ML21340A257

10 CFR 50.46 Thirty-Day Report of Significant ECCS Model Changes

ML21340A257
Person / Time
Site:	South Texas
Issue date:	12/06/2021
From:	Georgeson C South Texas
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
NOC-AE-21003858
Download: ML21340A257 (2)

Text

December 6, 2021 NOC-AE-21003858 10 CFR 50.46 (a)(3)(i) 10 CFR 50.46 (a)(3)(ii)

STI: 35252800 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001 South Texas Project Unit 1 Docket No. STN 50-498 10 CFR 50.46 Thirty-Day Report of Significant ECCS Model Changes

References:

1. Letter from M. Page to NRC Document Control Desk, South Texas Project Units 1 & 2 10 CFR 50.46 Annual Report of ECCS Model Revisions, March 4, 2019, NOC-AE-19003627, ML19063D875.

2. Letter from D. Roland to NRC Document Control Desk, South Texas Project Unit 1 10 CFR 50.46 Thirty-Day Report of Significant ECCS Model Changes, June 17, 2020, NOC-AE-20003738, ML20169A859.

3. Letter from Dennis J. Galvin (NRC) to G.T. Powell, "South Texas Project, Unit 1 -

Issuance of Amendment No. 219 to Revise Technical Specifications to Reduce Safety Injection Accumulators Minimum Pressures (Exigent Circumstances)

(EPID L-2020-LLA-0108)," May 28, 2020, AE-NOC-20003255, ML20141L612.

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 1 Emergency Core Cooling Model.

In Unit 1 Cycle 23, South Texas Project Unit 1 had reduced the Technical Specification minimum accumulator cover gas pressure to 500 psig to mitigate the effects of check valve leakage into the Low Head Safety Injection / Residual Heat Removal Header. This resulted in an estimated 3°F increase in Peak Clad Temperature (PCT) to the previous value of 2123°F as reported in Reference 1 for the limiting Emergency Core Cooling System (ECCS) analysis for the large break loss-of-coolant-accident (LBLOCA). The PCT value for Unit 1 Cycle 23 was 2126°F as stated in References 2 and 3.

For Unit 1 Cycle 24, the check valve leakage issue was remedied and the Technical Specification minimum nitrogen cover-pressure limit of all three Safety Injection Accumulators has been changed back to 590 psig. As a result, the PCT value for Unit 1 Cycle 24 is restored to 2123°F. The sum of the absolute magnitudes of all the individual changes is 93°F as listed in the enclosed table (Delta PCT column). Since the sum of the absolute magnitudes of the PCT changes from the analysis of record for Unit 1 Cycle 23 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 1 Cycle 24 PCT remains below the 10 CFR 50.46(b)(1) limit of 2200°F.

NOC-AE-21003858 Page 2 of 2 There are no commitments in this letter.

If there are any questions regarding this information, please contact Tim Hammons at 361-972-7347 or me at 361-972-7806.

(!£!

General Manager, Engineering th

Enclosure:

Unit 1 Cycle 24 Westinghouse LOCA Peak Clad Temperature Summary cc:

Regional Administrator, Region IV U.S. Nuclear Regulatory Commission 1600 E. Lamar Boulevard Arlington, TX 76011-4511

Enclosure NOC-AE-21003858 Page 1 of 1 Unit 1 Cycle 24 Westinghouse LOCA Peak Clad Temperature Summary Plant Name: SOUTH TEXAS 1 Utility Name: STPNOC EM: BASH AOR

Description:

Appendix K Large Break Summary Sheet Status Cycle 24 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

4. PWROG TCD Evaluation - Rebaseline of AOR 5

5. PWROG TCD Evaluation - Effect of TCD and 0 Assembly Power/Peaking Factor Burndown

6. Effect of Containment Purge 6

7. Rebaseline of AOR 46 AOR + ASSESSMENTS PCT = 2123 °F