05000424/LER-2020-002, Re Oil Leak Causes Ultimate Heat Sink to Be Inoperable Longer than Allowed by Technical Specifications
| ML20330A317 | |
| Person / Time | |
|---|---|
| Site: | Vogtle  |
| Issue date: | 11/25/2020 |
| From: | Pitts D Southern Nuclear Operating Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NL-20-1303 LER 2020-002-00 | |
| Download: ML20330A317 (4) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4242020002R00 - NRC Website | |
text
A Southern Nuclear November 25, 2020 Docket No:
50-424 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555-0001 R. Drayton Pitts Site Vice President Vogtle Units 1-2 Vogtle Electric Generating Plant - Unit 1 Licensee Event Report 2020-002-00 7821 River RD Waynesboro GA. 30830 706-848-0001 tel 706-848-3321 fax NL-20-1303 Oil Leak causes Nuclear Service Cooling Water system to operate in a condition prohibited by Technical Specifications 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, 2020-002-00 for Vogtle Electric Generating Plant Unit 1. This letter contains no NRC commitments. If you have any questions, please contact Matthew Horn at (706) 848-1544.
Respectfully submitted, Drayton Pitts Site Vice President Vogtle 1&2 RDP/KCW Enclosure: Unit 1 Licensee Event Report 2020-002-00 Cc: Regional Administrator NRR Project Manager - Vogtle 1 & 2 Senior Resident Inspector - Vogtle 1 & 2 RType: CVC7000
Vogtle Electric Generating Plant - Unit 1 Licensee Event Report 2020-002-00 Oil Leak causes Nuclear Service Cooling Water system to operate in a condition prohibited by Technical Specifications Enclosure Unit 1 Licensee Event Report 2020-002-00
Abstract
On September 29, 2020, Vogtle Electric Generating Plant Unit 1 was operating in Mode 1 at 100 percent power. The quarterly preventive maintenance (PM) was performed on the gearbox for fan 4 of the Unit 1, B-train Nuclear Service Cooling Water (NSCW) system. During this PM, it was discovered that the oil level in the gearbox was low. The last time the gearbox was verified to be full was July 7, 2020. Based on troubleshooting performed on the gearbox in November 2020, the oil only leaked out of the gearbox while it was running and leaked approximately 1.14 gallons per day while in operation. After reviewing the Integrated Plant Computer (IPC) data, the last time the fan ran was September 6. It was during this run on September 6, that the oil level in the gearbox would have dropped below the required level for the gearbox to remain operational.
When the oil level dropped on September 6, Technical Specification (TS) 3.7.9 Condition B should have been entered because one of the fan/spray cells was inoperable. However, because the oil level was not known to be low, this Condition was not entered.
TS 3.7.9 Required Action B.1 has a completion time of seven days or in accordance with the Risk Informed Completion Time Program. Because this condition was not entered, the plant operated in a condition prohibited by TS from the period of September 13 through November 4, when the leak was repaired.
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A. Event Description
On September 29, 2020, during the quarterly PM of the Unit 1, Bravo train Nuclear Service Cooling (NSCW)[BS] Water fan 4 gearbox, it was discovered that the oil level in the gearbox was low. During the last quarter PM on the gearbox on July 7, 2020, the oil level was at an acceptable level. It was determined through troubleshooting in November 2020 that the leakage from the gearbox was negligible while the fan was not in operation but was approximately 1.14 gallons per day while the gearbox was in operation. An analysis was performed using Integrated Plant Computer (IPC) data to determine when this fan had run between the last time the oil was checked on July 7 and when the oil was found to be low on September 29 and it was determined that the fan ran 12 days during this time.
Previous OE for the NSCW gearboxes shows that gearbox failures occur when more than nine gallons of oil are lost. When the gearbox was refilled on September 29, 2020, 10 gallons of oil were added. Comparing the rate of oil loss while the gearbox was operating, the capacity of the gearbox, 18.5 gallons, and the dates that the gearbox was in operation, it was determined that the last date at which the gearbox had enough oil to prevent failure was September 6. The gearbox was inoperable until it was repaired on November 4, 2020. This is contrary to Technical Specification 3.7.9 Condition B which states that the NSCW fan and its associated gearbox must be returned to service within seven days or the required actions be taken.
There were no other Structures, Systems, or Components (SSCs) that were out of service that were inoperable at the beginning of the event and contributed to the event.
B. Cause of Event
The gearbox seal was replaced on February 21, 2020 as part of the 36-month PM for the soft parts in the gearbox. Since the seal failed approximately seven months after its initial installation in February 2020, the most likely failure mechanism is either premature failure or improper installation.
C. Safety Assessment
Two separate 100 percent capacity trains of NSCW are present. At least one train is in operation during power generation.
During the time when the B-train NSCW Fan 4 was unable to perform its function, the A-train of NSCW was taken out of service four times. Once for approximately six minutes, a second time for approximately 13 minutes, a third time for approximately 5.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br />, a fourth time for approximately 11 minutes. During these times, the train was readily able to be returned to service. Therefore, the safety significance of this issue is very low.
D. Corrective Actions
The seal on the gearbox was replaced and this event will be evaluated under the Maintenance Rule program to determine if additional actions are required.
E. Previous Similar Events
The Unit 1 B NSCW Fan 1 gearbox was found with a low oil level in May of 2019. Several seals were replaced on the gearbox and the oil leak stopped.
Because the most recent oil leak occurred only seven months after the installation of a new seal, the most likely cause of the leak was premature failure of the seal or improper installation. This premature failure would not have been able to be predicted or prevented by the lessons learned from the previous oil leak in May of 2019.
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