Heavy water moderated reactor">heavy water moderated reactor</a>, built by Canada (<a href="/wiki/CANDU" class="mw-redirect" title="CANDU">CANDU</a>) and the Republic of India (AHWR), the <a href="/wiki/Advanced_gas_cooled_reactor" class="mw-redirect" title="Advanced gas cooled reactor">advanced gas cooled reactor</a> (AGCR), built by the United Kingdom, the <a href="/wiki/Liquid_metal_cooled_reactor" title="Liquid metal cooled reactor">liquid metal cooled reactor</a> (LMFBR), built by the Russian Federation, the Republic of France, and Japan, and the <a href="/wiki/RBMK" title="RBMK">graphite-moderated, water-cooled reactor</a> (RBMK or LWGR), found exclusively within the Russian Federation and former Soviet states. </p><p>Though <a href="/wiki/Electricity_generation" title="Electricity generation">electricity generation</a> capabilities are comparable between all these types of reactor, due to the aforementioned features, and the extensive experience with operations of the LWR, it is favored in the vast majority of new nuclear power plants. In addition, light-water reactors make up the vast majority of reactors that power <a href="/wiki/Nuclear_marine_propulsion" title="Nuclear marine propulsion">naval nuclear-powered vessels</a>. Four out of the five <a href="/wiki/Great_power" title="Great power">great powers</a> with nuclear naval propulsion capacity use light-water reactors exclusively: the British <a href="/wiki/Royal_Navy" title="Royal Navy">Royal Navy</a>, the Chinese <a href="/wiki/People%27s_Liberation_Army_Navy" title="People's Liberation Army Navy">People's Liberation Army Navy</a>, the French <a href="/wiki/Marine_nationale" class="mw-redirect" title="Marine nationale">Marine nationale</a>, and the United States <a href="/wiki/U.S._Navy" class="mw-redirect" title="U.S. Navy">Navy</a>. Only the Russian Federation's <a href="/wiki/Russian_Navy" title="Russian Navy">Navy</a> has used a relative handful of <a href="/wiki/Liquid_metal_cooled_reactor" title="Liquid metal cooled reactor">liquid-metal cooled reactors</a> in production vessels, specifically the <a href="/wiki/Alfa_class_submarine" class="mw-redirect" title="Alfa class submarine">Alfa class submarine</a>, which used <a href="/wiki/Lead-bismuth_eutectic" title="Lead-bismuth eutectic">lead-bismuth eutectic</a> as a reactor moderator and coolant, but the vast majority of Russian nuclear-powered boats and ships use light-water reactors exclusively. The reason for near exclusive LWR use aboard nuclear naval vessels is the level of inherent safety built into these types of reactors. Since light water is used as both a coolant and a neutron moderator in these reactors, if one of these reactors suffers damage due to military action, leading to a compromise of the reactor core's integrity, the resulting release of the light-water moderator will act to stop the nuclear reaction and shut the reactor down. This capability is known as a <a href="/wiki/Void_coefficient" title="Void coefficient">negative void coefficient of reactivity</a>. </p> <dl><dt>Currently offered LWRs include the following</dt> <dd></dd></dl> <ul><li><a href="/wiki/ABWR" class="mw-redirect" title="ABWR">ABWR</a></li> <li><a href="/wiki/AP1000" title="AP1000">AP1000</a></li> <li><a href="/wiki/APR-1400" title="APR-1400">APR-1400</a></li> <li><a href="/wiki/CPR-1000" title="CPR-1000">CPR-1000</a></li> <li><a href="/wiki/EPR_(nuclear_reactor)" title="EPR (nuclear reactor)">EPR</a></li> <li><a href="/wiki/VVER" title="VVER">VVER</a></li></ul> <div class="mw-heading mw-heading3"><h3 id="LWR_statistics">LWR statistics</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Light-water_reactor&action=edit&section=8" title="Edit section: LWR statistics"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r1251242444">.mw-parser-output .ambox{border:1px solid #a2a9b1;border-left:10px solid #36c;background-color:#fbfbfb;box-sizing:border-box}.mw-parser-output .ambox+link+.ambox,.mw-parser-output .ambox+link+style+.ambox,.mw-parser-output .ambox+link+link+.ambox,.mw-parser-output .ambox+.mw-empty-elt+link+.ambox,.mw-parser-output .ambox+.mw-empty-elt+link+style+.ambox,.mw-parser-output .ambox+.mw-empty-elt+link+link+.ambox{margin-top:-1px}html body.mediawiki .mw-parser-output .ambox.mbox-small-left{margin:4px 1em 4px 0;overflow:hidden;width:238px;border-collapse:collapse;font-size:88%;line-height:1.25em}.mw-parser-output .ambox-speedy{border-left:10px solid #b32424;background-color:#fee7e6}.mw-parser-output .ambox-delete{border-left:10px solid #b32424}.mw-parser-output .ambox-content{border-left:10px solid #f28500}.mw-parser-output .ambox-style{border-left:10px solid #fc3}.mw-parser-output .ambox-move{border-left:10px solid #9932cc}.mw-parser-output .ambox-protection{border-left:10px solid #a2a9b1}.mw-parser-output .ambox .mbox-text{border:none;padding:0.25em 0.5em;width:100%}.mw-parser-output .ambox .mbox-image{border:none;padding:2px 0 2px 0.5em;text-align:center}.mw-parser-output .ambox .mbox-imageright{border:none;padding:2px 0.5em 2px 0;text-align:center}.mw-parser-output .ambox .mbox-empty-cell{border:none;padding:0;width:1px}.mw-parser-output .ambox .mbox-image-div{width:52px}@media(min-width:720px){.mw-parser-output .ambox{margin:0 10%}}@media print{body.ns-0 .mw-parser-output .ambox{display:none!important}}</style><table class="box-Update plainlinks metadata ambox ambox-content ambox-Update" role="presentation"><tbody><tr><td class="mbox-image"><div class="mbox-image-div"><span typeof="mw:File"><span><img alt="" src="//upload.wikimedia.org/wikipedia/commons/thumb/5/53/Ambox_current_red_Americas.svg/42px-Ambox_current_red_Americas.svg.png" decoding="async" width="42" height="34" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/5/53/Ambox_current_red_Americas.svg/63px-Ambox_current_red_Americas.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/5/53/Ambox_current_red_Americas.svg/84px-Ambox_current_red_Americas.svg.png 2x" data-file-width="360" data-file-height="290" /></span></span></div></td><td class="mbox-text"><div class="mbox-text-span">This section needs to be <b>updated</b>.<span class="hide-when-compact"> Please help update this article to reflect recent events or newly available information.</span> <span class="date-container"><i>(<span class="date">July 2015</span>)</i></span></div></td></tr></tbody></table> <p>Data from the <a href="/wiki/International_Atomic_Energy_Agency" title="International Atomic Energy Agency">International Atomic Energy Agency</a> in 2009:<sup id="cite_ref-IAEA_-_LWR_11-0" class="reference"><a href="#cite_note-IAEA_-_LWR-11"><span class="cite-bracket">[</span>11<span class="cite-bracket">]</span></a></sup> </p> <table class="wikitable"> <tbody><tr> <td>Reactors in operation. </td> <td>359 </td></tr> <tr> <td>Reactors under construction. </td> <td>27 </td></tr> <tr> <td>Number of countries with LWRs. </td> <td>27 </td></tr> <tr> <td>Generating capacity (<a href="/wiki/Gigawatt" class="mw-redirect" title="Gigawatt">gigawatts</a>). </td> <td>328.4 </td></tr></tbody></table> <div class="mw-heading mw-heading2"><h2 id="Reactor_design">Reactor design</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Light-water_reactor&action=edit&section=9" title="Edit section: Reactor design"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The light-water reactor produces heat by controlled <a href="/wiki/Nuclear_fission" title="Nuclear fission">nuclear fission</a>. The nuclear <a href="/wiki/Reactor_core" class="mw-redirect" title="Reactor core">reactor core</a> is the portion of a <a href="/wiki/Nuclear_reactor" title="Nuclear reactor">nuclear reactor</a> where the nuclear reactions take place. It mainly consists of <a href="/wiki/Nuclear_fuel" title="Nuclear fuel">nuclear fuel</a> and <a href="/wiki/Control_rod" title="Control rod">control elements</a>. The pencil-thin nuclear fuel rods, each about 12 feet (3.7 m) long, are grouped by the hundreds in bundles called fuel assemblies. Inside each fuel rod, pellets of <a href="/wiki/Uranium" title="Uranium">uranium</a>, or more commonly <a href="/wiki/Uranium_oxide" title="Uranium oxide">uranium oxide</a>, are stacked end to end. The control elements, called control rods, are filled with pellets of substances like <a href="/wiki/Hafnium" title="Hafnium">hafnium</a> or <a href="/wiki/Cadmium" title="Cadmium">cadmium</a> that readily capture neutrons. When the control rods are lowered into the core, they absorb neutrons, which thus cannot take part in the <a href="/wiki/Chain_reaction" title="Chain reaction">chain reaction</a>. On the converse, when the control rods are lifted out of the way, more neutrons strike the fissile <a href="/wiki/Uranium-235" title="Uranium-235">uranium-235</a> or <a href="/wiki/Plutonium-239" title="Plutonium-239">plutonium-239</a> nuclei in nearby fuel rods, and the chain reaction intensifies. All of this is enclosed in a water-filled steel <a href="/wiki/Pressure_vessel" title="Pressure vessel">pressure vessel</a>, called the <a href="/wiki/Reactor_vessel" class="mw-redirect" title="Reactor vessel">reactor vessel</a>. </p><p>In the <a href="/wiki/Boiling_water_reactor" title="Boiling water reactor">boiling water reactor</a>, the heat generated by fission turns the water into steam, which directly drives the power-generating turbines. But in the <a href="/wiki/Pressurized_water_reactor" title="Pressurized water reactor">pressurized water reactor</a>, the heat generated by fission is transferred to a secondary loop via a heat exchanger. Steam is produced in the secondary loop, and the secondary loop drives the power-generating turbines. In either case, after flowing through the turbines, the steam turns back into water in the condenser.<sup id="cite_ref-European_Nuclear_Society_-_Light_water_reactor_12-0" class="reference"><a href="#cite_note-European_Nuclear_Society_-_Light_water_reactor-12"><span class="cite-bracket">[</span>12<span class="cite-bracket">]</span></a></sup> </p> <ul class="gallery mw-gallery-packed"> <li class="gallerybox" style="width: 384.66666666667px"> <div class="thumb" style="width: 382.66666666667px;"><span typeof="mw:File"><a href="/wiki/File:BoilingWaterReactor.gif" class="mw-file-description" title="Animated diagram of a boiling water reactor"><img alt="Animated diagram of a boiling water reactor" src="//upload.wikimedia.org/wikipedia/commons/thumb/4/4a/BoilingWaterReactor.gif/574px-BoilingWaterReactor.gif" decoding="async" width="383" height="200" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/4/4a/BoilingWaterReactor.gif 1.5x" data-file-width="625" data-file-height="327" /></a></span></div> <div class="gallerytext">Animated diagram of a <a href="/wiki/Boiling_water_reactor" title="Boiling water reactor">boiling water reactor</a></div> </li> <li class="gallerybox" style="width: 389.33333333333px"> <div class="thumb" style="width: 387.33333333333px;"><span typeof="mw:File"><a href="/wiki/File:PressurizedWaterReactor.gif" class="mw-file-description" title="Animated diagram of a pressurized water reactor"><img alt="Animated diagram of a pressurized water reactor" src="//upload.wikimedia.org/wikipedia/commons/thumb/a/a0/PressurizedWaterReactor.gif/581px-PressurizedWaterReactor.gif" decoding="async" width="388" height="200" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/a/a0/PressurizedWaterReactor.gif 1.5x" data-file-width="625" data-file-height="323" /></a></span></div> <div class="gallerytext">Animated diagram of a <a href="/wiki/Pressurized_water_reactor" title="Pressurized water reactor">pressurized water reactor</a></div> </li> </ul> <p>The water required to cool the condenser is taken from a nearby river or ocean. It is then pumped back into the river or ocean, in warmed condition. The heat can also be dissipated via a cooling tower into the atmosphere. The United States uses LWR reactors for electric power production, in comparison to the <a href="/wiki/Heavy_water_reactor" class="mw-redirect" title="Heavy water reactor">heavy water reactors</a> used in Canada.<sup id="cite_ref-Light_Water_Reactors_13-0" class="reference"><a href="#cite_note-Light_Water_Reactors-13"><span class="cite-bracket">[</span>13<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Control">Control</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Light-water_reactor&action=edit&section=10" title="Edit section: Control"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Control_rod" title="Control rod">Control rod</a></div> <figure typeof="mw:File/Thumb"><a href="/wiki/File:Reactor_Vessel_head.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/f/f8/Reactor_Vessel_head.jpg/250px-Reactor_Vessel_head.jpg" decoding="async" width="250" height="201" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/f/f8/Reactor_Vessel_head.jpg/375px-Reactor_Vessel_head.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/f/f8/Reactor_Vessel_head.jpg/500px-Reactor_Vessel_head.jpg 2x" data-file-width="1759" data-file-height="1417" /></a><figcaption>A <a href="/wiki/Pressurized_water_reactor" title="Pressurized water reactor">pressurized water reactor</a> head, with the control rods visible on the top</figcaption></figure> <p>Control rods are usually combined into control rod assemblies — typically 20 rods for a commercial pressurized water reactor assembly — and inserted into guide tubes within a fuel element. A control rod is removed from or inserted into the <a href="/wiki/Nuclear_reactor_core" title="Nuclear reactor core">central core</a> of a nuclear reactor in order to control the number of neutrons which will split further uranium atoms. This in turn affects the thermal power of the reactor, the amount of steam generated, and hence the electricity produced. The control rods are partially removed from the core to allow a <a href="/wiki/Chain_reaction" title="Chain reaction">chain reaction</a> to occur. The number of control rods inserted and the distance by which they are inserted can be varied to control the reactivity of the reactor. </p><p>Usually there are also other means of controlling reactivity. In the PWR design a soluble neutron absorber, usually <a href="/wiki/Boric_acid" title="Boric acid">boric acid</a>, is added to the reactor coolant allowing the complete extraction of the control rods during stationary power operation ensuring an even power and flux distribution over the entire core. Operators of the BWR design use the coolant flow through the core to control reactivity by varying the speed of the reactor recirculation pumps. An increase in the coolant flow through the core improves the removal of steam bubbles, thus increasing the density of the coolant/moderator with the result of increasing power. </p> <div class="mw-heading mw-heading3"><h3 id="Coolant">Coolant</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Light-water_reactor&action=edit&section=11" title="Edit section: Coolant"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Nuclear_reactor_coolant" title="Nuclear reactor coolant">Nuclear reactor coolant</a></div> <p>The light-water reactor also uses ordinary water to keep the reactor cooled. The cooling source, light water, is circulated past the reactor core to absorb the heat that it generates. The heat is carried away from the reactor and is then used to generate steam. Most reactor systems employ a cooling system that is physically separate from the water that will be boiled to produce pressurized steam for the <a href="/wiki/Turbines" class="mw-redirect" title="Turbines">turbines</a>, like the pressurized-water reactor. But in some reactors the water for the steam turbines is boiled directly by the reactor core, for example the boiling-water reactor. </p><p>Many other reactors are also light-water cooled, notably the <a href="/wiki/RBMK" title="RBMK">RBMK</a> and some military <a href="/wiki/Plutonium" title="Plutonium">plutonium</a>-production reactors. These are not regarded as LWRs, as they are moderated by <a href="/wiki/Graphite" title="Graphite">graphite</a>, and as a result their nuclear characteristics are very different. Although the coolant flow rate in commercial PWRs is constant, it is not in nuclear reactors used on <a href="/wiki/U.S._Navy" class="mw-redirect" title="U.S. Navy">U.S. Navy</a> ships. </p> <div class="mw-heading mw-heading3"><h3 id="Fuel">Fuel</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Light-water_reactor&action=edit&section=12" title="Edit section: Fuel"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Nuclear_fuel" title="Nuclear fuel">Nuclear fuel</a></div> <figure typeof="mw:File/Thumb"><a href="/wiki/File:Fuel_Pellet.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/2/28/Fuel_Pellet.jpg/250px-Fuel_Pellet.jpg" decoding="async" width="250" height="163" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/2/28/Fuel_Pellet.jpg/375px-Fuel_Pellet.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/2/28/Fuel_Pellet.jpg/500px-Fuel_Pellet.jpg 2x" data-file-width="1920" data-file-height="1250" /></a><figcaption>A <a href="/wiki/Nuclear_fuel" title="Nuclear fuel">nuclear fuel</a> pellet</figcaption></figure> <figure typeof="mw:File/Thumb"><a href="/wiki/File:Pellet_rod.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/4/4b/Pellet_rod.jpg/250px-Pellet_rod.jpg" decoding="async" width="250" height="163" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/4/4b/Pellet_rod.jpg/375px-Pellet_rod.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/4/4b/Pellet_rod.jpg/500px-Pellet_rod.jpg 2x" data-file-width="1920" data-file-height="1250" /></a><figcaption>Nuclear fuel pellets that are ready for fuel assembly completion</figcaption></figure> <p>The use of ordinary water makes it necessary to do a certain amount of enrichment of the uranium fuel before the necessary criticality of the reactor can be maintained. The light-water reactor uses <a href="/wiki/Uranium_235" class="mw-redirect" title="Uranium 235">uranium 235</a> as a fuel, enriched to approximately 3 percent. Although this is its major fuel, the <a href="/wiki/Uranium_238" class="mw-redirect" title="Uranium 238">uranium 238</a> atoms also contribute to the fission process by converting to <a href="/wiki/Plutonium_239" class="mw-redirect" title="Plutonium 239">plutonium 239</a>; about one-half of which is consumed in the reactor. Light-water reactors are generally refueled every 12 to 18 months, at which time, about 25 percent of the fuel is replaced. </p><p>The enriched UF<sub>6</sub> is converted into <a href="/wiki/Uranium_dioxide" title="Uranium dioxide">uranium dioxide</a> powder that is then processed into pellet form. The pellets are then fired in a high-temperature, sintering furnace to create hard, ceramic pellets of <a href="/wiki/Enriched_uranium" title="Enriched uranium">enriched uranium</a>. The cylindrical pellets then undergo a grinding process to achieve a uniform pellet size. The uranium oxide is dried before inserting into the tubes to try to eliminate moisture in the ceramic fuel that can lead to corrosion and hydrogen embrittlement. The pellets are stacked, according to each nuclear core's design specifications, into tubes of <a href="/wiki/Corrosion-resistant" class="mw-redirect" title="Corrosion-resistant">corrosion-resistant</a> metal alloy. The tubes are sealed to contain the fuel pellets: these tubes are called fuel rods. </p><p>The finished fuel rods are grouped in special fuel assemblies that are then used to build up the nuclear fuel core of a power reactor. The metal used for the tubes depends on the design of the reactor – <a href="/wiki/Stainless_steel" title="Stainless steel">stainless steel</a> was used in the past, but most reactors now use a <a href="/wiki/Zirconium_alloy" class="mw-redirect" title="Zirconium alloy">zirconium alloy</a>. For the most common types of reactors the tubes are assembled into bundles with the tubes spaced precise distances apart. These bundles are then given a unique identification number, which enables them to be tracked from manufacture through use and into disposal. </p><p>Pressurized water reactor fuel consists of cylindrical rods put into bundles. A uranium oxide ceramic is formed into pellets and inserted into zirconium alloy tubes that are bundled together. The zirconium alloy tubes are about 1 cm in diameter, and the fuel cladding gap is filled with <a href="/wiki/Helium" title="Helium">helium</a> gas to improve the conduction of heat from the fuel to the cladding. There are about 179-264 fuel rods per fuel bundle and about 121 to 193 fuel bundles are loaded into a <a href="/wiki/Reactor_core" class="mw-redirect" title="Reactor core">reactor core</a>. Generally, the fuel bundles consist of fuel rods bundled 14x14 to 17x17. PWR fuel bundles are about 4 meters in length. The zirconium alloy tubes are <a href="/wiki/Pressurized" class="mw-redirect" title="Pressurized">pressurized</a> with helium to try to minimize pellet cladding interaction which can lead to fuel rod failure over long periods. </p><p>In boiling water reactors, the fuel is similar to PWR fuel except that the bundles are "canned"; that is, there is a thin tube surrounding each bundle. This is primarily done to prevent local density variations from affecting <a href="/wiki/Neutronics" class="mw-redirect" title="Neutronics">neutronics</a> and <a href="/wiki/Thermal_hydraulics" title="Thermal hydraulics">thermal hydraulics</a> of the nuclear core on a global scale. In modern BWR fuel bundles, there are either 91, 92, or 96 fuel rods per assembly depending on the manufacturer. A range between 368 assemblies for the smallest and 800 assemblies for the largest U.S. BWR forms the reactor core. Each BWR fuel rod is back filled with helium to a pressure of about three atmospheres (300 kPa). </p> <div class="mw-heading mw-heading3"><h3 id="Moderator">Moderator</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Light-water_reactor&action=edit&section=13" title="Edit section: Moderator"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Neutron_moderator" title="Neutron moderator">Neutron moderator</a></div> <p>A neutron moderator is a medium which reduces the velocity of <a href="/wiki/Fast_neutrons" class="mw-redirect" title="Fast neutrons">fast neutrons</a>, thereby turning them into <a href="/wiki/Thermal_neutron" class="mw-redirect" title="Thermal neutron">thermal neutrons</a> capable of sustaining a nuclear chain reaction involving uranium-235. A good neutron moderator is a material full of atoms with light nuclei which do not easily absorb neutrons. The neutrons strike the nuclei and bounce off. After sufficient impacts, the velocity of the neutron will be comparable to the thermal velocities of the nuclei; this neutron is then called a thermal neutron. </p><p>The light-water reactor uses ordinary <a href="/wiki/Water" title="Water">water</a>, also called light water, as its neutron moderator. The light water absorbs too many neutrons to be used with unenriched natural uranium, and therefore <a href="/wiki/Uranium_enrichment" class="mw-redirect" title="Uranium enrichment">uranium enrichment</a> or <a href="/wiki/Nuclear_reprocessing" title="Nuclear reprocessing">nuclear reprocessing</a> becomes necessary to operate such reactors, increasing overall costs. This differentiates it from a <a href="/wiki/Heavy_water_reactor" class="mw-redirect" title="Heavy water reactor">heavy water reactor</a>, which uses <a href="/wiki/Heavy_water" title="Heavy water">heavy water</a> as a neutron moderator. While ordinary water has some heavy water molecules in it, it is not enough to be important in most applications. In pressurized water reactors the coolant water is used as a moderator by letting the neutrons undergo multiple collisions with light hydrogen atoms in the water, losing speed in the process. This moderating of neutrons will happen more often when the water is denser, because more collisions will occur. </p><p>The use of water as a moderator is an important safety feature of PWRs, as any increase in temperature causes the water to expand and become less dense; thereby reducing the extent to which neutrons are slowed down and hence reducing the reactivity in the reactor. Therefore, if reactivity increases beyond normal, the reduced moderation of neutrons will cause the chain reaction to slow down, producing less heat. This property, known as the negative <a href="/wiki/Temperature_coefficient" title="Temperature coefficient">temperature coefficient</a> of reactivity, makes PWRs very stable. In event of a <a href="/wiki/Loss-of-coolant_accident" title="Loss-of-coolant accident">loss-of-coolant accident</a>, the moderator is also lost and the active fission reaction will stop. Heat is still produced after the chain reaction stops from the radioactive byproducts of fission, at about 5% of rated power. This "decay heat" will continue for 1 to 3 years after shut down, whereupon the reactor finally reaches "full cold shutdown". Decay heat, while dangerous and strong enough to melt the core, is not nearly as intense as an active fission reaction. During the post shutdown period the reactor requires cooling water to be pumped or the reactor will overheat. If the temperature exceeds 2200 °C, cooling water will <a href="/wiki/Water_splitting#Thermal_decomposition_of_water" title="Water splitting">break down</a> into hydrogen and oxygen, which can form a (chemically) explosive mixture. Decay heat is a major risk factor in LWR safety record. </p> <div class="mw-heading mw-heading2"><h2 id="See_also">See also</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Light-water_reactor&action=edit&section=14" title="Edit section: See also"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><a href="/wiki/Nuclear_power" title="Nuclear power">Nuclear power</a></li> <li><a href="/wiki/Heavy_water_reactor" class="mw-redirect" title="Heavy water reactor">Heavy water reactor</a></li> <li><a href="/wiki/List_of_nuclear_reactors" class="mw-redirect" title="List of nuclear reactors">List of nuclear reactors</a></li> <li><a href="/wiki/Light_Water_Reactor_Sustainability_Program" title="Light Water Reactor Sustainability Program">Light-water reactor sustainability</a></li> <li><a href="/wiki/Breeder_Reactor" class="mw-redirect" title="Breeder Reactor">Breeder Reactor</a></li></ul> <div class="mw-heading mw-heading2"><h2 id="References">References</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Light-water_reactor&action=edit&section=15" title="Edit section: References"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r1239543626">.mw-parser-output .reflist{margin-bottom:0.5em;list-style-type:decimal}@media screen{.mw-parser-output .reflist{font-size:90%}}.mw-parser-output .reflist .references{font-size:100%;margin-bottom:0;list-style-type:inherit}.mw-parser-output .reflist-columns-2{column-width:30em}.mw-parser-output .reflist-columns-3{column-width:25em}.mw-parser-output .reflist-columns{margin-top:0.3em}.mw-parser-output .reflist-columns ol{margin-top:0}.mw-parser-output .reflist-columns li{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .reflist-upper-alpha{list-style-type:upper-alpha}.mw-parser-output .reflist-upper-roman{list-style-type:upper-roman}.mw-parser-output .reflist-lower-alpha{list-style-type:lower-alpha}.mw-parser-output .reflist-lower-greek{list-style-type:lower-greek}.mw-parser-output .reflist-lower-roman{list-style-type:lower-roman}</style><div class="reflist"> <div class="mw-references-wrap mw-references-columns"><ol class="references"> <li id="cite_note-Federation_of_American_Scientists_-_Early_Reactors-1"><span class="mw-cite-backlink">^ <a href="#cite_ref-Federation_of_American_Scientists_-_Early_Reactors_1-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-Federation_of_American_Scientists_-_Early_Reactors_1-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><style data-mw-deduplicate="TemplateStyles:r1238218222">.mw-parser-output cite.citation{font-style:inherit;word-wrap:break-word}.mw-parser-output .citation q{quotes:"\"""\"""'""'"}.mw-parser-output .citation:target{background-color:rgba(0,127,255,0.133)}.mw-parser-output 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.mw-parser-output .id-lock-subscription a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .cs1-ws-icon a{background-size:contain;padding:0 1em 0 0}.mw-parser-output .cs1-code{color:inherit;background:inherit;border:none;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;color:var(--color-error,#d33)}.mw-parser-output .cs1-visible-error{color:var(--color-error,#d33)}.mw-parser-output .cs1-maint{display:none;color:#085;margin-left:0.3em}.mw-parser-output .cs1-kern-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right{padding-right:0.2em}.mw-parser-output .citation .mw-selflink{font-weight:inherit}@media screen{.mw-parser-output .cs1-format{font-size:95%}html.skin-theme-clientpref-night .mw-parser-output .cs1-maint{color:#18911f}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .cs1-maint{color:#18911f}}</style><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://fas.org/sgp/othergov/doe/lanl/pubs/00416628.pdf">"Federation of American Scientists - Early reactor"</a> <span class="cs1-format">(PDF)</span><span class="reference-accessdate">. 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Retrieved <span class="nowrap">2012-12-28</span></span>. <q>... Afterwards, responding to Weinberg's interest, the fuel elements were arranged in lattices in water and the multiplication factors determined. ...</q></cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=ORNL+-+An+Account+of+Oak+Ridge+National+Laboratory%27s+Thirteen+Nuclear+Reactors&rft.pages=7&rft_id=http%3A%2F%2Finfo.ornl.gov%2Fsites%2Fpublications%2Ffiles%2FPub20808.pdf&rfr_id=info%3Asid%2Fen.wikipedia.org%3ALight-water+reactor" class="Z3988"></span></span> </li> <li id="cite_note-Oak_Ridge_National_Laboratory_-_X10-4"><span class="mw-cite-backlink"><b><a href="#cite_ref-Oak_Ridge_National_Laboratory_-_X10_4-0">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://web.archive.org/web/20121211023309/http://www.ornl.gov/info/news/cco/graphite.shtml">"ORNL - History of the X10 Graphite Reactor"</a>. Archived from <a rel="nofollow" class="external text" href="http://www.ornl.gov/info/news/cco/graphite.shtml">the original</a> on 2012-12-11<span class="reference-accessdate">. Retrieved <span class="nowrap">2012-12-30</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=ORNL+-+History+of+the+X10+Graphite+Reactor&rft_id=http%3A%2F%2Fwww.ornl.gov%2Finfo%2Fnews%2Fcco%2Fgraphite.shtml&rfr_id=info%3Asid%2Fen.wikipedia.org%3ALight-water+reactor" class="Z3988"></span></span> </li> <li id="cite_note-Idaho_National_Laboratory_-_Proving_the_principle-5"><span class="mw-cite-backlink"><b><a href="#cite_ref-Idaho_National_Laboratory_-_Proving_the_principle_5-0">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://web.archive.org/web/20120305164231/http://www.inl.gov/proving-the-principle/chapter_08.pdf">"INEEL - Proving the principle"</a> <span class="cs1-format">(PDF)</span>. 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Archived from <a rel="nofollow" class="external text" href="https://www.osti.gov/COROH/ORNL/Transcripts/Beall-Haubenreich%20OH.pdf">the original</a> <span class="cs1-format">(PDF)</span> on 2013-05-14. <q>... We were so nervous because there had never been a reactor fueled with enriched uranium go critical before. ...</q></cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=DOE+oral+history+presentation+program+-+Interview+of+LITR+operator+transcript&rft.pages=4&rft_id=http%3A%2F%2Fwww.osti.gov%2FCOROH%2FORNL%2FTranscripts%2FBeall-Haubenreich%2520OH.pdf&rfr_id=info%3Asid%2Fen.wikipedia.org%3ALight-water+reactor" class="Z3988"></span></span> </li> <li id="cite_note-8"><span class="mw-cite-backlink"><b><a href="#cite_ref-8">^</a></b></span> <span class="reference-text">National Research Council (U.S.). Committee on Future Nuclear Power, <i>Nuclear power: technical and institutional options for the future</i> National Academies Press, 1992, <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/0-309-04395-6" title="Special:BookSources/0-309-04395-6">0-309-04395-6</a> page 122</span> </li> <li id="cite_note-9"><span class="mw-cite-backlink"><b><a href="#cite_ref-9">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://web.archive.org/web/20180217023945/http://www.gdm-marketing.se/en/gdm-marketing">"GDM Marketing"</a>. 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Retrieved <span class="nowrap">2009-01-18</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=European+Nuclear+Society+-+Light+water+reactor&rft_id=http%3A%2F%2Fwww.euronuclear.org%2Finfo%2Fencyclopedia%2Fl%2Flightwaterreactor.htm&rfr_id=info%3Asid%2Fen.wikipedia.org%3ALight-water+reactor" class="Z3988"></span></span> </li> <li id="cite_note-Light_Water_Reactors-13"><span class="mw-cite-backlink"><b><a href="#cite_ref-Light_Water_Reactors_13-0">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://hyperphysics.phy-astr.gsu.edu/Hbase/NucEne/ligwat.html">"Light Water Reactors"</a><span class="reference-accessdate">. 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href="mw-data:TemplateStyles:r1129693374"><style data-mw-deduplicate="TemplateStyles:r1239400231">.mw-parser-output .navbar{display:inline;font-size:88%;font-weight:normal}.mw-parser-output .navbar-collapse{float:left;text-align:left}.mw-parser-output .navbar-boxtext{word-spacing:0}.mw-parser-output .navbar ul{display:inline-block;white-space:nowrap;line-height:inherit}.mw-parser-output .navbar-brackets::before{margin-right:-0.125em;content:"[ "}.mw-parser-output .navbar-brackets::after{margin-left:-0.125em;content:" ]"}.mw-parser-output .navbar li{word-spacing:-0.125em}.mw-parser-output .navbar a>span,.mw-parser-output .navbar a>abbr{text-decoration:inherit}.mw-parser-output .navbar-mini abbr{font-variant:small-caps;border-bottom:none;text-decoration:none;cursor:inherit}.mw-parser-output .navbar-ct-full{font-size:114%;margin:0 7em}.mw-parser-output .navbar-ct-mini{font-size:114%;margin:0 4em}html.skin-theme-clientpref-night .mw-parser-output .navbar li a abbr{color:var(--color-base)!important}@media(prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .navbar li a abbr{color:var(--color-base)!important}}@media print{.mw-parser-output .navbar{display:none!important}}</style><div class="navbar plainlinks hlist navbar-mini"><ul><li class="nv-view"><a href="/wiki/Template:Nuclear_fission_reactors" title="Template:Nuclear fission reactors"><abbr title="View this template">v</abbr></a></li><li class="nv-talk"><a href="/wiki/Template_talk:Nuclear_fission_reactors" title="Template talk:Nuclear fission reactors"><abbr title="Discuss this template">t</abbr></a></li><li class="nv-edit"><a href="/wiki/Special:EditPage/Template:Nuclear_fission_reactors" title="Special:EditPage/Template:Nuclear fission reactors"><abbr title="Edit this template">e</abbr></a></li></ul></div><div id="Types_of_nuclear_fission_reactor1378" style="font-size:114%;margin:0 4em">Types of <a href="/wiki/Nuclear_reactor#Fission" title="Nuclear reactor">nuclear fission reactor</a></div></th></tr><tr><td class="navbox-abovebelow" colspan="2"><div><div style="float: left;"><b><a href="/wiki/Neutron_moderator" title="Neutron moderator">Moderator</a></b></div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a class="mw-selflink selflink">Light water</a></th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0;background:none;"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Aqueous_homogeneous_reactor" title="Aqueous homogeneous reactor">Aqueous homogeneous</a></li> <li><a href="/wiki/Boiling_water_reactor" title="Boiling water reactor">Boiling</a> <ul><li><a href="/wiki/GE_BWR" title="GE BWR">BWR</a></li> <li><a href="/wiki/Advanced_boiling_water_reactor" title="Advanced boiling water reactor">ABWR</a></li> <li><a href="/wiki/Economic_Simplified_Boiling_Water_Reactor" title="Economic Simplified Boiling Water Reactor">ESBWR</a></li> <li><a href="/wiki/Kerena_boiling_water_reactor" class="mw-redirect" title="Kerena boiling water reactor">Kerena</a></li></ul></li> <li><a href="/wiki/Natural_nuclear_fission_reactor" title="Natural nuclear fission reactor">Natural fission</a></li> <li><a href="/wiki/Pressurized_water_reactor" title="Pressurized water reactor">Pressurized</a> <ul><li><a href="/wiki/AP1000" title="AP1000">AP1000</a></li> <li><a href="/wiki/APR-1400" title="APR-1400">APR-1400</a></li> <li><a href="/wiki/APR%2B" class="mw-redirect" title="APR+">APR+</a></li> <li><a href="/wiki/APWR" class="mw-redirect" title="APWR">APWR</a></li> <li><a href="/wiki/ATMEA1" class="mw-redirect" title="ATMEA1">ATMEA1</a></li> <li><a href="/wiki/CAP1400" title="CAP1400">CAP1400</a></li> <li><a href="/wiki/CPR-1000" title="CPR-1000">CPR-1000</a></li> <li><a href="/wiki/EPR_(nuclear_reactor)" title="EPR (nuclear reactor)">EPR</a></li> <li><a href="/wiki/Hualong_One" title="Hualong One">HPR-1000</a> <ul><li><a href="/wiki/ACPR1000" class="mw-redirect" title="ACPR1000">ACPR1000</a></li> <li><a href="/wiki/ACP1000" class="mw-redirect" title="ACP1000">ACP1000</a></li></ul></li> <li><a href="/wiki/VVER" title="VVER">VVER</a></li> <li><a href="/wiki/IPWR-900" title="IPWR-900">IPWR-900</a></li> <li>many others</li></ul></li> <li><a href="/wiki/Supercritical_water_reactor" title="Supercritical water reactor">Supercritical (SCWR)</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Heavy-water_reactor" class="mw-redirect" title="Heavy-water reactor">Heavy water</a><br /><span style="font-size:85%;"><span class="nobold">by <a href="/wiki/Nuclear_reactor_coolant" title="Nuclear reactor coolant">coolant</a></span></span></th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0;background:none;;background:whitesmoke;"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:1%;font-weight:normal;"><a href="/wiki/Deuterium_oxide" class="mw-redirect" title="Deuterium oxide">D<sub>2</sub>O</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Pressurized_heavy-water_reactor" title="Pressurized heavy-water reactor">Pressurized</a> <ul><li><a href="/wiki/CANDU_reactor" title="CANDU reactor">CANDU</a> <ul><li>CANDU 6</li> <li>CANDU 9</li> <li>EC6</li> <li>AFCR</li> <li><a href="/wiki/ACR-1000" class="mw-redirect" title="ACR-1000">ACR-1000</a></li></ul></li> <li><a href="/wiki/Carolinas%E2%80%93Virginia_Tube_Reactor" title="Carolinas–Virginia Tube Reactor">CVTR</a></li> <li><a href="/wiki/IPHWR" title="IPHWR">IPHWR</a> <ul><li><a href="/wiki/IPHWR-220" title="IPHWR-220">IPHWR-220</a></li> <li><a href="/wiki/IPHWR#IPHWR-540" title="IPHWR">IPHWR-540</a></li> <li><a href="/wiki/IPHWR-700" title="IPHWR-700">IPHWR-700</a></li></ul></li> <li><a href="/wiki/Nuclear_energy_in_Argentina" class="mw-redirect" title="Nuclear energy in Argentina">PHWR KWU</a></li> <li><a href="/w/index.php?title=MZFR&action=edit&redlink=1" class="new" title="MZFR (page does not exist)">MZFR</a></li> <li><a href="/wiki/%C3%85gestaverket" class="mw-redirect" title="Ågestaverket">R3</a></li> <li><a href="/wiki/R4_nuclear_reactor" title="R4 nuclear reactor">R4 Marviken</a></li></ul></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;font-weight:normal;"><a href="/wiki/H2O" class="mw-redirect" title="H2O">H<sub>2</sub>O</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/w/index.php?title=HWLWR&action=edit&redlink=1" class="new" title="HWLWR (page does not exist)">HWLWR</a> <ul><li><a href="/wiki/Fugen_Nuclear_Power_Plant" title="Fugen Nuclear Power Plant">ATR</a></li> <li><a href="/wiki/Gentilly_Nuclear_Generating_Station#Gentilly-1" title="Gentilly Nuclear Generating Station">HW BLWR 250</a></li></ul></li> <li><a href="/wiki/Steam-generating_heavy_water_reactor" class="mw-redirect" title="Steam-generating heavy water reactor">Steam-generating (SGHWR)</a></li> <li><a href="/wiki/Advanced_heavy-water_reactor" title="Advanced heavy-water reactor">AHWR</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;font-weight:normal;"><a href="/wiki/Organic_matter" title="Organic matter">Organic</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/WR-1" title="WR-1">WR-1</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;font-weight:normal;"><a href="/wiki/Carbon_dioxide" title="Carbon dioxide">CO<sub>2</sub></a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/w/index.php?title=HWGCR&action=edit&redlink=1" class="new" title="HWGCR (page does not exist)">HWGCR</a> <ul><li><a href="/wiki/Brennilis_Nuclear_Power_Plant" title="Brennilis Nuclear Power Plant">EL-4</a></li> <li><a href="/w/index.php?title=Kernkraftwerk_Niederaichbach&action=edit&redlink=1" class="new" title="Kernkraftwerk Niederaichbach (page does not exist)">KKN</a></li> <li><a href="/wiki/KS_150" title="KS 150">KS 150</a></li> <li><a href="/wiki/Lucens_reactor" title="Lucens reactor">Lucens</a></li></ul></li></ul> </div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><div style="display: inline-block; line-height: 1.2em; padding: .1em 0;"><a href="/wiki/Graphite-moderated_reactor" title="Graphite-moderated reactor">Graphite</a><br /><span style="font-size:85%;"><span class="nobold">by <a href="/wiki/Nuclear_reactor_coolant" title="Nuclear reactor coolant">coolant</a></span></span></div></th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0;background:none;"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:1%;font-weight:normal;">Water</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th id="H2O22" scope="row" class="navbox-group" style="width:2.5em;font-weight:normal;"><a href="/wiki/H2O" class="mw-redirect" title="H2O">H<sub>2</sub>O</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Obninsk_Nuclear_Power_Plant" title="Obninsk Nuclear Power Plant">AM-1</a></li> <li><a href="/wiki/Beloyarsk_Nuclear_Power_Station#Early_reactors" title="Beloyarsk Nuclear Power Station">AMB-X</a></li> <li><a href="/wiki/EGP-6" title="EGP-6">EGP-6</a></li> <li><a href="/wiki/RBMK" title="RBMK">RBMK</a></li></ul> </div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;font-weight:normal;"><a href="/wiki/Gas-cooled_reactor" title="Gas-cooled reactor">Gas</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:2.5em;font-weight:normal;"><a href="/wiki/Carbon_dioxide" title="Carbon dioxide">CO<sub>2</sub></a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/UNGG_reactor" title="UNGG reactor"><i>Uranium Naturel Graphite Gaz</i> (UNGG)</a></li> <li><a href="/wiki/Magnox" title="Magnox">Magnox</a></li> <li><a href="/wiki/Advanced_Gas-cooled_Reactor" class="mw-redirect" title="Advanced Gas-cooled Reactor">Advanced gas-cooled (AGR)</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:2.5em;font-weight:normal;"><a href="/wiki/Helium" title="Helium">He</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Gas_turbine_modular_helium_reactor" title="Gas turbine modular helium reactor">GTMHR</a> <ul><li><a href="/w/index.php?title=MHR-T&action=edit&redlink=1" class="new" title="MHR-T (page does not exist)">MHR-T</a></li></ul></li> <li><a href="/wiki/UHTREX" title="UHTREX">UHTREX</a></li> <li><a href="/wiki/Very-high-temperature_reactor" class="mw-redirect" title="Very-high-temperature reactor">VHTR (HTGR)</a> <ul><li><a href="/wiki/Pebble-bed_reactor" title="Pebble-bed reactor">PBR (PBMR)</a> <ul><li><a href="/wiki/AVR_reactor" title="AVR reactor">AVR</a></li> <li><a href="/wiki/HTR-10" title="HTR-10">HTR-10</a></li> <li><a href="/wiki/HTR-PM" title="HTR-PM">HTR-PM</a></li> <li><a href="/wiki/THTR-300" title="THTR-300">THTR-300</a></li></ul></li> <li><a href="/w/index.php?title=Prismatic_block_reactor&action=edit&redlink=1" class="new" title="Prismatic block reactor (page does not exist)">PMR</a></li></ul></li></ul> </div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;font-weight:normal;"><a href="/wiki/Molten_salt_reactor" class="mw-redirect" title="Molten salt reactor">Molten-salt</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th id="Fluorides19" scope="row" class="navbox-group" style="width:2.5em;font-weight:normal;"><a href="/wiki/FLiBe" title="FLiBe">Fluorides</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Fuji_Molten_Salt_Reactor" title="Fuji Molten Salt Reactor">Fuji MSR</a></li> <li><a href="/wiki/Liquid_fluoride_thorium_reactor" title="Liquid fluoride thorium reactor">Liquid-fluoride thorium reactor (LFTR)</a></li> <li><a href="/wiki/Molten-Salt_Reactor_Experiment" title="Molten-Salt Reactor Experiment">Molten-Salt Reactor Experiment (MSRE)</a></li> <li><a href="/wiki/Integral_Molten_Salt_Reactor" title="Integral Molten Salt Reactor">Integral Molten Salt Reactor (IMSR)</a></li> <li><a href="/wiki/TMSR-500" class="mw-redirect" title="TMSR-500">TMSR-500</a></li> <li><a href="/wiki/TMSR-LF1" title="TMSR-LF1">TMSR-LF1</a></li></ul> </div></td></tr></tbody></table><div></div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><div style="display: inline-block; line-height: 1.2em; padding: .1em 0;">None<br /><span class="nobold">(<a href="/wiki/Fast-neutron_reactor" title="Fast-neutron reactor">fast-neutron</a>)</span></div></th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0;background:none;"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><td colspan="2" class="navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Fast_breeder_reactor" class="mw-redirect" title="Fast breeder reactor">Breeder (FBR)</a></li> <li><a href="/wiki/Integral_fast_reactor" title="Integral fast reactor">Integral (IFR)</a></li> <li><a href="/wiki/Liquid_metal_cooled_reactor" title="Liquid metal cooled reactor">Liquid-metal-cooled (LMFR)</a></li> <li><a href="/wiki/Small,_sealed,_transportable,_autonomous_reactor" title="Small, sealed, transportable, autonomous reactor">Small sealed transportable autonomous (SSTAR)</a></li> <li><a href="/wiki/Traveling_wave_reactor" title="Traveling wave reactor">Traveling-wave (TWR)</a></li> <li><a href="/wiki/Energy_Multiplier_Module" title="Energy Multiplier Module">Energy Multiplier Module (EM2)</a></li> <li><a href="/wiki/Reduced_moderation_water_reactor" title="Reduced moderation water reactor">Reduced-moderation (RMWR)</a></li> <li><a href="/wiki/Fast_Breeder_Test_Reactor" title="Fast Breeder Test Reactor">Fast Breeder Test Reactor (FBTR)</a></li> <li><a href="/wiki/Dual_fluid_reactor" title="Dual fluid reactor">Dual fluid reactor (DFR)</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;font-weight:normal;"><a href="/wiki/Generation_IV_reactor" title="Generation IV reactor">Generation IV</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Sodium-cooled_fast_reactor" title="Sodium-cooled fast reactor">Sodium (SFR)</a> <ul><li><a href="/wiki/BN-350_reactor" title="BN-350 reactor">BN-350</a></li> <li><a href="/wiki/BN-600_reactor" title="BN-600 reactor">BN-600</a></li> <li><a href="/wiki/BN-800_reactor" title="BN-800 reactor">BN-800</a></li> <li><a href="/wiki/BN-1200_reactor" title="BN-1200 reactor">BN-1200</a></li> <li><a href="/wiki/CFR-600" title="CFR-600">CFR-600</a></li> <li><a href="/wiki/Ph%C3%A9nix" title="Phénix">Phénix</a></li> <li><a href="/wiki/Superph%C3%A9nix" title="Superphénix">Superphénix</a></li> <li><a href="/wiki/Prototype_Fast_Breeder_Reactor" title="Prototype Fast Breeder Reactor">PFBR</a></li> <li><a href="/wiki/FBR-600" title="FBR-600">FBR-600</a></li> <li><a href="/wiki/China_Experimental_Fast_Reactor" title="China Experimental Fast Reactor">CEFR</a></li> <li><a href="/wiki/Dounreay#Prototype_Fast_Reactor_(PFR)" title="Dounreay">PFR</a></li> <li><a href="/wiki/PRISM_(reactor)" title="PRISM (reactor)">PRISM</a></li></ul></li> <li><a href="/wiki/Lead-cooled_fast_reactor" 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