05000443/LER-2016-002
| 04-26-2016 | On March 2, 2016 at 1312 hours0.0152 days <br />0.364 hours <br />0.00217 weeks <br />4.99216e-4 months <br />, during a plant cooldown, a valid actuation of the emergency feedwater system (EFW) occurred when B steam generator levels reduced to 20%. The lowering level was a result of the unanticipated tripping of the start up feed pump on low condensate storage tank level while it was the feed source to the steam generators. The start up feed pump was restarted and feed flow had been restored when the actuation took place. No adverse consequences resulted from this event.
The cause of the event is the on-shift operating crew was processing multiple procedure sections in parallel resulting in steps being performed out of sequence. Corrective action is to develop and deliver a case study outlining the event and clearly establishing opefations leadership positions on procedure use. NRC. FORM SFR s) APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2018 comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by Internet e-mail to used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection. NRC FORM'366A U.S. NUCLEAR REGULATORY COMMISSION (11-015) 8%' 05000- Seabrook Station 443 ContentsDescription of the EventOn March 2, 2016 at 1312 hours0.0152 days <br />0.364 hours <br />0.00217 weeks <br />4.99216e-4 months <br />, during a plant cooldown, a valid actuation of the emergency feedwater [BA] system occurred when B steam generator levels [AB, SG] reduced to 20%. The lowering level was a result of the unanticipated tripping of the start up feed pump (SUFP) on low condensate storage tank (CST) level while it was the feed source to the steam generators (SG). The SUFP was restarted and feed flow had been restored when the actuation took place. At the time of the event, the plant was in mode 3 and commencing cooldown at approximately 557 degrees F. The plant had been stable following a reactor trip due to a turbine trip that occurred approximately 10 hours1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br /> earlier at 0253 with the SUFP supplying SG inventory from the CST through the normal feedwater header. Decay heat removal was accomplished via SG steam flow to the condenser steam dump system. During the process of swapping the SUFP suction from the CST to the hotwell condensate cleaning filters, a low suction pressure occurred at the SUFP resulting in a pump trip. During restoration of the SUFP, a low-low SG water level signal occurred and the turbine-driven and motor-driven EFW pumps automatically started at 1312 resulting in restoration and stabilization of SG inventory. Subsequently, the SUFP was again used as the preferred feedwater source for SG inventory and decay heat removal. This event resulted in a valid actuation of the EFW system and met the reporting criteria of 10 CFR 50.72(b)(3)(iv)(A). An eight hour report was made to the NRC at approximately 1813 on March 2, 2016 (event number 51765). This event is of regulatory significance because it resulted in actuation of a system provided to mitigate the consequences of an accident. No adverse consequences resulted from this event and this incident had no adverse impact on the health and safety of the public or the plant and its personnel. This event did not involve a safety system functional failure. No inoperable structures, systems or components contributed to this event. Cause of the EventAn analysis of this event found the cause to be the on-shift operating crew was processing multiple procedure sections in parallel resulting in steps being performed out of sequence. Analysis of the EventThe EFW System provides the capability to remove heat from the Reactor Coolant System during emergency conditions when the Main Feedwater System is not available. The system components, instrumentation, and power supplies are sized and designed with sufficient redundancy to maintain the system's safety-related functions under all credible accident conditions. The combination of one turbine- driven pump and one motor-driven pump provides a diversity of power sources to assure delivery of feedwater under emergency conditions. The Emergency Feedwater System will be actuated automatically on loss of offsite power, low-low level in any of the steam generators, safety injection signals or an ATWS mitigation system actuation signal. During this event the EFW system responded as designed and functioned successfully when the low SG water level occurred. In addition, the EFW pumps take suction from the lower elevation of the CST and are not subject to the same suction limitation as the SUFP, which normally has its suction aligned to the upper elevation of the CST. The reactor decay heat was relatively low given more than 10 hours1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br /> decay time since reactor shut down. The CST water level at the time of the low suction pressure trip was approximately 227,800 gallons. The minimum required volume is 212,000 gallons; therefore there was significant water inventory available in the CST to supply the EFW pumps if needed for long term decay heat removal. Although the trip of the SUFP was unexpected, the reason for the trip was quickly diagnosed and understood such that the function of the SUFP was actually recovered (suction was re-aligned and the pump started) prior to the low-low SG level signal occurring. The SUFP was out of service for a total time of 24 minutes and the EFW pumps operated for seven minutes. Thus, both EFW pumps remained automatically functional/available and the SUFP remained manually functional/available via recovery. Corrective Actions1. Develop and deliver a case study outlining this event and clearly establishing operations leadership position on Major Plant Evolution (MPE) procedure use. 2. Incorporate case study review as a recurring activity with a minimum periodicity of 2 years. Similar Events reactor protection system resulting from low water levels in steam generators A and C. The root cause for this event was attributed to the Operations Department's liberal expectations and standards for implementation of certain procedures that direct major plant evolutions, which led to the operating crew's failure to assess potential risks associated with performing a plant cooldown without placing the residual heat removal (RHR) system in service. Additional InformationThe Energy Industry Identification System (EIIS) codes are included in this LER in the following format: [EIIS system identifier, EIIS component identifier]. NRC FORIV1366A U.S. NUCLEAR REGULATORY COMMISSION (11-015) == CONTINUATION SHEET == |
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| Seabrook Station - | |
| Event date: | 0-2-2016 |
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| Report date: | 04-26-2016 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| Initial Reporting | |
| ENS 51765 | 10 CFR 50.72(b)(3)(iv)(A), System Actuation |
| 4432016002R00 - NRC Website | |