05000247/LER-2016-003
| 05-06-2016 | On March 7, 2016, during a refueling outage the control switch for the 21 Main Boiler Feedwater Pump (MBFP) was positioned to trip and the 21 MBFP tripped as designed but the MBFP discharge valve BFD-2-21 failed to fully close. MBFP discharge valve BFD-2-21 was declared inoperable and Technical Specification (TS) 3.7.3 (Main Feedwater Isolation) Condition C (One or both MBFP discharge valves inoperable) was entered. Troubleshooting on the valve determined the close torque switch contact finger was out of position within the contact holder. This misalignment allowed the contact finger to move out of the proper position causing Motor Operated Valve (MOV) BFD-2-21 to fail to close.
Direct cause was valve BFD-2-21 close torque- switch was out of position. The apparent cause was the MOV preventive maintenance procedure lacked the level of detail and direction to provide the appropriate guidance to recognize the susceptibility associated with the orientation of the close torque switch contact finger bracket opening and spreading of the "U" shape bracket. Corrective actions included replacement of the defective torque switch, inspection and testing. A case study from this event will be developed and included in the continual ESP training. The adequacy of the guidance on work instruction on the arrangement/alignment of the contact "U" shape brackets will be evaluated and the necessary guidance provided. The event had no significant effect on public health and safety. NRC FORM366AU.S. NUCLEAR REGULATORY COMMISSION FACILITY NAME (1) DOCKET (2) LER NUMBER (6) PAGE (3) Note: The Energy Industry Identification System Codes are identified within the brackets a. ContentsDESCRIPTION OF EVENTOn March 7, 2016, at approximately 00:10 hours, during plant shutdown for refueling outage cycle 22, while in Mode 3 (Hot Standby), the control switch {33} for the 21 Main Boiler Feedwater Pump (MBFP) {SJ} was positioned to trip and the 21 MBFP tripped as designed but the MBFP discharge valve BFD-2-21 {ISV}failed to close. Operations observed a duel light indication for BFD-2-21 valve position on Control Room Panel FAF identifying the valve failed to fully close. MBFP discharge valve BFD-2-21 was declared inoperable and Technical Specification (TS) 3.7.3 (Main Feedwater Isolation) Condition C (One or both MBFP discharge valves inoperable) was entered. TS 3.7.3 Required Action C.1 is to close or isolate the MBFP discharge valves within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />,. and C.2 verify MBFP discharge valves are closed or isolated once per 7 days. At 3:15 hours, valve BFD-2-21 was manually closed and de-energized then cracked open 20 hand wheel turns off its seat'to eliminate. thermal binding concerns. The condition was recorded in the Indian Point Energy Center (IPEC) Corrective Action Program (CAP) in Condition Report CR-IP2-2016-01236. On March 7, 2016, troubleshooting commenced at approximately 19:47 hours, to determine the cause of the valve BFD-2-21 failure to close. On March 9, 2016, during . troubleshooting.of'valve BFD-2-21, when the limit switch compartment cover was removed the close torque switch contact finger was found slipped out of position within the contact holder. Inspection of the failed torque switch identified that the "U" shaped contact holder was slightly bent 'or spread open and the tabs at each end of the holder were not parallel with each other. Engineering concluded this misalignment would allow the contact finger to have free play within the contact holder. Excessive free play within the contact holder contributed to the contact finger moving out of the proper position. In addition, the orientation and arrangement of BFD-2-21 actuator/torque switch is such that
This orientation would make it easier for the contact finger to slip out of the gap. On March 9, 2016, the torque switch was replaced and the valve stroke tested satisfactory. Discussions were held with the original torque switch manufacturer (Limitorque) (OEM) and they recommended that during installation of the new torque switch specific additional inspections be performed and the Indian Point MOV preventive maintenance (PM) procedure be enhanced. Limitorque also recommended an enhancement which could provide a' heavier duty compression spring (located under the contact finger) which would aid in preventing recurrence of this type failure. After a major PM on the valve, inspections' and diagnostic testing were performed to monitor torque switch operation and proper torque switch contact holder assembly. The closed circuit for motor operated valve (MOV) BFD-2-21 is supervised by"limit switch 8. Limit switch 8 (LS8) is set to open and de-energize the motor after the valve disc contacts the valve seat (closed position). The closed torque switch is in series with the close LS8 and provides mechanical overload protection. The closed torque switch is set high enough so that normal operation of BFD-2-21 will not cause its contacts to open. The closed torque switch is bypassed using Limit Switch 9 (LM9) for the first two seconds of the closing stroke. This ensures full motor capability is available to start the valve close which will initiate the trip signals to the MBFPs. After two seconds the close torque switch bypass is out of the circuit and the valve will continue to close until either LS8 or the Close torque switch contacts opens. The MBFP discharge valve BFD-2-21 is a motor operated gate valve with a torque switch, model number SMB-3 (actuator) manufactured by Limitorque {L200} (Flowserve)-
Corrective ActionsThe following corrective actions have been or will be performed under Entergy's. Corrective Action Program to address the cause and prevent recurrence:
Event AnalysisThe event is reportable under 10 CFR 50.73(a) (2)(i)(B). The licensee shall report any operation or condition which was prohibited by the plant's TS. This condition meets the reporting criteria because TS 3.7.3 (Main Feedwater System) requires the two MBFP discharge valves and the trip function to be operable. TS 3.7.3 Condition C (One or both MBFP discharge valves inoperable) required action C.1 is to close or isolate MBFP discharge valve within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> and C.2 verify MBFP discharge valve is closed or isolated once per 7 days. As a result of discovering on March 7, 2016, that MBFP discharge valve BFD-2-21 would not close and that would not haVe closed upon demand due to a failed torque switch, TS 3.7:3 Condition C was not met. Valve BFD-2-21-was last demonstrated operable on December 5, 2015, when there was a reactor trip and no reported issue with valve closure. There was no safety system functional failure reportable under 10 CFR 50.73(a)(2)(v). The MBFP discharge valve BFD-2-22 for the 22 MBFP was operable and isolation of Main FW from the 21 MBFP could have been accomplished in accordance with TS Basis 3.7.3.a by closure of the Main FW Regulating Valves (MFRVs), trip of the MBFPs, and the closure of all four Low Flow Main FW Bypass Valves (FBVs). Past Similar EventsA review was performed of the past three years of Licensee Event Reports (LERs) for events reporting a TS violation due to inoperable MBFPs. No LERs were identified. Safety SignificanceThis event had no effect on the health and safety of the public. There were no actual safety consequences for the event because there were no accidents or events during the degraded condition. Isolation of the main FW system is necessary to mitigate accident and transient conditions [Main Steam Line Breaks (SLB), SG Tube Ruptures, and Excessive Heat Removal Due to FW System Malfunction]. Main FW must be isolated to prevent excessive reactor coolant system cooldown, containment overpressure, and steam line overfill. Main FW isolation is initiated by either an Engineered Safety Feature Actuation System (ESFAS) safety injection (SI) signal or a high steam generator water level signal. Main FW isolation to all four SGs is provided by either 1) Closure of all four main FW regulating valves (MFRVs) and all four Low Flow Main FW Bypass Valves (FBVs), or 2) Closure of both MBFP discharge valves which initiates closure of all eight FW Isolation Valves (MFIVs), and the trip of both MBFPs. Either of these combinations is capable of achieving main FW isolation to all four SGs within the time limits assumed in the accident analysis. If all eight valves referenced in item 1 close, main FW isolation to all four SGs is completed within time limits that satisfy accident analysis assumptions. To establish redundancy for main FW isolation safety function, the SI ESFAS or High SG Level signal also provides a direct signal- that closes the two MBFP discharge valves. When both MBFP discharge valves move off the open seat, the relay actuates and generates a signal that initiates closure of the four main FW isolation valves (MFIVs) and the four Low Flow FIVs. For this event, all FW isolation capabilities were operable except the 22 MBFP discharge valve BFD-2-21. This event was bounded by the analyzed event described in FSAR Section 14.1.10, (Excessive Heat Removal Due to Feedwater System Malfunctions). Excessive FW additions is an analyzed event postulated to occur from a malfunction of the FW control system or an operator error which results in the opening of a FW control valve. The analysis assumes one FW valve opens fully resulting in the excessive FW flow to one SG. For the FW system malfunction at full power, the FW flow resulting from a fully open control valve is terminated by the SG high level signal that closes all FW control valves and trips the MBFPs. The SG high water level signal also produces a signal to trip the main turbine which initiates a reactor trip. The analysis for all cases of the excessive FW addition initiated at full power conditions with and without automatic rod control, show that the minimum DNBR remains above the applicable safety analysis DNBR limit. In the case of excessive FW flow with the reactor at zero power, the resulting transient is similar to, but less severe than the hypothetical steamline break transient and is bounded by the analysis in UFSAR Section 14.2.5 (Rupture of a Steam Pipe). |
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| Indian Point 2 | |
| Event date: | 03-07-2016 |
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| Report date: | 05-06-2016 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 2472016003R00 - NRC Website | |
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