ULNRC-05378, CFR 50.46 Annual Report, ECCS Evaluation Model Revisions

CFR 50.46 Annual Report, ECCS Evaluation Model Revisions

ML070740535
Person / Time
Site:	Callaway
Issue date:	03/07/2007
From:	Fitzgerald D AmerenUE, Union Electric Co
To:	Document Control Desk, NRC/NRR/ADRO
References
ULNRC-05378
Download: ML070740535 (11)

Text

AmerenUE PO Box 620 CallawayPlant Fulton, MO 65251 March 7, 2007 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Mail Stop P1-137 Washington, DC 20555-0001 ULNRC-05378 Ladies and Gentlemen:

DOCKET NUMBER 50-483 CALLAWAY PLANT UNION ELECTRIC COMPANY wAmeren 10 CFR 50.46 ANNUAL REPORT UE ECCS EVALUATION MODEL REVISIONS 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 period from March 2006 to March 2007. Attachment 2 provides an ECCS Evaluation Model Margin Assessment which accounts for all peak cladding temperature (PCT) changes resulting from the resolution of prior issues as they apply to Callaway. There are no PCT changes since the current Large Break and Small Break LOCA analyses became effective on November 1, 2005 with the implementation of License Amendment 168 for the replacement steam generators. Reference 1 below provided the last annual 10 CFR 50.46 report.

The Large Break and Small Break LOCA tables included in Attachment 2 remain unchanged from those discussed in Reference 1 and are enclosed here for completeness only. The PCT values determined in the Large Break and Small Break LOCA analyses of record, when combined with all PCT margin allocations, remain below the 2200'F regulatory limit. As such, no reanalysis is planned by AmerenUE.

This letter does not contain any new commitments. If you have any questions on this report, please contact Mr. Dave Shafer at (573) 676-4722.

Sincerely, David T. Fitzgerald Manager - Regulatory Affairs 4c) o) 4A ocO2 a subsidiary of Ameren Corporation

ULNRC-05378 March 7, 2007 Page 2 GGY/jdg Attachments

Reference:

1) ULNRC-05260 dated 3-9-06

ULNRC-05378 March 7, 2007 Page 3 cc:

Mr. Bruce S. Mallett Regional Administrator U.S. Nuclear Regulatory Commission Region IV 611 Ryan Plaza Drive, Suite 400 Arlington, TX 76011-4005 Senior Resident Inspector Callaway Resident Office U.S. Nuclear Regulatory Commission 8201 NRC Road Steedman, MO 65077 Mr. Jack N. Donohew (2 copies)

Licensing Project Manager, Callaway Plant Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Mail Stop O-7D1 Washington, DC 20555-2738 Missouri Public Service Commission Governor Office Building 200 Madison Street P.O. Box 360 Jefferson City, MO 65102-0360 Deputy Director Department of Natural Resources P.O. Box 176 Jefferson City, MO 65102

ULNRC-05378 March 7, 2007 Page 4 bcc:

C. D. Naslund A. C. Heflin D. T. Fitzgerald G. A. Hughes D. E. Shafer S. L. Gallagher (100)

L. M. Belsky (NSRB)

K. A. Mills P. M. Bell A160.0761 G. G. Yates Certrec Corporation 4200 South Hulen, Suite 630 Fort Worth, TX 76109 (Certrec recieves ALL attachments as long as they are non-safeguards and public disclosed.)

Send the following without attachments:

Ms. Diane Hooper Mr. Dennis Buschbaum Supervisor, Licensing Comanche Peak SES WCNOC P.O. Box 1002 P.O. Box 411 Glen Rose, TX 76043 Burlington, KS 66839 Mr. Scott Bauer Mr. Stan Ketelsen Regulatory Affairs Manager, Regulatory Services Palo Verde NGS Pacific Gas & Electric P.O. Box 52034 Mail Stop 104/5/536 Mail Station 7636 P.O. Box 56 Phoenix, AZ 85072-2034 Avila Beach, CA 93424 Mr. Scott Head Mr. John O'Neill Supervisor, Licensing Pillsbury, Winthrop, Shaw, Pittman LLP South Texas Project NOC 2300 N Street N.W.

Mail Code N5014 Washington, DC 20037 P.O. Box 289 Wadsworth, TX 77483 ATTACHMENT ONE CHANGES TO THE WESTINGHOUSE ECCS EVALUATION MODEL AND PCT PENALTY ASSESSMENTS 1

TABLE OF CONTENTS

1. BASH Minimum and Maximum Time Step Sizes

2. PAD Version 4.0 Implementation

3. NOTRUMP EM Refined Break Spectrum

4. General Code Maintenance 2

1. BASH MINIMUM AND MAXIMUM TIME STEP SIZES A review of some recent BASH Evaluation Model (EM) sensitivity calculations led to a recommendation to reduce the minimum and maximum time step sizes in BASH during reflood.

These changes are being recommended for generic application and have been evaluated for impact on existing analysis results. These changes represent a closely-related group of Non-Discretionary Changes in accordance with Section 4.1.2 of WCAP-13451.

Sensitivity calculations using BASH and SMUJUTH show that reducing the minimum and maximum time step sizes in BASH during reflood results in either a negligible change or a modest increase in the integral flooding rate for most cases, leading to an estimated impact of 0°F for 10 CFR 50.46 reporting purposes. One case for a plant other than Callaway showed a decrease in the integral flooding rate late in reflood and was evaluated for 10 CFR 50.46 impact on a plant-specific basis. This issue results in a 00 F PCT assessment against the large break LOCA analysis of record for Callaway.

2. PAD VERSION 4.0 IMPLEMENTATION A recent BASH-EM evaluation predicted an increase in the peak cladding temperature (PCT) for integral fuel burnable absorber (JFBA) fuel that was attributed primarily to the use of fuel rod initial conditions based on PAD Version 4.0. This result called into question the basis for forward-fit implementation of PAD Version 4.0, and existing IFBA analyses based on PAD Version 3.4 were reviewed to identify conditions that could lead to similar behavior. For each potentially-affected analysis, the estimated PCT impact due to PAD Version 4.0 implementation was assessed on a plant-specific basis. This change represents a Non-Discretionary Change in accordance with Section 4.1.2 of WCAP-13451.

The 10 CFR 50.46 assessments for this issue were determined on a plant-specific basis.

Callaway is unaffected by this issue since the BASH-EM analysis used fuel rod initial conditions based on PAD Version 4.0. Therefore, this issue results in a 0°F PCT assessment against the large break LOCA analysis of record for Callaway.

3. NOTRUMP EM REFINED BREAK SPECTRUM During the course of reviewing several extended power uprate and replacement steam generator Small Break LOCA (SBLOCA) analyses, the NRC questioned the break spectrum analyzed in the NOTRUMP EM. The NRC was concerned that the resolution of the break spectrum used in the NOTRUMP EM (1.5, 2, 3, 4, and 6 inch cases) may not be fine enough to capture the worst break with regard to limiting peak clad temperature as per 10 CFR 50.46. That is, the plant could be SBLOCA-limited with regard to overall LOCA results.

3 In response to this, Westinghouse performed some preliminary work indicating that, in some cases, more limiting results could be obtained from non-integer break sizes; however, the magnitude of the impact was far less than that shown in preliminary work performed by the NRC. Based on this, Westinghouse performed evaluations to determine if all currently operating plants would maintain compliance with the 10 CFR 50.46 acceptance criteria when considering a refined SBLOCA break spectrum. It should be noted that use of a refined break spectrum is not an error, but a change, since evaluating only integer break sizes has been the standard practice since the initial licensing of NOTRUMP.

Consistent with the method described in Westinghouse letter LTR-NRC-06-44, "Transmittal of LTR-NRC-06-44 NP-Attachment, 'Response to NRC Request for Additional Information on the Analyzed Break Spectrum for the Small Break Loss of Coolant Accident (SBLOCA)

NOTRUMP Evaluation Model (NOTRUMP EM), Revision 1,' (Non-Proprietary)," July 14, 2006, plants with low SBLOCA PCTs (i.e., less than 1700'F) and overall SBLOCA results that are significantly non-limiting when compared with large break LOCA (LBLOCA) results, no explicit refined break spectrum calculations were performed, leading to an estimated impact of 00 F for 10 CFR 50.46 reporting purposes. Callaway is such a plant, with a peak small break LOCA PCT of 1043°F (4-inch break case) and a peak large break LOCA PCT of 1939°F. For plants other than Callaway with high SBLOCA PCTs (i.e., equal to or greater than 1700'F),

explicit refined break spectrum calculations were performed, and PCT penalties were assessed, if necessary. Therefore, this issue results in a 0°F PCT assessment against the small break LOCA analysis of record for Callaway.

4. GENERAL CODE MAINTENANCE Various changes in code input and output format have been made to enhance usability and help preclude errors in analyses. This includes both input changes (e.g., more relevant input variables defined and more common input values used as defaults) and input diagnostics designed to preclude unreasonable values from being used, as well as various changes to code output which have no effect on calculated results. In addition, various updates were made to eliminate inactive coding, improve active coding, and enhance commenting, both for enhanced usability and to facilitate code debugging when necessary. These changes represent Discretionary Changes that will be implemented on a forward-fit basis in accordance with Section 4.1.1 of WCAP-13451.

The nature of these changes leads to an estimated PCT impact of 0°F on the large and small break LOCA analyses of record for Callaway.

4 ATTACHMENT TWO ECCS EVALUATION MODEL MARGIN ASSESSMENT FOR CALLAWAY 1

LARGE BREAK LOCA A. ANALYSIS OF RECORD (AOR) PCT = 1939°F B. PRIOR ECCS MODEL ASSESSMENTS + 0°F C. CURRENT LOCA MODEL ASSESSMENTS - + O°F March 2007 LICENSING BASIS PCT + MARGIN ALLOCATIONS 1939 0 F ABSOLUTE MAGNITUDE OF MARGIN ALLOCATIONS 00 F SINCE LAST LBLOCA 30-DAY REPORT 2

SMALL BREAK LOCA A. ANALYSIS OF RECORD (AOR) PCT = 1043°F B. PRIOR ECCS MODEL ASSESSMENTS + 0°F C. CURRENT ECCS MODEL ASSESSMENTS - + 0 0F March 2007 LICENSING BASIS PCT + MARGIN ALLOCATIONS 1043 0F ABSOLUTE MAGNITUDE OF MARGIN ALLOCATIONS 0°F SINCE LAST SBLOCA 30-DAY REPORT 3