05000456/FIN-2009004-04
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Finding | |
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Title | Reactor Trip Due to Trip of 2C Reactor Coolant Pump |
Description | An Unresolved Item (URI) was self-revealed when, on July 30, 2009, the Unit 2 reactor experienced an automatic reactor trip from full power due to a trip of the 2C RCP. The 2C RCP tripped on overcurrent following an automatic bus transfer due to the loss of SAT 242-1 on a SPR actuation. At 8:59 p.m. on July 30, 2009, Unit 2 received a SPR actuation on SAT 242-1. As a result, the feed breakers for SAT 242-1 and SAT 242-2 opened as designed, which de-energized the 6.9 kV Busses 258 and 259. Both busses automatically transferred to UATs 241-1 and 241-2. Following the transfer of Bus 258 to UAT 241-2, the 2C RCP, which was powered by Bus 258, tripped unexpectedly on overcurrent. This resulted in a Unit 2 reactor trip due to less than four RCPs running at greater than 30 percent reactor power. The reactor trip resulted in a turbine-generator trip that caused UATs 241-1 and 241-2 to become de-energized, which in turn caused the remaining three RCPs to trip off due to loss of power to their buses. The loss of both SATs and both UATs resulted in a loss of offsite power to all Unit 2 emergency and nonemergency electrical buses. The licensee declared an Unusual Event due to a loss of offsite power greater than 15 minutes. The condition was reported to the NRC in Event Notification 45238 in accordance with 10 CFR 50.72(a)(1)(i) for declaration of the Unusual Event, 10 CFR 50.72(b)(2)(iv)(B) due to actuation of the reactor protection system while the reactor was critical, and 10 CFR 50.72(b)(3)(iv)(A) for valid actuation of the AF system. Following the reactor trip, the 2A and 2B EDGs started and loaded 4 kV safety-related Busses 241 and 242 and the 2A and 2B AF pumps started. Since nonsafety-related equipment was not powered immediately following the reactor trip, operators were unable to use steam dump valves and the condenser for normal heat removal. Therefore, the operators used a feed & bleed method of cooling and depressurizing by pumping water into the steam generators with the AF pumps and removing the steam through steam generator power operated relief valves to the atmosphere. This process continued until the afternoon of July 31, 2009, when reactor coolant system pressure was low enough to place the RH system in the shutdown cooling mode. The Unusual Event was terminated at 12:36 a.m. on August 2, 2009, when offsite power was restored to the safety-related 4 kV busses through SAT 242-2. Initial investigations by the licensee were unable to determine the cause of the SAT 242-1 SPR actuation. Though the plant normally operates with SATs 242-1 and 242-2 tied together, each is capable of powering Unit 2 alone. Therefore, the licensee manually disconnected SAT 242-1 from SAT 242-2 and started up Unit 2 using only SAT 242-2 on August 4, 2009. Unit 2 reached full power on August 6, 2009. Further investigation by the licensee included a Root Cause Evaluation focused on why the 2C RCP unexpectedly tripped and a separate apparent cause evaluation focused on why the SPR actuated on SAT 242-1. The licensee completed both investigations but new information has raised questions about the results of the root cause evaluation. At the conclusion of the inspection period, the licensee was reviewing the new information that may impact the completed Root Cause Evaluation. Pending the results of that review, this issue will remain open as an URI. (URI 05000457/2009004-04 |
Site: | Braidwood ![]() |
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Report | IR 05000456/2009004 Section 4OA3 |
Date counted | Sep 30, 2009 (2009Q3) |
Type: | URI: |
cornerstone | Mitigating Systems |
Identified by: | Self-revealing |
Inspection Procedure: | IP 71153 |
Inspectors (proximate) | R Ng B Dickson M Mitchell B Palagi R Walton M Perry A Garmoe R Skokowski M Thorpe-Kavanaugh T Hartman J Gallj Benjamint Go M Perry A Garmoe R Skokowski C Scott S Bakhsh V Meghani C Lipa |
INPO aspect | |
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Finding - Braidwood - IR 05000456/2009004 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Braidwood) @ 2009Q3
Self-Identified List (Braidwood)
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