05000338/LER-2024-002-01, Ih EDG Failure to Achieve Rated Speed / Frequency During Surveillance Testing
| ML25043A286 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 02/12/2025 |
| From: | Hilbert L Virginia Electric & Power Co (VEPCO) |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| 24-357A LER 2024-002-01 | |
| Download: ML25043A286 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3382024002R01 - NRC Website | |
text
VIRGINIA ELECTRIC AND POWER COMPANY RICHMOND, VIRGINIA 23261 10CFR50.73 Virginia Electric and Power Company North Anna Power Station 1022 Haley Drive Mineral, Virginia 23117 February 12, 2025 Attention: Document Control Desk U. S. Nuclear Regulatory Commission Washington, DC 20555-0001
Dear Sir or Madam:
Serial No.:
24-357 A NAPS:
RAP Docket Nos.: 50-338 License Nos.: NPF-4 Pursuant to 1 0CFR50.73, Virginia Electric and Power Company hereby submits the following Licensee Event Report applicable to North Anna Power Station Unit 1.
Report No. 50-338/2024-002-01 This report has been reviewed by the Facility Safety Review Committee and will be forwarded to the Management Safety Review Committee for its review.
Sincerely, Lisa Hilbert Site Vice President North Anna Power Station Enclosure Commitments contained in this letter: None cc:
United States Nuclear Regulatory Commission Region II Marquis One Tower 245 Peachtree Center Ave., NE, Suite 1200 Atlanta, Georgia 30303-1257 NRC Senior Resident Inspector North Anna Power Station
Abstract
On October 9, 2024, at 1315 hours0.0152 days <br />0.365 hours <br />0.00217 weeks <br />5.003575e-4 months <br /> with Unit 1 in Mode 1, 100% power, while conducting routine surveillance testing of the 1 H Emergency Diesel Generator (EOG) under 1-PT-82.2A, 1-EE-EG-1 H Simulated Loss of Offsite Power, the engine speed was observed to be at 880 RPM / 58.5 Hz and the control room operator had no speed control. Investigation into the event identified the mechanical governor speed control vernier to not be at the correct speed setting. The identified primary cause is the organizational weakness to recognize the significance in documenting and monitoring position-able controls for Woodward governor-controlled components.
Unit 2 was not impacted by this event. Since the 1 H EOG was not able to meet its surveillance requirement for frequency, this event is reportable per 10 CFR 50.73(a)(2)(i)(B) for Operation or Condition Prohibited by Technical Specifications. The health and safety of the public were not affected by this event.
1.0 Description of Event
- 2. DOCKET NUMBER
- 3. LER NUMBER I
00338 D
NUMBER NO.
I YEAR SEQUENTIAL REV
~-I 002 1-0 On October 9, 2024, at 1315 hours0.0152 days <br />0.365 hours <br />0.00217 weeks <br />5.003575e-4 months <br /> with Unit 1 in Mode 1, 100% power, the control room team was unable to control 1 H Emergency Diesel Generator (EOG) (EIIS System EK, Component DG) speed with the EMER GEN 1 H SPEED/LOAD CONTROL switch during the performance of 1-PT-82.2A, 1-EE-EG-1 H Simulated Loss of Offsite Power. The engine speed was observed to be at 880 RPM/ 58.5 Hz when the lack of speed control was discovered. Investigation into the event identified the mechanical governor speed control vernier to not be at the correct speed setting, 18.7 4 versus a desired setting of 20.96. The identified primary cause is the organizational weakness to recognize the significance in documenting and monitoring position-able controls for Woodward governor-controlled components.
The primary control unit is the electronic governor which controls engine speed at 900 RPM / 60 Hz. The mechanical governor although physically attached to the engine is the back up control unit. Whichever control unit is set with the lowest operating speed is in control by design. The mechanical governor is equipped with manual speed control via a speed control knob or vernier position indicator. The mechanical governor is also equipped with a mechanical slow speed and high-speed stop device. The slow speed stop is set to approximately 500 RPM and the high-speed stop is set to 945 RPM (equivalent to 63 Hz). When the EDGs are in AUTO, the mechanical governor speed setting is set at the 945 RPM dial setting or high-speed stop. This setting allows for the electronic governor to be in control of the system as it maintains the lower operating set point of 900 RPM / 60 Hz. With the 1 H EOG mechanical governor speed control found at 18. 7 4 and engine operating at 880 RPM which is equivalent to 58.5 Hz the mechanical governor-maintained control of the engine speed as it was below the 900 RPM control point of the electronic governor. Therefore, the engine was operating outside of the minimum Technical Specification and UFSAR set points, considered inoperable, and secured by operations. This event is reportable per 10 CFR 50.73(a)(2)(i)(B) for Operation or Condition Prohibited by Technical Specifications.
2.0 Significant Safety Consequences and Implications
The EOG is normally analyzed at 60.5 Hz. This is due to the higher frequency increases in the demand of Brake Horsepower (BHP) which in turn increases the realized KW loading of the bus. The most heavily loaded EDG is 1 H which normally has a Technical Specification limit analyzed loading of 3342 KV A/2966 KW. This results in a running current of 1438.5A. Accounting for the deviation in frequency to 58.5 Hz, the running load of the EOG is reduced to 2999 KV A/2620 KW. This results in a running current of 393.5A. The EDG's rated continuous load current is noted as 520A. Therefore, the expected loading of the bus at 58.5 Hz is bound by North Anna specific calculations and would pose no operational challenges to the EDG's ability to carry bus loads. The 1 H EOG would have auto started, output breaker closed, electrical loads sequenced on the bus, and the engine, electrical generator, voltage regulator, and governor controls would have functioned supporting continuous operation at 58.5 Hz. Additionally, there would be no impact to the design basis safety analysis for a Large Break Loss Of Coolant Accident (LBLOCA), and no adverse impact to the PRA Success criteria for this
~vent. The health and safety of the public were not affected by this event.
~.O Cause of the Event
- 2. DOCKET NUMBER I
00338
- 3. LER NUMBER NUMBER NO.
I YEAR SEQUENTIAL REV
~-,
002 1-0 Investigation into the event identified the mechanical governor speed control vernier to not be at the correct speed setting.
The identified primary cause is the organizational weakness to recognize the significance in documenting and monitoring position-able controls for Woodward governor-controlled components. The position-able controls are not alarmed and do not have an immediately identifiable system response while these components are in standby. The missed opportunity to routinely validate these settings challenges system readiness.
While the reason for the 1 H governor speed setting being below the required setting could not be determined with certainty, a Human Performance concern exists within the self-check process (STAR). Proper self-check would have prevented the component misposition. Self-check processes are critical for correct task performance and ensures individual accountability of outcomes. In addition, inconsistencies exist between the various EOG controlling documents. Specifically, operation of speed control is not uniform.
4.0 Immediate Corrective Action
rrhe vernier was returned to the correct setting and 1-PT-82.2A was performed satisfactorily.
5.0 Additional Corrective Actions
Using a dynamic learning activity (DLA), Operations will determine the extent of Operator Self-Check/Stop-Think-Act-Review (STAR) effectiveness. The results of this evaluation will be used to perform a Performance Gap Analysis (PGA).
6.0 Actions to Prevent Recurrence Operations initiated increased monitoring for the EOG speed settings and made permanent changes to Operator Rounds.
J\\dditionally, Operations has initiated changes to EOG procedures to include documenting the Governor Vernier setting in the post-operational checklist. This has been extended to include the governors for the Turbine Driven Auxiliary Feedwater Pumps and the Station Blackout Diesel.
7.0 Similar Events
No similar events have been noted at North Anna.
8.0 Additional Information
Unit 2 was not impacted by this event. The health and safety of the public were not affected by this event. Page 3
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