05000400/LER-2021-001, Automatic Reactor Trip Due to Faults on Non-Segregated Bus from Unit Auxiliary Transformer 1B
| ML21047A011 | |
| Person / Time | |
|---|---|
| Site: | Harris  |
| Issue date: | 02/16/2021 |
| From: | Dills J Duke Energy Progress |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 2021-001-00 | |
| Download: ML21047A011 (4) | |
| Event date: | |
|---|---|
| Report date: | |
| 4002021001R00 - NRC Website | |
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John R. Dills Plant Manager Shearon Harris Nuclear Power Plant 5413 Shearon Harris Road New Hill, NC 27562-9300 10 CFR 50.73 February 16, 2021 Serial: RA-21-0034 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001 Shearon Harris Nuclear Power Plant, Unit 1 Docket No. 50-400/Renewed License No. NPF-63 Subject: Licensee Event Report 2021-001-00 Ladies and Gentlemen:
Duke Energy Progress, LLC, submits the enclosed Licensee Event Report 2021-001-00 in accordance with 10 CFR 50.73 for Shearon Harris Nuclear Power Plant, Unit 1 (HNP). On December 16, 2020, with HNP in Mode 1, HNP experienced an automatic reactor trip due to lock-out of the main generator. The 6.9 kilovolt non-segregated bus from the Unit Auxiliary Transformer 1B to the Auxiliary Bus 1B was impacted by faults on the bus.
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 Chuck Yarley at (984) 229-2477.
Sincerely, John R. Dills Enclosure: Licensee Event Report 2021-001-00 cc:
J. Zeiler, NRC Senior Resident Inspector, HNP M. Mahoney, NRC Project Manager, HNP NRC Regional Administrator, Region II
Abstract
On December 16, 2020, At 08:51, Shearon Harris Nuclear Power Plant, Unit 1 (HNP) experienced an automatic reactor trip due to lock-out of the main generator. The generator lock-out was triggered by phase-to-phase faults that occurred on the 6.9 kilovolt non-segregated bus from the Unit Auxiliary Transformer 1B to the Auxiliary Bus 1B.
Based on forensics and causal analysis, the event was initiated by electrical faults impacting the non-segregated bus within a wall penetration between the Turbine Building (TB) and the Reactor Auxiliary Building (RAB). Degraded bus insulation (Noryl) combined with a medium to conduct the current (water) resulted in faults on the bus. The bus within the penetration is inaccessible and insulation had not been proactively replaced despite known degradation mechanisms. In addition, the installed configuration of the wall penetration did not match the original design and was not being maintained to ensure weather tight characteristics. Bus insulation will be replaced to ensure ongoing insulation integrity and bus penetrations will be restored to design configuration. Further actions will be taken to emphasize lessons learned from the event, including the need to proactively address known issues.Page of 05000-
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D. Corrective Actions
The site will seal the TB/RAB expansion joint to prevent water from reaching the TB/RAB wall penetration. The eight non-segregated bus penetrations will also be sealed against water and will be restored to match the design configuration. A preventative maintenance strategy will be implemented to periodically assess the wall penetrations. The buses will be inspected and a strategy shall be implemented to ensure bus insulation integrity. Alternatively, the buses can be replaced with cable rated for medium voltage loads. The faulted bus will be repaired. This event will be included in senior leadership training as well as in Electrical Maintenance and Engineering training.
E. Safety Analysis
Upon loss of power from UAT-1B, the power supply was automatically fast transferred from UAT-1B to SUT-1B, maintaining the power supply to the associated safety bus. Loads from UAT-1A were also fast transferred to SUT-1A, as per plant design following a main generator lock-out signal. The trip was not complex, with all safety systems functioning as designed during and following the reactor trip. This condition had no impact on the health and safety of the public.
F. Additional Information
There have been no events similar to the event documented in this LER in the past three years.
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Shearon Harris Nuclear Power Plant, Unit 1 400 2021 001 00