05000316/LER-2002-007
| Donald C. Cook Nuclear Plant Unit 2 | |
| Event date: | 11-5-2002 |
|---|---|
| Report date: | 12-13-2002 |
| 3162002007R00 - NRC Website | |
Donald C. Cook Nuclear Plant Unit 2 05000-316 17. TEXT (If more space is required, use additional copies of NRC Form (366A) Conditions Prior to Event Unit 1 - Mode 1, 100 percent power Unit 2 - Mode 1, 100 percent power
Description of Event
On November 2, 2002, at 0827 hours0.00957 days <br />0.23 hours <br />0.00137 weeks <br />3.146735e-4 months <br />, the Unit 2 CD Emergency Diesel Generator (EDG) was declared inoperable and Technical Specification (TS) 3.8.1.1, Action "b", was entered in preparation for routine surveillance testing in accordance with TS 4.8.1.1.2.a.5.
During the test, approximately 10 minutes after the EDG reached full load of 3500 kilowatts (kW), the Unit 2 CD EDG load began oscillating approximately 150 kW. Load on the Unit 2 CD EDG was reduced to approximately 2500 kW and the oscillations ceased.
Subsequently, Donald C. Cook Nuclear Plant (CNP) began maintenance activities to troubleshoot and correct the cause of the load oscillations.
CD EDG governor [EK - 65]. Following tuning, the EDG was loaded to 3500 kW. Upon reaching full load, the Unit 2 CD EDG load began oscillating approximately 200 kW.
The load was again reduced to approximately 2500 kW and the oscillations ceased. At this time, CNP determined the probable cause of the load oscillation was an equipment malfunction associated with the EDG speed control circuitry. To correct the cause of the load oscillations, CNP replaced both the electronic governing module (EGM) and the governor hydraulic actuator (EGB).
On November 3, 2002, at approximately 1108 hours0.0128 days <br />0.308 hours <br />0.00183 weeks <br />4.21594e-4 months <br />, the Unit 2 CD EDG governor EGM and EGB modules were replaced and post maintenance testing (PMT) of the new equipment was performed. The PMT activities included tuning of the new governor. During the tuning activity, the Unit 2 CD EDG speed was increased using the EGB. At approximately 2222 hours0.0257 days <br />0.617 hours <br />0.00367 weeks <br />8.45471e-4 months <br /> on November 3, 2002, the EGM was placed in service and the EDG speed began - swinging, resulting in high field amperage and voltage. The Unit 2 CD EDG was subsequently tripped.
On November 4, 2002, at approximately 0318 hours0.00368 days <br />0.0883 hours <br />5.257936e-4 weeks <br />1.20999e-4 months <br />, the EGM was replaced again and PMT testing was resumed. During preparations for paralleling the Unit 2 CD EDG to the "A" train of the 4 kV distribution system to perform a full load test, a 1-ampere fuse opened in the EDG synchronizing circuit and the EDG test was terminated at 0942 hours0.0109 days <br />0.262 hours <br />0.00156 weeks <br />3.58431e-4 months <br /> on November 4, 2002. Additionally, the synchronizing circuitry is not necessary for the EDG to perform it's safety function. Upon returning the Unit 2 CD EDG to full load, the load began oscillating approximately 500 kW. Additionally, hydraulic CD EDG was tripped at 1749 hours0.0202 days <br />0.486 hours <br />0.00289 weeks <br />6.654945e-4 months <br /> on November 4, 2002. The cause of the failure of the newly installed EGB is under investigation.
17. TEXT (if more space is required, use additional copies of NRC Form (366A) On November 4, 2002, at 2007 hours0.0232 days <br />0.558 hours <br />0.00332 weeks <br />7.636635e-4 months <br />, CNP contacted the NRC to request enforcement discretion to preclude entry into MODE 3 for Unit 2 at 1427 hours0.0165 days <br />0.396 hours <br />0.00236 weeks <br />5.429735e-4 months <br /> on November 5, 2002.
To accomplish this, CNP requested that the Unit 2 72-hour allowed outage time for TS 3.8.1.1, Action "b", be extended by an additional 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. At 2235 hours0.0259 days <br />0.621 hours <br />0.0037 weeks <br />8.504175e-4 months <br /> on November 4, 2002, CNP was granted enforcement discretion.
On November 5, 2002, a 1-ampere fuse and the original EGB were installed and PMT was resumed at approximately 1126 hours0.013 days <br />0.313 hours <br />0.00186 weeks <br />4.28443e-4 months <br />. The Unit 2 CD EDG load was again raised to 3500 kW and remained stable. PMT and operability testing were satisfactorily completed at 2159 hours0.025 days <br />0.6 hours <br />0.00357 weeks <br />8.214995e-4 months <br /> on November 5, 2002, and the Unit 2 CD EDG was declared "available.
On November 6, 2002, at 0049 hours5.671296e-4 days <br />0.0136 hours <br />8.101852e-5 weeks <br />1.86445e-5 months <br /> the Unit 2 CD EDG was declared "operable," and TS 3.8.1.1, Action "b" was exited. The Unit 2 CD EDG was inoperable for approximately 88 hours0.00102 days <br />0.0244 hours <br />1.455026e-4 weeks <br />3.3484e-5 months <br />.
Because the amount of time required to correct this condition exceeded the 72-hour allowed outage time requirements of TS 3.8.1.1, Action "b", this condition is reportable in accordance with 50.73(a)(2)(i)(B).
Cause of Event` CNP is conducting a formal root cause investigation into the failure of the Unit 2 CD EDG governor. This root cause investigation is ongoing, and includes hardware failure analysis at the vendor facility. CNP has completed an apparent cause evaluation and concluded the probable cause of the surveillance test failure was failure of the EGM.
Unforeseen difficulties were experienced during the governor replacement and associated post-maintenance testing. These difficulties included an apparent failure of the replacement (EGM and EGB), failure of a 1-ampere fuse in the EDG synchronizing circuitry, and the associated post-installation governor tuning activities. The results of these difficulties required greater time than that provided for in the allowed outage time requirements of TS 3.8.1.1, Action "b".
In accordance with the guidance established in NUREG-1022, Revision 2, "Event Reporting Guidelines," Part 5.1.5, "Supplemental Information and Revised LERs", CNP will issue a supplement to this LER if the final root cause determination for this event differs significantly from the apparent cause.
Analysis of Event
The EDGs provide an automatic onsite source of emergency power for accident mitigation and safe shutdown in the event normal offsite power is lost. At the time of the event, normal offsite power was available and no adverse weather or system outages that could affect its availability were anticipated. Further, the redundant Unit 2 AB EDG was operable.
17. TEXT (If more space is required, use additional copies of NRC Form (366A) CNP performed an evaluation using the updated 2001 CNP probabilistic risk assessment model. The results of the evaluation indicated there was no net increase in risk due to operating the plant for an additional 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> with the Unit 2 CD EDG unavailable when compared with the risk associated with a plant shutdown. A detailed discussion of the analysis is contained in letter AEP:NRC:2016-04, "Request For Notice Of Enforcement Discretion From Technical Specification 3.8.1.1 Limiting Condition for Operation for the CD Emergency Diesel Generator," dated November 6, 2002. CNP concluded that no act was taken or condition established that presented a common-mode failure threat to the redundant Unit 2 AB EDG. This conclusion was based on the fact that no maintenance or testing common to both the Unit 2 AB and CD EDGs was performed and no other common work activity in the vicinity of the Unit 2 AB and CD EDG speed regulators was performed. In addition, the Unit 2 AB and CD EDG EGMs were not installed at the same time.
Corrective Actions
The Unit 2 CD EDG governor was replaced, tested, and declared operable.
CNP is conducting a formal root cause investigation into the failure of the Unit 2 CD EDG governor. This root cause investigation is ongoing, and includes hardware failure analysis at the vendor facility.
Previous Similar Events
temperature during battery equalizing charge.
CNP has reviewed the corrective actions associated with the above LERs and determined that the corrective actions implemented could not have prevented the occurrence of this event.