05000316/LER-2009-001
| Donald C. Cook Nuclear Plant | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 3162009001R01 - NRC Website | |
Conditions Prior to Event 100 percent reactor power
Description of Event
Control Room Operators performed a manual Reactor [RCT] trip in response to a malfunctioning reactor coolant pump (RCP) [P] seal [SEAL]. All control rods [AA] fully inserted and the auxiliary feedwater system (AFW) [BA] started and performed as designed; this included the East and West AFW pumps and the turbine driven AFW pump.
No structures, systems, or components'were inoperable at the start of the event and contributed to the event.
The event commenced on July 26, 2009, at 1458 hours0.0169 days <br />0.405 hours <br />0.00241 weeks <br />5.54769e-4 months <br /> when Control Room Operators received the annunciator [ANN] for RCP 22 Seal 1 Leakoff Flow Low. At this time, the low range seal leakoff flow indicated 0.90 gpm and lowering. Based on the low seal leakoff flow, the annunciator response procedure directed the operators to the RCP malfunction procedure.
The RCP malfunction procedure requires removing the RCP from service when seal leakoff flow is less than 1.0 gallon per minute (gpm) and temperature is continuously rising on either the lower bearing water or on the Number 1 seal leakoff. With the seal leakoff flow of 0.81 gpm and lowering, the lower bearing water temperature was 167 degrees Fahrenheit and rising, and the Number 1, seal leakoff temperature was 178 degrees Fahrenheit and rising.
With the criteria met to remove the malfunctioning RCP from service, control room operators performed the following actions in accordance with the RCP malfunction procedure:
- reactor was manually tripped - entered procedure for reactor trip or safety injection - 22 RCP was tripped The reactor trip was uncomplicated and all major plant components functioned as designed; as such, there were no safety system functional failures. The reactor trip was reported in accordance with 10 CFR 50.72(b)(2)(iv)(B). The AFW actuation was reported in accordance with 10 CFR 50.72(b)(3)(iv)(A). The report text inadvertently referenced an automatic reactor protection system actuation rather than the engineered safety feature actuation when discussing the AFW pump starts. The reactor trip and AFW actuation are reportable as a Licensee Event Report (LER) in accordance with 10 CFR 50.73(a)(2)(iv)(A).
This LER supplement is being submitted to include information related to the completed root cause evaluation. It replaces the previous LER in its entirety.
Cause of Event
The immediate cause of the trip was manual actuation due to a malfunctioning RCP seal. The root cause of the lowering RCP 22 seal leakoff flow was a failure by the station to recognize that a buildup of normal corrosion products had the potential to enter the seal, causing seal failure.T Corrosion products present in the RCP seal area accumulated and bound the mating surface of the double-delta seal to the Number. 1 insert.T This binding eliminated the necessary tolerance for axial movement,T seizing the Number 1 seal and causing the loss of seal leakoff flow.
The RCP seal had been in service since the March 2009 refueling outage.
Analysis of Event
No Probabilistic Risk Assessment study was generated as no risk significant equipment failures posed elevated risk. It is recognized that there was an RCP seal malfunction, but the malfunction affected the seal by closing it off and preventing significant leak-off past the seal face.
Based on review of the control room log and Plant Process Computer (PPC) information, along with the post-trip review, from which the information above was obtained, all plant systems performed as designed to shut down the unit and remove decay heat following the July 26, 2009, trip and the event did not represent a significant risk. No risk-significant equipment functions were affected/failed and no significant operator actions outside those required for normal trips were required.
Corrective Actions
The RCP 22 seal assembly was inspected and replaced.
The RCP 21 seal assembly was inspected and replaced.
A comprehensive plan has been developed and will be implemented for flushing the RCP seal components.
Previous Similar Events
LERs for both units for the past three years were reviewed for similar events.
While there have been reactor trips, none have been manual reactor trips which were performed as a result of RCP malfunction.