05000296/LER-2022-002, Both Standby Liquid Control Subsystems Inoperable Due to an Insufficient Boron Injection Rate
| ML22353A631 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 12/19/2022 |
| From: | Sivaraman M Tennessee Valley Authority |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| LER 2022-002-00 | |
| Download: ML22353A631 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability |
| 2962022002R00 - NRC Website | |
text
Post Office Box 2000, Decatur, Alabama 35609-2000 December 19, 2022 10 CFR 50.73 10 CFR 50.4(a)
ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Browns Ferry Nuclear Plant, Unit 3 Renewed Facility Operating License No. DPR-68 NRC Docket No. 50-296
Subject:
Licensee Event Report 50-296/2022-002 Both Standby Liquid Control Subsystems Inoperable Due to an Insufficient Boron Injection Rate The enclosed Licensee Event Report provides details of the inoperability of both Standby Liquid Control subsystems due to an insufficient boron injection rate. Tennessee Valley Authority is submitting this report in accordance with Title 10 of the Code of Federal Regulations (10 CFR) 50.73(a)(2)(vii) as an event where a single cause or condition caused two independent trains or channels to become inoperable in a single system designed to shut down the reactor and maintain it in a safe shutdown condition.
There are no new regulatory commitments contained in this letter. Should you have any questions concerning this submittal, please contact Chris L. Vaughn, Site Licensing Manager, at (256) 729-2636.
Respectfully, Manu Sivaraman Site Vice President Enclosure: Licensee Event Report 50-296/2022-002 Both Standby Liquid Control Subsystems Inoperable Due to an Insufficient Boron Injection Rate
U.S. Nuclear Regulatory Commission Page 2 December 19, 2022
cc (w/ Enclosure):
NRC Regional Administrator - Region II NRC Senior Resident Inspector - Browns Ferry Nuclear Plant NRC Project Manager - Browns Ferry Nuclear Plant
Abstract
On October 18, 2022 at 1440 Central Daylight Time (CDT), following a routine surveillance test, Browns Ferry Nuclear Plant, (BFN), Unit 3 declared both trains of the Standby Liquid Control (SLC) system inoperable for failing to meet boron injection rate acceptance criteria.
This resulted in a single cause or condition that caused two independent trains or channels to become inoperable in a single system designed to shut down the reactor and maintain it in a safe shutdown condition. At the time, it was believed that this could have prevented the SLC system from fulfilling its safety function to shut down the reactor and maintain it in a safe shutdown condition. However, an engineering evaluation later determined that the SLC system remained capable of fulfilling its required safety function throughout this event.
Upon investigation, it was discovered that this event resulted from an ineffective corrective action for the issue identified in Condition Report (CR) 1439832, where all of parameters used in the Anticipated Transient Without Scram (ATWS) equivalency equation could individually meet Technical Specifications (TS), yet still fail the acceptance criteria. SLC system operability was restored on October 18, 2022 at 2053 CDT, after an additional 80 kg of sodium pentaborate was added to the BFN, Unit 3 SLC tank. This increased the boron concentration of the SLC solution, which raised the boron injection rate to an acceptable level. As a corrective action to prevent or reduce the probability of recurrence, BFN will develop and implement an improved method for determining SLC pump flow rates. This will include benchmarking other plants to incorporate their best practices to improve the accuracy and repeatability of SLC pump flow rate measurements.
A. Immediate Corrective Actions
The addition of SPB into the BFN, Unit 3 SLC tank restored the boron injection rate to an acceptable level, as indicated by the re-calculated value of the ATWS equivalence calculation performed as part of 3-SR-3.1.7.3 B. Corrective Actions to Prevent Recurrence or to reduce the probability of similar events occurring in the future As a corrective action to prevent or reduce the probability of event recurrence, BFN will develop and implement an improved method for determining SLC pump flow rates. This will include benchmarking other plants to incorporate their best practices to improve the accuracy and repeatability of SLC pump flow rates measurements.
VII. Previous Similar Events at the Same Site
A search of LERs from BFN, Units 1, 2, and 3 over the last five years identified no similar events.
VIII. Additional Information
There is no additional information.
IX.
Commitments
There are no new commitments.