05000458/LER-2022-003, Division 1 Standby Diesel Generator Speed Sensor Power Supply Failure
| ML22244A098 | |
| Person / Time | |
|---|---|
| Site: |  |
| Issue date: | 09/01/2022 |
| From: | Karenina Scott Entergy Nuclear Operations |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| RBG-48194 LER 2022-003-00 | |
| Download: ML22244A098 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 4582022003R00 - NRC Website | |
text
E)entergy RBG-48194 Kent Scott Site Vice President 225-381-4374 10 CFR 50.73 September 01, 2022 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001
Subject:
Licensee Event Report 50-458 / 2022-03-00, Division 1 Standby Diesel Generator Speed Sensor Power Supply Failure River Bend Station - Unit 1 NRC Docket Nos. 50-458 Renewed Facility Operating License No. NPF-47 In accordance with 10 CFR 50. 73, enclosed is the subject Licensee Event Report.
This document contains no commitments.
Should you have any questions, please contact Mr. Tim Schenk, Regulatory Assurance Manager, at 225-381-4177.
Enclosure:
cc:
Licensee Event Report 50-458 / 2022-03-00, Division 1 Standby Diesel Generator Speed Sensor Power Supply Failure NRC Region IV Regional Administrator - Region IV NRC Senior Resident Inspector - River Bend Station NRC Project Manager - River Bend Station Entergy Nuclear Operations, Inc., River Bend Station, 5485 U.S. Highway 61, St. Francisvil[e, LA 70775
RBG-48194 Enclosure Page 1 of 1 Enclosure RBG-48194 Licensee Event Report 50-458 / 2022-03-00, Division 1 Standby Diesel Generator Speed Sensor Power Supply Failure Entergy Nuclear Operations, Inc., River Bend Station, 5485 U.S. Highway 61, St. Francisville, LA 70775
Abstract
On July 04, 2022, at 2115 Central Time, while River Bend Station, Unit 1 was operating in Mode 1 at 100 percent power, the Division 1 Standby Diesel Generator was declared Inoperable due to failure of redundant power supplies in the speed control circuitry. This was discovered during monthly surveillance testing. The failedpower supplies provide power to the exciter flash circuitry and ramp governor control. This condition would have prevented the Division 1 Standby Diesel Generator from providing power to Division 1 Emergency Loads.
The issue was determined to be reportable in accordance with 10 CFR 50.73(a)(2)(v)(A), (B), (C), and (D) as any event or condition that could have prevented the fulfillment of the safety function of structures or systems. This event was not reportable in accordance with 10 CFR 50. 72 because the Division 2 Standby Diesel Generator was operable and available at the time of discovery.
The condition was corrected by replacing the power supplies on July 07, 2022.
EVENT DESCRIPTION
On July 04, 2022, at 2115 Central Time, River Bend Station, Unit 1 (RBS) was operating in Mode 1 at 100 percent power. There were no other structures, systems, or components (SSCs) that were inoperable that contributed to this event.
A failure was identified in the speed control circuitry of the Division 1 Standby Diesel Generator (EGS-EG1A) [EK] [DG] during monthly surveillance testing per STP-309-0201, Division I Diesel Generator Operability Test. EGS-EG1A was,declared inoperable due to the speed control circuitry failure and documented in the RBS Corrective Action Program in CR-RBS-2022-03801.
EGS-EG1A speed control circuit contains redundant Dynalco SDC-2000, 125 VDC to 24 VDC power supply converters (EGS-E/EX43A and EGS-E/EY 43A) [CNV]. These components supply power to individual speed switches and tachometers.
EGS-E/EY43A also supplies power to Emergency Response Information System (ERIS) [ID] computer point (EGSEY009) [SI]. The speed control circuit is designed such that either one of the power supplies is sufficient to allow field flash and loading of the diesel genetator. These power supplies were refurbished by Paragon and installed in December 2020. The failures occurred after approximately 1.5 years with an expected replacement frequency of 8 years.
Timeline of events:
06/01/22 - STP-309-0201, Division 1 Diesel Generator Operability Test completed. This was the last known successful operability run for EGS-EG1A. This verified that both EGS-E/EX43A and EGS-E/EY 43A were functioning properly on 06/01/22 because the local tachometers and EGSEY009 provided proper indication.
06/08/22 - ERIS computer point, EGSEY009 "flatlined" starting on 06/08/22, which is most likely when EGS-E/EY43A lost power.
This was not a normally monitored component and went undetected until troubleshooting identified the condition on 07/05/22.
06/12-13/22-Performed STP-309-0202, Division 2 Diesel Generator Operability Test.The normal requirements of this test resulted in 0.63 hours7.291667e-4 days <br />0.0175 hours <br />1.041667e-4 weeks <br />2.39715e-5 months <br /> of Unavailability for the Division 2 Standby Diesel Generator (EGS-EG 1 B) [EK] [DG].
07/04/22-EGS-EG1A, Division 1 Emergency Diesel Generator was declared inoperable.
07/05/22 - Trouble shooting determined the failure of both power supplies EGS-E/EX43A and EGSE/EY43A.
07 /05/22 - Trouble shooting determined that both power supplies had blown fuses.
07 /05/22 - Common Mode Failure evaluation determined that EGS-EG 1 B utilizes the same exact design and manufacturer for these components. However, voltage readings for EGS-E/EX43B and EGS-E/EY 43B were satisfactory leading to the conclusion that the failure was not currently present in EGS-EG 1 B.
07 /05/22 - Common Mode Failure evaluation excluded the Division 3 High Pressure Core Spray Diesel Generator due to differing designs.
07/06/22 - RBS function testing to determine the cause of the blown fuses was inconclusive.
07/07/22-Completed installation of EGS-E/EX43A and EGS-E/EY43A power supplies per Engineering Change (EC-87792). The new Phoenix power supplies are designed with external lights to provide positive indication of power status.
07/07/22 - Completed post maintenance testing and declared EGS-EG1A operable.
08/04/22 - The failed Dynalco SDC-2000 power supplies were shipped to an outside vendor, Engine Systems Inc., to perform a detailed failure analysis. Preliminary results are expected in September 2022.
As stated in the timeline above, monthly surveillance testing rendered EGS-EG1 B unavailable for a total of 0.63 hours7.291667e-4 days <br />0.0175 hours <br />1.041667e-4 weeks <br />2.39715e-5 months <br /> during June 12-13, 2022. The discovery of EGSEY009 "flatlined" starting on June 08, 2022, means that EGS-E/EY 43A most likely lost power at that time. Although either EGS-E/EY 43A or EGS-E/EX43A functioning properly would allow EGS-EG1A to load, the timing of EGS-E/EX43A power loss is unknown. Therefore, this condition is being reported in accordance with 10 CFR 50.73(a)(2)(v) as "Any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to: (A)
Shut down the reactor and maintain it in a safe shutdown condition; (B) Remove residual heat; (C) Control the release of radioactive material; or (D) Mitigate the consequences of an accident." This event was not an ENS notification because EGS-EG1 B was operable and available at the time of discovery. Page 2 of 3 (08-2020)
U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 08/31/2023 LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET (See NUREG-1022, R.3 for instruction and guidance for completing this form https ://www.nrc.gov/readi ng-rm/doc-col lections/nuregs/staff /sr1 022/r3D River Bend Station, Unit 1 05000- 458 YEAR 2022
SAFETY ASSESSMENT
- 3. LER NUMBER SEQUENTIAL NUMBER 003 REV NO.
00 This assessment is being performed under the assumption that EGS-E/EX43A lost power on June 08, 2022, the same day that EGSEY009 "flatlined" which indicated that EGS-E/EY43A had lost power. This would have made EGS-EG1A unavailable from June 08, 2022, until July 07, 2022, when the new Phoenix power supplies were installed and EGS-EG1A was declared operable.
On June 12-13, 2022, EGS-EG1B was placed in Maintenance Mode and made unavailable fora total of 0.63 hours7.291667e-4 days <br />0.0175 hours <br />1.041667e-4 weeks <br />2.39715e-5 months <br /> to support normal surveillance testing. If an actual Loss of Offsite Power had occurred while EGS-E 1 B was in Maintenance Mode, operators would have restored it back to Operational Mode in accordance with AOP-0050, STATION BLACKOUT and/or SOP-0053, STANDBY DIESEL GENERATOR AND AUXILIARIES. EGS-EG1B was available for most of time that EGS-EG1Awas unavailable. Additionally, no Loss of Offsite Power or Loss of Coolant Accident occurred during this time, therefore this event was of minimal significance to the health and safety of the public.
EVENT CAUSE
The direct cause of this event is currently unknown. The RBS troubleshooting plan identified blown fuses internally to both power supplies. The team understood that a blown fuse is not a cause but a symptom and continued to perform preliminary testing on the removed power supplies which produced inconclusive results.
The inconclusive results of testing the faulty power supplies at RBS dictated that a failure analysis would be required by an outside vendor. Both failed power supplies were shipped to Engine Systems, Inc. on August 04, 2022. RBS is scheduled to receive preliminary results in September 2022. RBS plans to submit a supplemental report detailing the results of the vendor failure analysis.
CORRECTIVE ACTIONS
Completed:
Replaced EGS-EG1A power supplies, EGS-E/EX43A and EGS-E/EY43A. The new design by Phoenix has external indication of power status.
Replaced EGS-EG1 B power supplies, EGS-E/EX43B and EGS-E/EY 438. The new design by Phoenix has external indication of power status.
Revised OSP-0028 LOG REPORT - NORMAL SWITCHGEAR, CONTROL, AND DIESEL GENERATOR BUILDINGS to include local monitoring of EGS-E/EX43A, EGS-E/EY43A, EGS-E/EX438, and EGS-E/EY 438 power supply lights once per shift.
Revised OSP-0027 LOG REPORT - MAIN CONTROL ROOM to include monitoring ERIS computer points associated with Division 1, 2, and 3 Diesel Generator tachometers from the Main Control Room once per shift.
Planned actions tracked in the Corrective Action Program:
Revise the Adverse Condition Analysis product to incorporate findings and learnings from the vendor failure analysis. The intent is to present the updated document to station management.
Submit a supplement to this Licensee Event Report to incorporate the findings of the vendor failure analysis.
PREVIOUS SIMILAR EVENTS
None NOTE:
Energy Industry Identification System (EIIS) codes and component codes are identified in the text of this report as [XX]. Page 3 of 3