05000346/LER-2020-002, Manual Reactor Trip on Trip of Reactor Coolant Pumps Due to Loss of 13.8 Kv Bus Potential Transformer Fuse
| ML20157A121 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  (NPF-003) |
| Issue date: | 05/26/2020 |
| From: | Bezilla M Energy Harbor Nuclear Corp |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| L-20-122 LER 2020-002-00 | |
| Download: ML20157A121 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation 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)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(iv), System Actuation |
| 3462020002R00 - NRC Website | |
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harbor Mark B. Bezilla Site Vice President, Davis-Besse Nuclear May 26, 2020 L-20-122 ATTN: Document Control Desk United States Nuclear Regulatory Commission Washington, D.C. 20555-0001
Subject:
Davis-Besse Nuclear Power Station, Unit 1 Docket Number 50-346, License Number NPF-3 Licensee Event Report 2020-002 Davis-Besse Nuclear Power Station 5501 N. State Route 2 Oak Harbor, Ohio 43449 419-321-7676 10 CFR 50.73 Enclosed is Licensee Event Report (LER) 2020-002, "Manual Reactor Trip on Trip of Reactor Coolant Pumps due to loss of 13.8 KV Bus Potential Transformer Fuse." This event is being reported pursuant to 10 CFR 50.73(a)(2)(iv)(A).
There are no regulatory commitments contained in this letter or its enclosure. The actions described represent intended or planned actions and are described for information only. If there are any questions or if additional information is required, please contact Mr. James M. Vetter, Manager - Regulatory Compliance and Emergency Response, at (419) 321-7393.
Sincerely, t'.l", Mc:c::::.l1:ts ~
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Mark B. Bezilla JCS Enclosure: LER 2020-002 cc: NRC Region Ill Administrator NRC Resident Inspector NRR Project Manager Utility Radiological Safety Board
NRC FORM366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 4/30/2020 (04-2020) 3.Page Davis-Besse Nuclear Power Station, Unit 1 05000 346 1 OF 4
- 4. Title:
Manual Reactor Trip on Trip of Reactor Coolant Pumps due to loss of 13.8 kV Bus Potential Transformer Fuse
- 5. Event Date
- 6. LER Number
- 7. Report Date
- 8. Other Facilities Involved I
Sequential I Rev Facility Name Docltet Number Month Day Year Year Number No.
Month Day Year 05000 Facility Name Docket Number 03 25 2020 2020 -
002 -
00 05 26 2020 05000
- 9. Operating Mode
- 11. This Report is Submitted Pursuant to the Requirements of 10 CFR §: (Check all that apply) 20.2201(b) 20.2203(a)(3)(i)
- 50. 73(a)(2)(ii)(A) 50.73(a)(2)(viii)(A) 2 20.2201(d) 20.2203(a)(3)(ii) 50.73(a)(2)(ii)(B) 50.73(a)(2)(viii)(B) 20.2203(a)(1) 20.2203(a)(4) 50.73(a)(2)(iii) 50.73(a)(2)(ix)(A) 20.2203(a)(2)(i) 50.36(c)(1 )(i)(A) 181 50.73(a)(2)(iv)(A) 50.73(a)(2)(x)
- 10. Power Level 20.2203(a)(2)(ii) 50.36(c)(1)(ii)(A) 50.73(a)(2)(v)(A) 73.71 (a)(4) 20.2203(a)(2)(iii) 50.36(c)(2) 50.73(a)(2)(v)(B)
- 73. 71 (a)(5) 20.2203(a)(2)(iv) 50.46(a)(3)(ii) 50.73(a)(2)(v)(C) 73.77(a)(1) 0 20.2203(a)(2)(v)
- 50. 73(a)(2)(i)(A) 50.73(a)(2)(v)(D) 73.77(a)(2)(i) 20.2203(a)(2)(vi) 50.73(a)(2)(i)(B)
- 50. 73(a)(2)(vii)
- 73. 77(a)(2)(ii) 50.73(a)(2)(i)(C)
Other (Specify in Abstract below or in
CAUSE OF EVENT
- 2. DOCKET NUMBER 346 YEAR 2020
- 3. LER NUMBER SEQUENTIAL NUMBER 002 The direct cause of this event was determined to be a spurious failure of the 13.8 kV Bus B, Potential Transformer PT-1, B-phase fuse. This caused three (3) operating 13.8 kV motors (RCP 1-2, RCP 2-1, and Circulating Water Pump 4) to trip off.
The primary cause of the 13.8 kV Bus B-phase fuse failure (and subsequent manual reactor trip) was due to the replacement fuses specified by a 2014 equivalency evaluation were not appropriate for this application.
These replacement fuses were installed in 2014 as a replacement fuse for the installed fuses that were obsolete.
ANALYSIS OF EVENT
REV NO.
00 A Probabilistic Risk Assessment (PRA) qualitative evaluation was performed for the March 25, 2020 manual scram. This qualitative screening resulted in very low safety significance as the deficiency in question did not result in a loss of mitigation equipment relied upon to transition the plant to a stable shutdown condition. A conservative quantitative analysis of this uncomplicated* plant scram resulted in a delta Core Damage Frequency (CDF) that is well below the thresholds for very small increases in risk as discussed in Regulatory Guide 1.174. The risk of this event is therefore considered very low safety significance in accordance with the Regulatory Guidance.
Reportability Discussion:
The manual actuation of the Reactor Protection System was reported in accordance with 10 CFR
- 50. 72(b)(2)(iv)(B) at 1528 hours0.0177 days <br />0.424 hours <br />0.00253 weeks <br />5.81404e-4 months <br /> on March 25, 2020 (Event Number 54611 ). The manual actuation of the Reactor Protection System is reportable as a Licensee Event Report per 10 CFR 50.73(a)(2)(iv){A) within 60 days of occurrence. All safety systems performed as required in response to the event, and no loss of safety functions occurred.
CORRECTIVE ACTIONS
Completed Actions:
All three (3) fuses for the 13.8 kV Bus B Potential Transformer PT-1 were replaced prior to reactor restart.
An engineering review was performed to identify an appropriate replacement for the 15.5CAV0.5E fuse type in the 13.8 kV potential transformer.
Scheduled Actions:
The fuses for the 8 PTs identified as being the same fuse in similar applications as the PT fuse involved in this event are scheduled to be replaced.
Lessons learned from this event will be discussed with engineering personnel to perform a more comprehensive risk review when performing equivalency evaluations.
PREVIOUS SIMILAR EVENTS
05000 -
346 YEAR 2020 SEQUENTIAL NUMBER 002 REV NO.
00 A similar event occurred within the previous 3 years involving the fuse type replaced by the 2014 equivalency evaluation. On November 24, 2018, DBNPS Start-up Transformer 02 Voltmeter El6210 was found indicating low voltage, similar to this event. In this condition, Bus B would not have been able to transfer to the selected reserve source (X02). Troubleshooting found the B-phase fuse blown for 13.8 kV Cubicle HB0S PT-2. All three (3) fuses for HB0S PT-2 were replaced. No cause analysis of the fuse failure was performed. This November 2018 event did not result in an LER reportable event. Page4 of 4