05000280/LER-2015-003
| Surry Power Station, Unit 1 | |
| Event date: | 10-13-2015 |
|---|---|
| Report date: | 12-11-2015 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 2802015003R00 - NRC Website | |
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1.0 DESCRIPTION OF THE EVENT On October 13, 2015 at 1815 hours0.021 days <br />0.504 hours <br />0.003 weeks <br />6.906075e-4 months <br />, with Unit 1 at 100 percent power and Unit 2 at 93.5 percent power at the end of life coastdown, Unit 1 experienced a reactor trip initiated from a turbine trip by main generator trip. The main generator trip was due to a loss of the main generator field [EIIS-TB] that caused a loss of field protection relay to trip.
Automatic systems responded to the reactor/turbine trip as designed. All three auxiliary feedwater (AFW) pumps [EIIS-BA-P] automatically initiated on low-low steam generator (SG) water level providing flow to the SGs [EI1S-AB-SG]. Following the reactor trip, reactor coolant system (RCS) temperature fell below the nominal temperature of 547 degrees Fahrenheit and reached a minimum of 542 degrees Fahrenheit. The lower temperature was due to the expected opening of at least one SG power operated relief valve (PORV) [EIIS-AB-RV], injection of AFW flow, valve alignment of gland steam being supplied by main steam versus auxiliary steam and leakby of a moisture separator reheater steam supply control valve [EIIS-SB-FCV]. Due to the primary cooldown, the main steam trip valves [EIIS-SB-ISV] were closed at 1836 hours0.0213 days <br />0.51 hours <br />0.00304 weeks <br />6.98598e-4 months <br /> as directed by emergency operating procedures and the plant was stabilized using SG PORVs. AFW was subsequently secured by procedural guidance and Unit 1 was placed in hot shutdown using normal operating procedures.
At 2120 hours0.0245 days <br />0.589 hours <br />0.00351 weeks <br />8.0666e-4 months <br />, a four-hour report was made pursuant to 10CFR50.72(b)(2)(iv)(B) due to valid automatic actuation of Reactor Protection Systems and an eight-hour report was made pursuant to 10CFR50.72(b)(3)(iv)(A) due to automatic actuation of the AFW system.
This report is being submitted pursuant to 10CFR50.73(a)(2)(iv)(A) as an event that resulted in the automatic actuation of the Reactor Protection System and the AFW system.
2.0 SIGNIFICANT SAFETY CONSEQUENCES AND IMPLICATIONS This event resulted in no safety consequences or implications. There was no testing or surveillances in progress when the reactor trip occurred. Appropriate operator actions were taken in accordance with emergency operating procedures and the unit was quickly brought to a stable condition. Station equipment relied upon to mitigate the event responded as designed. Therefore, the health and safety of the public were not affected.
Surry Power Station 05000 - 280 3.0 CAUSE The direct cause of the loss of main generator field of the Unit 1 generator was an electrical fault in the main generator exciter spacer coupling. Disassembly of the generator exciter found damage to the electrical connections between the exciter, spacer coupling and generator. The electrical fault was caused by a poor connection between one of the main generator exciter coupling butterfly leads and axial lead. The poor connection was due to a deficiency in the assembly process when the connection was last assembled during a refueling outage in May 2015.
4.0 IMMEDIATE CORRECTIVE ACTION(S) Following the reactor trip, control room operators acted promptly to place the unit in a safe, shutdown condition in accordance with emergency operating procedures.
5.0 ADDITIONAL CORRECTIVE ACTIONS A root cause evaluation (RCE) team was assembled to determine the cause of this event and to recommend corrective actions. The leakby of the moisture separator reheater steam supply control valve has been repaired and Engineering is evaluating the valve alignment of gland steam being supplied by main steam versus auxiliary steam.
6.0 ACTIONS TO PREVENT RECURRENCE Additional corrective actions to prevent deficiencies during the assembly process will be identified when the RCE is completed and will be implemented through the corrective action program.
7.0 SIMILAR EVENTS None 8.0 MANUFACTURER/MODEL NUMBER Siemens Westinghouse/Mark III 9.0 ADDITIONAL INFORMATION Unit 2 was at 93.5 percent power at the end of life coastdown and remained unaffected by the Unit 1 reactor trip.