ML25055A253
| ML25055A253 | |
| Person / Time | |
|---|---|
| Site: | 05000025, 05000026 |
| Issue date: | 03/03/2025 |
| From: | Southern Nuclear Company |
| To: | Division of Operating Reactor Licensing |
| Lamb J, NRR/DORL/LPL2-1 | |
| References | |
| EPID L-2025-LLA-0035 | |
| Download: ML25055A253 (1) | |
Text
Vogtle Electric Generating Plant Units 3 and 4 License Amendment Request Add a New Tcold - High Function to Technical Specification Table 3.3.8-1 for Passive Residual Heat Removal Actuation Logic Changes Post-submittal Meeting: March 3, 2025 (Submitted ML25045A166)
Agenda Introduction Background - Reason for Change PRHR HX Actuation Logic
- Current Logic
- Proposed Logic
- Safety Analysis Impact Technical Specification (TS) 3.3.8 Planned Change Schedule
3 New TS 3.3.8 Tcold - High Function for PRHR Actuation Logic Changes
New TS 3.3.8 Tcold - High Function for PRHR Actuation Logic Changes Background - Reason for Change
- Address lessons learned from October 17, 2018 Haiyang Unit 2 event:
- Feedwater pump trip led to reactor trip and subsequent startup feedwater (SFW) initiation
- Resulted in decrease in the cold leg temperatures
- Operators attempt to prevent a Safeguards signal from being generated on Tcold - Low 2
- Result: Low-2 SG NR Level coupled with Low-2 SFW Flow, which generated an automatic PRHR HX actuation
- Result: Reducing Tcold further leading to a Safeguards actuation
- Unnecessary PRHR actuation challenges operations that could lead to excessive cooldowns and unnecessary Safeguards actuation on Tcold - Low 2
- 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 4
New TS 3.3.8 Tcold - High Function for PRHR Actuation Logic Changes Current PRHR Actuation Logic (Shown on UFSAR Figure 7.2-1, Sheets 7 and 8)
SG Narrow Range (NR) Water Level - Low 2 [TS 3.3.8, Function 20]
Startup Feedwater Flow - Low 2 [TS 3.3.11]
Logic:
Coincidence of 2-of-4 channels below SG water level Low-2 in either SG, after a preset time delay, coincident with 1-of-2 SFW flow Low-2 feeding same steam generator SG Wide Range (WR) Water Level - Low 2 [TS 3.3.8, Function 21]
Logic:
Coincidence of 2-of-4 channels below SG water level Low-2 in either SG Proposed PRHR Actuation Logic Changes SG Narrow Range Water Level - Low 2 [TS 3.3.8, Function 20]
Startup Feedwater Flow - Low 2 [TS 3.3.11 ]
RCS Cold Leg Temperature (Tcold) - High [TS 3.3.8, New Function 11.b]
Logic:
Coincidence of 2-of-4 channels below SG water level Low-2 in BOTH SGs, after a preset time delay, coincident with 1-of-2 SFW flow in BOTH SGs AND Coincidence of 2-of-4 channels above Tcold - High in either loop SG WR Water Level - Low 2 (in either SG) [TS 3.3.8, Function 21] -- Unchanged 5
New TS 3.3.8 Tcold - High Function for PRHR Actuation Logic Changes Basis for Proposed PRHR Actuation Logic Changes
- Basis: Any one SG is capable of removing all decay heat and, therefore, SG heat sink has not been lost until both SGs are affected
- Basis: PRHR HX actuation will not occur if a potential overcooling event is in progress (i.e., RCS below Tcold - High)
- No changes are being made to the Reactor trip on either SG Low-2 NR level
- No hardware changes required except for sequence of events (SOE) cards added in non-safety SOE cabinets (not within the scope of the LAR) 6
New TS 3.3.8 Tcold - High Function for PRHR Actuation Logic Changes Safety Analysis Impacts (Reference UFSAR Table 15.0-6)
- Logic requiring both SGs vs one has no impact since both are symmetrically affected
- The addition of concurrent Tcold was simulated in LOFTRAN, resulting in a 16.4 sec delay in reaching Tcold setpoint
- However, the SG NR Level signal includes a preset time delay (unchanged by this activity) that is much greater than the 16.4 second Tcold delay. As such, the Tcold delay has no impact
- PRHR actuated by SG WR Level (1-of-2 SGs to actuate)
- Delay in reaching Low-2 SG WR level (compared to SG NR actuation) more than offset by heat removal from intact SG
New TS 3.3.8 Tcold - High Function for PRHR Actuation Logic Changes Precedent
- Prior V34 LAR also added new ESFAS Function to TS Table 3.3.8-1 (Function 1.a, Containment Pressure - Low)
- LAR submitted January 31, 2017 via ND-17-0182 [ML17031A446]
- V34 Amendments 90 and 89, respectively [ML17241A109]
- No specific discussion of implementation of the associated software changes
- No Requests for Additional Information 8
New TS 3.3.8 Tcold - High Function for PRHR Actuation Logic Changes Licensing Basis Impact Examples (Refer to LAR Attachments)
- TS Table 3.3.8-1 Function 11 becomes 11.a (existing Tcold - Low 2) and add new Function 11.b for Tcold - High (also conforming TS Bases for TS 3.3.8 & 3.3.11)
- UFSAR Sections 7.2 & 7.3 and Figure 7.2-1
- UFSAR Sections 15.2.6 & 15.2.7 and Table 15.2-1
- Additional Conforming Changes as seen in the LAR Attachments 9
New TS 3.3.8 Tcold - High Function for PRHR Actuation Logic Changes Presubmittal Meeting NRC Questions (October 15, 2024 - ML24290A158)
Will the addition of Function 11b affect other limiting conditions for operation? SNC: No Can SNC describe how the system works? SNC: LAR Section 2.1 & this presentation Slide 3 Can SNC describe other events that are credited for wide range level as referred to on slide 6?
SNC: LAR Section 3 Is the loss of emergency alternating current power and feedwater line break affected by the proposed TS change? SNC: No, as discussed in LAR Section 3 Does the Safety Injection actuation occur for the analysis of the loss of normal feedwater event?
SNC: Yes; refer to UFSAR Table 15.2-1 Sheet 6, S Signal Which Chapter 15 events would be affected by the proposed TS change? SNC: None, as discussed in LAR Section 3 What is the supporting rationale for any assertions that those events are not affected by the proposed TS changes? SNC: as discussed in LAR Section 3 For the events that were affected by the proposed TS changes, what are results to demonstrate applicable acceptance criteria are met? SNC: as discussed in LAR Section 3 10
New TS 3.3.8 Tcold - High Function for PRHR Actuation Logic Changes Presubmittal Meeting NRC Questions (October 15, 2024 - ML24290A158)
Will the addition of Tcold - High meet single failure criteria? SNC: Yes Will SNC provide its setpoint calculation and uncertainty analysis for Tcold - High? SNC: The setpoint for the new Tcold - High function will be developed, implemented, and documented in accordance with the requirements of TS 5.5.8, Setpoint Program (Setpoint Program being unique to V34 Licensing Basis)
What are the required software changes for Tcold - High? SNC: See next bullet Will SNC use Interim Staff Guidance #6 (ISG-6) for the proposed change? SNC: The software changes necessary for implementation of the proposed amendment are currently being developed. Those changes will follow the NRC approved WCAP-16096, Software Program Manual for Common Q Systems (Reference 2), as modified by WCAP 15927, Design Process for AP1000 Common Q Safety Systems (Reference 3), as specified in UFSAR Chapter 7. DI&C-ISG-06 guidance is not applicable for this request, consistent with prior precedent (next bullet).
Can SNC identify any applicable precedent LARs and that the proposed submittal considered? SNC: See LAR Section 4.2 (V34 Amendment for new ESFAS TS Table 3.3.8-1 Function 1.a, Containment Pressure
- Low)
Did SNC consider precedents (e.g., a simple software-only change to a Common Q (preferably) or any other digital protection system) and the resolution of requests for additional information for those precedents? SNC: None found beyond the V34 Amendment referenced above 11
New TS 3.3.8 Tcold - High Function for PRHR Actuation Logic Changes Schedule
- SNC Request NRC Issuance of Amendment:
Prior to Unit 4 1st Refueling Outage (Early Fall 2025)
- SNC Planned Implementation:
Unit 3: 2nd Refueling Outage - Spring 2026 Unit 4: 1st Refueling Outage - Early Fall 2025 12