NOC-AE-250041, CFR 50.46 Thirty-Day Report of Significant ECCS Model Changes
| ML25328A162 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 11/24/2025 |
| From: | Georgeson C South Texas |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| NOC-AE-25004135, STI: 35813086 | |
| Download: ML25328A162 (0) | |
Text
November 24, 2025 NOC-AE-25004135 10 CFR 50.46 (a)(3)(i) 10 CFR 50.46 (a)(3)(ii)
STI: 35813086 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001 South Texas Project Unit 2 Docket No. STN 50-499 10 CFR 50.46 Thirty-Day Report of Significant ECCS Model Changes In accordance with the requirements of 10 CFR 50.46(a)(3)(ii), STP Nuclear Operating Company (STPNOC) is submitting a 30-day report for a significant change in the South Texas Unit 2 Emergency Core Cooling Model.
For Unit 2 Cycle 25, there is a large break loss-of-coolant-accident (LBLOCA) Peak Clad Temperature (PCT) penalty of 13F due to gamma energy deposition model (GEDM). The total PCT for Unit 2 LBLOCA is 2136F. See enclosure for the detailed PCT Summary.
Since the absolute value of the PCT changes from the analysis of record for Unit 2 Cycle 25 exceeds 50°F, the change is considered significant in accordance with 10 CFR 50.46(a)(3)(i).
No schedule for reanalysis is proposed, since the Unit 2 Cycle 25 PCT remains below the 10 CFR 50.46(b)(1) limit of 2200°F.
There are no commitments in this letter.
If there are any questions regarding this information, please contact Zachary Dibbern at 361-972-4336 or me at 361-972-7806.
Chris Georgeson General Manager, Strategic Projects and Engineering Design
Enclosure:
Evaluation of the South Texas Project Unit 2 Cycle 25 LOCA RSAC GEDM Violation cc:
Regional Administrator, Region IV U.S. Nuclear Regulatory Commission 1600 E. Lamar Boulevard Arlington, TX 76011-4511 C. H. Georgeson Digitally signed by C. H. Georgeson Date: 2025.11.24 12:43:24 -06'00'
Enclosure NOC-AE-25004135 Page 1 of 2 EVALUATION OF THE SOUTH TEXAS PROJECT UNIT 2 CYCLE 25 LOCA RSAC GEDM VIOLATION
Background
The South Texas Project Unit 2 Cycle 25 reload core design resulted in a violation of the gamma energy deposition model (GEDM) loss-of-coolant accident (LOCA) reload safety analysis checklist (RSAC) limit used in the large-break LOCA analysis. This violation was evaluated for South Texas Project Unit 2 Cycle 25 and represents a change in a plant configuration or associated set point(s), distinguished from an evaluation model change in Section 4 of WCAP-13451.
Affected Evaluation Models(s) 1981 Westinghouse Large Break LOCA Evaluation Model with BASH Estimated Effect The impact of the Cycle 25 GEDM violation was estimated to result in a 13°F increase to the calculated large-break LOCA peak cladding temperature (PCT) for South Texas Project Unit 2.
Enclosure NOC-AE-25004135 Page 2 of 2 Westinghouse LOCA Peak Clad Temperature Summary Plant Name:
SOUTH TEXAS 2 Utility Name:
STPNOC EM:
BASH AOR
Description:
Appendix K Large Break Summary Sheet Status Cycle 25 PCT (°F)
ANALYSIS-OF-RECORD 2090 ASSESSMENTS Delta PCT
(°F)
- 1. IMP Database Error Corrections 0
- 2. PAD Version 4.0 Implementation
-30
- 3. LOCBART Pellet Volumetric Heat Generation Rate 6
- 6. Effect of Containment Purge 6
- 7. Rebaseline of AOR 46