05000443/LER-2011-002
| Seabrook Station | |
| Event date: | 10-06-2011 |
|---|---|
| Report date: | 12-02-2011 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| Initial Reporting | |
| ENS 47327 | 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation, 10 CFR 50.72(b)(3)(iv)(A), System Actuation |
| 4432011002R00 - NRC Website | |
Description of Event
At approximately 1226 on October 6, 2011 with the plant operating in Mode 1 at 100% power, Seabrook experienced a plant trip on low steam generator [AB, SG] water levels following loss of an operating main feed pump [SJ, P]. The main feed pump tripped on low suction pressure while restoring a condensate pump [SD, P] to service following maintenance. During restoration of the pump, air entered the condensate system and caused a drop in condensate pump discharge pressure, which resulted in a low pressure condition at the suction of the main feed pump. The trip of the main feed pump on low suction pressure initiated a turbine [TA, TRB] setback; however, with reduced feedwater flow, steam generator levels decreased to the low level reactor trip setpoint. The automatic systems functioned as designed. The emergency feedwater [BA] system automatically actuated and recovered steam generator levels.
Cause of Event
The root cause of the air intrusion into the condensate system, which resulted in a trip of the main feed pump and the subsequent reactor trip, was the lack of a procedure for restoring a condensate pump to service during operation at power.
Analysis of Event
The condensate system includes three fifty percent capacity condensate pumps with two pumps in service during normal operation. Two fifty percent capacity' turbine-driven main feed pumps receive:water from the condensate system and deliver water to the steam generators. The main feed pumps are provided with an automatic trip on low suction pressure.
The plant trip occurred during restoration of a condensate pump, which had been removed from service for replacement of the rotating element. During venting of the condensate pump, air intrusion into the operating condensate pumps caused a sharp drop in discharge pressure and large flow oscillations. The pressure drop exceeded the main feed pump low suction pressure trip setpoint, and the trip of the feed pump initiated a turbine setback. In response to lowering steam generator levels as a result of the setback, the Unit Shift Supervisor directed a manual reactor trip; however, an automatic reactor trip actuated on low steam generator levels before the operators initiated a manual trip. The emergency feedwater system automatically actuated and recovered steam generator levels.
This event resulted in a valid actuation of the reactor protection system and met the reporting criteria of 10 CFR 50.72(b)(2)(iv)(B) and 10 CFR 50.72 (b)(3)(iv)(A). A four hour report was made to the NRC at approximately 1517 on October 6, 2011 (event number 47327). This event is of regulatory significance because it resulted in actuation of a system provided to mitigate the consequences of an accident. This event had no adverse impact on the plant or on the health and safety of the public because any failure in the non-safety class portion of the condensate and feedwater systems has no effect on the safety of the reactor. No inoperable structures, systems, or components contributed to this event. This condition did not involve a safety system functional failure.
Corrective Actions
The corrective action for the root cause of this event revised the operating procedure to provide instructions for filling and venting a condensate pump following maintenance.
Additional Information
The Energy Industry Identification System (EDS) codes are included in this LER in the following format: [EDS system identifier, EDS component identifier].
Similar Events while the plant was shutdown. This LER reported an actuation of the RPS on low steam generator water level as the result of a procedure deficiency.
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