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Report date | Site | Event description | |
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05000528/LER-2016-003 | 21 November 2016 | Palo Verde | On September 21, 2016, at 0142 Mountain Standard Time (MST), containment isolation valve SGA-UV-1134 failed to stroke closed from the control room during containment isolation valve testing. The failure resulted in an unplanned entry into Technical Specification Limiting Condition of Operation (LCO) 3.6.3, Containment Isolation Valves. On September 22, 2016, it was concluded the valve was in a configuration that rendered the pneumatic operator incapable of operating the valve, including remote operation and automatic closure in the event of a main steam isolation system signal. The valve had been in this configuration since last operated on June 28, 2016. Therefore, the valve was inoperable longer than the required 4-hour completion time of LCO 3.6.3 Condition C. On September 22, 2016, at 1457 MST, SGA-UV-1134 was properly closed, declared operable, and LCO 3.6.3 was exited. This event was caused by human error when procedural guidance was not used to return SGA-UV-1134 to its neutral locked configuration following testing on June 28, 2016. Actions have been initiated to ensure proper procedural guidance is used to lock SGA-UV-1134 in the future. On June, 26, 2015, LER 50-530/2015-002 reported a condition prohibited by LCO 3.0.4 that occurred on May 1, 2015, when Unit 3 entered Modes 4 and 3 while in the applicability of LCO 3.7.4. On May 2, 2015, automatic dump valve, SGB- HV-178, was stroked with steam while in Mode 3 and discovered to be inoperable due to human error incurred during post- maintenance assembly prior to entering Mode 4. |
05000530/LER-2015-004, Condition Prohibited by Technical Specifications 3.0.4 and 3.7.2 Due to an Inoperable Main Steam Isolation Valve | 9 October 2015 | Palo Verde | On August 13, 2015, at approximately 2106, the Unit 3 main steam isolation valve SGE-UV-181 (MSIV-181) B actuator train was declared inoperable and Technical Specification (TS) Limiting Condition for Operation (LCO) 3.7.2, Condition A, was entered due to a failed fitting on the air supply line. To correct the condition the failed fitting was replaced and an additional pipe support was installed on the air-line. Following retests, the MSIV-181 B actuator train was restored to operable status and LCO 3.7.2, Condition A, was exited on August 15, 2015, at approximately 1830. A similar air-line fitting failure had occurred on the Unit 3 MSIV-181 B actuator train on May 19, 2015. The investigation of this condition following the second failure determined the MSIV-181 B actuator train air-line configuration was modified in the spring 2015 Unit 3 refueling outage and was inoperable from the time Unit 3 entered Mode 4 on May 1, 2015, at 0258, following the outage because the air-line tubing was not adequately supported following the design change. The investigation of the two fitting failures is still in progress. The cause of this condition and any additional corrective actions will be reported in a supplement to this Licensee Event Report. No similar conditions have been reported by PVNGS in the last three years. |
05000530/LER-2015-003, Damaged High Pressure Safety Injection Pump Motor Journal Bearing | 29 July 2015 | Palo Verde | On May 30, 2015, emergent maintenance on the Unit 3 train A high pressure safety injection (HPSI) pump motor outboard journal bearing performed under Nuclear Regulatory Commission (NRC) approved notice of enforcement discretion 15-4-01 exceeded the Technical Specification Limiting Condition for Operation (LCO) completion time for LCO 3.5.3, Emergency Core Cooling Systems - Operating, Condition C.1. The HPSI pump had been removed from service on May 27, 2015, at 0628, for planned routine maintenance. During maintenance, it was discovered that the motor outboard journal bearing was damaged. The bearing was replaced and the pump was declared operable on May 30, 2015, at 1710. The root cause was work instruction weaknesses which resulted in improper reassembly of the HPSI pump motor during planned maintenance in the Unit 3 spring 2015 refueling outage. Immediate corrective actions replaced the damaged outboard motor bearing and properly reassembled the pump and motor. To prevent recurrence, maintenance procedures will be revised to provide enhanced guidance for pump and motor reassembly. An additional action will determine training enhancements needed to address weaknesses with maintenance personnel knowledge. No previous-similar events have been reported to the NRC by PVNGS in the prior three years. |
05000530/LER-2015-002, Condition Prohibited by Technical Specification 3.0.4 Due to an Inoperable Atmospheric Dump Valve (ADV) | 26 June 2015 | Palo Verde | in preparation for plant startup. On May 2, 2015, when plant conditions needed to test atmospheric dump valves (ADV) with steam were achieved, testing of ADVs was initiated. At 1739 on May 2, 2015, testing determined that ADV SGB-HV-178 (ADV-178) would not stroke more than approximately 13 percent open. Operations personnel declared ADV-178 inoperable and entered Technical Specification Limiting Condition of Operation (LCO) 3.7.4, Atmospheric Dump Valves, Condition A. An investigation determined ADV-178 was inoperable when Unit 3 entered Mode 4. Inspection of ADV-178 determined internal sealing rings were improperly installed during maintenance performed in the refueling outage. The valve was repaired and tested and declared operable at 0853 on May 7, 2015. The causes of the event were human error by maintenance personnel and inadequacies with the procedure used to perform the valve maintenance. Corrective actions will revise work instructions to provide detailed guidance for valve re-assembly and to require verifications of proper re-assembly. A similar event was reported in LER 50-529/2012-003-00 which resulted when testing in Mode 3 following refueling activities identified an inoperable steam supply valve for the steam driven auxiliary feedwater pump. |
05000529/LER-2015-001, Condition Prohibited by Technical Specification (TS) Limiting Condition for Operation (LCO) 3.3.5, Engineered Safety Features Actuation System (ESFAS) | 25 March 2015 | Palo Verde | On January 11, 2015, at 0024, Unit 2 received a plant computer monitoring system (RJ) alarm on point SASB22, indicating the setpoint for the bistable relay that compares pressures between Steam Generators (SGs) was approaching the technical (RK) and went unnoticed until late in the shift. Operators then verified the annunciator for SG differential pressure (DP) was not alarming and SG pressures were normal. The significance of the RJ alarm was not apparent because the value was displayed in units of voltage versus DP. On January 24, 2015, further questioning determined the setpoint for the bistable that monitors differential pressure between SGs had exceeded its allowable value. Channel B SG Pressure Difference-High was declared inoperable and SG Level 2-Low was placed in bypass per LCO 3.3.5, Condition A. The direct cause of the event was setpoint drift of the SASB22 bistable relay caused by potentiometers that had not recently been wiped clean. The root cause was the lack of an annunciated alarm for SASB22 and associated alarm response procedure to ensure the alarm condition was promptly acknowledged, understood, and correctly addressed within TS time limitations. No previous similar events have been reported to the NRC by PVNGS in the prior three years. |