05200025/LER-2024-001, Condition Prohibited by Technical Specification Limiting Condition of Operation 3.1.6 Control Bank Overlap Limits Exceeded Due to Inadequate Procedure Guidance
| ML24078A343 | |
| Person / Time | |
|---|---|
| Site: | Vogtle  |
| Issue date: | 03/18/2024 |
| From: | Coleman J Southern Nuclear Operating Co |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| ND-24-0046 LER 2024-001-00 | |
| Download: ML24078A343 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 0252024001R00 - NRC Website | |
text
._ Southern Nuclear Jamie Coleman Director, Regulatory Affairs 3535 Colonnade Parkway Birmingham, Al. 35243 205.992.5000 March 18, 2024 ND-24-0046 10 CFR 50.73(a)(2)(i)(B)
Docket No.:
52-025 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Southern Nuclear Operating Company Vogtle Electric Generating Plant (VEGP) - Unit 3 Licensee Event Report 2024-001-00 Condition Prohibited by Technical Specification Limiting Condition of Operation 3.1.6 Control Bank Overlap Limits Exceeded Due to Inadequate Procedure Guidance Ladies and Gentlemen:
In accordance with the requirements of 10 CFR 50.73(a)(2)(i)(B), Southern Nuclear Operating Company is submitting the enclosed Licensee Event Report for VEGP Unit 3.
This letter contains no regulatory commitments. If you have questions regarding the enclosed information, please contact Will Garrett at (706) 848-7154.
Respectfully submitted,
~~
Jamie Coleman Director, Regulatory Affairs Southern Nuclear Operating Company JC/kjd/cbg
Enclosure:
Unit 3 Licensee Event Report 2024-001-00 CC:
Regional Administrator, Region II VPO Project Manager Senior Resident Inspector - Vogtle Units 3 & 4 Director, Environmental Protection Division - State of Georgia
Vogtle Electric Generating Plant - Unit 3 Licensee Event Report 2024-001-00 Condition Prohibited by Technical Specification Limiting Condition of Operation 3.1.6 Control Bank Overlap Limits Exceeded Due to Inadequate Procedure Guidance Enclosure Unit 3 Licensee Event Report 2024-001-00
Abstract
On January 20, 2024, at approximately 2000 EDT, with Vogtle Electric Generating Plant (VEGP) Unit 3 in Mode 1 at 100 percent power, a condition prohibited by the plant technical specifications (TS) was discovered after entry was made into Limiting Condition of Operation (LCO) 3.1.6, Condition B "Control bank sequence or overlap limits not met". Operators responded timely by entering Condition B of LCO 3.1.6 and completing the TS required actions to verify shutdown margin within the limits specified in the Core Operating Limits Report (COLR) and to restore overlap to within limits. The tip-to-tip distance between two control rod banks was one step less than allowed by the COLR, but this was not identified during three recently performed surveillances, which resulted in missed entries into Condition B of LCO 3.1.6. The cause was determined to be inadequate surveillance procedure guidance to specify an effective method to verify control rod overlap. The corrective action to revise the surveillance procedure was completed.
This event is being reported under 10 CFR 50.73(a)(2)(i)(B). VEGP Units 1, 2, and 4 were unaffected by this event.
EVENT DESCRIPTION
I
- 2. DOCKET NUMBER 00025 I YEAR I
202* I-I
- 3. LER NUMBER SEQUENTIAL NUMBER 001 REV NO.
1-G On January 20, 2024, at approximately 2000 EDT, with Vogtle Electric Generating Plant (VEGP) Unit 3 in Mode 1 at 100 percent power, the tip-to-tip overlap between two control rod banks [EIIS: AA I ROD] was discovered to be one step less than the required COLR limit during the performance of a 12-hour technical specification (TS) surveillance. When operators identified the surveillance requirement not satisfied, they responded timely by entering LCO 3.1.6 Condition B "Control bank sequence or overlap limits not met" and completing the required actions to verify shutdown margin and to restore the overlap to within limits. Upon further investigation, it was discovered that three recent performances of this surveillance did not determine the two control rod banks had tip-to-tip distance exceeding the COLR limits. This resulted in missed entries into Condition B of LCO 3.1.6 and exceeding the TS required action completion times. At the time of discovery, the plant staff was using a method of manually calculating the overlap tip-to-tip distance and comparing to the COLR limits, which correctly evaluated not meeting the surveillance requirement. Other methods to determine the tip-to-tip distance allowed by the surveillance were used in the performance of the surveillances that were missed. These other allowed methods were determined to be ineffective because they relied upon receiving a control rod out of sequence indication or alarm [EIIS: AA I ALM] which was not received during these specific surveillance performances.
There were no structures, systems, or components that were inoperable at the beginning of the event that contributed to the event. This event is reportable under 10 CFR 50.73(a)(2)(i)(B) as operation or condition prohibited by plant's TS.
EVENT CAUSE ANALYSIS
The cause of the control rod overlap limit not being detected during surveillance was inadequate procedure guidance to specify an effective overlap verification method (e.g., manual calculation) to detect abnormal conditions absent receiving a control rod out of sequence indication or alarm.
SAFETY ASSESSMENT
There were no safety consequences due to this event because all control rods remained operable, core power distribution remained within applicable limits, and shutdown margin was maintained during each occurrence. The operators responded timely upon discovery of the event by successfully performing LCO 3.1.6 Condition B required actions to verify shutdown margin and restore the control bank overlap to within limits. No safety systems were required to respond as a result of the event. VEGP Units 1, 2, and 4 were unaffected by this event.
CORRECTIVE ACTIONS
A standing order was established to provide timely instruction to the operating shifts, and the surveillance procedure was revised to require operators to manually record rod position and calculate the tip-to-tip distance to verify the overlap is within the COLR limits following control rod movements.
Additional corrective actions, as applicable, associated with this event will be taken in accordance with the plant corrective action program.
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