ML25063A190
| ML25063A190 | |
| Person / Time | |
|---|---|
| Site: | Vogtle  |
| Issue date: | 03/19/2025 |
| From: | John Lamb NRC/NRR/DORL/LPL2-1 |
| To: | Southern Nuclear Operating Co |
| References | |
| EPID L-2025-LLA-0035 | |
| Download: ML25063A190 (1) | |
Text
March 19, 2025 LICENSEE:
Southern Nuclear Operating Company, Inc.
FACILITY:
Vogtle Electric Generating Plant, Units 3 and 4
SUBJECT:
SUMMARY
OF MARCH 3, 2025, OBSERVATION MEETING HELD WITH SOUTHERN NUCLEAR OPERATING COMPANY, INC., REGARDING A LICENSE AMENDMENT REQUEST TO CHANGE TABLE 3.3.8-1 FOR VOGTLE ELECTRIC GENERATING PLANT, UNITS 3 AND 4 (EPID L-2025-LLA-0035)
On March 3, 2025, an Observation meeting was held between the U.S. Nuclear Regulatory Commission (NRC) and representatives of Southern Nuclear Operating Company, Inc. (SNC, the licensee). The purpose of the meeting was for SNC to describe its license amendment request (LAR) for Vogtle Electric Generating Plant (Vogtle), Units 3 and 4.
On February 14, 2025 (Agencywide Documents and Access Management System (ADAMS)
Accession No. ML25045A166), SNC submitted an LAR to add to Technical Specification (TS)
Table 3.3.8-1 a new Tcold - High function for passive residual heat removal (PRHR) actuation logic at Vogtle, Units 3 and 4.
A pre-submittal meeting was held on October 15, 2024, and the meeting summary is located at ADAMS Accession No. ML24290A158.
A list of attendees is provided as an Enclosure.
On February 12, 2025 (ML25043A003), the meeting was noticed on the NRC public web page.
The NRC staff opened the meeting with introductory remarks and a roll call of the attendees.
The SNC representative presented slides located at ADAMS Accession No. ML25055A253.
SNC representatives discussed the following topics: (1) background - reason for the change, (2) PRHR heat exchanger (HX) actuation logic, (3) current logic, (4) proposed logic, (5) safety analysis impact, (6) TS 3.3.8 planned change, (7) schedule, and (8) discussion.
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Background===
SNC representatives stated that the reason for the proposed change is to address the Haiyang, Unit 2, event that occurred on October 17, 2018. The SNC representative said that the Haiyang, Unit 2, feedwater pump tripped which led to a reactor trip, and a subsequent startup feedwater (SFW) initiation; this resulted in a decrease in the cold leg temperatures. The Haiyang, Unit 2, operators attempted to prevent a safeguards signal from being generated on Tcold - Low-2. This resulted in Low-2 Steam Generator (SG) Narrow Range (NR) level coupled with Low-2 SFW flow, which generated an automatic PRHR HX actuation, reducing Tcold further leading to a safeguards actuation.
SNC representatives stated that unnecessary PRHR actuation challenges operations that could lead to excessive cooldowns and unnecessary safeguards actuation on Tcold - Low 2. The SNC representative said that the unnecessary generation of a safeguards actuation is a highly undesirable challenge to safety systems, places stresses on the plant, and imposes significant recovery efforts.
PRHR HX Actuation Logic Vogtle, Units 3 and 4, TS 3.3.1 is Reactor Trip System (RTS) Instrumentation. The limiting condition of operation (LCO) 3.3.1 states:
The RTS instrumentation for each Function in Table 3.3.1-1 shall be OPERABLE.
Vogtle, Units 3 and 4, TS 3.3.11 is Engineered Safety Feature Actuation System (ESFAS)
Startup Feedwater Flow Instrumentation. The LCO 3.3.11 states:
Two channels of ESFAS Startup Feedwater Flow - Low 2 instrumentation for each startup feedwater line shall be OPERABLE.
Vogtle, Units 3 and 4, TS 3.3.8 is Engineered Safety Feature Actuation System (ESFAS)
Instrumentation. The LCO 3.3.8 states:
The ESFAS instrumentation channels for each Function in Table 3.3.8-1 shall be OPERABLE.
TS Table 3.3.8-1 has, in part, the following functions:
Number Function 11 RCS [Reactor Coolant System] Cold Leg Temperature (Tcold) - Low 2 20 SG [Steam Generator] Narrow Range [NR] Water Level - Low 2 21 SG Wide Range [WR] Water Level - Low 2 SNC representatives stated that the following are the proposed PRHR actuation logic changes:
Revise PRHR actuation logic to require low level with low flow on both SGs, and Revise PRHR HX actuation with coincident at least one loop of RCS above Tcold - High setpoint.
SNC representatives said that (1) there are no changes being made to the reactor trip on either SG Low-2 NR level, (2) there are no changes being made to PRHR actuation on either SG Low-2 WR level, and (3) there are no hardware changes required except for sequence of events (SOE) cards added in non-safety SOE cabinets; however this is not within scope of the proposed LAR.
Schedule By letter dated February 14, 2025, SNC requested that the NRC staff complete its safety review of the proposed LAR by August 29, 2025. SNC representative stated that SNC needs the proposed LAR for the Vogtle, Unit 4, refueling outage, scheduled for early fall 2025.
Discussion The NRC staff asked the following questions:
Where is the description of the software changes?
Has SNC considered following the guidance in the interim staff guidance (ISG) No.
DI&C-ISG-06, Licensing Process, Revision 2, Dec. 2018 (ML18269A259), to describe the software changes in the LAR?
Was the loss of alternating current and feedwater break accident analyses considered?
Public Questions There was one member of the public in attendance. One public member asked the following questions:
On slide 4, about the reason for the change, it is stated that on the Haiyang Unit 2 event in October 2018, the feedwater pump trip led to a reactor trip and subsequent SFW initiation. Does Vogtle 3 and 4 use SFW in the event of main feedwater pump trip, too?
In the discussion of safety analysis impacts, it seems now there is the possibility of a new situation created by this proposal that did not exist before. There can be one SG removing heat, while the other SG is not removing heat, without causing actuation of the PRHR. There is a discussion of the adequacy of heat removal, and maybe some transients, due to having only one SG removing heat. Is there a discussion of the material and structural integrity concerns for this new situation (one SG removing heat; the other SG not removing much heat, a partial loss of normal function). The problem is that the situation is not symmetrical, and it is asymmetrical, and that asymmetry can cause thermal stresses and fatigue.
Vogtle would get SFW flow on trip of the main feedwater pumps, as Haiyang did. Why the response at Vogtle for a similar event in 2024 was different than Haiyang Unit 2, in that SNC did not get initiation of SFW?
The SFW system supplies feedwater to the SGs during plant startup, hot standby and shutdown conditions, and during transients in the event of main feedwater system unavailability. The SFW system is non-safety-related and is provided to remove the core decay heat after the reactor trip during postulated non-loss-of-coolant accident (non-LOCA) event. Decay heat removal maintains core subcooling and prevents water relief from the pressurizer safety valves by preventing heatup of the RCS. The SFW pumps automatically start following anticipated transients, in part, as described above.
Event Report #57215 - Vogtle, Unit 3, Manual Reactor Trip and Automatic Safeguards Actuation On July 8, 2024, with Vogtle, Unit 3, in Mode 1 at 100 percent power, the reactor was manually tripped due to main feedwater pump (MFWP) A minimum flow control valve (FCV) failing to open, which resulted in lowering SG water level. Additionally, an automatic safeguards actuation occurred due to the cooldown of the RCS. Operations responded and stabilized the plant. The cause of the event was an unexpected change in the MFWP minimum FCV from closed to fully open due to foreign material inside the valve positioner. The valve positioner was replaced and an initial extent of condition review performed. In addition, a design change was made to initiate an automatic rapid power reduction upon failure of an MFWP minimum FCV, which will reduce the impact on SG water levels and eliminate the associated need to trip the reactor.
Event Report #57326 - Vogtle, Unit 3, Automatic Reactor Trip and Manual Safeguards Actuation On September 17, 2024, with Vogtle, Unit 3, in Mode 1 at 100 percent power, the reactor automatically tripped due to the PRHR HX outlet FCV failing to open. A manual safeguards actuation was initiated due to the lowering pressurizer water level resulting from the RCS cooldown that was caused by the PRHR HX outlet FCV failing to open. The automatic reactor trip was caused by a signal when the PRHR HX outlet FCV opened. The failure of the control valve did not inhibit the residual heat removal system from functioning as it is passive. The RCS maximum allowable cooldown rate was exceeded (TSP 3.4.3). The limit is 100 degrees F per hour above 350 degrees F. The maximum observed cooldown rate was 226 degrees F per hour. The cause of the event was an unexpected change in the PRHR HX outlet FCV from closed to fully open due to failure of a fuse in the power supply of the valves air-operated solenoid. The PRHR HX outlet FCV solenoid, fuse, component interface module (CIM), and CIM baseplate were replaced and tested to ensure the circuit functions as designed. In addition, an extent of condition review was performed to identify associated fuses used in the plant to be replaced.
Closing Remarks The NRC staff did not make any regulatory decisions during the meeting. The NRC staff is in the process of thoroughly reviewing the LAR submitted by SNC on February 14, 2025. The NRC staff will make any regulatory decisions in writing in a timely manner. Public Meeting Feedback forms were available, but no comments were received.
The meeting adjourned at 12:37 pm eastern time.
Please direct any inquiries to me at John.Lamb@nrc.gov or 301-415-3100.
/RA/
John G. Lamb, Senior Project Manager Plant Licensing Branch, II-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos.52-025 and 52-026
Enclosure:
List of Attendees cc: Listserv
Enclosure LIST OF ATTENDEES MARCH 3, 2025, PRE-SUBMITTAL MEETING WITH SOUTHERN NUCLEAR COMPANY REGARDING A PROPOSED LICENSE AMENDMENT REQUEST TO CHANGE TABLE 3.3.8-1 VOGTLE ELECTRIC GENERATING PLANT, UNITS 3 AND 4 ATTENDEE REPRESENTING John G. Lamb U.S. Nuclear Regulatory Commission (NRC)
Mike Markley NRC Zach Turner NRC Jo Ambrosini NRC Khadija West NRC Nichols Soliz NRC Angelo Stubbs NRC Norbert Carte NRC Summer Sun NRC Darrell Murdock NRC Dave Beaulieu NRC Doug Bollock NRC Ankur Bhattacharya NRC Milton Valentin NRC Ken Lowery Southern Nuclear Operating Company (SNC)
Ryan Joyce SNC Brad Chamberlain SNC Adam Coker SNC Kimberly Yennerell SNC Dan Williamson SNC Eddie Grant SNC Neil Haggerty SNC William Howell SNC Katie Swab SNC Robert Nicoletto Westinghouse Ali Alibeji Westinghouse Christopher Sommer Westinghouse Blaise Macioce Westinghouse Thomas Joseph Westinghouse Kyle Freiberger Westinghouse Thomas McLaughlin Westinghouse Ryan Rossman Westinghouse Natalie Rogers Westinghouse Warren R. Odess-Gillett Westinghouse Neil Archambo SNC Contractor Peter LeBlond SNC Contractor Susan Sterrett Public
ML25063A198 (Package)
ML25043A003 (Meeting Notice)
ML25055A253 (SNC Slides)
ML25063A190 (Meeting Summary)
OFFICE DORL/LPL2-1/PM DORL/LPL2-1/LA DSS/SNSB/BC DEX/EICB/BC NAME JLamb KZeleznock DMurdock FSacko DATE 03/03/2025 03/10/2025 03/06/2025 03/07/2025 OFFICE DORL/LPL2-1/BC DORL/LPL2-1/PM NAME MMarkley JLamb DATE 03/19/2025 03/19/2025