05000482/LER-2019-001, Re Valid Actuation of One of the Emergency Diesel Generators

Re Valid Actuation of One of the Emergency Diesel Generators

ML19281C061
Person / Time
Site:	Wolf Creek
Issue date:	07/18/2019
From:	Bayer R Wolf Creek
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
WO 19-0027 LER 2019-001-00
Download: ML19281C061 (4)

LER-2019-001, Re Valid Actuation of One of the Emergency Diesel Generators

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)(iii) 10 CFR 50.73(a)(2)(ix)(A) 10 CFR 50.73(a)(2)(x) 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)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(i)
4822019001R00 - NRC Website

text

Robert J. Bayer Plant Manager U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555 July 18, 2019 WO 19-0027

Subject:

Docket No. 50-482:

Licensee Event Report 2019-001-00, "Loss of Startup Transformer Results in Emergency Diesel Generator Actuation" To Whom It May Concern:

The enclosed Licensee Event Report (LER) 2019-001-00 is being submitted pursuant to 10 CFR 50.73(a)(2)(iv)(A) regarding a valid actuation of one of the emergency diesel generators at Wolf Creek Generating Station.

This letter contains no commitments. If you have any questions concerning this matter, please contact me at (620) 364-4015, or Ron Benham at (620) 364-4204.

RJB/rlt

Enclosure:

LER 2019-001-00 cc:

S. A. Morris (NRC), w/e N. O'Keefe (NRC), w/e B. K. Singal (NRC), w/e Senior Resident Inspector (NRC), w/e Sincerely, Robert J. Bayer P.O. Box 411 / Burlington, KS 66839 / Phone: (620) 364-8831 An Equal Opportunity Employer M/F/HCNET

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 03/31/2020 (04-2018)

, the NRG may not conduct or sponsor, and a person is not required to respond to, the information collection.

3.Page Wolf Creek Generating Station 05000 482 1

OF 3

4. Title Loss of Startup Transformer Results in Emergency Diesel Generator Actuation

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 05 24 2019 2019 -

001 -

00 07 18 2019 05000

9. Operating 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)

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 20.2203(a)(1)

D 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) 0 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)

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)

J'.. /.ti};:.;:}... *

.. **. D 50.73(a)(2)(i)(C)

D Other (Specify in Abstract below or in "Hot collar testing" was performed on the transformer bushings to determine if they needed to be replaced. The results indicated that the bushings were acceptable for continued service. Continuity checks were also performed with satisfactory results.

BASIS FOR REPORTABILITY This event is being reported in accordance with 10 CFR 50.73(a)(2)(iv)(A) as an event or condition that resulted in manual or automatic actuation of any of the systems listed in paragraph (a)(2)(iv)(B) of 10 CFR 50.73. For the event that occurred on May 24, 2019, loss of power to the NB002 bus resulted in an undervoltage condition and subsequent automatic actuation of the "B" emergency diesel generator. In addition, an auxiliary feedwater actuation signal was generated which resulted in the starting of the "B" motor driven auxiliary feedwater pump.

CAUSE

The most probable cause of the startup transformer failure is that the presence of bird activity caused an initial short, either phase to phase, or phase to ground. This initial fault caused the loss of one phase. This caused an increased potential on the other two phases. The increased potential requires the presence of an even larger air gap to keep arcing from occurring. In addition, immediately following the initial fault, there was plasma material remaining in the air. These caused further faults which resulted in the loss of all three phases of the startup transformer.

CORRECTIVE ACTIONS

All of the rodent covers were re-installed taking care to limit the size as much as possible on any openings. Additional corrective actions currently being considered include installing auto foggers in the transformer yard and switchyard to try to reduce the presence of birds around the transformers, and obtaining customized rodent/bird covers that would prevent smaller animals or birds from entering the bushing lug areas.

SAFETY SIGNIFICANCE

The "B" EDG, as well as its associated load sequencer, responded as required. During the time the startup transformer was inoperable, the "B" EDG continued to supply power to the NB002 bus. In addition, the offsite source serving the NB001 bus didn't experience any interruptions. Therefore both trains of Class 1 E power were operable during this event.

Since all safety related equipment operated as designed, the safety significance of this event was low.

OPERATING EXPERIENCE/PREVIOUS EVENTS A review of Wolf Creek LERs for the past three years identified one other occurrence of a loss of one source of offsite power which resulted in an emergency diesel generator actuation (LER 2016-002-00). However, this event was caused by human error related to incorrect wiring terminations being made during maintenance, rather than the presence of wildlife. Page 3

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