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During plant cooldown/depressurization in … During plant cooldown/depressurization in Mode 3, an Over Temperature (OT) Delta Temperature reactor trip signal was generated. The reactor Trip Breakers opened as designed (all rods were previously inserted). Additionally, a low Tavg/P-4 Feedwater Isolation Signal was generated and all Bypass Feedwater Regulation Valves closed (open for long-cycle recirculation operation). No Feedwater Isolation Valves were open at the time. All systems performed as designed.</br>Actual loop Delta T's (Th - Tc) never exceeded 3.3 degrees F, well below the calculated OT Delta T setpoint. But plant Delta T calculations are based on narrow range Th and Tc instruments with scaling to low limits. When actual plant temperature was lowered to the lower limits of each instrument, calculated Delta T increased to the OT Delta T setpoint causing the reactor trip signal. Existing procedure guidance did not adequately ensure that the reactor trip breakers are open prior to initiating a partial plant cooldown.</br>The plant was stabilized. The long-cycle recirculation was re-established and plant cooldown/depressurization was recommenced, as originally planned to 340 degrees F and 925 psig.</br>The licensee notified the NRC Resident Inspector.</br>* * * RETRACTION ON 11/9/2006 AT 12:19 FROM THOMAS G. PETRAK TO MARK ABRAMOVITZ * * *</br>Alvin W. Vogtle, Unit 1, Operating License no. NPF-68, Event Notification #42942 is retracted. The event reported in the notification which occurred during the Unit 1 cooldown in Mode 3 was not representative of the conditions under which the Over Temperature Delta Temperature (OTDT) setpoint is intended to operate. The setpoint is intended to provide protection while the reactor is in Modes 1 and 2. As the cooldown progressed from Normal Operating Pressure and Temperature (NOPT), eventually the Reactor Coolant System (RCS) hot and cold leg temperature indications reached the low end of their ranges or scales. Further reductions of temperature resulted in artificial indications of core power (delta-T) that cannot be relied upon as a valid input to the OTDT protective function.</br>The actuation of the Reactor Protection System (RPS) is not considered to be a valid actuation. As such, this is not reportable under 10 CFR 50.72(b)(3)(iv)(A).</br>The Unit 1 Feedwater Isolation caused from the OTDT reactor trip is not a function is listed in 10 CFR 50.72(b) (3)(iv)(B) as a system whose actuation is required to be reported under 10 CFR 50.72(b)(3)(iv)(A).</br>The licensee notified the NRC Resident Inspector.ensee notified the NRC Resident Inspector.
16:23:00, 28 October 2006 +
42,942 +
16:02:00, 28 October 2006 +
16:23:00, 28 October 2006 +
During plant cooldown/depressurization in … During plant cooldown/depressurization in Mode 3, an Over Temperature (OT) Delta Temperature reactor trip signal was generated. The reactor Trip Breakers opened as designed (all rods were previously inserted). Additionally, a low Tavg/P-4 Feedwater Isolation Signal was generated and all Bypass Feedwater Regulation Valves closed (open for long-cycle recirculation operation). No Feedwater Isolation Valves were open at the time. All systems performed as designed.</br>Actual loop Delta T's (Th - Tc) never exceeded 3.3 degrees F, well below the calculated OT Delta T setpoint. But plant Delta T calculations are based on narrow range Th and Tc instruments with scaling to low limits. When actual plant temperature was lowered to the lower limits of each instrument, calculated Delta T increased to the OT Delta T setpoint causing the reactor trip signal. Existing procedure guidance did not adequately ensure that the reactor trip breakers are open prior to initiating a partial plant cooldown.</br>The plant was stabilized. The long-cycle recirculation was re-established and plant cooldown/depressurization was recommenced, as originally planned to 340 degrees F and 925 psig.</br>The licensee notified the NRC Resident Inspector.</br>* * * RETRACTION ON 11/9/2006 AT 12:19 FROM THOMAS G. PETRAK TO MARK ABRAMOVITZ * * *</br>Alvin W. Vogtle, Unit 1, Operating License no. NPF-68, Event Notification #42942 is retracted. The event reported in the notification which occurred during the Unit 1 cooldown in Mode 3 was not representative of the conditions under which the Over Temperature Delta Temperature (OTDT) setpoint is intended to operate. The setpoint is intended to provide protection while the reactor is in Modes 1 and 2. As the cooldown progressed from Normal Operating Pressure and Temperature (NOPT), eventually the Reactor Coolant System (RCS) hot and cold leg temperature indications reached the low end of their ranges or scales. Further reductions of temperature resulted in artificial indications of core power (delta-T) that cannot be relied upon as a valid input to the OTDT protective function.</br>The actuation of the Reactor Protection System (RPS) is not considered to be a valid actuation. As such, this is not reportable under 10 CFR 50.72(b)(3)(iv)(A).</br>The Unit 1 Feedwater Isolation caused from the OTDT reactor trip is not a function is listed in 10 CFR 50.72(b) (3)(iv)(B) as a system whose actuation is required to be reported under 10 CFR 50.72(b)(3)(iv)(A).</br>The licensee notified the NRC Resident Inspector.ensee notified the NRC Resident Inspector.
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