{"id":14045,"date":"2017-03-11T13:22:55","date_gmt":"2017-03-11T13:22:55","guid":{"rendered":"http:\/\/sitepourvtc.com\/?page_id=14045"},"modified":"2022-10-21T17:03:42","modified_gmt":"2022-10-21T17:03:42","slug":"lwr-light-water-reactor","status":"publish","type":"page","link":"https:\/\/sitepourvtc.com\/nuclear-power-plant\/reactor-types\/lwr-light-water-reactor\/","title":{"rendered":"LWR &#8211; Light Water Reactor"},"content":{"rendered":"<div   id="8n9s8rpp6h"    class=\"su-quote su-quote-style-default\"><div   id="8n9s8rpp6h"    class=\"su-quote-inner su-u-clearfix su-u-trim\">The <strong>light water reactor<\/strong>, abbreviated as LWR, is a thermal reactor in which <strong>light water<\/strong> (ordinary water) is used as a <a title=\"Neutron Moderator\" href=\"http:\/\/sitepourvtc.com\/neutron-moderator\/\">moderator<\/a> as well as the reactor coolant. It is the most common type of nuclear reactor.<\/div><\/div>\n<p>The most common nuclear reactors are <strong>light water reactors (LWR)<\/strong>, in which\u00a0<strong>light water<\/strong> (ordinary water) is used as a <a title=\"Neutron Moderator\" href=\"http:\/\/sitepourvtc.com\/neutron-moderator\/\">moderator<\/a> and the cooling medium. The use of ordinary water makes it necessary to use an <a title=\"Enriched Uranium\" href=\"http:\/\/sitepourvtc.com\/nuclear-power-plant\/nuclear-fuel\/uranium\/enriched-uranium\/\">enriched uranium fuel<\/a> to <strong>maintain<\/strong> the <a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/nuclear-fission-chain-reaction\/reactor-criticality\/\"><b>reactor\u2019s criticality<\/b><\/a> along the entire fuel cycle (e.g.,, for an 18-month fuel cycle).<\/p>\n<figure id=\"attachment_71\" aria-describedby=\"caption-attachment-71\" style=\"width: 178px\" class=\"wp-caption alignright\"><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2014\/10\/WWER-1000-reactor.png\"><img loading=\"lazy\" class=\"wp-image-71 size-medium\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2014\/10\/WWER-1000-reactor-188x300.png\" alt=\"WWER-1000 reactor\" width=\"188\" height=\"300\" srcset=\"https:\/\/sitepourvtc.com\/wp-content\/uploads\/2014\/10\/WWER-1000-reactor-188x300.png 188w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2014\/10\/WWER-1000-reactor-643x1024.png 643w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2014\/10\/WWER-1000-reactor.png 735w\" sizes=\"(max-width: 188px) 100vw, 188px\" \/><\/a><figcaption id=\"caption-attachment-71\" class=\"wp-caption-text\">Description of VVER-1000 reactor.<br \/>1) Control Element Drive Mechanism<br \/>2) Reactor vessel head<br \/>3) Reactor pressure vessel<br \/>4) Coolant inlet-outlet nozzles<br \/>5) Downcomer for coolant<br \/>6) Neutron reflector<br \/>7) fuel assemblies<br \/>Source: www.wikipedia.org<\/figcaption><\/figure>\n<p><strong>Light water reactors<\/strong> are thermal reactors that use<a title=\"Thermal Neutron\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-particles\/neutron\/thermal-neutron\/\"> thermal neutrons <\/a>to sustain the <a title=\"Nuclear Fission Chain Reaction\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/nuclear-fission-chain-reaction\/\">chain reaction<\/a>. In general, LWR\u2019s are divided into two categories:<\/p>\n<ul>\n<li><a title=\"PWR \u2013 Pressurized water reactor\" href=\"http:\/\/sitepourvtc.com\/pwr-pressurized-water-reactor\/\"><strong>Pressurized water reactors (PWR)<\/strong><\/a> \u2013 are characterized by the high-pressure primary circuit (to keep the water in<strong> a liquid state<\/strong>)<\/li>\n<\/ul>\n<ul>\n<li><a title=\"BWR \u2013 Boiling water reactor\" href=\"http:\/\/sitepourvtc.com\/bwr-boiling-water-reactor\/\"><strong>Boiling water reactors (BWR)<\/strong> <\/a>\u2013 are characterized by controlled boiling in the primary circuit.<\/li>\n<\/ul>\n<p><strong>Pressurized water reactors<\/strong> use a <a title=\"Reactor Pressure Vessel\" href=\"http:\/\/sitepourvtc.com\/nuclear-power-plant\/nuclear-reactor\/reactor-pressure-vessel\/\">reactor pressure vessel (RPV)<\/a> to contain the<a title=\"Nuclear Fuel\" href=\"http:\/\/sitepourvtc.com\/nuclear-power-plant\/nuclear-fuel\/\"> nuclear fuel<\/a>, <a title=\"Neutron Moderator\" href=\"http:\/\/sitepourvtc.com\/neutron-moderator\/\">moderator<\/a>, <a title=\"Control Rods\" href=\"http:\/\/sitepourvtc.com\/nuclear-power-plant\/control-rods\/\">control rods<\/a>, and coolant. They are cooled and moderated by <strong>high-pressure liquid water<\/strong> (e.g.,, at the pressure of 16MPa). At this pressure, water boils at approximately 350\u00b0C (662\u00b0F). The inlet temperature of the water is about 290\u00b0C (554\u00b0F). The water (coolant) is heated in the reactor core to approximately 325\u00b0C (617\u00b0F) as the water flows through the core. As it can be seen, the reactor has approximately 25\u00b0C <strong>subcooled coolants<\/strong> (distance from the saturation).<\/p>\n<p><strong>Boiling water reactors<\/strong> are cooled and moderated by water like a PWR, but at a lower pressure (of about 7MPa), which allows the water to <strong>boil inside<\/strong> the pressure vessel producing the steam that runs turbines. A BWR is like a PWR but with many differences. The BWRs don\u2019t have any <a title=\"Steam Generator\" href=\"http:\/\/sitepourvtc.com\/steam-generator\/\"><strong>steam generators<\/strong><\/a>. Unlike a PWR, there is no primary and secondary loop. The thermal efficiency of these reactors can be higher, and they can be simpler and even potentially more stable and safe. But the disadvantage of this concept is that any fuel leak can make the water radioactive and that radioactivity can reach the turbine and the rest of the loop.<\/p>\n<div   id="8n9s8rpp6h"    class=\"collapsible-container\">\n<h2>Light water as the moderator<\/h2>\n<p>To be an <strong>effective moderator<\/strong>, the probability of <a title=\"Elastic Scattering Cross-section\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/nuclear-engineering-fundamentals\/neutron-nuclear-reactions\/neutron-elastic-scattering\/elastic-scattering-cross-section\/\">elastic reaction<\/a> between <a title=\"Neutron\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-particles\/neutron\/\">neutron<\/a> and the nucleus must be high. In terms of <a title=\"Neutron Cross-section\" href=\"http:\/\/sitepourvtc.com\/neutron-cross-section\/\">cross-sections<\/a>, the elastic scattering cross-section of a moderator\u2019s nucleus must be high. Therefore high elastic scattering cross-section is important but does not describe the comprehensive capabilities of moderators. Three new material variables must be defined to describe the capabilities of a material to slow down neutrons:<\/p>\n<ul>\n<li><a title=\"Average Logarithmic Energy Decrement\" href=\"http:\/\/sitepourvtc.com\/glossary\/neutron-moderatoraverage-logarithmic-energy-decrement\/\"><strong>The Average Logarithmic Energy Decrement (\u03be)<\/strong><\/a><\/li>\n<li><a title=\"Macroscopic Slowing Down Power \u2013 MSDP\" href=\"http:\/\/sitepourvtc.com\/glossary\/macroscopic-slowing-down-power-msdp\/\"><strong>The Macroscopic Slowing Down Power (MSDP)<\/strong><\/a><\/li>\n<li><a title=\"Moderating Ratio \u2013 MR\" href=\"http:\/\/sitepourvtc.com\/glossary\/moderating-ratio-mr\/\"><strong>The Moderating Ratio (MR)<\/strong><\/a><\/li>\n<\/ul>\n<p><strong>Light water<\/strong> has the <strong>highest \u03be<\/strong> and <strong>\u03c3<sub>s<\/sub><\/strong> among the moderators (resulting in the <strong>highest MSDP<\/strong>) shown in the table. Still, its <strong>moderating ratio is low<\/strong> due to its relatively higher absorption cross-section.<\/p>\n<figure id=\"attachment_13064\" aria-describedby=\"caption-attachment-13064\" style=\"width: 630px\" class=\"wp-caption aligncenter\"><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2015\/11\/moderation-ratio-table.png\"><img loading=\"lazy\" class=\"size-full wp-image-13064\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2015\/11\/moderation-ratio-table.png\" alt=\"Table of moderating ratios MR for some materials.\" width=\"640\" height=\"274\" srcset=\"https:\/\/sitepourvtc.com\/wp-content\/uploads\/2015\/11\/moderation-ratio-table.png 640w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2015\/11\/moderation-ratio-table-300x128.png 300w\" sizes=\"(max-width: 640px) 100vw, 640px\" \/><\/a><figcaption id=\"caption-attachment-13064\" class=\"wp-caption-text\">Table of moderating ratios for some materials.<\/figcaption><\/figure>\n<h2>Heavy Water Reactors<\/h2>\n<p><strong>The most efficient moderator<\/strong> is heavy water. Heavy water has <strong>lower \u03be<\/strong> and <strong>\u03c3<sub>s<\/sub><\/strong>\u00a0but has the <strong>highest moderating ratio<\/strong> due to its lowest neutron <a title=\"Neutron Absorption Cross-section\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/nuclear-engineering-fundamentals\/neutron-nuclear-reactions\/neutron-absorption\/neutron-absorption-cross-section\/\">absorption cross-section<\/a>. Therefore heavy water is commonly used as a moderator in <a title=\"CANDU \u2013 Heavy Water Reactor\" href=\"http:\/\/sitepourvtc.com\/candu-heavy-water-reactor\/\"><strong>pressurized heavy water reactors (PHWR)<\/strong><\/a>. Most PHWR are heavy water-cooled and moderated pressurized water reactors. Instead of using a single large reactor vessel like a PWR or BWR, the nuclear core is contained in hundreds of pressure tubes. PHWRs generally use natural uranium (0.7% U-235) oxide or slightly enriched uranium as fuel. Hence they need a more efficient moderator, in this case, <strong>heavy water (D<sub>2<\/sub>O)<\/strong>.<\/p>\n<\/div>\n<div   id="8n9s8rpp6h"    class=\"su-divider su-divider-style-dotted\" style=\"margin:20px 0;border-width:2px;border-color:#999999\"><\/div>\n<div   id="8n9s8rpp6h"     class=\"lgc-column lgc-grid-parent lgc-grid-100 lgc-tablet-grid-100 lgc-mobile-grid-100 lgc-equal-heights \"><div   id="8n9s8rpp6h"     class=\"inside-grid-column\">\u00a0 <div   id="8n9s8rpp6h"    class=\"su-accordion su-u-trim\"><div   id="8n9s8rpp6h"    class=\"su-spoiler su-spoiler-style-default su-spoiler-icon-plus su-spoiler-closed\" data-scroll-offset=\"0\"><div   id="8n9s8rpp6h"    class=\"su-spoiler-title\" tabindex=\"0\" role=\"button\"><span class=\"su-spoiler-icon\"><\/span>References:<\/div><div   id="8n9s8rpp6h"    class=\"su-spoiler-content su-u-clearfix su-u-trim\"><strong>Nuclear and Reactor Physics:<\/strong>\n<ol>\n<li>J. R. Lamarsh, Introduction to Nuclear Reactor Theory, 2nd ed., Addison-Wesley, Reading,\u00a0MA (1983).<\/li>\n<li>J. R. Lamarsh, A. J. Baratta, Introduction to Nuclear Engineering, 3d ed., Prentice-Hall, 2001, ISBN: 0-201-82498-1.<\/li>\n<li>W. M. Stacey, Nuclear Reactor Physics, John Wiley &amp; Sons, 2001, ISBN: 0- 471-39127-1.<\/li>\n<li>Glasstone, Sesonske. Nuclear Reactor Engineering: Reactor Systems Engineering,\u00a0Springer; 4th edition, 1994, ISBN:\u00a0978-0412985317<\/li>\n<li>W.S.C. Williams. Nuclear and Particle Physics.\u00a0Clarendon Press; 1 edition, 1991, ISBN:\u00a0978-0198520467<\/li>\n<li>G.R.Keepin. Physics of Nuclear Kinetics.\u00a0Addison-Wesley Pub. Co; 1st edition, 1965<\/li>\n<li>Robert Reed Burn, Introduction to Nuclear Reactor Operation, 1988.<\/li>\n<li>U.S. Department of Energy, Nuclear Physics and Reactor Theory.\u00a0DOE Fundamentals Handbook,\u00a0Volume 1 and 2.\u00a0January\u00a01993.<\/li>\n<\/ol>\n<p><strong><\/strong><strong>Advanced Reactor Physics:<\/strong><\/p>\n<ol>\n<li>K. O. Ott, W. A. Bezella, Introductory Nuclear Reactor Statics, American Nuclear Society, Revised edition (1989), 1989, ISBN: 0-894-48033-2.<\/li>\n<li>K. O. Ott, R. J. Neuhold, Introductory Nuclear Reactor Dynamics, American Nuclear Society, 1985, ISBN: 0-894-48029-4.<\/li>\n<li><span style=\"font-weight: 400;\">D. L. Hetrick, Dynamics of Nuclear Reactors, American Nuclear Society, 1993, ISBN: 0-894-48453-2.\u00a0<\/span><\/li>\n<li>E. E. Lewis, W. F. Miller, Computational Methods of Neutron Transport, American Nuclear Society, 1993, ISBN: 0-894-48452-4.<\/li>\n<\/ol>\n<\/div><\/div><\/div><div   id="8n9s8rpp6h"    class=\"su-divider su-divider-style-dotted\" style=\"margin:15px 0;border-width:2px;border-color:#999999\"><\/div><\/div><\/div><div   id="8n9s8rpp6h"    class=\"su-divider su-divider-style-default\" style=\"margin:15px 0;border-width:2px;border-color:#999999\"><\/div><div   id="8n9s8rpp6h"     class=\"lgc-column lgc-grid-parent lgc-grid-33 lgc-tablet-grid-33 lgc-mobile-grid-100 lgc-equal-heights \"><div   id="8n9s8rpp6h"     class=\"inside-grid-column\"><\/div><\/div><div   id="8n9s8rpp6h"     class=\"lgc-column lgc-grid-parent lgc-grid-33 lgc-tablet-grid-33 lgc-mobile-grid-100 lgc-equal-heights \"><div   id="8n9s8rpp6h"     class=\"inside-grid-column\">\n<h2>See above:<\/h2>\n<p>Reactor Types<a href=\"http:\/\/sitepourvtc.com\/nuclear-power-plant\/reactor-types\/\" class=\"su-button su-button-style-flat\" style=\"color:#606060;background-color:#ffffff;border-color:#cccccc;border-radius:10px;-moz-border-radius:10px;-webkit-border-radius:10px\" target=\"_self\"><span style=\"color:#606060;padding:7px 20px;font-size:16px;line-height:24px;border-color:#ffffff;border-radius:10px;-moz-border-radius:10px;-webkit-border-radius:10px;text-shadow:0px 0px 0px #000000;-moz-text-shadow:0px 0px 0px #000000;-webkit-text-shadow:0px 0px 0px #000000\"><i class=\"sui sui-link\" style=\"font-size:16px;color:#5d5d5d\"><\/i> <\/span><\/a><\/p><\/div><\/div><div   id="8n9s8rpp6h"     class=\"lgc-column lgc-grid-parent lgc-grid-33 lgc-tablet-grid-33 lgc-mobile-grid-100 lgc-equal-heights \"><div   id="8n9s8rpp6h"     class=\"inside-grid-column\"><\/div><\/div>\n","protected":false},"excerpt":{"rendered":"<p>The most common nuclear reactors are light water reactors (LWR), in which\u00a0light water (ordinary water) is used as a moderator and the cooling medium. The use of ordinary water makes it necessary to use an enriched uranium fuel to maintain the reactor\u2019s criticality along the entire fuel cycle (e.g.,, for an 18-month fuel cycle). Light &#8230; <a title=\"LWR &#8211; Light Water Reactor\" class=\"read-more\" href=\"https:\/\/sitepourvtc.com\/nuclear-power-plant\/reactor-types\/lwr-light-water-reactor\/\" aria-label=\"More on LWR &#8211; Light Water Reactor\">Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"parent":273,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"generate_page_header":""},"_links":{"self":[{"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/pages\/14045"}],"collection":[{"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/comments?post=14045"}],"version-history":[{"count":4,"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/pages\/14045\/revisions"}],"predecessor-version":[{"id":32921,"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/pages\/14045\/revisions\/32921"}],"up":[{"embeddable":true,"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/pages\/273"}],"wp:attachment":[{"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/media?parent=14045"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}