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 Report dateSiteEvent description
05000446/LER-2017-00322 January 2018Comanche Peak
Comanche Peak Nuclear Power Plant, Unit 2

On November 25, 2017 Comanche Peak, Unit 2 received alarms indicating a trip of both main feedwater pumps. After confirming a decreasing water level in all four steam generators, the control room initiated a manual reactor trip. All safety systems responded as designed including the automatic start of the auxiliary feedwater system. The cause of the trip of both main feedwater pumps could not be positively identified. Causal analysis indicates that a prior plant modification maintained power to abandoned relays in the Solid State Protection System that may have caused both main feedwater pumps to trip. Subsequent actions were taken to remove the fuses that provided power to the abandoned relays on both Unit 1 and Unit 2 to eliminate recurrence from this possible source. Additional corrective actions have been entered into the Comanche Peak Corrective Action Program.

All times below are in Central Standard Time (CST).

05000446/LER-2017-00122 January 2018Comanche Peak

At 1124 Central Daylight Time on August 11, 2017, Comanche Peak Nuclear Power Plant (CPNPP) Unit 2 experienced an automatic Auxiliary Feedwater System actuation during a Turbine trip. The plant was stabilized at 3 percent reactor power with the Auxiliary Feedwater System feeding all Steam Generators with all levels within their normal bands. The cause of the Turbine trip was high water level in Steam Generator 2-02 related to the mechanical malfunction of a Steam Generator 2-02 flow control bypass valve. The valve '.

malfunctioned due to a loose locknut on the valve hand wheel. Corrective actions included repair of the Steam Generator 2-02 flow control bypass valve. All times in this report are approximate and Central Daylight Time unless noted otherwise.

05000445/LER-2016-00122 August 2016Comanche Peak

At 1005 on June 9, 2016, during routine periodic predictive maintenance thermography activities, the 'A' phase connection to the Unit 1, Train A Safety Chiller was identified to be at an elevated temperature. Inspection found three of the six electrical connections associated with the chiller to be un-torqued. Subsequent investigation found the affected connections should have been torqued on May 10, 2016 as part of restoration actions following planned preventive maintenance. On June 22, 2016 an evaluation was completed that determined the Unit 1, Train A Safety Chiller was inoperable from May 28, 2016 to June 9, 2016.

The cause of this event was the restoration and post work activities by Maintenance personnel did not ensure that the Unit 1, Train A Safety Chiller was properly configured per procedure and ready to be turned over to Operations. Corrective actions included replacing the Phase 'A' cable and dashpot relay and re-torqueing the Phase 'B' and 'C' dashpot relay terminations. The applicable procedure will be revised before the next scheduled performance to have the equipment specific thermography inspection performed as a part of the maintenance restoration/post work activities.

All times in this report are approximate and Central Time unless noted otherwise.

05000446/LER-2015-00118 September 2015Comanche Peak

On July 10, 2015 at 1304 Comanche Peak Nuclear Power Plant, Unit 2 exceeded a 72 hour limiting condition for operation (LCO), after being granted a period of enforcement discretion, due to a through-wall leak found on the "B" train of the Safety Injection (SI) system piping at the 3/4" socket weld coupling to valve 2SI-0055. The flaw resulted in declaring the "B" train of SI inoperable. This event was reportable under 10 CFR 50.73(a)(2)(i)(B) as an operation or condition which was prohibited by the plant's Technical Specifications. A Notification of Enforcement Discretion (NOED) was granted by the NRC at 0920 on July 10, 2015. The repair process issues leading to the NOED request were the requirement to apply a freeze seal to allow installation of a new vent valve to allow adequate static refill of the system and complete dye penetrant testing of the weld, ultrasonic examination of the suction piping to verify the system full of water, and pump testing to establish operability of the system. The most probable cause of the through-wall leak was determined to be an original weld defect which resulted in a stress concentration that allowed otherwise acceptable tensile loads to cause propagation of a through-wall crack. The corrective action was to grind out the weld and repair (re-weld).

This event had no adverse effect upon the health and safety of the public.

All times in this report are approximate and Central Daylight Time unless noted otherwise.

05000445/LER-2014-0023 April 2014Comanche Peak

On February 4, 2014, Luminant Power recognized Operating Experience at another station to be potentially applicable to Comanche Peak Nuclear Power Plant (CPNPP). An NRC inspection report described a failure to comply with reactor coolant system (RCS) Pressure/Temperature (P/T) Limits when RCS pressure decreases below 0 pounds per square inch gauge (PSIG). At the time of discovery, CPNPP's Pressure Temperature Limit Report (PTLR) only described pressures equal to or greater than 0 PSIG. However, since early 1996, CPNPP's analyses and procedures allowed drawing a vacuum during RCS refill following refuelings. Therefore, Luminant Power is conservatively reporting RCS pressure below 0 PSIG as a violation of Technical Specification 3.4.3 "RCS Pressure and Temperature (P/T) Limits.

The coordination of the change in RCS operating conditions was less than adequate, in that the associated affected documents were not revised as a result of failing to correctly identify the documents and/or involve all applicable parties, as well as the subtlety of the PTLR pressure value discrepancy. The apparent cause of not maintaining RCS pressure within the limits described in the PTLR was a legacy design implementation error. The apparent mental model by licensed operations personnel was not aligned with the literal applicability of the PTLR curves, in that the curves are applicable during RCS vacuum fill conditions, and not limited to only heat-up, cool-down, and inservice leak/hydrostatic testing conditions. Luminant Power interpreted the PTLR to only apply to RCS pressure conditions above atmospheric pressure, and therefore did not consider it in conflict with the adoption of the vacuum refill analysis and procedure. Corrective actions included revising the PTLR to specify negative 14.7 pounds per square inch gage (PSIG) as the lower limit. The explicit PTLR compliance error during vacuum refill did not adversely affect the health and safety of the public or station personnel.

All times in this report are approximate and Central Daylight Time unless noted otherwise.

05000446/LER-2011-00322 August 2011Comanche PeakOn April 15, 2011, Unit 2 was in Mode 6 for the 2RF12 refueling outage. At 1130 hours, a 12 drop per minute (dpm) fuel oil leak was discovered on the Train B Emergency Diesel Generator (EDG 2-02). The leak was not corrected during 2RF12 because the leak was believed to be through the pipe threads, it did not constitute a structural failure, and the size of the leak did not affect the operability of EDG 2-02. On May 10, 2011, a 24-hour run of EDG 2-02 was commenced at 2304 hours per Technical Specification (TS) requirements. At the start of the run, the fuel leak was 12 dpm. Over the course of the run, the leak worsened, until at the 13-hour point it exceeded one liter per minute (lpm). EDG 2-02 was secured and declared inoperable at 1326 on May 11, 2011. Repairs were completed at 0425 hours on May 12, 2011 and EDG 2-02 was declared operable. The cause of the event was fatigue failure caused by long-term vibration stresses. Corrective actions included inspecting EDGs 1-01, 1-02, and 2-01, and no other leaks were identified. All times in this report are approximate and Central Time unless noted otherwise.
05000445/LER-2010-00223 June 2010Comanche Peak


On January 20, 2010, Comanche Peak Nuclear Power Plant (CPNPP) Unit 1 was in Mode 3 during a planned outage and Unit 2 was in Mode 1 operating at 100% power. At 1827 hours, during review of an Oconee INPO OE report, parallels were discovered between the Oconee design and the CPNPP design. Further investigation determined that the required completion times for TS 3.3.2, Condition J, may not have been completed in the past when Units 1 and 2 were operating at low power with only one MFWP providing MFW flow.

The cause analysis of this event determined that the plant design and original operating philosophy was not compatible with the NRC's clarification of the intent of TS 3.3.2, Function 6.g. Corrective actions include the completion of procedure changes on Unit 1 to ensure compliance with TS. Since Unit 2 has been operating at 100% power with both MFW pumps in service since discovery of this condition, corresponding changes to the Unit 2 procedures will be completed prior to removing one MFW pump from service during the next shutdown of Unit 2 or prior to startup of Unit 2 from any event which results in an unplanned trip of Unit 2.

All times in this report are approximate and Central Standard Time unless noted otherwise.

05000446/LER-2009-00111 February 2010Comanche Peak

On December 14, 2009, at 0800 hours, Comanche Peak Nuclear Power Plant (CPNPP) Unit 2 was in Mode 1 at 100% power. A channel calibration on Unit 2 Train B Neutron Flux Monitoring System (Gamma-Metrics) resulted in the inoperability of channels in different systems: Unit 2 containment pressure channel 4, and Channel 4 of the Overtemperature N-16 and Overpower N-16 reactor trips.

When the test equipment being used for the channel calibration was disconnected from the Gamma- Metrics system, the affected control room indications returned to normal. The cause of this event was grounding the Gamma-Metrics system to current paths and ground loops which served to couple a voltage potential through the plant grounding system to the affected plant parameters. Completed corrective actions include: 1) A Maintenance Standing Order was issued to control the use of test equipment that has the ability to ground a floating circuit, and (2) The shield cable ground was corrected for the Unit 2 containment pressure channel 3 and 4 main control board indicators. Planned corrective actions include procedure changes to improve the control and use of test equipment.

All times in this report are approximate and Central Standard Time unless noted otherwise.