05000270/LER-2021-001, B Motor Driven Emergency Feedwater Pump Past Inoperability Resulted in Condition Prohibited by Technical Specifications
| ML21277A218 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 10/04/2021 |
| From: | Snider S Duke Energy Carolinas |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| RA-21-0271 LER 2021-001-00 | |
| Download: ML21277A218 (4) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 2702021001R00 - NRC Website | |
text
Steven M. Snider Vice President Oconee Nuclear Station Duke Energy ON01VP l 7800 Rochester Hwy Seneca, SC 29672 o: 864.873.3478 f: 864.873.5791 Steve.Snider @duke-energy.com RA-21-0271 10 CFR 50.73 October 4th, 2021 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-00011 Oconee Nuclear Station, Unit 2 Docket No. 50-270/DPR-47
Subject:
Licensee Event Report 2021-001-00 Ladies and Gentlemen:
Duke Energy Carolinas, LLC, submits the enclosed Licensee Event Report 2021-001-00 in accordance with 10 CFR 50.73 for Oconee Nuclear Station, Unit 2 (ONS). This report describes a condition where the past inoperability of an emergency feedwater pump exceeded the time allowed by Technical Specifications. This event had no significance with respect to the health and safety of the public.
There are no regulatory commitments contained within this report.
Please refer any questions regarding this submittal to Laura Boyce, Senior Nuclear Engineer, Regulatory Affairs, at 864-873-6774.
Sincerely, Steven M. Snider Vice President Oconee Nuclear Station Enclosures: Licensee Event Report 2021-001-00 cc: J. Nadel, NRC Senior Resident Inspector, ONS S. Williams, NRC Project Manager, ONS NRC Regional Administrator, Region II
Abstract
On August 2, 2021 at 0430 EDT, the 2B motor driven emergency feedwater pump (MDEFWP or MDEFW pump) was removed from service for planned train maintenance. Unit 2 was in MODE 1 at 100 percent power. At 1714, the 2B MDEFW pump tripped while starting a bump for rotation test following completion of planned maintenance. The cause of the 2B MDEFW pump trip was determined to be failure of a shorting block in the secondary circuit of the protective over current relay. The shorting screws on the block had loosened, allowing the circuit to open, causing arcing, and a distorted current waveform that tripped the protective over current relay. The cause of this event was discovered on August 3, 2021.
A subsequent cause evaluation determined that a similar 2B MDEFW pump trip on February 1, 2021 was also caused by the intermittent poor electrical connection due to the loose shorting screws. Although the 2B MDEFW pump passed the post-maintenance testing in February 2021 and successfully completed a subsequent surveillance in April 2021, the follow-up evaluation determined that the 2B MDEFW pump was inoperable from February 1, 2021 to August 4, 2021; which is longer than the technical specification (TS) limiting condition for operation (LCO) 3.7.5, Condition A, seven day allowed outage time.
Therefore this condition is being reported as a condition prohibited by TS under 10 CFR 50.73(a)(2)(i)(B).Page of 05000-
- 3. LER NUMBER YEAR SEQUENTIAL NUMBER REV NO.
CAUSAL FACTORS The 2B MDEFW pump trip was a result of an intermittent poor electrical connection due to the loose current transformer (CT) shorting screws on the shorting block in the secondary circuit of the protective over current relay.
CORRECTIVE ACTIONS
- 1. The affected shorting block was replaced.
- 2. Shorting screws were tightened.
- 3. Shorting jumpers were installed.
- 4. Extent of condition reviews were completed of the secondary side wiring of the other MDEFW pumps for the use of shorting blocks and tightness of shorting block screws. There was no observed arcing or associated damage to the shorting blocks.
SAFETY ANALYSIS
The subject event was evaluated using the Oconee Probabilistic Risk Assessment (PRA) model and found to be of very low safety significance. For the time period from February 1, 2021 to August 4, 2021, either the 2A MDEFW pump and/or Unit 2 TDEFW pump was available to provide the required heat removal capability. Either of these pumps is sufficient to provide the required heat removal capability. Thus, it is concluded that the impact of this event on overall plant risk is insignificant and had no impact on public health and safety.
ADDITIONAL INFORMATION
Energy Industry Identification System (EIIS) codes are identified in the text as [XX]. This event is considered Industry Reporting and Information System (IRIS) reportable.
A review of Duke Energy's Corrective Action Program did not identify any Oconee LERs or events in the last three years that involved the same underlying concerns as this event.
There were no releases of radioactive materials, radiation exposures or personnel injuries associated with this event.
3 3
Oconee Nuclear Station Unit 2 00270 2021 001 00