05000443/LER-2016-002, Regarding Emergency Feedwater System Actuation on Steam Generator Low-Low Level
| ML16123A117 | |
| Person / Time | |
|---|---|
| Site: | Seabrook  |
| Issue date: | 04/26/2016 |
| From: | Ossing M NextEra Energy Seabrook |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| SBK-L-16062 LER 16-002-00 | |
| Download: ML16123A117 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(viii)(B) 10 CFR 50.73(a)(2)(ix)(A) 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(i) |
| 4432016002R00 - NRC Website | |
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U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001 Seabrook Station Licensee Event Report (LER) 2016-002-00 April 26, 2016 10 CFR 50.73 Docket No. 50-443 SBK-L-16062 Emergency Feedwater System Actuation on Steam Generator Low-Low Level Enclosed is Licensee Event Report (LER) 2016-002-00. This LER reports an event that occurred at Seabrook Station on March 2, 2016. This event is being reported pursuant to the requirements of 10 CFR 50.73(a)(2)(iv)(A).
Should you require further information regarding this matter, please contact me at (603) 773-7512.
cc:
D. Dorman, NRC Region I Administrator R. Gladney, NRC Project Manager P. Cataldo, NRC Senior Resident Inspector Sincerely, N extEra Energy Seabrook, LLC NextEra Energy Seabrook, LLC, P.O. Box 300, Lafayette Road, Seabrook, NH 03874
Enclosure to SBK-L-16062
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2018 (11-2015) c
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, the NRG may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 1. FACILITY NAME 2.: DOCKET NUMBER
- 3. PAGE Seabrook Station 05000 443 1 OF 3
- 4. TITLE Emergency Feedwater System Actuation on Steam Generator Low-Low Level
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED I
SEQUENTIAL I REV FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR NUMBER NO.
MONTH DAY YEAR 05000 FACILITY NAME DOCKET NUMBER 03 02 2016 2016 -
002 -
00 04 26 2016 05000
- 9. OPERA TING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)
D 20.2201 (b)
D 20.2203(a)(3)(i)
D 50.73(a)(2)(ii)(A)
D 50.73(a)(2)(viii)(A) 3 D
20.2201 (d)
D 20.2203(a)(3)(ii)
D 50.73(a)(2)(ii)(B)
D 50.73(a)(2)(viii)(B)
D 20.2203(a)(1)
D 20.2203(a)(4)
D so.73(a)(2)(iii)
D 50.73(a)(2)(ix)(A)
D 20.2203(a)(2)(i)
D 50.36(c)(1)(i)(A)
[{] 50.73(a)(2)(iv)(A)
D 50.73(a)(2)(x)
- 10. POWER LEVEL D
20.2203(a)(2)(ii)
D 50.36(c)(1)(ii)(A)
D 50.73(a)(2)(v)(A)
D 73.71(a)(4)
D 20.2203(a)(2)(iii)
D so.36(c)(2)
D 50.73(a)(2)(v)(B)
D 73.71(a)(5)
D 20.2203(a)(2)(iv)
D so.46(a)(3)(ii)
D 50.73(a)(2)(v)(C)
D 73.77(a)(1) 000 D
20.2203(a)(2)(v)
D 50.73(a)(2)(i)(A)
D 50.73(a)(2)(v)(D)
D 73.77(a)(2)(i)
D 20.2203(a)(2)(vi)
D 50.73(a)(2)(i)(B)
D 50.73(a)(2)(vii)
D 73.77(a)(2)(ii)
D 50.73(a)(2)(i)(C)
D OTHER Specify in Abstract below or in =
Description of the Event 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 [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 commencmg 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 ofSG 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 517 65). 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 Event
An 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 Event
The 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 of24 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.
Description of the Event 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 [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 commencmg 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 ofSG 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 517 65). 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 Event
An 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 Event
The 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 of24 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.
NRC FORIVl366A (11-'!2015)
- 1. FACILITY NAME I
Seabrook Station
Corrective Actions
LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET
- 2. DOCKET NUMBER I 05000- I 443 Page3 of3 U.S. NUCLEAR REGULATORY COMMISSION
- 3. LER NUMBER D
NUMBER NO.
I YEAR SEQUENTIAL REV
~-I 002 1-0
- 1. Develop and deliver a case study outlining this event and clearly establishing operations leadership position on Major Plant Evolution (MPE) procedure use_
- 2.
Incoi-porate case study review as a recurring activity with a minimum periodicity of2 years_
Similar Events
LER 2009-001, Reactor Protection System Actuation on Steam Generator Low Water Level, reported the actuation of the 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 Information
The Energy Industry Identification System (EIIS) codes are included in this LER in the following format: [EIIS system identifier, EIIS component identifier].