05000370/LER-2023-001, Manual Actuation of the Unit 2 Motor Driven Auxiliary Feedwater Pumps
| ML23151A370 | |
| Person / Time | |
|---|---|
| Site: | Mcguire |
| Issue date: | 05/31/2023 |
| From: | Pigott E Duke Energy Carolinas |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| RA-23-0123, 02467460 LER 2023-001-00 | |
| Download: ML23151A370 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 3702023001R00 - NRC Website | |
text
-,DUKE ENERGY Serial No: RA-23-0123 May 31, 2023 U.S. Nuclear Regulatory Commission Washington, D.C. 20555 ATTENTION: Document Control Desk Subject: Duke Energy Carolinas, LLC McGuire Nuclear Station, Unit 2 Docket No. 05000370 Renewed License No. NPF-17 Licensee Event Report 2023-001-00 Nuclear Condition Report Number 02467460 Edward R. Pigott Site Vice President McGuire Nuclear Station Duke Energy MG01VP 112700 Hagers Ferry Road Huntersville, NC 28078 o: 980.875.4805 Edward.Pigott@duke-energy. com 10 CFR 50.73 Pursuant to 10 CFR 50. 73 Section (a)(2)(iv)(A), attached is Unit 2 Licensee Event Report (LER) 2023-001-00, regarding manual actuation of the Auxiliary Feedwater Motor Driven Pumps in response to potential equipment failure.
This event is considered to have no significance with respect to the health and safety of the public. There are no regulatory commitments contained in this LER.
If questions arise regarding this LER, please contact Jeff Sanders at 980-875-4680.
Sincerely, Edward R. Pigott Duke Energy McGuire Nuclear Station Site Vice President Attachment U.S. Nuclear Regulatory Commission RA-23-0123 Page 2
cc: Laura A. Dudes Administrator Region II U.S. Nuclear Regulatory Commission Marquis One Plaza 245 Peachtree Center Avenue NE Suite 1200, 30303-1257
J. Klos Project Manager (McGuire)
U.S. Nuclear Regulatory Commission Mail Stop O-9-E3 11555 Rockville Pike Rockville, MD 20852
Chris Safouri NRC Senior Resident Inspector McGuire Nuclear Station
Abstract
On April 2, 2023, at 0341, Operations entered the Senior Reactor Operator Decision Making Process after receiving a report that called into question the functionality of the operating 2B Main Feedwater (MFW) Pump Recirculation Valve, 2CF-81. At the time, Unit 2 was in Mode 3, the 2B MFW pump was feeding the steam generators, and the 2A MFW Pump Recirculation Valve 2CF-76 was nonfunctional. At 0352 hours0.00407 days <br />0.0978 hours <br />5.820106e-4 weeks <br />1.33936e-4 months <br />, Operations manually started the Auxiliary Feedwater (AFW) Motor Driven Pumps to feed the steam generators to allow corrective maintenance on the MFW System. The AFW Motor Driven Pumps started as designed. Flow to the steam generators was not adversely impacted during this sequence.
Subsequent investigation determined that the 2A and 2B MFW recirculation piping experienced abnormal vibration when flow was introduced through valves 2CF-76 and 2CF-81, making the valves susceptible to failure. The recirculation piping had recently been modified to replac e the carbon steel elbow piping immediately downstream of the valves with a stainless steel target tee configuration. To mitigate the issue, the target tee was replaced with the original carbon steel elbow arrangement. This event had no impact on the health and safety of the public.
BACKGROUND
The following information is provided to assist readers in understanding the event described in this LER.
Applicable Energy Industry Identification [EIIS] system and component codes are enclosed within brackets.
Feedwater System [SJ]:
The Main Feedwater System (MFW) takes treated Condensat e System water, heats it further to improve the plant's thermal cycle efficiency, and delivers it at the required flow rate, pressure, and temperature to the steam generators (SGs). The MFW is designed to maintain proper vessel water levels with respect to reactor power output and turbine steam requirements.
Auxiliary Feedwater System [BA]:
The Auxiliary Feedwater System (AFW) automatically supplies feedwater to the SGs to remove decay heat from the Reactor Coolant System (RCS) upon the loss of normal feedwater supply. The AFW mitigates the consequences of any event with loss of normal feedwater. The design basis of the AFW is to supply water to the SGs to remove decay heat and other residual heat by delivering at least the minimum required flow rate to the SGs.
The AFW is designed to start automatically for any event requiring emergency feedwater. The AFW Motor Driven Pumps will automatically provide feedwater when initiated on any of the following conditions:
- 1. Trip of both main feedwater pumps
- 2. AMSAC Actuation (AMSAC - Anticipated Transient Without Scram (ATWS) Mitigation System Activation Circuitry)
- 3. Two out of four (2/4) low-low level alarms in any one SG
- 4. Initiation of a safety injection signal
- 5. Loss of power to the 4160V essential bus (Blackout)
The AFW Turbine Driven Pump will automatically provide feedwater when initiated on any of the following conditions:
- 1. Two out of four (2/4) low-low level alarms in any two SGs
- 2. Loss of power to the 4160V essential bus (Blackout)
EVENT DESCRIPTION
On April 1, 2023, McGuire Unit 2 was preparing to exit the 2023 spring refueling outage by entering Mode 3 and subsequently heating the Reactor Coolant System to full temperature and pressure. During the refueling outage and prior to plant heat up, an Engineering Change (EC 419577) was implemented to (1) replace the piping downstream of the MFW Pump Recirculation Valves 2CF-76 and 2CF-81 with stainless steel material, (2) replace the elbow immediately downstream of valves 2CF-76 and 2CF-81 with a target tee configuration, and (3) upgrade the pressure and temperature ratings of piping between 2CF-76/81 and 2CF-77/82. Subsequently, during MFW pump startup activities after completion of the modification, the 2A and 2B MFW recirculation piping experienced abnormal vibration when flow was introduced through the recirculation valves.
On April 2, 2023, at 0341, Operations entered the Senior Reactor Operator Decision Making Process after receiving a report that called into question the functionality of the operating 2B MFW Pump Recirculation Valve, 2CF-81. At the time, Unit 2 was in Mode 3, the 2B MFW pump was feeding the steam generators, and the 2A MFW Pump Recirculation Valve 2CF-76 was nonfunctional. At 0352 hours0.00407 days <br />0.0978 hours <br />5.820106e-4 weeks <br />1.33936e-4 months <br />, Operations manually started the Auxiliary Feedwater (AFW) Motor Driven Pumps to feed the steam generators to allow corrective maintenance on the MFW System. The AFW Motor Driven Pumps started as designed. Flow to the steam generators was not adversely impacted during this sequence.
Subsequent investigation determined that turbulent flow through the target tee caused abnormal vibration, making the recirculation valves susceptible to failure. As a means of mitigating the issue, the Engineering Change was revised to return the outlet configuration of 2CF-76 and 2CF-81 back to its original short radius elbow configuration of schedule 80 carbon steel. After completion of the Engineering Change revision, the MFW pumps were successfully restarted, vibration levels were consistent with normal operation, and the recirculation valves functioned as required. The 2A and 2B AFW Motor Driven Pumps were secured, and unit startup activities continued.
Sequence of Events (times are approximate)
- 04/01/23 12:16 - Unit 2 entered Mode 3
- 04/02/23 00:42 - The Unit 2 Reactor Coolant System reached full temperature and pressure.
- 04/02/23 00:56 - The 2A MFW pump was placed in service.
- 04/02/23 02:39 - The control room received annunciator alarm 2AD-8 A4 (MFW Pump Discharge Hi Pressure) due to 2CF-76 failing closed. The control room also received indications of Unit 2 Condensate flow lowering consistent with 2CF-76 closing and responded by opening 2CF-81 manual loader to mitigate the 2A MFW pump high discharge pressure.
- 04/02/23 03:22 - The 2B MFW pump was placed in service.
- 04/02/23 03:32 - The 2A MFW pump was removed from service by the control room.
- 04/02/23 03:41 -Senior Reactor Operator Decision Making process entered. The Decision was made to feed the steam generators with the AFW Motor Driven Pumps.
- 04/02/23 03:52 - The control room started the 2A and 2B AFW Motor Driven Pumps.
- 04/02/23 04:03 - The 2B MFW pump was removed from service by the control room.
- 04/02/23 04:05 - The Unit 2 AFW Motor Driven Pumps are providing feed flow to all Unit 2 steam generators.
- 04/03/23 23:24 - The 2B MFW pump was placed back into service.
- 04/03/23 23:28 - The control room secured the 2A and 2B AFW Motor Driven Pumps.
- 04/04/23 21:10 - The 2A MFW pump was placed back into service.
REPORTABILITY DETERMINATION
Manual actuation of the AFW Motor Driven Pumps meets the threshold for an 8-hour report in accordance with § 50.72(b)(3)(iv)(A), Any event or condition that results in valid actuation of any of the systems listed in paragraph (b)(3)(iv)(B) of this section, except when the actuation results from and is part of a pre-planned sequence during testing or reactor operation. § 50.72(b)(3)(iv)(B) lists the AFW System as a system within the scope of § 50.72(b)(3)(iv)(A).
On April 2, 2023, at 1129, Operations reported the manual actuation of the AFW Motor Driven Pumps to the NRC Operations Center as a valid actuation in accor dance with § 50.72(b)(3)(iv)(A). The Event Notification (EN) is documented as EN 56451.
This LER satisfies the corresponding written reporting criteria in 10 CFR 50.73(a)(2)(iv)(A), "Any event or condition that resulted in manual or automatic actuation of any of the systems listed in paragraph (a)(2)(iv)(B).
CAUSAL FACTORS
A cause investigation determined that the risk of an adverse impact, due to an unvalidated design assumption on turbulent flow, was not recognized when modifying the MFW pump recirculation lines.
CORRECTIVE ACTIONS
The previously implemented Engineering Change was revised to return the plant to its former configuration by replacing the newly installed target tees with schedule 80 carbon steel short radius elbows. Engineering Change procedural guidance was also revised to require risk assessments for First-Of-A-Kind (FOAK) or First-In-A-While (FIAW) plant modifications.
SAFETY ANALYSIS
Operations manually started the AFW Motor Driven Pumps prior to removing the 2B MFW pump from service. The AFW Motor Driven Pumps started as designed, and feed flow to the steam generators was not adversely impacted during this event. All plant systems responded as expected. Therefore, it is concluded that the impact on core damage risk was very small, and the event had no impact on public health and safety.
ADDITIONAL INFORMATION
A review of previous Licensee Event Reports was conducted to determine if this was a recurring event (i.e.,
similar event with the same cause or same failure mode). No previous similar events were identified within the past three years associated with manual actuation of the AFW System. Therefore, this is not considered a recurring event.