Operational factors that affect the multiplication in PWRs<\/a><\/p>\nThis exactly but in the opposite direction acts after a reactor trip<\/strong> (SCRAM<\/strong>) from the Hot Full Power state (HFP). It is logical as power defects act against power increase, they also act against power decrease<\/strong>. When reactor power is decreased quickly<\/strong>, as in the case of reactor trip<\/strong>, power defect causes a positive reactivity insertion, and the initial rod insertion must be sufficient to make the reactor safe subcritical<\/strong>. Similarly, as in the HZP state, the integral worth of all control and emergency rods (PWRs) is, for example -9000pcm. It is equal to \u03c1 = -9000\/600 = -15\u03b2 = -0.09<\/em>. (\u03b2= 600pcm = 0.006<\/em>). <\/strong>Also, in this case, a prompt drop occurs. The prompt drop is quicker than the deaccumulation of heat from fuel pellets. For this negative reactivity, the prompt drop is equal to:<\/p>\nn2<\/sub>\/n1<\/sub> = 0.006\/(0.006+0.09)=0.063<\/p>\nbut the subsequent power decrease is strongly influenced by core (fuel and moderator) temperature changes. After reaching stable temperature, the neutron flux may continue to fall (when subcritical) according to the stable period. Obviously, if the power defect for PWRs <\/strong>is about 2500pcm<\/strong> (about 4 \u03b2eff), the control rods must weigh more than 2500pcm<\/strong> to achieve the subcritical condition<\/strong>. The control rods must weigh more than 2500pcm plus the value of SDM<\/strong> (SHUTDOWN MARGIN) to ensure the safe subcritical condition<\/strong>. The total weight of control rods is design-specific, but, for example, it may reach about 6000 to 9000pcm. To ensure that the control rods can cause a safe shut down of the reactor<\/strong>, they must be maintained above a minimum rod height (rods insertion limits) specified in the technical specifications.<\/p>\nA distinction should be made between indicated reactor power level measured by excore neutron detectors after shutdown and the actual thermal power level. The indicated reactor power level, usually known as nuclear power<\/strong>, is the power produced directly from fission in the reactor core. Still, the actual thermal power<\/strong> drops more slowly due to decay heat<\/strong> production, as previously discussed. Although<\/b> approximately 5 to 6% of the steady-state reactor power before the shutdown, Decay heat diminishes to less than 1% of the pre-shutdown power level after about one hour.<\/p>\n<\/span> Thermal Power vs. Nuclear Power<\/div>In general, we have to distinguish between three types of power outputs in power reactors.<\/p>\n
\n- Nuclear Power. <\/strong>Since the thermal power produced by nuclear fissions is proportional to neutron flux level, the most important is a measurement of the neutron flux<\/strong> from the reactor safety point of view. The neutron flux is usually measured by excore neutron detectors<\/strong>, which belong to the so-called excore nuclear instrumentation system (NIS)<\/strong>. The excore nuclear instrumentation system monitors the reactor\u2019s power level by detecting neutron leakage from the reactor core. The excore nuclear instrumentation system is considered a safety system because it provides inputs to the reactor protection system<\/strong> during startup and power operation. This system is of the highest importance for reactor protection systems because changes in the neutron flux can be almost promptly recognized<\/strong>\u00a0only via this system.<\/li>\n
- Thermal Power. <\/strong>Although nuclear power<\/strong> provides a prompt response to neutron flux changes and is an irreplaceable system, it must be calibrated<\/strong>. The accurate thermal power<\/strong> of the reactor can be measured only by methods based on the\u00a0energy balance<\/strong> of the primary circuit or the energy balance of the secondary circuit. These methods provide accurate reactor power, but these methods are insufficient for safety systems. Signal inputs to these calculations are, for example, the hot leg temperature or the flow rate through the feedwater system, and these signals change\u00a0very slowly<\/strong>\u00a0with neutron power\u00a0changes.<\/li>\n
- Electrical Power. <\/strong>Electric power is the rate at which electrical energy is generated by the generator. For example, for a typical nuclear reactor with thermal power of 3000 MWth<\/strong>, about ~1000MWe of electrical power is generated in the generator.<\/li>\n<\/ul>\n<\/div><\/div><\/div>\n<\/div>\n
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<\/span>References:<\/div>Nuclear and Reactor Physics:<\/strong>\n\n- J. R. Lamarsh, Introduction to Nuclear Reactor Theory, 2nd ed., Addison-Wesley, Reading,\u00a0MA (1983).<\/li>\n
- J. R. Lamarsh, A. J. Baratta, Introduction to Nuclear Engineering, 3d ed., Prentice-Hall, 2001, ISBN: 0-201-82498-1.<\/li>\n
- W. M. Stacey, Nuclear Reactor Physics, John Wiley & Sons, 2001, ISBN: 0- 471-39127-1.<\/li>\n
- Glasstone, Sesonske. Nuclear Reactor Engineering: Reactor Systems Engineering,\u00a0Springer; 4th edition, 1994, ISBN:\u00a0978-0412985317<\/li>\n
- W.S.C. Williams. Nuclear and Particle Physics. Clarendon Press; 1 edition, 1991, ISBN: 978-0198520467<\/li>\n
- G.R.Keepin. Physics of Nuclear Kinetics. Addison-Wesley Pub. Co; 1st edition, 1965<\/li>\n
- Robert Reed Burn, Introduction to Nuclear Reactor Operation, 1988.<\/li>\n
- U.S. Department of Energy, Nuclear Physics and Reactor Theory. DOE Fundamentals Handbook, Volume 1 and 2. January 1993.<\/li>\n
- Paul Reuss, Neutron Physics. EDP Sciences, 2008. ISBN: 978-2759800414.<\/li>\n<\/ol>\n
<\/strong>Advanced Reactor Physics:<\/strong><\/p>\n\n- K. O. Ott, W. A. Bezella, Introductory Nuclear Reactor Statics, American Nuclear Society, Revised edition (1989), 1989, ISBN: 0-894-48033-2.<\/li>\n
- K. O. Ott, R. J. Neuhold, Introductory Nuclear Reactor Dynamics, American Nuclear Society, 1985, ISBN: 0-894-48029-4.<\/li>\n
- D. L. Hetrick, Dynamics of Nuclear Reactors, American Nuclear Society, 1993, ISBN: 0-894-48453-2.\u00a0<\/span><\/li>\n
- 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>