ULNRC-06497, 10 CFR 50.46 Annual Report ECCS Evaluation Model Revisions

10 CFR 50.46 Annual Report ECCS Evaluation Model Revisions

ML19087A040
Person / Time
Site:	Callaway
Issue date:	03/28/2019
From:	Wink R Ameren Missouri, Union Electric Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
ULNRC-06497
Download: ML19087A040 (11)

Text

'.t.. ~~meren M I SSO U RI March 28, 2019 ULNRC-06497 U.S. Nuclear Regulatory Commission Attn; Document Control Desk Washington, DC 20555-0001 Ladies and Gentlemen:

10 CFR 50.46 DOCKET NUlVIBER 50-483 CALLA WAY PLANT UNIT 1 UNION ELECTRIC CO. RENEWED FACILITY OPERATING LICENSE NPF-30 10 CFR 50.46 ANNUAL REPORT ECCS EVALUATION MODEL REVISIONS Callaw ay Plant Ameren Missouri hereby submits the annual report required per 10 CFR 50.46(a)(3) for Callaway Plant. Attachment 1 to this letter describes changes to the Westinghouse ECCS Large Break and Small Break Loss of Coolant Accident (LOCA) Evaluation Models which have been implemented for Callaway during the time pe1iod from March 2018 to March 2019. Attacluuent 2 pro v ides an ECCS Evalnation Model Margin Assessment which accounts for all peak cladding temperature (PCT) changes resulting from the resolutinn o f prior issues as they apply to Callaway. No new PCT penalties are included in these attachments. References 1 through 13 provided annual 10 CFR 50.46 reports that were issued after the LOCA analysis were revised to r e flect the installation of the replacement steam generators in 2005. The PCT v alues detennined in the Large Break and Small Break LOCA analysis of record , when combined with all PCT margin allocations , remain below the 2200°F regulatory limit. However , in March 2014 Ameren Missouri was informed by Westinghouse that the absolute magnih1de of the Large Break Loss of Coolant Accident (LBLOCA) penalty assessments that have accumulated since the cunent analysis of record (replacement steam generator analysis approved in Callaway License Amendment 168) e ceeded 50°F. A s such , Reference 9 was submitted within the requirements of 10 CFR 50.46(a)(3)(ii), and contains a commitment to reanalyze the Large Break and Sma11 Break Loss of Coolant Accidents using the NRC-approved version ofWCAP-16996-P, " Realistic LOCA Evaluation Methodology Applied to the Full Spectrum of Break Sizes (FULL SPECTRUM LOCA Methodology)".

T his reanalysis will be completed on a schedule to be detennined as part of the 10 CFR 50.46c rulemakiug process . ......................

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.. ............. ........ ... ................ ........ ... . , ............. , .. -, ...... . 83 15 Coun ty Ro a d 459 . Steedman , MO 65077 . Am e r e nMi ss ouri.com ULNRC-06497 Marc11 28 , 2019 Page 2 of 4 Th.is letter does not contain new commitments. If you have any questions on this report, please contact Mr. Tom Elwood at (314) 225-1905.

JBL

References:

1) ULNRC-05 260 dated 3-9-0 6 2) ULNRC-05378 dated 3-7

-0 7 3) ULNRC-05475 dated 3-4-08 4) ULNRC-05600 dated 3-4-09 5) ULNRC-05683 dated 3-1-10 6) ULNRC-05769 dated 3-1-1 l 7) ULNRC-05840 dated 3-1-12 8) ULNRC-05968 dated 3-6-13 9 ULNRC-06098 dated 3-25-14 10) ULNRC-06203 dated 3-31-15 11) ULNRC-06292 dated 3-30-16 12) ULNRC-06361 dated 3-30-17 13) ULNRC-06428 dated 3-29-18 Attachments

Sincerely , id!-Manger, Regulatory Affairs 1. Changes to the Westinghouse ECCS Evaluation Model and PCT Penalty Assessments

2. ECCS Evaluation Model Margin Assessment for Callaway : : : : : . : : ; : : ; : : : : . : : : : :

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ULNRC-06497 March 28 , 2019 Page 3 of 4 cc: Mr. Scott A. M01Tis Regional Administrator U.S. Nuclear Regulatory Commission Region IV 1600 East Lamar Boulevard Arlington, TX 76011-4511 Senior Resident Inspector Callaway Resident Office U.S. Nuclear Regulatory Commission 8201 NRC Road Steedman, MO 65077 Mr. L. John Klos Project Manager, Callaway Plant Office ofNudear Reactor Regulation U.S. Nuclear Regulatory Corrunission Mail Stop 09£3 Washington, DC 20555-0001

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ULNRC-06497 March 2 8 2019 Page 4 of 4 Index and send hardcopy to QA File A160.076 1 Hardcopy:

Certrec Corporation 6100 Western Place , Suite 1050 Fort Worth, TX 76107 Electronic distribution fo1* the following can be made via Other Situations ULNRC Distribution:

F. M. Diya T. E. Herrmam1 B. L. Cox. F. J. Bianco S. P. Banker R. C. Wink T. B. Elwood Corporate Communications NSRB Secretary STARS Regulatory Affairs Mr. Jay Silberg (Pillsbury Winthrop Shaw Pittinan LLP) Missouri Public Service Conunission

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Attachment 1 to ULNRC-06497 ATTACHMENT ONE CHANGES TO THE WESTINGHOUSE ECCS EVALUATION MODEL AND PCT PENALTY ASSESSMENTS 1

Attachment l to ULNRC-06497 TABLE OF CONTENTS 1. FUEL ROD GAP CONDUCTANCE ERROR 2. RADIATION HEAT TRANSFER MODEL ERROR 3. SBLOCTA PRE-DNB CLADDING SURFACE HEAT TRANSFER COEFFICIENT CALCULATION

4. GENERAL CODE MAINTENANCE 2

Attachment 1 to ULNRC-06497

1. FUEL ROD GAP CONDUCTANCE ERROR An en-or was identified in the fuel rod gap conductance model in the NOTRUMP computer code (reactor coolant system response model). The error is associated with the use of an incon-ect temperature in the calculation of the cladding emissivity term. This e1rnr corresponds to a Discretionary Change as described in Section 4.1.2 of WCAP-13451..

Based on a combination of engineering judgment of the phenomena and physics o f a small break LOCA and sensitivity calculations performed with the advanced plant v ersion ofNOTRUMP , Westinghouse has concluded that this e1TOr has a negligible effect , leading to an estimated Peak Cladding Temperature (PCT) impact of 0°F on small break LOCA analysis results. 2. RADIATION HEAT TRANSFER MODEL ERROR Two enors were discovered in the calculation of the radiation heat transfer coefficient within the fuel rod model of the NOTRUMP computer code (reactor coolant system response model). First , existing logic did not preclude non-physical negative or large (negative or positive) radiation heat transfer coefficients from being calculated.

These en-oneous calculations occuned when the vapor temperature e x ceeded the cladding surface temperature or when the predicted temperature difference was less than 1 °F. Second , a temperature tenn incorrectl y used degrees Fahrenhe i t instead of Rankine. These errors represent a closely related group of Non-Discretionary problems in accordance wfth Section 4.1.2 of WCAP-13451.

Based on a combination of engineering judgment of the phenomena and physics of a small break LOCA, and sensiti v ity calculations perfonned with the advanced plant version ofNOTRUMP , Westinghouse has concluded that this error has a negligible effect , leading to an estimated Peak Cladding Temperature (PCT) impact of 0°F on small break LOCA analysis resl.llts. 3. SBLOCT A PRE-DNB CLADDING SURF ACE HEAT TRANSFER COEFFICIENT CALCULATION Two e1rnrs were discovered in the pre-departure from nucleate boiling {pre-DNB) cladding surface heat transfe r coefficient calculation i n the SBLOCTA code ( cladding heat-up ca1culatfons). The first eno r is a result of inconsistent time units (hours vs. seconds) in the parameters used for the calculation of the Re y nolds and Prandtl number s, and the second en-or relates to an inconect diameter used to develop the area tenn in the cladding smface heat flux calculation. Both of these issues impact the calculation of the pre-DNB convective heat transfer coefficient , representing a closely related group of Non-Discretionary Changes to the Evaluation Model as described in Section 4.1.2 of WCAP-13451. These enors have been con-ected in the SBLOCTA code. Because this condition occurred prior t o DNB , it was judged that the s e e1Tors l1ad nci direct impact on the cladding heat-up related to the core uncover period. A s eries of validation tests were perfonned by Westinghous e and confirmed that tbese error s have a negligible effect on SBLOCA analysis results , leading to an estimated Peak Cladding Temperature (PCT) impact of 0°F. 3 Attachment 1 to ULNRC-06497

4. GENERAL CODE MAINTENANCE Various changes have been made to enhance the usability of the codes and to help preclude errors in analyses.

This includes items *such as modifying input variable definitions , ututs, and defaults; improving the input diagnostic checks* enhancing the code output; optimizing active coding; and eliminating inacti v e coding. These changes have been evaluated for impact on existing Small Break LOCA analysis results and they represent Discretionary Changes that will be implemented on a fit basis in accordance with Section 4.1.1 of WCAP-1345.

Westinghouse has judged tlus issue to have an estimated PCT impact of 0°F on existing Small Break LOCA analysis results. 4 Attaclu11ent 2 to ULNRC-06497 ATTACHMENT TWO ECCS EVALUATION MODEL MARGIN ASSESSMENT FOR CALLAWAY Attachment 2 to ULNRC-06497 A. B. C. LARGE BREAK LOC A ANALYSIS OF RECORD (AOR) PRIOR ECCS MODEL ASSESSMENTS CURRENT LOCA MODEL ASSESSMENTS

-March 2018 LICENSING BASIS PCT+ MARGIN ALLOCATIONS ABSOLUTE MAGNITUDE OF MARGIN ALLOCATIONS PCT= 1939°F + 58°F +oop 1997°F 5gop SINCE LAST ANALYSIS OF RECORD OR LBLOCA 30-DA Y REPORT 2 Attachment 2 to ULNRC-06497 A. B. C. SMALL BREAK LOCA ANAL YS1S OF RECORD (AOR) PRIOR ECCS MODEL ASSESSMENTS CURRENT ECCS MODEL ASSESSMENTS

-March2018 LICENSING BASIS PCT+ MARGIN ALLOCATIONS ABSOLUTE MAGNITUDE OF MARGIN ALLOCATIONS PCT= 1043°F + oop + 0°F 1043°F 0°F SINCE LAST ANALYSIS OF RECORD OR SBLOCA 30-DAY REPORT 3