05000277/LER-2019-001, Regarding Emergency Bus Breaker Relay Failure Results in Loss of Safety Function
| ML19109A097 | |
| Person / Time | |
|---|---|
| Site: | Peach Bottom  |
| Issue date: | 04/11/2019 |
| From: | Pat Navin Exelon Generation Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| CCN:19-60 LER 2019-001-00 | |
| Download: ML19109A097 (7) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 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)(iii) 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) 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 2772019001R00 - NRC Website | |
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~ Exelon Generation CCN: 19-60 April 11, 2019 U. S. Nuclear Regulatory Commission ATIN: Document Control Desk Washington, DC 20555-0001 10CFR 50.73 Peach Bottom Atomic Power Station (PBAPS) Unit 2 and Unit 3 Renewed Facility Operating License No. DPR-44 and DPR-56 NRG Docket No. 50-277 and 50-278
Subject:
Licensee Event Report (LER) 2-19-001 Enclosed is a Licensee Event Report concerning a loss of a safety function following a partial loss of off-site power. In accordance with NEI 99-04, the regulatory commitment contained in this correspondence is to restore compliance with the regulations. The specific methods that have been planned to restore and maintain compliance are discussed in the LER. If you have any questions or require additional information, please do not hesitate to
. contact Matthew Retzer at 717-456-3351.
Patrick D. Navin Site Vice President Peach Bottom Atomic Power Station PDN/dnd/lR 4219191 Enclosure cc:
US NRG, Administrator, Region I US NRG, Senior Resident Inspector R. R. Janati, Commonwealth of Pennsylvania D. Tancabel, State of Maryland B. Watkins, PSE&G, Financial Controls and Co-Owner Affairs
bee:
Sr. Vice President, Mid-Atlantic Operations Site Vice President-PBAPS Plant Manager-PBAPS Director Operations-PBAPS Sr. Mgr. - Operations Spt & Svcs Shift Ops Superintendent - PBABS Operations Support Manager - PBAPS Director, Site Training-PBAPS Manager, PBAPS Operations Training Manager, Regulatory Assurance-PBAPS Sr. Regulatory Assurance Engineer-PBAPS Manager, Licensing Manager, PBAPS Nuclear Oversight - PB, SMB4-5 Commitment Coordinator Director, Mid-Atlantic Licensing Sr. Manager, PRA - Corporate Greenlee, Scot Krueger, Greg INPO Records via ICES Report (Site OPEX Coordinator)
Records Management - PB
NRC FORM 366 U.S. NUCLEAR REG.ULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 03/31/2020 (04-2018)
, the NRC may not conduct or sponsor, and a
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person is not required to respond to, the information collection.
3.Page Peach Bottom Atomic Power Station Unit 2 05000277 1
OF 5
- 4. Title Emergency Bus Breaker Relay Failure Results in Loss of Safety Function
- 5. Event Date
- 6. LEA 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 Peach Bottom Atomic Power Sta. Unit 3 05000278 Facility Name Docket Number 02 11 2019 2019 -
001 00 04 11 2019
- 9. Operating Mode
- 11. This Report is Submitted Pursuant to the Requirements of 1 O 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)
D 20.2201(d)
D 20.2203(a)(3)(ii)
D 50.73(a)(2)(ii)(B)
D 50.73(a)(2)(viii)(B) 1 D
D 20.2203(a)(1) 20.2203(a)(4)
D 50.73(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 50.36(c)(2).
D 50.73(a)(2)(v)(B)
D 73.71 (a)(5)
D 20.2203(a)(2)(iv)
D 50.46(a)(3)(ii)
D 50.73(a)(2)(v)(C)
D 73.77(a)(1) 100%
D 20.2203(a)(2)(v)
D 50.73(a)(2)(i)(A)
~ 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 D
.£ 50.73(a)(2)(i)(C)
Other (Specify in Abstract below or in
- -.:-~:.-..,
Troubleshooting identified that a failed timing relay caused the E434 transformer breaker to not automatically close. The relay was rep.laced and post-maintenance testing performed to restore E434 breaker function. The E4 diesel generator was returned to ari operable status at 1559 hours0.018 days <br />0.433 hours <br />0.00258 weeks <br />5.931995e-4 months <br /> on February 12, 2019.
The failed off-site lightning arrester was replaced and the 220-08 line was re-energized. The source was returned to an operable status at 1921 hours0.0222 days <br />0.534 hours <br />0.00318 weeks <br />7.309405e-4 months <br /> on February 12, 2019, and TS 3.8.1 Condition A was exited.
The source was inoperable for a total of 20 hours2.314815e-4 days <br />0.00556 hours <br />3.306878e-5 weeks <br />7.61e-6 months <br /> and 49 minutes.
Analysis of Event
Equipment required for safe shutdown of the plant is supplied with power from eight independent 4kV emergency switchgear buses (four for each unit). The 4kV buses are normally supplied by either of two preferred offsite sources via emergency auxiliary transformers. Upon loss of power from one of the preferred offsite sources, automatic fast transfer is made to the other offsite source. If both preferred offsite sources are lost, emergency power will be supplied by four standby diesel generators, each of which can supply power to two 4kV buses, one for each unit.
The 4kV emergency buses supply power directly to larger loads and to 480 volt load centers for smaller loads. The E434 transformer breaker supplies power to the E434 480 volt load center, which powers valves needed for Unit 3 'D' Core Spray pump operation and support equipment for the E4 diesel generator. The E434 load center supports operability of the electrical power distribution system for TS 3.8.7 and the E434 breaker needs to be closed to meet TS SR 3.8.7.1. On February 11, 2019, between 2232 hours0.0258 days <br />0.62 hours <br />0.00369 weeks <br />8.49276e-4 months <br /> and 2250 hours0.026 days <br />0.625 hours <br />0.00372 weeks <br />8.56125e-4 months <br />, the E434 breaker was open, resulting in one Unit 3 AC electrical power distribution subsystem to be inoperable (TS 3.8.7 Condition C) for 18 minutes. In reviewing this event for reportability, a past operability review determined that the Unit 3 'B' Core Spray loop was inoperable during this time period because valves needed for maintaining the loop operable are powered from the E434 load center. TS 3.0.6 allows for TS Required Actions to not be entered for a supported system as long as there is not a loss of safety function.
At the time the E434 breaker was open, the Unit 3 'A' Core Spray loop was inoperable for planned maintenance. As a result, both loops of Core Spray were inoperable (TS 3.5.1 Condition I).
The E4 diesel generator was discovered ~md declared to be inoperable at 0430 hours0.00498 days <br />0.119 hours <br />7.109788e-4 weeks <br />1.63615e-4 months <br /> on February 12, 2019, due to the inability of the E434 breaker to automatically close, as required for E4 operability by TS SR 3.8.1.11.c.2 and SR 3.8.1.19.c.2 (LOCA/LOOP surveillance tests). These surveillance requirements ensure the 480 volt load centers are sequenced onto the 4kV busses within three seconds after the 4kV busses are energized by the diesel generators following a total loss of offsite power. In reviewing this event for reportability, a past operability review determined the E4 diesel generator was inoperable beginning at 2232 hours0.0258 days <br />0.62 hours <br />0.00369 weeks <br />8.49276e-4 months <br /> on February 11, 2019. As a result, the E4 diesel generator was inoperable for 17 hours1.967593e-4 days <br />0.00472 hours <br />2.810847e-5 weeks <br />6.4685e-6 months <br /> and 27 minutes.
YEAR 2019 -
- 3. LER NUMBER SEQUENTIAL NUMBER 001 At 0616 hours0.00713 days <br />0.171 hours <br />0.00102 weeks <br />2.34388e-4 months <br /> on February 12, 2019, the 'A' Core Spray loop was returned to an operable status. As a result, both loops of Core Spray would have been inoperable (TS 3.5.1 Condition I) for 7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br /> and 44 minutes.
This event is being reported in accordance with the following:
REV NO.
00 1 OCFR 50.73(a)(2)(v)(D) - Any event or condition that could have prevented the fulfillment of the safety function of systems needed to mitigate the consequences of an accident.
On February 11, 2019, between 2232 and 0616 hours0.00713 days <br />0.171 hours <br />0.00102 weeks <br />2.34388e-4 months <br /> (7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br /> and 44 minutes), both the 'A' and
'B' Core Spray loops would not have been able to perform their safety function, resulting in a loss of the Core Spray system safety function.
e 1 OCFR 50.73(a)(2)(iv)(A) - Manual or automatic a~tuation of general containment isolation valves in more than one system The fast transfer to the alternate off-site power source caused a momentary loss of power to electrical distribution panels, resulting in a Group II and Ill containment isolation in both units.
This resulted in valve movement in more than one system, including Reactor Water Cleanup, and Drywell Equipment and Floor Drains. The isolations occurred as designed and are expected with the momentary loss _of power. They did not occur as a result of plant conditions that would require a containment isolation. They are therefore classified as invalid.
There were no actual safety consequences as a result of this event. The plant's safety analysis assumes one ED-G is unavailable. Although the loss of the Core Spray system safety function would impact the ability to mitigate a design bases accident, the amount of time it was inoperable is within the time allowed by TS 3.0.3 for the condition to exist prior to entering a shutdown condition. At all times operators in the control room would have been able to restore core spray function by closing the E434 breaker.
Cause of the Event
The cause of the initial event, loss of the 220-08 off-site source, was determined to* be due to a failed lightning arrester located at an off-site substation. The failure of the E434 transformer breaker was the resulted of a failed Agastat ETR series time delay relay for the E434 breaker. Investigation by an off-site vendor determined the relay failed due to a catastrophic failure of the resistor and varistor in the power input circuit of the relay timing board. The relay was manufactured in 2008 and installed in 2013. The relay is replaced on a 12-year frequency and calibrated every four years.
Corrective Actions
The lightning arrester and the E434 breaker relay were replaced. Additional corrective actions are documented in the corrective action program.
Previous Similar Occurrences SEQUENTIAL NUMBER 001 REV NO.
00 During a surveillance test for the E42 4kV bus on October 4, 2012, a similar Agastat ETR relay exhibited a.
longer than expected time delay in closing due to higher than normal resistance in the time delay adjustment potentiometer. The normally de-.energized relay was 22 years old at the time of the failure. For the event described in this LER, the normally energized relay was approximately 1 O years old, had been in service for approximately six years, and was not beyond the allowable service life when* the failure occurred. Page _5 _ of __§_