05000315/LER-2011-002
| Donald C. Cook Nuclear Plant Unit 1 | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| Initial Reporting | |
| ENS 47477 | 10 CFR 50.72(b)(3)(iv)(A), System Actuation |
| 3152011002R00 - NRC Website | |
Conditions Prior to Event 100 percent reactor power.
Description of Event
On November 25, 2011, at 0517 hours0.00598 days <br />0.144 hours <br />8.54828e-4 weeks <br />1.967185e-4 months <br />, in response to rising vibrations of the Unit 1 East Main Feedwater Pump (MFP)[SJ][P], Donald C. Cook Nuclear Plant (CNP) control room operators initiated the Rapid Power Reduction Procedure in an effort to quickly lower power to remove the East MFP from service. At 0522 hours0.00604 days <br />0.145 hours <br />8.630952e-4 weeks <br />1.98621e-4 months <br />, operators tripped the East MFP due to rapidly rising vibrations and entered the procedure for Loss of One Main Feed Pump, which directs manually starting Auxiliary Feedwater (AFW) pumps [BA], as required. Operators manually started both Motor Driven AFW Pumps and the Turbine Driven AFW Pump. Power was lowered and stabilized at approximately 58 percent.
Manually starting the AFW Pumps in response to actual plant conditions resulting from equipment failure was reported in accordance with 10 CFR 50.72(b)(3)(iv)(A), Event Notification 47477, submitted on November 25, 2011. The event is also reportable as a Licensee Event Report (LER) in accordance with 10 CFR 50.73(a)(2)(iv)(A).
Cause of Event
The Unit 1 East MFP was removed from service due to high vibrations.
The East MFP was found with a cracked turbine [TRB] rotor shaft during initial inspection.
A Root Cause Evaluation (RCE) was commenced regarding the high vibrations and is in progress. If the RCE results conclude substantially different information than reported, then a supplement to this LER will be submitted.
Analysis of Event
Manually starting the Unit 1 AFW Pumps as part of a procedurally-directed action in response to the loss of one main feed pump is a conservative action to assure that feedwater is maintained to the unit's Steam Generators (SGs) [TB] when main feedwater flow has been significantly reduced while reducing reactor and turbine power. This action does not disable any equipment, nor does it adversely affect mitigation of any plant events. In the event a reactor trip was not avoided, the AFW Pumps were already operating, avoiding dependence on automatic actuation circuitry to provide AFW to the SGs. Thus, manually starting AFW Pumps reduces risk during an event where main feedwater flow may be challenged by removing reliance on automatic actuation to start the AFW Pumps via the additional operator direction to start AFW Pumps as required" based on operator judgment.
Corrective Actions
Completed Corrective Actions
The Unit 1 East MFP turbine rotor and coupling [CPLG] were replaced. The Unit 1 East MFP was returned to service on December 4, 2011.
Planned Corrective Actions
None.
Previous Similar Events
LERs for both CNP Unit 1 and Unit 2 for the past three years were reviewed for similar events related to 10 CFR 50.73(a)(2)(iv)(A) reporting criteria for system actuation. The following were identified:
05000315-2010-003-00, Manual AFW Actuation in Response to Manual MFP Trip On December 13, 2010, at 2117 hours0.0245 days <br />0.588 hours <br />0.0035 weeks <br />8.055185e-4 months <br />, the Unit 1 East MFP was manually tripped as condenser [CONE)] vacuum lowered toward the low vacuum setpoint due to debris intrusion within the lake cooling water side of the MFP condenser. All three AFW pumps were manually started when the East MFP was required to be removed from service.
05000315-2010-002-00, Manual AFW Actuation in Response to MFP Failure On May 2, 2010, at 0855 hours0.0099 days <br />0.238 hours <br />0.00141 weeks <br />3.253275e-4 months <br />, the Unit 1 East MFP was removed from service quickly due to failure of a bearing. All three AFW pumps were manually started when the East MFP was required to be removed from service.