05000270/LER-2021-002, Actuation of the Keowee Hydroelectric Station Due to Loss of AC Power to the Unit 2 Main Feeder Buses
| ML22026A530 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 01/26/2022 |
| From: | Snider S Duke Energy Carolinas |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| RA-22-0049 LER 2021-002-00 | |
| Download: ML22026A530 (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) |
| 2702021002R00 - NRC Website | |
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Steven M. Snider
( ~ DUKE Vice President Oconee Nuclear Station ENERGY Duke Energy ON01SC l 7800 Rochester Hwy Seneca, SC 29672
o.864.873.3478 f: 864.873.5791 Steve.Snider@duke-energy.com
January 26, 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 270/2021-002, Revision 00 - Actuation of the Keowee Hydroelectric Station Due to Loss of AC Power to the Unit 2 Main Feeder Buses
Licensee Event Report 270/2021-002, 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 Sam Adams, Regulatory Affairs, at (864) 873-3348.
Sincerely,
Steven M. Snider Vice President Oconee Nuclear Station
Enclosure: Licensee Event Report 270-2021-002 Rev.00
RA-22-0049 January 26, 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 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO.3150-0104 EXPIRES: 08/31/2023 (08-2020)
Oconee Nuclear Station Unit 2 0500000270 i 1 OF4
- 4. Title Actuation of the Keowee Hydroelectric Station Due to Loss of AC Power to the Unit 2 Main Feeder Buses
- 5. Event Date 6. LER Number 7. Report Date 8. Other Facilities Involved Sequential Rev Facility Name Docket Number Month Day Year Year Number No. Month Day Year Oconee Nuclear Station Unit 1 0500000269 11 27 2021 2021 002 00 01 26 2022 Facility Name Docket Number NA 05000
- 9. Operating Mode 11. This Report is Submitted Pursuant to the Requirements of10 CFR §: (Check all that apply) 20.2203(a)(3)(i) 50.73(a)(2)(ii)(A) 50.73(a)(2)(viii)(A) 5 * * *
- 20.2201(b)
- * *
- 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. PowerLevel * * *
- 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) 000 * * *
- 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
CAUSAL FACTORS
A Prompt Investigation Response Team (PIRT) was convened to determine why the procedure failed to ensure the transfer switches were in the correct positions. The PIRT identified the direct cause to be an inaccurate procedure step related to positioning/verifying Start-up Bus Differential Relay Control switches.
The causes for the inaccurate procedure step are:
- 1. Procedure revision generated with technical errors in the procedure.
- 2. Procedure revision reviewed with technical errors in the procedure and not identified and corrected by the reviewers.
CORRECTIVE ACTIONS
Immediate:
- 1. Units 1 and 2 were restored to the appropriate power alignment.
- 2. The inaccurate procedure was revised.
Planned:
- 1. Revise all labeling associated with the Start-up Transformer Differential Relay transfer switches to improve human factors.
- 2. Reinforce procedure change development requirements and expectations for use of human error reduction tools for procedure writers.
- 3. Reinforce procedure review and validation requirements and expectations for use of job aids and human error reduction tools with procedure reviewers and validators.
- 4. Conduct procedure review process training.
SAFETY ANALYSIS
A qualitative risk evaluation was performed to consider the potential impacts of this event on plant safety. The CT-1 and CT-2 Lockout Event on 11/27/2021 affected Unit 1 and Unit 2 but did not have any impact on public health and safety.
For Unit 1, the event did not cause a plant transient and remained online with internal electrical loads continuing to be supplied from the normal power source (Auxiliary Transformer 1T). If the normal power source had been lost, electrical loads would have transferred automatically to the alternate offsite power source fed from Transformer CT-
- 5. Additionally, the Keowee Emergency Power System started automatically and was running in standby and was available to supply loads via the underground power path to Transformer CT-4. As a result, the lockout event had a negligible impact on Unit 1 core damage risk since there was no transient, the AC power support function was maintained, and there was no loss of mitigating equipment.
Unit 2 was shut down in Mode 5 beginning the process of unit start-up following a refueling outage when the lockout occurred. The LPI System was running in decay heat removal mode when power from CT-2 was lost. However, power was restored automatically from the Standby Buses (via CT-5 offsite power) and the running pump automatically restarted and resumed decay heat removal circulation without operator action. Both Keowee units NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 08/31/2023 (08-2020)
Oconee Nuclear Station Unit 2 0500000270 NUMBER NO.
2021 002 00 automatically started and were running in standby and available to restore power if offsite power from Transformer CT-5 had failed. Given the low decay conditions present on Unit 2, significant time was also available for additional operator recovery actions if they had been needed. Therefore, given the significant defense-in-depth and time available for recovery actions, this event is judged to have a very low risk of core damage.
With no loss of normal cooling, emergency power available from Keowee, and significant time available for additional recovery actions, the loss of CT-2 event had an insignificant impact on Unit 2 core damage risk.
Thus, it is concluded that the impact of the CT-1/CT-2 lockout event on overall plant risk is insignificant 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.
This event is considered INPO IRIS Reportable. There were no releases of radioactive materials, radiation exposures or personnel injuries associated with this event.