05000339/LER-2006-001
| Respond To, The Information Collection. | |
| Event date: | 1-6-2006 |
|---|---|
| Report date: | 01-09-2007 |
| 3392006001R00 - NRC Website | |
FACILITY NAME (1) DOCKET LER NUMBER (6) PAGE (3) 1.0 DESCRIPTION OF THE EVENT On November 16, 2006, at 0226 hours0.00262 days <br />0.0628 hours <br />3.736772e-4 weeks <br />8.5993e-5 months <br /> with Unit 2 operating at 100 percent power an automatic reactor trip occurred. The initiating signal was the "B" steam generator (SG) (EIIS System AB, Component SG) low level coincident with a steam flow greater than feed flow mismatch caused by closure of the "B" main feed regulating valve (MFRV) (EIIS System SJ, Component FCV). This resulted in a reactor and turbine trip.
Control Room personnel responded to the event in accordance with emergency procedure E-0, Reactor Trip or Safety Injection. Control Room personnel stabilized the plant using ES-0.1 Reactor Trip recovery. Initially, Reactor Coolant System (RCS) (EllS System AB) pressure and temperature decreased to approximately 1950 psig and 544 degrees Fahrenheit. Subsequently, RCS pressure and temperature returned to their normal programmed values.
Following the reactor trip the Reactor Protection System (RPS) and all Engineered Safety Feature Actuation System (ESFAS) (EIIS System JE) equipment responded as designed including proper operation of AMSAC, and the Auxiliary Feedwater System (AFW) (EIIS System BA). No other major equipment issues were noted.
At 0357 hours0.00413 days <br />0.0992 hours <br />5.902778e-4 weeks <br />1.358385e-4 months <br /> a 4 hour4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> Non-Emergency Report was made to the NRC in accordance with 10 CFR 50.72 (b)(2)(iv)(B) for an event causing actuation of the Reactor Protection System when the reactor is critical. An 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> Non-Emergency Report was also made to the NRC in accordance with 10 CFR 50.72 (b)(3)(iv)(A) for an event causing actuation of the Auxiliary Feedwater System.
2.0 SIGNIFICANT SAFETY CONSEQUENCES AND IMPLICATIONS This event posed no significant safety implications because the RPS and ESFAS systems functioned as designed following the reactor trip. Therefore, the health and safety of the public were not affected by this event.
This event is reportable pursuant to 10 CFR 50.73 (a)(2)(iv)(A) for a condition that resulted in an automatic actuation of any engineered safety feature including the reactor protection system.
3.0 CAUSE Cause of the automatic reactor trip was the "B" SG low level coincident with a steam flow greater than feed flow mismatch. The initiating signal was caused by closure of the "B" MFRV. Closure of the "B" MFRV was the result of a failed isolator card that provides steam flow input to the "B" SG water level control circuit. The isolator card failure (i.e., de energized) was determined to be a failure of one or more transistors in the power supply FACILITY NAME (1) DOCKET LER NUMBER (6) circuit of the card. The root cause of the transistor failure is age-related degradation.
Investigation determined that the failed card was installed in 1977 and had only been periodically calibrated and not undergone any repair or refurbishment during that time.
The improvements in failure rate since 1993 combined with the lack of a clear industry standard or Westinghouse Guideline for 7300 System Printed Circuit Board (PCB) expected life led to PCBs remaining in service without replacement or refurbishment unless a failure occurred.
The extent of condition applies to those 7300 system PCBs that have exceeded the 15 year recommended life expectancy stated in the latest draft (dated Dec. 2006) of the 7300 System Life Cycle Management Planning Sourcebook. The extent of cause applies to PCBs in all systems, which currently do not have a replacement/refurbishment strategy.
A review of history shows no other failures of this isolator card have occurred and therefore this event is not considered a repeat. A reactor trip of Unit 2 that occurred in March 2003 was attributed to a fuse failure in the driver card, which caused the "C" Main Feedwater Control Valve to close. The corrective actions from that event focused solely on the driver cards. At that time fuses were inspected on both units with repairs made to several cards.
4.0 IMMEDIATE CORRECTIVE ACTION(S) Control Room personnel responded to the event in accordance with emergency procedure E-0, Reactor Trip or Safety Injection. Control Room personnel stabilized the plant using ES-0.1 Reactor Trip Recovery. All safety systems responded appropriately. The unit was stabilized at no-load conditions, the Main Feedwater System was placed in service to all three S/Gs and the AFW System secured and returned to normal AUTO/Standby alignment. Subsequently, Control Room personnel transitioned to 2-0P-1.5 in preparation for unit re-start.
5.0 ADDITIONAL CORRECTIVE ACTIONS The "B" MFRV failed isolator card was replaced and a successful functional test was performed. Unit 2 entered Mode 1 at 0336 hours0.00389 days <br />0.0933 hours <br />5.555556e-4 weeks <br />1.27848e-4 months <br /> on November 17, 2006. Unit 2 achieved 100 percent power at 0143 hours0.00166 days <br />0.0397 hours <br />2.364418e-4 weeks <br />5.44115e-5 months <br /> on November 18, 2006.
6.0 ACTIONS TO PREVENT RECURRENCE The root cause evaluation determined a need to develop a replacement/refurbishment strategy for 7300 System PCBs in "critical" control loops, including work scope for the 2007 refueling outages, for PCBs that are 15 years or older. Also, to develop a systematic replacement/refurbishment strategy for the remaining 7300 PCB applications. Preventive Maintenance procedures are being established to ensure reliable system performance of FACILITY NAME (1) DOCKET LER NUMBER (6) PAGE (3) the 7300 Process Protection & Control System equipment based on Industry Best Practices.
7.0 SIMILAR EVENTS LER N2-03-001-00 dated 03/31/03, documents an automatic reactor trip from "C" steam generator low level coincident with a steam flow greater than feed flow mismatch caused by closure of the "C" MFRV. Closure of the "C" MFRV was the result of a failed driver card in the SG water level control system for "C" SG. The driver card failed as a result of a blown fuse. The corrective actions from this event focused solely on the driver cards.
Fuses were inspected on both units with repairs made to several cards.
8.0 ADDITIONAL INFORMATION At the time of this event Unit 1 was in Mode 3 preparing for re-start following a mid-cycle outage.
Component information:
Description:
8 Isolator Card Mark No. 02-MS-FM-2484A Manufacturer: Westinghouse W893 Model No.:
8 2837Al2G03 Serial No.:
8 89489