05000281/LER-2015-002
| Surry Power Station, Unit 2 | |
| Event date: | 09-16-2015 |
|---|---|
| Report date: | 11-04-2015 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 2812015002R00 - NRC Website | |
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1.0 DESCRIPTION OF THE EVENT The purpose of the Emergency Bus Undervoltage and Degraded Voltage Protection Test is to provide quarterly testing of undervoltage and degraded voltage protection schemes of the emergency bus trains as required by Surry Technical Specifications.
The Undervoltage Protection Channels consist of three individual single phase relays [EIIS-ED-RLY]. These relays provide input to a two out of three coincident relay logic for operation. One of the functions of the undervoltage circuits is to sense a loss of voltage condition and place the respective emergency bus on the Emergency Diesel Generator (EDG) [EIIS-EK-DG].
On September 16, 2015, at 2014 hours0.0233 days <br />0.559 hours <br />0.00333 weeks <br />7.66327e-4 months <br /> with Units 1 and 2 operating at 100 percent power, an undervoltage signal was generated during performance of the Emergency Bus Undervoltage and Degraded Voltage Protection Test. As a result, EDG 2 started and loaded as designed on the Unit 2 'H' emergency bus.
During performance of the test, the 'A' phase undervoltage portion of the test was successfully completed and an indication light verified that 'A' phase was left in its normal energized condition. At 2014 hours0.0233 days <br />0.559 hours <br />0.00333 weeks <br />7.66327e-4 months <br />, when testing of the 'B' phase began, a undervoltage signal was generated and EDG 2 started and assumed the load of the Unit 2 'H' emergency bus. The test was terminated and operations initiated the abnormal procedure for loss of the Unit 2 'H' emergency bus. At 2216 hours0.0256 days <br />0.616 hours <br />0.00366 weeks <br />8.43188e-4 months <br /> on September 17, 2015, normal source power was restored to the 'H' bus and EDG 2 was unloaded, taken offline and placed back in automatic at 2244 hours0.026 days <br />0.623 hours <br />0.00371 weeks <br />8.53842e-4 months <br /> on September 17, 2015.
On September 17, 2015 at 0027 hours3.125e-4 days <br />0.0075 hours <br />4.464286e-5 weeks <br />1.02735e-5 months <br />, an event notification was made to the NRC in accordance with 10 CFR 50.72(b)(3)(iv)(A) for valid actuation of EDG 2 following loss of the Unit 2 'H' emergency bus during performance of the Emergency Bus Undervoltage and Degraded Protection Test.
This report is being submitted, pursuant to, 10 CFR 50.73(a)(2)(iv)(A), for automatic actuation of the EDG.
2.0 SIGNIFICANT SAFETY CONSEQUENCES AND IMPLICATIONS This event resulted in no safety consequences or implications. Appropriate operator actions were taken in accordance with abnormal operating procedures and the unit remained at 100 percent power. Station equipment was available and responded as designed. Therefore, the health and safety of the public were not affected.
Surry Power Station 05000 - 281 3.0 CAUSE Troubleshooting determined that upon completion of the 'A' phase undervoltage test, the 'A' single phase relay did not reset. However, an indication light verified that 'A' phase was in its normal powered condition. Therefore, when the 'B' phase undervoltage test began and the 'B' phase relay was deenergized, the two out of three coincident logic was met resulting in the normal power supply breaker to the 'H' bus to open, as designed. EDG 2 started and loaded as designed on the Unit 2 'H' emergency bus.
The direct cause of the `A' single phase relay not resetting was debris and warping in the relay slug chamber and signs of heat damage. These conditions prevented smooth movement of the relay slug in the chamber and resulted in it sticking and preventing the relay contacts from changing state.
The apparent cause of the undervoltage signal and resultant loss of the Unit 2 'H' emergency bus was a procedural deficiency that relied upon a light indication of power to the relay but did not verify the position of the relay after each step of the undervoltage test.
4.0 IMMEDIATE CORRECTIVE ACTION(S) Normal offsite power was restored to the 'H' bus at 2216 hours0.0256 days <br />0.616 hours <br />0.00366 weeks <br />8.43188e-4 months <br /> on September 17, 2015 and EDG 2 was unloaded, taken offline and placed back in automatic. The failed relay was replaced.
6.0 ADDITIONAL CORRECTIVE ACTIONS An apparent cause evaluation was completed to investigate the event.
6.0 ACTIONS TO PREVENT RECURRENCE The procedures for Emergency Bus Undervoltage and Degraded Voltage Protection Tests have been revised to physically validate the state of the emergency bus relays to ensure the two out of three logics will not be satisfied if a relay fails to energize.
7.0 SIMILAR EVENTS None 8.0 MANUFACTURER/MODEL NUMBER Westinghouse/ARD44OUR 9.0 ADDITIONAL INFORMATION Unit 1 was at 100% power and remained unaffected by the starting of EDG 2.