05000387/LER-2015-008

LER-2015-008, 1 of 4

Susquehanna Steam Electric Station Unit 1
Event date:	11-10-2015
Report date:	12-15-2015
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
3872015008R00 - NRC Website

CONDITIONS PRIOR TO THE EVENT

Unit 1 — Mode 1, 100 percent Rated Thermal Power Unit 2 — Mode 1, 100 percent Rated Thermal Power There were no systems, structures, or components that were inoperable at the start of the event and contributed to the event.

EVENT DESCRIPTION

On November 10, 2015, during the completion of an evaluation for a failed surveillance test that occurred on September 22, 2015, a condition was identified that in 2014, a degraded Reactor Protection System [EllS: JC] Electrical Protection Assembly (EPA) breaker [El IS: BKR] logic card had been installed in the Unit 1 Reactor Protection System, resulting in an unplanned inoperability of the 'A' train of the Unit 1 Reactor Protection System (RPS).

On September 22, 2015, during the performance of surveillance testing under SM-158-002 (RPS 'A' RPS, the as-found underfrequency trip setpoint for the EPA breaker (1CB-S003A-G) in the Unit 1 'A' train of the Alternate RPS power supply, could not be determined because the function did not operate at as low as approximately 40 Hertz (Hz). At approximately 40Hz, the undervoltage characteristic took over and issued the trip. The Technical Specification (TS) 3.3.8.2.2 Surveillance Requirement (SR) underfrequency allowable value is > 57 Hz. The underfrequency trip setpoint test was subsequently attempted multiple times with the same result. An attempt to calibrate the trip setpoint was also made by adjusting the underfrequency trip potentiometer. However, a trip on underfrequency was still not issued. Because the underfrequency trip setpoint was not achieved, TS 3.3.8.2.2 was not met. The overvoltage and undervoltage functions were successfully tested and remained within TS 3.3.8.2.2 SR allowable values.

At the time the TS 3.3.8.2.2 surveillance test failed on September 22, 2015, the Unit 1 Primary RPS power supply was in service and supplying power to the Unit 1 RPS bus.

INVESTIGATION

The evaluation reviewed the performance history of the 1A RPS EPA breaker 1CB-S003A-G that failed to trip on September 22, 2015. It was identified that on September 3, 2000, the Unit 2 'B' Primary RPS EPA breaker 2CB-S003BB failed to trip on underfrequency when tested. The logic card that was installed in this breaker was GE 148C6118G003, serial number 94F700-05. Post-failure analysis performed in 2000 did not identify a cause for the failure of the logic card. The logic card was subsequently returned to SSES, calibrated and tested upon receipt and returned to active spare part status.

On September 25, 2014, the logic cards in the Unit 1 1CB-S003A-E and 1CB-S003A-G RPS EPA breakers were replaced due to the as-found underfrequency setpoint being outside of the TS allowable setpoint during routine surveillance testing in 2013. The new logic card that was installed in the 1CB-S003A-G breaker was the same card GE 148C6118G003, serial number 94F700-05 that failed TS underfre uenc surveillance INVESTIGATION (cont.) testing in September 2000. Post-maintenance testing was subsequently performed on September 25, 2014 in accordance with SM 158 002, which successfully tested the underfrequency, undervoltage and overvoltage trip functions.

On December 12, 2014, due to an identified trend in underfrequency setpoints being found below the TS 3.3.8.2.2 allowable value for the RPS EPA breakers, the underfrequency setpoint tolerance was changed to accommodate vendor-specific repeatability of the setting (+1- 0.2 Hz) to ensure the circuit maintains its calibration within the TS SR 3.3.8.2.2 allowable value of > 57 Hz. This also included the 1CB-S003A-G RPS EPA breaker.

Based on the occurrence of a prior failure (on September 3, 2000) for the same logic card with the same symptoms as the failure that occurred on September 22, 2015, the SSES evaluation concluded that an inadequate parts quality existed.

REPORTABILITY

Based on the history and cause, SSES has concluded that the logic card was intermittently degraded prior to the failed surveillance on September 22, 2015. Specifically, this condition existed from the time the logic card was installed in the Unit 1 'A' train of RPS on September 25, 2014. As such, this condition existed for a period of time longer than allowed by Technical Specifications 3.3.8.2.2. As a result, this condition is being reported in accordance with 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by Technical Specifications.

CAUSE OF THE EVENT

The direct cause of the failure of the Alternate RPS 1CB-S003A-G breaker was due to an intermittently degraded circuit (logic) card.

The apparent cause of the Alternate RPS 1CB-S003A-G breaker failure was due to the installation of a poor quality spare electrical protection logic card in 2014. This component was sent to the OEM for analysis in 2000, but no failure was detected during that testing. As a result, SSES incorrectly concluded that the logic card did not contribute to the 2000 failure, and therefore, did not further investigate the cause or direct the logic card to be discarded to ensure a component with an intermittent failure mode was not returned to spare part status.

ANALYSIS/SAFETY SIGNIFICANCE

Actual consequences — There were no plant conditions which warranted an underfrequency trip during the time the logic card was installed. As such, no actual consequences to the health and safety of the public.

Potential consequences — The failure of the EPA breakers to trip could potentially compromise protection to downstream RPS equipment relating to sustained over/under voltage or underfrequency conditions.

CORRECTIVE ACTIONS

Completed —

• The failed logic card was replaced and the Unit 1 Alternate RPS EPA breaker was declared operable.

Planned —

• Evaluate diagnosis and repair results for EPA breaker logic card (GE 148C6118G003 serial number 94F700-05). Ensure that either the failure is duplicated at the test facility, repaired and confirmed to no longer have the failure or the card is discarded. If there is uncertainty regarding the effectiveness of the repair, ensure the logic card is discarded.

• Validate the quality of spare parts for GE 148C6118G003, Catalog number 0091062912 in the SSES warehouse. Ensure the stocked spare parts do not have a failure history or were conclusively repaired. If the quality cannot be validated, discard and re-stock with new parts.

PREVIOUS SIMILAR EVENTS

Setpoints Out of Calibration