Station blackout at Browns Ferry Unit One - Oak Ridge National ...

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32 Room. Also, Using a portable self-powered potentiometer, station person nel can monitor local pressure suppression chamber and drywell tempera tures which are sensed by installed thermocouple elements. Following the restoration of normal AC power, either by recovery of the offsite power sources or by the delayed but finally successful loading of the onsite diesel-generators, the Instrumentation and Control buses would be re-energized, restoring all normal Control Room instrumentation for use in monitoring the normal recovery.
33 6. OPERATOR ACTIONS DURING STATION BLACKOUT AND NORMAL RECOVERY In the event of a Station Blackout, the immediate result would be a turbine trip, reactor scram, and Main Steam Isolation Valve (MSIV) clo sure, which would all occur automatically with no operator action; the re actor would be shut down and isolated behind the closed MSIVs within 30 seconds following the initiating loss of offsite power. Immediately fol lowing the isolation, the reactor vessel pressure would increase to the setpoints of as many relief valves as are required to terminate the pres sure increase. The affected relief valves would open to pass steam di rectly from the reactor vessel to a terminus beneath the water level in the pressure suppression pool so that the released steam is condensed. The core water void collapse caused by both the scram and the pres sure increase following MSIV closure would result in a rapid drop in re actor vessel water level to some point below the lower limit of level in dication available in the Control Room under Station Blackout conditions [13.41 m (528 in.) above vessel zero]. Standard Browns Ferry Emergency Operating Instructions for immediate action following reactor scram and MSIV closure call for the operator to manually initiate both the HPCI and the RCIC systems. The combined injection flow of 0.353 m3/s (5600 GPM) would rapidly restore the level into the indicating range and the operator would secure the HPCI system when the indicated level reached a point equivalent to about 13.72 m (540 in.) above vessel zero. The level would then continue to increase due to the remaining 0.038 m /s (600 GPM) of RCIC system flow and the heatup and expansion of the injected water, but at a slower rate. For pressure control, standard procedure is for the operator to remote-manually operate the primary relief valves as necessary to cycle the reactor vessel pressure between 7.69 and 6.31 MPa (1100 and 900 psig). This prevents the automatic actuation of the relief valves [lowest setpoint: 7.72 MPa (1105 psig)], and since the pressure reduction following automatic actuation is only 0.34 MPa (50 psi), greatly reduces the total number of relief valve actuations. The purpose is to decrease the oppor tunity for a relief valve to stick open, and to allow the operator to al ternate the relief valves which are in effect passing the decay heat energy to the pressure suppression pool; this more evenly distributes the pool heatup. Throughout the period of Station Blackout, the operator would operate the RCIC system intermittently as necessary to maintain the reactor vessel level in the indicating range, i.e., between 13.41 and 14.94 m (528 and 588 in.) above vessel zero. Thus, it is expected that the operator would turn on the RCIC system at an indicated level of about 13.61 m (538 in.) and turn the system off at about 14.68 m (578 in.). The periods of RCIC system operation would become less frequent as the decay heat intensity subsides during a prolonged Station Blackout; after the first hour, the operator would find it necessary to run the RCIC system for only about one-third of the time. This is illustrated in Sect. 7. As previously discussed, the operator would control reactor vessel pressure by remote-manual operation of the relief valves. It is important that the operator take action to begin to lower the reactor vessel pres sure to about 0.79 MPa (100 psig) within 60 min following the inception of
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Page 17 and 18: 2. DESCRIPTION OF STATION BLACKOUT
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93 Table 9.2 Browns Ferry Nuclear P
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105 Time (sec) Event 821.5 min. Dry
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107 Time (sec) Event 3.0 Turbine tr
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123 Figure 9.12 shows the reactor v
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161 10. PLANT STATE RECOGNITION AND
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163 power, characterized by the una
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165 11. INSTRUMENTATION AVAILABLE F
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167 12. IMPLICATIONS OF RESULTS The
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169 Blackout while the unit battery
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1. Browns Ferry FSAR, Appendix F. 1
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175 33. W. G. Anderson, P. W. Huber
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177 ACKNOWLEDGEMENT Mr. William A C
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181 **$CONTINUOUS SYSTEM MODELING P
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184 * CALCULATION OF FLOW RESISTANC
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186 * TPMETO=INITIAL TEMP : SP META
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188 * RETURNS: DOWNCOMER HEIGHT!ABO
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* * * 191 INTERFACE VARIABLES : RV
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193 DUMSPG-EPSSP-t-EPHSP+EPNSP-e-EP
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197 APPENDIX B MODIFICATION TO MARC
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SNLCOOL SEND 202 INDUCE NC0B*2, NHP
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205 Appendix D PRESSURE SUPPRESSION
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SUPPRESSION CHAMBER TOROIDAL HEADER
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209 types of transients: (1) LOCA-r
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211 steam condensation oscillations
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213 originally developed for vertic
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217 APPENDIX E A COMPENDIUM OF INFO
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219 E.3 HPCI Pump Suction The HPCI
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221 E.5 Turbine Trips On an HPCI tu
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223 APPENDIX F A COMPENDIUM OF INFO
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225 normally open AC-motor-operated
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227 F.6 System Isolation The Primar
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229 APPENDIX G EFFECT OF TVA-ESTIMA
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