05000457/LER-2015-002
| Braidwood Station, Unit 2 | |
| Event date: | 10-05-2015 |
|---|---|
| Report date: | 12-04-2015 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| Initial Reporting | |
| ENS 51450 | 10 CFR 50.72(b)(3)(iv)(A), System Actuation |
| 4572015002R00 - NRC Website | |
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A. Plant Operating Conditions Before the Event:
Event Date:
October 5, 2015 Unit: 2 Mode: 3 Reactor Power: 000 percent Unit 2 Reactor Coolant System [AB]: Temperature: 532 degrees F, Pressure: 1927 psig No structures, systems or components were inoperable at the start of this event that contributed to the event.
B. Description of Event:
NOTE: During normal operation, feedwater (FW) [SJ] to the steam generators is provided by two turbine-driven FW pumps. During plant shutdown, feedwater is normally transferred to a startup FW pump, or alternately, a motor- driven FW pump. The startup FW pump is the preferred pump at operation below 15% power to provide better steam generator level control.
On October 4, 2015 at 2317 hours0.0268 days <br />0.644 hours <br />0.00383 weeks <br />8.816185e-4 months <br />, during the planned Unit 2 down power for entry into a refueling outage the start- up FW pump failed to start. As a result, the motor driven FW pump (MDFWP) was used to supply FW to the steam generators for decay heat removal and cooldown.
On October 5, 2015 at 0038 hours4.398148e-4 days <br />0.0106 hours <br />6.283069e-5 weeks <br />1.4459e-5 months <br />, with the unit in Mode 3, MDFWP high journal bearing temperatures exceeded limits, and the pump was manually secured. To maintain steam generator levels, the operating crew initially attempted to use condensate booster [SD] pumps as a feedwater source, followed by initiating actions to manually start auxiliary feedwater (AF) [BA].
At 0105 hours0.00122 days <br />0.0292 hours <br />1.736111e-4 weeks <br />3.99525e-5 months <br />, the 2C steam generator low level reactor trip/AF actuation (Lo-2) level setpoint of 36.3 percent was reached, resulting in an auto actuation of both trains of the AF system and an automatic reactor trip signal. The reactor trip system functioned as expected. There were no issues following the auto initiation of AF. This condition is being reported in accordance with 10CFR50.73(a)(2)(iv)(A), any event or condition that resulted in the manual or automatic actuation of the reactor protection system (RPS) with the reactor not critical, and an automatic actuation of the auxiliary feedwater system. This LER is being submitted in follow-up to NRC Event Notification (ENS) 51450 made on October 5, 2015.
C. Cause of Event
The auto actuation of the AF pumps was due to the startup FW pump failing to start on demand and the MDFWP not operating within procedural prescribed bearing temperature limits at reduced flow.
The cause of the failure of the startup FW pump to start was due to a pump starting interlock not making up. For the MDFWP, subsequent to the event it was determined that the elevated bearing temperatures observed were normal for the conditions the pump was operated.
D. Safety Consequences:
This condition had no actual safety consequences impacting plant or public safety. The AF pumps started and supplied water to the steam generators as expected on a Lo-2 steam generator level.
Normal FW flow is not required to support design basis accidents. Loss of normal FW flow is a postulated design basis accident, which results in actuation of the AF system. The AF system was available and automatically actuated as required to support the loss of normal feedwater. Therefore there was no loss of safety function due to this event.
E. Corrective Actions:
Corrective action planned — For the startup FW pump, a post-maintenance test will be created to perform an interlock check following maintenance of the startup FW pump.
Corrective action completed — For the MDFWP, the procedure requirement to secure the pump was revised to incorporate revised bearing temperatures.
F. Previous Occurrences:
There have been no previous Licensee Event Reports at Braidwood on this issue.
G. Component Failure Data:
Manufacturer Nomenclature Model Mfg. Part Number Pacific Pumps Div. Dresser Start-up Feedwater Pump 10 X 19 XS HVC N/A