{"id":26724,"date":"2020-03-15T07:10:40","date_gmt":"2020-03-15T07:10:40","guid":{"rendered":"http:\/\/sitepourvtc.com\/?page_id=26724"},"modified":"2023-07-14T10:11:58","modified_gmt":"2023-07-14T10:11:58","slug":"incore-nuclear-instrumentation","status":"publish","type":"page","link":"https:\/\/sitepourvtc.com\/nuclear-power-plant\/nuclear-reactor\/nuclear-instrumentation\/incore-nuclear-instrumentation\/","title":{"rendered":"Incore Nuclear Instrumentation"},"content":{"rendered":"<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\">\n<p>The <strong>incore nuclear instrumentation system<\/strong> measures <a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/nuclear-engineering-fundamentals\/neutron-nuclear-reactions\/neutron-flux-neutron-intensity\/\">neutron flux distribution<\/a> and temperatures in the reactor core. The purposes of the incore instrumentation system are to provide detailed information on <strong>neutron flux distribution<\/strong> and fuel assembly outlet temperatures at selected core locations. The incore instrumentation system provides data acquisition and usually performs no protective or plant operational control functions.<\/p>\n<p>The incore instrumentation system includes:<\/p>\n<ul>\n<li><strong>Incore neutron flux monitoring system<\/strong><\/li>\n<li><strong>Incore temperature monitoring system<\/strong><\/li>\n<\/ul>\n<p>Westinghouse Technology Systems Manual, Section 9.2. Incore Instrumentation System. &lt;available from: https:\/\/www.nrc.gov\/docs\/ML1122\/ML11223A264.pdf&gt;.<\/p>\n<h2>Incore Neutron Flux Monitoring System<\/h2>\n<p>The <strong>incore neutron monitoring system<\/strong> consists of incore detectors with sufficient sensitivity to measure localized neutron flux distribution variations within the <a href=\"http:\/\/sitepourvtc.com\/nuclear-power-plant\/nuclear-reactor-core\/\">reactor core<\/a>. It must be noted that in power reactor cores, the flux distribution and power distribution are significantly influenced by many factors. Therefore, the temperature in an operating reactor varies from point to point within the system. Consequently, there is always <strong>one fuel rod<\/strong> and <strong>one local volume<\/strong> <strong>hotter<\/strong> than all the rest. <strong>Peak power limits<\/strong> must be introduced to limit these <strong>hot places<\/strong>. The peak power limits are associated with a<a href=\"http:\/\/sitepourvtc.com\/nuclear-engineering\/heat-transfer\/boiling-and-condensation\/boiling-crisis-critical-heat-flux\/\"><strong> boiling crisis<\/strong><\/a> and the conditions that could cause fuel pellet melt. The incore neutron flux monitoring system provides detailed information on neutron flux distribution and thus the margins to these <a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/reactor-operation\/normal-operation-reactor-control\/hot-channel-factors-peaking-factors\/\">peak power limits<\/a>.<\/p>\n<p>The incore neutron flux monitoring system usually utilizes:<\/p>\n<ul>\n<li><strong>miniature fission chambers<\/strong><\/li>\n<li><strong>self-powered neutron detectors<\/strong><\/li>\n<\/ul>\n<p>These movable flux detectors that are usually placed into the <strong>instrumentation tube<\/strong> of a <strong>fuel assembly<\/strong>\u00a0can monitor the entire length of selected fuel assemblies to provide an extremely accurate,<strong> three-dimensional map<\/strong> of the <strong>neutron flux distribution<\/strong>. Neutron flux reconstruction can also be performed in the rest of the reactor core using these data. The data obtained from the incore neutron flux monitoring system is usually (depending on certain reactor design) used to:<\/p>\n<ol>\n<li>This data can be used to determine the power distribution in the core at any time during the fuel cycle. The monitored power distribution is used to verify that the following power distribution hot channel factors comply with technical specification limits:\n<ol>\n<li>The <a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/reactor-operation\/normal-operation-reactor-control\/heat-flux-hot-channel-factor-fqz\/\">Heat Flux Hot Channel Factor \u2013 F<sub>Q<\/sub>(z)<\/a> is defined as: <em>The ratio of the maximum local linear power density, where there is a minimal margin to limiting fuel temperature (during AOOs), to the average local linear power density in the core.<\/em><\/li>\n<li>The <a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/reactor-operation\/normal-operation-reactor-control\/nuclear-enthalpy-rise-hot-channel-factor\/\">Nuclear Enthalpy Rise Hot Channel Factor \u2013 F<sub>N\u0394H<\/sub><\/a> is defined as: <em>The ratio of the integral of linear power along the fuel rod on which minimum departure from nucleate boiling ratio occurs (during AOOs) to the average fuel rod power in the core.<\/em><\/li>\n<\/ol>\n<\/li>\n<li>This data can be used to determine <a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/reactor-operation\/fuel-burnup\/\">fuel burn-up<\/a>\u00a0and isotopic fuel inventories in the core at any time during the fuel cycle.<\/li>\n<li>This data can be used to calibrate the excore power range nuclear instruments for axial flux difference (AFD)<\/li>\n<li>This data can be used to verify that the quadrant power tilt ratio (QPTR) meets the technical specification limit.<\/li>\n<li>The data will also provide trends of core conditions so that corrective action can be taken before a condition becomes excessive.<\/li>\n<\/ol>\n<p>See also: <a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/neutron-diffusion-theory\/power-distribution-conventional-reactors\/\">Power Distribution in PWR<\/a><\/p>\n<p>See also: <a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/neutron-diffusion-theory\/numerical-solution-diffusion-equation\/nodal-method-in-neutron-diffusion\/\">Nodal Method in Neutron Diffusion<\/a><\/p>\n<h2>Incore Temperature Monitoring System<\/h2>\n<p>The <strong>incore neutron temperature monitoring system<\/strong> consists of incore thermocouples positioned at preselected locations to measure fuel assembly coolant outlet temperature for monitoring the core radial power sharing and coolant <a href=\"http:\/\/sitepourvtc.com\/nuclear-engineering\/thermodynamics\/what-is-energy-physics\/what-is-enthalpy\/\">enthalpy<\/a> distribution. Coolant outlet temperatures are more or less influenced by lateral flow mixing, and for some reactor designs, this system has another purpose, such as monitoring safety functions. This data (coolant outlet temperatures) may be (depending on certain reactor design) used to:<\/p>\n<ol>\n<li>Provide the operators with indications of inadequate core cooling conditions during emergencies (e.g., <strong>core overtemperature<\/strong>)<\/li>\n<li>Provide information about temperature rise in the fuel assembly. This may indicate a serious core condition (e.g., <strong>channel blockage<\/strong>) and should be investigated.<\/li>\n<li>Provide inputs to the subcooling margin monitors<\/li>\n<li>Provide inputs to plant computational computer applications which use core-exit temperatures to determine fuel assembly enthalpy rises and limited power distribution information.<\/li>\n<\/ol>\n<p>Westinghouse Technology Systems Manual, Section 9.2. Incore Instrumentation System. &lt;available from: https:\/\/www.nrc.gov\/docs\/ML1122\/ML11223A264.pdf&gt;.<\/p>\n<h2>Self-Powered Neutron Detector<\/h2>\n<p><strong>Self-Powered Neutron Detectors<\/strong> (<strong>SPND<\/strong>) are neutron detectors widely used in reactors to monitor <a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/nuclear-engineering-fundamentals\/neutron-nuclear-reactions\/neutron-flux-neutron-intensity\/\">neutron flux<\/a> due to their adaptability for in-core severe environments. <strong>SPNDs<\/strong> may be a part of the incore neutron flux monitoring system, which provides detailed information on neutron flux distribution and thus the margins to these peak power limits. These detectors use its neutron activation material&#8217;s basic <a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/radioactive-decay\/\">radioactive decay<\/a> process to produce an output signal. As the name implies, \u00a0<strong>SPNDs do not require an external voltage source<\/strong> to create a voltage potential in the detector. Instead, a current is produced in the detector as the result of <strong>neutron activation<\/strong> and subsequent <a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/radioactive-decay\/beta-decay-beta-radioactivity\/\"><strong>beta decay<\/strong><\/a> of the detector itself. Because of the emission of these beta particles (electrons), the wire becomes more and more positively charged. The positive potential of the wire causes a current to flow in the resistor, R. The electron current from beta decay can be measured directly with an ammeter.<\/p>\n<p>There are two main advantages of the self-powered neutron detector:<\/p>\n<ul>\n<li>Very little instrumentation is required, usually only a millivoltmeter or an ammeter<\/li>\n<li>The emitter material has a much greater lifetime than boron or uranium-235 lining used in fission chambers.<\/li>\n<\/ul>\n<p>On the other hand, there are also disadvantages, and one is associated with the fact that currents, even at full power operation, are very low. Therefore, SPNDs cannot provide information about flux distribution at low power operation (10% and less). The main disadvantage of the self-powered neutron detector is that the emitter material decays with a characteristic half-life, which determines the detector&#8217;s response time. Depending on the response time, these detectors are broadly classified as:<\/p>\n<ul>\n<li><strong>Prompt response detectors<\/strong>. The prompt response detectors such as Cobalt and Inconel are used in reactor protection and regulation applications.<\/li>\n<li><strong>Delayed response detectors<\/strong>. The delayed response detectors like Vanadium and Rhodium are widely used for Flux Mapping Systems (FMS).<\/li>\n<\/ul>\n<p>The typical SPND is a coaxial cable consisting of:<\/p>\n<ul>\n<li><strong>Emitter<\/strong>. An inner electrode is made from a material that absorbs a neutron and undergoes radioactive decay by emitting an electron (beta decay). The emitter is usually made of rhodium and is used to produce electrons.<\/li>\n<li><strong>Insulation. <\/strong>The emitter is surrounded by insulation, usually made of aluminum oxide.<\/li>\n<li><strong>Collector<\/strong>. The metal walls of the detector encase these parts and serve as a collector for the produced electrons.- The collector is attached to ground potential,<\/li>\n<\/ul>\n<p><strong>Self-powered neutron detectors<\/strong> are usually placed into the instrumentation tube of a fuel assembly. They can monitor the entire length of selected fuel assemblies to provide an extremely accurate,<strong> three-dimensional map<\/strong> of the <strong>neutron flux distribution<\/strong>. Neutron flux reconstruction can also be performed in the rest of the reactor core using these data.<\/p>\n<p>Typical materials used for the emitter are cobalt, cadmium, rhodium, and vanadium. These materials should be used because they possess relatively high melting temperatures and relatively high cross sections to thermal neutrons and are compatible with the SPND manufacturing process.<\/p>\n<p>Special Reference: William H. Todt, Sr. CHARACTERISTICS OF SELF-POWERED NEUTRON DETECTORS USED IN POWER REACTORS. Imaging and Sensing Technology Corporation. New York.<\/p>\n<h3>Rhodium Emitter &#8211; Rhodium-based SPND<\/h3>\n<p>One possible material is <strong>rhodium<\/strong> as the emitter. An SPND with a rhodium emitter has relatively <strong>high sensitivity<\/strong>\u00a0and <strong>high burn-up rate,<\/strong> perturbs the local power density, and has a (<strong>two-fold<\/strong>) <strong>delayed signal<\/strong>. A <strong>rhodium-based\u00a0detector<\/strong> is the beta-current type of self-powered detector, which uses the following activation reaction to produce a current that can be measured.<\/p>\n<p><sup>1<\/sup>n + <sup>103<\/sup>Rh \u2192 <sup>104<\/sup>Rh \u2192 <sup>104<\/sup>Pd + \u03b2<\/p>\n<p>As can be seen, a neutron captured by rhodium-103 causes a rhodium-103 atom to become a radioactive <strong>rhodium-104<\/strong> atom. The rhodium-104 then decays into palladium-104 plus a <a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-particles\/beta-particle\/\">beta particle<\/a> (<a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-particles\/what-is-electron-properties-of-electron\/\">electron<\/a>). The beta particle has enough energy to pass through the insulator and reach the collector. The <a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/radioactive-decay\/radioactive-decay-law\/half-life\/\">half-life<\/a> of activated rhodium-104 is 42.3 seconds, which delays the emission of the charged particle. The rhodium-based detector uses this production of beta particles (electrons) to create a current that is proportional to the number of neutrons captured by the emitter, which is also proportional to local reactor power density. A portion of the detector&#8217;s current flow is due to <a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-particles\/photon\/gamma-ray\/\">gamma rays<\/a>. A background correction is performed via a background detector consisting of the same components as the detector to compensate for this erroneous signal, except the rhodium is removed.<\/p>\n<p>Rhodium-103 has a <a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/nuclear-engineering-fundamentals\/neutron-nuclear-reactions\/neutron-capture-radiative-capture\/neutron-capture-cross-section\/\">capture cross-section<\/a> of <strong>133 barns<\/strong> for thermal neutrons and a resonance at 1.25 eV. This reaction leads to the production of <sup>104<\/sup>Rh with T<sub>1\/2<\/sub> = 42 sec, which is beta radioactive. It must be noted about 11 barns belong to a reaction in which an <a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/atom-properties-of-atoms\/nuclides\/isomers\/\">isomer <sup>104m<\/sup>Rh<\/a> is produced (with T<sub>1\/2<\/sub> = 4.4 min).<\/p>\n<p>The following characteristics are typical when used in thermal power reactors (e.g., PWR).<\/p>\n<ul>\n<li>The rhodium burn-up rate is 0.39% per month in a thermal neutron flux of 10<sup>13<\/sup>n\/cm<sup>2<\/sup>\/sec.<\/li>\n<li>92% of the signal has a half-life of 42 seconds.<\/li>\n<li>8% of the signal has a half-life of 4.4 minutes.<\/li>\n<li>The beta emission has an energy of 2.44 MeV.<\/li>\n<\/ul>\n<h3>Vanadium Emitter &#8211; Vanadium-based SPND<\/h3>\n<p>An SPND with a vanadium emitter has relatively low sensitivity, low burn-up rate, minimal perturbation of the local power density, and a very long delayed signal. A vanadium-based detector is the beta-current type of self-powered detector, which uses the following activation reaction to produce a current that can be measured.<\/p>\n<p><sup>1<\/sup>n + <sup>51<\/sup>V \u2192 <sup>52<\/sup>V \u2192 <sup>52<\/sup>Cr + \u03b2<\/p>\n<p>Vanadium-51 has a capture cross-section of 4.9 barns for <a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-particles\/neutron\/thermal-neutron\/\">thermal neutrons<\/a> without resonances. This reaction leads to the production of <sup>52<\/sup>V with T<sub>1\/2<\/sub> = 3.74 min, which is <a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/radioactive-decay\/beta-decay-beta-radioactivity\/\">beta radioactive<\/a>.<\/p>\n<p>The following characteristics are typical when used in thermal power reactors (e.g., PWR).<\/p>\n<ul>\n<li>The vanadium burnup rate is 0.012% per month in a thermal neutron flux of 10<sup>13<\/sup>n\/cm<sup>2<\/sup>\/sec.<\/li>\n<li>99% of the signal has a half-life of 3.8 minutes.<\/li>\n<li>1% of the signal is prompt.<\/li>\n<li>The subsequent beta emission has an energy of 2.6 MeV.<\/li>\n<\/ul>\n<\/div><\/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\"><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\">\n<p><strong>Radiation Protection:<\/strong><\/p>\n<ol>\n<li>Knoll, Glenn F., Radiation Detection and Measurement 4th Edition, Wiley, 8\/2010. ISBN-13: 978-0470131480.<\/li>\n<li>Stabin, Michael G., Radiation Protection, and Dosimetry: An Introduction to Health Physics, Springer, 10\/2010. ISBN-13: 978-1441923912.<\/li>\n<li>Martin, James E., Physics for Radiation Protection 3rd Edition, Wiley-VCH, 4\/2013. ISBN-13: 978-3527411764.<\/li>\n<li>U.S.NRC, NUCLEAR REACTOR CONCEPTS<\/li>\n<li>U.S. Department of Energy, Instrumentation, and Control. DOE Fundamentals Handbook, Volume 2 of 2. June 1992.<\/li>\n<\/ol>\n<p><strong>Nuclear and Reactor Physics:<\/strong><\/p>\n<ol>\n<li>J. R. Lamarsh, Introduction to Nuclear Reactor Theory, 2nd ed., Addison-Wesley, Reading, MA (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, Springer; 4th edition, 1994, ISBN: 978-0412985317<\/li>\n<li>W.S.C. Williams. Nuclear and Particle Physics. Clarendon Press; 1 edition, 1991, ISBN: 978-0198520467<\/li>\n<li>G.R.Keepin. Physics of Nuclear Kinetics. Addison-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. DOE Fundamentals Handbook, Volume 1 and 2. January 1993.<\/li>\n<li>Paul Reuss, Neutron Physics. EDP Sciences, 2008. ISBN: 978-2759800414.<\/li>\n<\/ol>\n<\/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=\"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>Nuclear Instrumentation<a href=\"http:\/\/sitepourvtc.com\/nuclear-power-plant\/nuclear-reactor\/nuclear-instrumentation\/\" 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":"","protected":false},"author":1,"featured_media":0,"parent":26704,"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\/26724"}],"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=26724"}],"version-history":[{"count":2,"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/pages\/26724\/revisions"}],"predecessor-version":[{"id":38390,"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/pages\/26724\/revisions\/38390"}],"up":[{"embeddable":true,"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/pages\/26704"}],"wp:attachment":[{"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/media?parent=26724"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}