{"id":18401,"date":"2018-08-22T17:45:57","date_gmt":"2018-08-22T17:45:57","guid":{"rendered":"http:\/\/sitepourvtc.com\/?page_id=18401"},"modified":"2023-02-02T07:20:14","modified_gmt":"2023-02-02T07:20:14","slug":"power-plant-control-electric-power-control","status":"publish","type":"page","link":"https:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/reactor-operation\/normal-operation-reactor-control\/power-plant-control-electric-power-control\/","title":{"rendered":"Power Plant Control &#8211; Electric Power Control"},"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\"><div   id="8n9s8rpp6h"    class=\"su-spacer\" style=\"height:10px\"><\/div>\n<figure id=\"attachment_17812\" aria-describedby=\"caption-attachment-17812\" style=\"width: 290px\" class=\"wp-caption alignright\"><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/05\/Temperature-gradients-typical-PWR-steam-generator.png\"><img loading=\"lazy\" class=\"size-medium wp-image-17812\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/05\/Temperature-gradients-typical-PWR-steam-generator-300x212.png\" alt=\"Steam generator - counterflow heat exchanger\" width=\"300\" height=\"212\" srcset=\"https:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/05\/Temperature-gradients-typical-PWR-steam-generator-300x212.png 300w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/05\/Temperature-gradients-typical-PWR-steam-generator.png 807w\" sizes=\"(max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-17812\" class=\"wp-caption-text\">Temperature gradients in a typical PWR steam generator.<\/figcaption><\/figure>\n<p>As was written, after synchronization of the generator, the reactor control system is usually switched to <strong>automatic control,<\/strong> and the additional power increase is in this mode. The power plant is then controlled by the plant control system that coordinates the NSSS and the turbine control system. The interfacing variable is, in this case, the<strong> core inlet temperature<\/strong>, which is fully determined by <strong>steam pressure<\/strong> inside<a title=\"Steam Generator\" href=\"http:\/\/sitepourvtc.com\/steam-generator\/\"> steam generators<\/a>. Note that the core inlet temperature and the steam pressure are <strong>interconnected<\/strong>\u00a0since heat (or power) transferred across a steam generator is:<\/p>\n<p style=\"text-align: center;\"><strong>q = h . \u0394T<\/strong><\/p>\n<p>\u00a0where:<\/p>\n<ul>\n<li><em>q<\/em> is the amount of heat transferred (heat flux), W\/m<sup>2,<\/sup> i.e., thermal power per unit area<\/li>\n<li><em>h<\/em> is heat transfer coefficient, W\/(m<sup>2<\/sup>.K)<\/li>\n<li>\u0394<em>T<\/em> is the difference in temperature across the steam generator (in this case, the difference between the average temperature of the reactor coolant &#8211; Tavg and the saturation temperature determined by system pressure.<\/li>\n<\/ul>\n<p>For all practical purposes, the heat transfer coefficient (h) is constant since the heat transfer coefficient is a function of the materials used in constructing the steam generator. The U-tubes are completely covered with water.<\/p>\n<p>See also:\u00a0<a title=\"What is Steam Turbine \u2013 Description and Characteristics\" href=\"http:\/\/sitepourvtc.com\/nuclear-power-plant\/turbine-generator-power-conversion-system\/what-is-steam-turbine-description-and-characteristics\/\"><strong>Steam Turbine<\/strong><\/a><\/p>\n<p>A reactor is in automatic control follows the core inlet temperature &#8211; <strong>T<sub>in<\/sub><\/strong> (or the core average temperature &#8211; <strong>T<sub>avg<\/sub><\/strong>). Note that T<sub>avg<\/sub> = (T<sub>out<\/sub> + T<sub>in<\/sub>) \/ 2. When there is a difference between the actual T<sub>in<\/sub>\u00a0and the temperature T<sub>in set<\/sub>, which is set in the system, the reactor control system initiates control rods movement. For example, when T<sub>in, actual<\/sub> &gt; T<sub>in, set<\/sub>, the reactor control system automatically inserts control rods to decrease T<sub>in, actual<\/sub>. The <strong>reactor thermal power remains constant<\/strong> because the rod&#8217;s movement only offsets the reactivity from the difference (T<sub>in, actual<\/sub> &#8211; T<sub>in, set<\/sub>) x <a title=\"Moderator Temperature Coefficient \u2013 MTC\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/nuclear-fission-chain-reaction\/reactivity-coefficients-reactivity-feedbacks\/moderator-temperature-coefficient-mtc\/\">MTC<\/a> = moderator defect.<\/p>\n<p>On the other hand, if the energy demand in the external system increases, more energy is removed from the reactor system, causing the temperature of the reactor coolant (T<sub>in<\/sub>) to decrease. As the reactor coolant temperature decreases, positive reactivity is added, resulting in a corresponding increase in reactor power level. This reactor power increase occurs without any change in control rods position and without any change in boron concentration. The same inherent stability can be observed as the energy demand on the system is decreased.<\/p>\n<figure id=\"attachment_17846\" aria-describedby=\"caption-attachment-17846\" style=\"width: 290px\" class=\"wp-caption alignright\"><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/05\/Steam-Turbine-scheme-min.png\"><img loading=\"lazy\" class=\"size-medium wp-image-17846\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/05\/Steam-Turbine-scheme-min-300x155.png\" alt=\"Steam turbine of typical 3000MWth PWR\" width=\"300\" height=\"155\" srcset=\"https:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/05\/Steam-Turbine-scheme-min-300x155.png 300w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/05\/Steam-Turbine-scheme-min-1024x529.png 1024w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/05\/Steam-Turbine-scheme-min.png 1642w\" sizes=\"(max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-17846\" class=\"wp-caption-text\">Schema of a steam turbine of a typical 3000MWth PWR.<\/figcaption><\/figure>\n<p>It must be added in case of disconnected automatic control, the turbine controls the steam pressure, and the reactor control system is in a manual regime. In this case, a control rods insertion causes a decrease in reactor thermal power since the steam pressure remains constant. The turbine load decreases as the reactor thermal power decreases.<\/p><\/div><\/div><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>Self-regulating properties of nuclear reactor<\/div><div   id="8n9s8rpp6h"    class=\"su-spoiler-content su-u-clearfix su-u-trim\">Operating with a <strong>negative MTC<\/strong>\u00a0is\u00a0favorable operational characteristics also during\u00a0<strong>power\u00a0changes<\/strong>. <span data-preserver-spaces=\"true\">There is an exact\u00a0<\/span><strong><span data-preserver-spaces=\"true\">energy balance<\/span><\/strong><span data-preserver-spaces=\"true\"> between the primary and secondary circuits at normal operation. Therefore when the operator decreases the load on the turbine (e.g., due to a grid requirement), the steam demand decreases (see the initial electrical output decrease in the picture). <\/span>At this moment, the reactor will produce more heat than the steam turbine can consume. This<strong>\u00a0disbalance<\/strong> causes the steam pressure the saturation temperature in the steam generators to increase (see II. pressure at the picture). As a result of increasing saturation temperature in the steam generators, the <strong>moderator temperature<\/strong> will simply increase (see inlet temperature). Increasing the temperature of the moderator adds <strong>negative\u00a0reactivity<\/strong>, which reduces reactor power (without any operator intervention). As can be seen, to a certain extent, the reactor is <strong>self-regulating,<\/strong> and the reactor power may be controlled via the steam turbine and via grid requirements. This feature is limited because the range of allowable inlet temperatures is limited. It is power plant-specific, but in general, power changes of the order of units of % are common.\n<p>See also: <a title=\"Reactor Stability\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/reactor-dynamics\/reactor-stability\/\">Reactor Stability<\/a><\/p>\n<p><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2016\/03\/self-regulating-reactor-min.png\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-14077\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2016\/03\/self-regulating-reactor-min.png\" alt=\"self-regulating reactor-min\" width=\"900\" height=\"720\" srcset=\"https:\/\/sitepourvtc.com\/wp-content\/uploads\/2016\/03\/self-regulating-reactor-min.png 900w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2016\/03\/self-regulating-reactor-min-300x240.png 300w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2016\/03\/self-regulating-reactor-min-177x142.png 177w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2016\/03\/self-regulating-reactor-min-147x118.png 147w\" sizes=\"(max-width: 900px) 100vw, 900px\" \/><\/a><\/p><\/div><\/div><\/div><div   id="8n9s8rpp6h"    class=\"su-divider su-divider-style-dotted\" style=\"margin:15px 0;border-width:2px;border-color:#999999\"><\/div>Back to the automatic control, in which reactor control system controls the floating T<sub>in, actual\u00a0<\/sub>and is actuated when T<sub>in, actual<\/sub>\u00a0 &#8211; T<sub>in, actual\u00a0<\/sub>is greater than the preset deadband. From this point of view (T<sub>in<\/sub> or T<sub>avg <\/sub>control), usually, three regimes are defined:\n<ul>\n<li><strong>Constant Pressure Regime (sliding T<\/strong><strong><sub>avg<\/sub><\/strong><strong>). <\/strong>Constant pressure (p<sub>steam<\/sub>) regime means that the reactor control system maintains the steam pressure inside steam generators (or at the turbine inlet) constant as turbine load changes. Also, in this case, the automatic system follows \u00a0T<sub>avg, set<\/sub>, but T<sub>avg, set<\/sub> is a function of turbine load. For example, increasing turbine load causes steam pressure to decrease. The reactor control system would sense this decrease in steam pressure and withdraw control rods to increase the reactor coolant temperature. This type of reactor control produces ideal steam conditions at the main turbine inlet for all loads from the initial load (e.g., 30%) to 100% load. The temperature difference (\u0394T) between the primary and secondary sides is increased by raising T<sub>avg<\/sub> or proportionally by raising T<sub>in<\/sub>. The disadvantage of this type of control scheme is that minimal changes in turbine load require (negative MTC) intervention of the reactor control system. Moreover, there are problems within a high reactor outlet temperature (T<sub>out<\/sub>), which approaches saturation values. Therefore it is not widely used in PWRs, especially U-tube steam generators.<\/li>\n<li><strong>Constant T<\/strong><strong><sub>avg<\/sub><\/strong><strong> Regime (sliding p<\/strong><strong><sub>steam<\/sub><\/strong><strong>). <\/strong>Constant T<sub>avg<\/sub> regime means that the reactor control system maintains the average core temperature of the reactor coolant constant as turbine load changes. The automatic system follows \u00a0T<sub>avg, set<\/sub>, which is constant. For example, increasing turbine load causes steam pressure to decrease. This, in turn, causes T<sub>avg<\/sub> to decrease because the turbine uses more energy than that produced by the reactor. The reactor control system would sense this decrease in T<sub>avg<\/sub> and withdraw control rods to increase the reactor coolant temperature. This regime causes minimal changes in the reactivity of the core due to minimal changes in the average coolant temperature. Since the coolant temperature remains constant, the coolant volume does not change, and therefore, the pressurizer level remains constant for all load conditions. The disadvantage of this type of control scheme is that steam conditions (steam pressure) significantly change from hot zero power to full load, which is unacceptable.<\/li>\n<li>\n<figure id=\"attachment_18390\" aria-describedby=\"caption-attachment-18390\" style=\"width: 290px\" class=\"wp-caption alignright\"><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/08\/Reactor-Control-Turbine-Control.png\"><img loading=\"lazy\" class=\"size-medium wp-image-18390\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/08\/Reactor-Control-Turbine-Control-300x199.png\" alt=\"Reactor Control - Turbine Control\" width=\"300\" height=\"199\" srcset=\"https:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/08\/Reactor-Control-Turbine-Control-300x199.png 300w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/08\/Reactor-Control-Turbine-Control.png 607w\" sizes=\"(max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-18390\" class=\"wp-caption-text\">Sliding Tavg and Sliding psteam Regime. The automatic system follows Tavg, set, but Tavg, the set is a function of turbine load, and it is programmed for the best performance of the entire system.<\/figcaption><\/figure>\n<p><strong>Sliding T<\/strong><strong><sub>avg<\/sub><\/strong><strong> and Sliding p<\/strong><strong><sub>steam <\/sub><\/strong><strong>Regime. <\/strong>This regime combines the previous regimes. The automatic system follows \u00a0T<sub>avg, set<\/sub>, but T<sub>avg, set<\/sub> is a function of turbine load, and it is programmed for the best performance of the entire system. Sometimes, there are many programmed functions of T<sub>avg, set<\/sub> for different purposes (e.g., for initial power increase, load-follow, or coast down). The control scheme most often selected to control the reactor is the sliding T<sub>avg<\/sub> and sliding p<sub>steam<\/sub> regime. This regime is a compromise between the other two regimes of control and contains some of the advantages and disadvantages of each.<\/p><\/li>\n<\/ul>\n<\/div><\/div><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. Clarendon Press; 1 edition, 1991, ISBN: 978-0198520467<\/li>\n<li>G.R.Keepin. Physics of Nuclear Kinetics. Addison-Wesley Pub.\u00a0 o; 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<\/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>Normal Operation<a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/reactor-operation\/normal-operation-reactor-control\/\" 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":18387,"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\/18401"}],"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=18401"}],"version-history":[{"count":3,"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/pages\/18401\/revisions"}],"predecessor-version":[{"id":37016,"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/pages\/18401\/revisions\/37016"}],"up":[{"embeddable":true,"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/pages\/18387"}],"wp:attachment":[{"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/media?parent=18401"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}