ML24275A233
| ML24275A233 | |
| Person / Time | |
|---|---|
| Site: | Palo Verde  |
| Issue date: | 06/28/2024 |
| From: | Arizona Public Service Co |
| To: | William Orders NRC/NRR/DORL/LPL4 |
| Orders, William | |
| References | |
| Download: ML24275A233 (1) | |
Text
Safety Injection Tank Pressure Band Pre-Submittal Meeting Palo Verde Nuclear Generating Station Date 06/28/2024
2 Agenda Introduction Case for Action Description Analytical Work Proposed Technical Specification Changes Schedule
3 Case for Action Recent plant operating experience resulted in a station-initiated effort to increase Safety Injection Tank (SIT) reliability.
Four examples of unexpected SIT depressurization over the last two years across all three units:
Three failed open SIT vent valves.
One cracked weld.
The current allowable SIT pressure band is narrower than necessary, resulting in the need for more frequent operation of the SIT vent valves.
4 Description Analytical work was initiated to increase the SR 3.5.1.3 and SR 3.5.2.3 upper limit on the SIT pressure:
Re-analyze large break Loss of Coolant Accident (LOCA)
Determined no impact on small break LOCA as it uses minimum pressure.
Existing long term core cooling analysis remains bounding Re-analyze containment pressure/temperature Parallel activities:
A license amendment was submitted on 3/8/2024 to extend the Limited Condition for Operation (LCO) Action time, APS letters 102-08610 (6/29/2023) and 102-08734 (2/23/2024):
Provides time for the station to plan and implement a repair.
Plant modification to address the design of the vent valve is being evaluated.
5 Analytical Work - LOCA Large Break LOCA is impacted by increasing the maximum SIT pressure, as Small Break LOCA is more limiting at minimum SIT pressure.
The various analyses were re-evaluated assuming a maximum SIT pressure of 675 psia versus the original pressure of 652 psia. The results remain acceptable (<2200°F):
Westinghouse CE16STD and CE16NGF Appendix K large break LOCA:
Increase of 2°F in Peak Cladding Temperature (PCT) for the limiting case (2129.6°F to 2131.0°F).
No change in methodology.
Framatome CE16HTP realistic large break LOCA:
Increase of 39°F in PCT (1752°F to 1791°F).
No change in methodology.
6 Analytical Work - Containment P/T The Containment pressure and temperature analyses were re-evaluated to account for the higher maximum SIT pressure.
The reanalysis was done using the GOTHIC code:
The previously used COPATTA code is no longer supported.
Benchmarked GOTHIC to COPATTA.
This methodology change will be included in the submittal.
The results for containment peak pressure:
Technical Specification 5.5.16.b Pa of 58.0 psig remains unchanged.
No impacts of concern to the containment temperature profiles.
7 Proposed Changes Revise SR 3.5.1.3 to specify the analytical band of 602 psia to 675 psia.
Previously 600 psig to 625 psig Instrument uncertainties will continue to be accounted for in the surveillance procedures.
Revise SR 3.5.2.3 to specify the analytical band of 250 psia to 675 psia.
Previously 260 psig to 625 psig Instrument uncertainties will continue to be accounted for in the surveillance procedures.
Corresponding updates to the Technical Specification Bases will be made.
8 TS Changes - SR 3.5.1.3
9 TS Changes - SR 3.5.2.3 Note: TS page 3.5.2-2 is impacted by an unrelated change to the SIT volume SR 3.5.2.2 requested in APS letters 102-08610 (6/29/2023) and 102-08734 (2/23/2024).
10 SR Example Operation Not Allowed Analytical and Proposed TS SR Limit 675 psia Instrument Loop Uncertainty and Atmospheric Conversion ST Limit 650 psig Operation Allowed
11 SR Example Comparison (Current vs Proposed)
TS 3.5.1 Current TS Proposed TS Changes Note: Final values are rounded.
TS SR Value (PSIG)
Atmosphereic Pressure Uncertainty Analysis Value (PSIA) 625 14.2 12 651 Upper Limit 600 14.2
-12 602 Lower Limit ST Procedural Limit (PSIG)
Atmosphereic Pressure Uncertainty Analysis Value and TS SR Value (PSIA) 650 14.2 10.8 675 Upper Limit 600 14.2
-12 602 Lower Limit
12 Schedule Planned submittal - mid-July 2024 Requested approval - June 1, 2025 90-day implementation period
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