05000269/LER-2024-001, Unit 1, Standby Shutdown Facility (Ssf) Pressurizer Level Switch Configuration Caused by Legacy Procedure Deficiency Resulted in Condition Prohibited by Technical Specifications
| ML24354A337 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 12/19/2024 |
| From: | Denise Wilson Duke Energy Carolinas |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| RA-24-0310 LER 2024-001-00 | |
| Download: ML24354A337 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| 2692024001R00 - NRC Website | |
text
David Wilson Nuclear Support Services Manager Oconee Nuclear Station Duke Energy ON01VP l 7800 Rochester Hwy Seneca, SC 29672 o. 864.873.3451 f: 864.873.3411 David.Wilson2@duke-energy.com RA-24-0310 December 19, 2024 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 1 Docket Number: 50-269 Renewed Operating Licenses: DPR-38
Subject:
Licensee Event Report 269/2024-001, Revision 00 - Standby Shutdown Facility (SSF) Pressurizer Level Switch Configuration Caused by Legacy Procedure Deficiency Resulted in Condition Prohibited by Technical Specifications Licensee Event Report 269/2024-001, 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, David A. Wilson Manager, Nuclear Support Services Oconee Nuclear Station Enclosure: Licensee Event Report 269/2024-001 Rev.00
RA-24-0310 December 19, 2024 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. Nick Smalley NRC Senior Resident Inspector Oconee Nuclear Station
Abstract
On November 7th, 2024 Unit 1 was in Mode 5 for a planned refueling outage when a Unit 1 Pressurizer Heater Group did not turn on during the routine performance of a power transfer test. Troubleshooting revealed an issue with the Unit 1 SSF Pressurizer Level Switch which was replaced in July 2022. Acceptance criteria in the calibration procedure for post-maintenance testing (PMT) was incorrect based on the needed function of the circuit but was met as written during performance. A latent procedure error introduced into the calibration procedure resulted in the SSF controlled pressurizer heaters being rendered inoperable within allowable pressurizer water level bands. The calibration procedure was revised, the configuration of the Unit 1 SSF Pressurizer Level Switch was corrected, and the power transfer test was completed with all acceptance criteria met. An Extent of Condition was also performed for the Unit 2 and Unit 3 SSF pressurizer heaters control circuits. Both the Unit 2 and 3 Pressurizer Level Switches were found to be configured correctly. There is a planned corrective action to review similar calibration procedures to validate acceptance criteria.
- 4. Title Standby Shutdown Facility (SSF) Pressurizer Level Switch Configuration Caused by Legacy Procedure Deficiency Resulted in Condition Prohibited by Technical SpecificationsPage of
- 3. LER NUMBER YEAR SEQUENTIAL NUMBER REV NO.
052 050 CAUSAL FACTORS A latent procedure error (prior to 1999) introduced into the calibration procedure resulted in the acceptance criteria being the opposite logic than that which was required; such that the level permissive logic of the SSF controlled pressurizer heaters rendered the heater groups inoperable within allowable level bands.
CORRECTIVE ACTIONS
Immediate:
- 1. The calibration procedure was revised with the corrected acceptance criteria.
- 2. The configuration of the Unit 1 SSF Pressurizer Level Switch was corrected, and the power transfer test was completed with all acceptance criteria met.
- 3. An Extent of Condition was performed for the Unit 2 and Unit 3 SSF pressurizer heaters control circuits. Both the Unit 2 and Unit 3 Pressurizer Level Switches were found to be configured correctly.
Planned:
Review similar calibration procedures to validate acceptance criteria.
SAFETY ANALYSIS
This event had no impact on the health and safety of the public and a very low impact to core damage risk.The SSF powered pressurizer heaters are intended to offset the ambient heat losses from the pressurizer to maintain subcooled natural circulation conditions to assure core cooling. The unavailability of pressurizer heater power would allow the pressurizer to cool via ambient heat losses. Sustained ambient heat loss from the pressurizer could result in a loss of subcooled margin, however, core cooling can be maintained with SSF ASW removing decay heat and SSF RC Makeup providing seal cooling and makeup flow.
During an event requiring SSF activation, procedural guidance turns on pressurizer heaters with an adequate liquid level.
The operator would detect the identified issue impacting the pressurizer heaters within 20 minutes. Simulator validation performed for overheating scenarios indicates that ambient cooling of the pressurizer would require more than 16 hours1.851852e-4 days <br />0.00444 hours <br />2.645503e-5 weeks <br />6.088e-6 months <br /> before a loss of subcooling would occur. Several options including the use of the Protected Service Water System (PSW) exist to recover pressurizer heaters during this time frame. If heaters are not recovered sustained ambient heat loss from the pressurizer would result in condensation of the steam bubble. A transition to controlling RCS pressure using SSF letdown would allow subcooled water-solid operation to be established without challenging the pressurizer relief valve setpoints.
In conclusion, this event had no impact on the health and safety of the public and a very low impact on overall plant risk because of the significant time available to recover the pressurizer heaters and the ability to control RCS pressure using the SSF letdown system.
ADDITIONAL INFORMATION
A review of Duke Energys Corrective Action Program did not identify any Oconee LERs or events in the last three years that involved similar underlying concerns or reasons as this event. This event is considered INPO IRIS Reportable. There were no releases of radioactive materials, radiation exposures orpersonnel injuries associated with this event.
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