ML24282A982
| ML24282A982 | |
| Person / Time | |
|---|---|
| Site: | Vogtle  (NFP-091, NPF-092) |
| Issue date: | 10/08/2024 |
| From: | Southern Nuclear Operating Co |
| To: | NRC/NRR/DORL/LPL2-1 |
| References | |
| EPID L-2024-LRM-0116 | |
| Download: ML24282A982 (1) | |
Text
Planned 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 Presubmittal Meeting: October 15, 2024
Agenda Background - Reason for Change PRHR HX Actuation Logic Current Logic Proposed Logic Safety Analysis Impact Technical Specification (TS) 3.3.8 Planned Change Summary Schedule Discussion
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 3
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 3.3.1, 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 3.3.1, 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 3.3.1, Function 20]
Startup Feedwater Flow - Low 2 [TS 3.3.11 ]
RCS Cold Leg Temperature (Tcold) - High [TS 3.3.1, 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 [TS 3.3.1, Function 21] -- Safety Analysis Credit Unchanged 4
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 5
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
- However, addition of concurrent Tcold was simulated in LOFTRAN, resulting in a 16.4 sec delay in reaching Tcold setpoint
- LONF remains a non-limiting scenario for pressurizer overfill. The important peak pressurizer volume changes by only 1 ft³ (from 1369 ft³), which is insignificant
- 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 Licensing Basis Impact Examples
- 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 Section 6.3.3
- 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 Impacts Being Evaluated (likely) 7
New TS 3.3.8 Tcold - High Function for PRHR Actuation Logic Changes Schedule
- Target Transmittal to NRC:
December 2024
- SNC Request NRC Issuance of Amendment:
12 Months After NRC Acceptance of LAR Submittal
- SNC Planned Implementation:
Unit 3: 2nd Refueling Outage - Spring 2026 Unit 4: 2nd Refueling Outage - Spring 2027 8
New TS 3.3.8 Tcold - High Function for PRHR Actuation Logic Changes Discussion 9