05000287/LER-2022-001, Response Actions Resulted in Brief Inoperability of Both Onsite and Offsite Emergency AC Power Paths
| ML22087A512 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 03/28/2022 |
| From: | Snider S Duke Energy Carolinas |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| RA-22-0116 LER 2022-001-00 | |
| Download: ML22087A512 (6) | |
| 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)(iv)(A), System Actuation 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) |
| 2872022001R00 - NRC Website | |
text
Steven M. Snider Vice President Oconee Nuclear Station Duke Energy ON01SC l 7800 Rochester Hwy Seneca, SC 29672 o. 864.873.3478 f: 864.873.5791 Steve.Snider@duke-energy.com RA-22-0116 March 28, 2022 10 CFR 50.73 Attn: Document Control Desk U. S. Nuclear Regulatory Commission 11555 Rockville Pike Rockville, MD 20852-2746 Duke Energy Carolinas, LLC Oconee Nuclear Station Unit 2 Docket Number: 50-270 Renewed Operating Licenses: DPR-49
Subject:
Licensee Event Report 287/2022-001, Revision 00 - Response Actions Resulted in Brief Inoperability of Both Onsite and Offsite Emergency AC Power Paths Licensee Event Report 287/2022-001, Revision 00, is being submitted pursuant to the requirements of 10 CFR 50.73 to provide notification of the subject event.
There are no regulatory commitments associated with this LER.
There are no unresolved corrective actions necessary to restore compliance with NRC requirements.
If there are questions, or further information is needed, contact Laura Boyce, Regulatory Affairs, at (864) 873-6774.
Sincerely, Steven M. Snider Vice President Oconee Nuclear Station Enclosure: Licensee Event Report 287-2022-001 Rev.00
RA-22-0116 March 28, 2022 Page 2 cc (w/Enclosure):
Ms. Laura Dudes, Administrator, Region II U.S. Nuclear Regulatory Commission Marquis One Tower 245 Peachtree Center Ave., NE, Suite 1200 Atlanta, GA 30303-1257 Mr. Shawn Williams, Project Manager U.S. Nuclear Regulatory Commission 11555 Rockville Pike Mail Stop O-08B1A Rockville, MD 20852-2738 Mr. Jared Nadel NRC Senior Resident Inspector Oconee Nuclear Station
NRC FORM 366 (08-2020)
NRC FORM 366 (08-2020)
U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 08/31/2023 LICENSEE EVENT REPORT (LER)
(See Page 2 for required number of digits/characters for each block)
(See NUREG-1022, R.3 for instruction and guidance for completing this form http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/)
- 1. Facility Name Oconee Nuclear Station Unit 3
- 2. Docket Number 0500000287
- 3. Page 1 OF 4
- 4. Title Response Actions Resulted in Brief Inoperability of Both Onsite and Offsite Emergency AC Power Paths
- 5. Event Date
- 6. LER Number
- 7. Report Date
- 8. Other Facilities Involved Month Day Year Year Sequential Number Rev No.
Month Day Year Facility Name NA Docket Number NA 01 26 2022 2022 001 00 03 28 2022 Facility Name Docket Number NA NA
- 9. Operating Mode 1
- 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) 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) 50.73(a)(2)(iv)(A) 50.73(a)(2)(x)
- 10. Power Level 100 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) 20.2203(a)(2)(v) 50.73(a)(2)(i)(A) 50.73(a)(2)(v)(D) 73.77(a)(2)(ii) 20.2203(a)(2)(vi) 50.73(a)(2)(i)(B) 50.73(a)(2)(vii) 73.77(a)(2)(iii) 50.73(a)(2)(i)(C)
Other (Specify in Abstract below or in CONTINUED declared OPERABLE. An offsite power source was restored through CT-5 within 15 minutes. Following troubleshooting of the actuated breaker failure relay, transformer CT-3 was restored and all offsite and the onsite overhead power sources were returned to service by 1651 EST. Because of the power alignment at the time of the event, ONS Units 1, 2, and 3 did not experience a loss of AC power and did not initiate any actuation signal to the KHS Units.
The CT-3 transformer lockout was caused by an invalid actuation of a breaker failure relay in the 230kV Switchyard. The momentary loss of safety function was caused by response actions following lockout of the CT-3 transformer.
Because the overhead and underground emergency power paths were briefly concurrently inoperable on Unit 3, this event is being reported as an event or condition that could have prevented fulfillment of a safety function in accordance with 10 CFR 50.73(a)(2)(v)(A-D).
CAUSAL FACTORS The CT-3 transformer lockout was caused by an invalid actuation of a breaker failure relay in the 230kV Switchyard. The momentary loss of safety function was caused by response actions following lockout of the CT-3 transformer.
CORRECTIVE ACTIONS
Immediate:
- 1. Isolated PCB-28 breaker failure relay
- 2. Restored transformer CT-3
- 3. Replaced PCB-28 breaker failure relay Planned:
Plan and schedule maintenance on 230kV Switchyard PCB breaker failure relays associated with Start-up Transformers such that the affected Unit maintains at least one additional emergency power path or is outside the MODE of applicability.
SAFETY ANALYSIS
A risk evaluation was performed that determined that the brief inoperability of both onsite and offsite emergency power paths for Unit 3 did not have a significant impact on public health and safety.
The CT-3 lockout did not cause a plant transient and Unit 3 remained online with internal electrical loads supplied from the normal power source (Auxiliary Transformer 3T). However, the CT3 lockout made the primary offsite power path and Keowee Overhead Emergency Power path to Unit 3 unavailable. The Keowee Underground Emergency Power path was available along with an alternate offsite power source via transformer CT5 from the Fant Black Line. Additional defense-in-depth to ensure safe shutdown was available from the Turbine-Driven Emergency Feedwater Pump, Protected Service Water (PSW) System, the Standby Shutdown Facility (SSF), and portable FLEX Equipment.
CONTINUED In response to the CT-3 lockout, the operations staff followed procedural guidance to align offsite power from CT5 to the Standby Buses. For Unit 1 and Unit 2, this action briefly made the Keowee Underground Emergency Power Path technically inoperable but it was still available. For Unit 3, this action briefly caused the emergency power system for both Keowee paths to be technically inoperable. However, the system remained available during the short evolution of the procedure. This action implements a risk reduction measure that allows the alternate offsite power source to be automatically aligned to the Main Feeder Buses if normal power is lost. This alternate alignment was maintained until power from CT3 was restored.
As a result, the lockout event and procedural response had a very low impact on core damage risk since there was no transient, AC power was maintained, emergency power was available, and additional defense-in-depth measures were also available. Therefore, it is concluded that the impact of the brief inoperability of both onsite and offsite emergency AC power paths on overall plant risk is very low and had no impact on public health and safety.
ADDITIONAL INFORMATION
A review of Duke Energys Corrective Action Program did not identify any Oconee LERs or events in the last 3 years that involved the same underlying concerns or reasons as this event.
Energy Industry Identification System (EIIS) codes are identified in the text as [XX].
This event is considered INPO IRIS Reportable.
There were no releases of radioactive materials, radiation exposures, or personnel injuries associated with this event.