ULNRC-05475, CFR 50.46 Annual Report, ECCS Evaluation Model Revisions

CFR 50.46 Annual Report, ECCS Evaluation Model Revisions

ML080780469
Person / Time
Site:	Callaway
Issue date:	03/04/2008
From:	Graessle L AmerenUE, Union Electric Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
ULNRC-05475
Download: ML080780469 (12)

Text

AmerenUE P0 Box 620 Cal/awayPlant Fulton, MO 65251 March 4, 2008 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Mail Stop P1-137 Washington, DC 20555-0001 ULNRC-05475 Ladies and Gentlemen:

DOCKET NUMBER 50-483 CALLAWAY PLANT UNION ELECTRIC COMPANY 10 CFR 50.46 ANNUAL REPORT 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 2007 to March 2008. 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. References 1 and 2 below provided annual 10 CFR 50.46 reports that were issued after the LOCA analyses were revised to reflect the installation of the replacement steam generators in 2005.

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. Scott Maglio at (573) 676-8719.

Sincerely, Luke H. Graessle Manager - Regulatory Affairs a subsidiary of Ameren Corporation

ULNRC-05475 March 4, 2008 Page 2 GGY/nls Attachments

References:

1) ULNRC-05260 dated 3-9-06

2) ULNRC-05378 dated 3-7-07

ULNRC-05475 March 4, 2008 Page 3 cc:

Mr. Elmo E. Collins, Jr.

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 Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Mail Stop O-8B1 Washington, DC 20555-2738 Mr. Mohan C. Thadani (2 copies)

Licensing Project Manager, Callaway Plant Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Mail Stop O-8G14 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-05475 March 4, 2008 Page 4 Index and send hardcopy to QA File A160.0761 Hardcopy:

Certrec Corporation 4200 South Hulen, Suite 630 Fort Worth, TX 76109 (Certrec receives ALL attachments as long as they are non-safeguards and may be publicly disclosed).

Electronic distribution for the following can be made via Responses and Reports ULNRC Distribution:

C. D. Naslund A. C. Heflin Mr. Ron Reynolds, Director (SEMA)

Mr. Edward Gray, Senior REP Planner (SEMA)

Mr. John Campbell, REP Planner (SEMA)

L. H. Graessle G. A. Hughes S. A. Maglio S. L. Gallagher L. M. Belsky (NSRB)

T. B. Elwood Ms. Diane M. Hooper Mr. Dennis Buschbaum Supervisor, Licensing TXU Power WCNOC Comanche Peak SES P.O. Box 411 P.O. Box 1002 Burlington, KS 66839 Glen Rose, TX 76043 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 Floyd Gilzow Deputy Director Department of Natural Resources P.O. Box 176 Jefferson City, MO 65102 to ULNRC-05475 ATTACHMENT ONE CHANGES TO THE WESTINGHOUSE ECCS EVALUATION MODEL AND PCT PENALTY ASSESSMENTS 1

to ULNRC-05475 TABLE OF CONTENTS

1. LOCBART Pellet Volumetric Heat Generation Rate

2. BASH Pellet Volumetric Heat Generation Rate

3. Errors in Reactor Vessel Nozzle Data Collections

4. LOCBART Specific Heat Model for Optimized ZIRLOTM Cladding

5. Pump Weir Resistance Modeling

6. LOCBART Oxide-to-Metal Ratio

7. Large Break LOCA Evaluation for Increased Sump Screen Metal Mass

8. General Code Maintenance 2

to ULNRC-05475

1. LOCBART PELLET VOLUMETRIC HEAT GENERATION RATE The LOCBART code has been modified to correct an inverted term in the calculation of the pellet volumetric heat generation rate. This change affects the steady-state and transient heat generation for all three rods and could result in either an increase or decrease in peak cladding temperature for a given calculation. This change represents a Non-Discretionary Change in accordance with Section 4.1.2 of WCAP-13451.

The LOCBART Pellet Volumetric Heat Generation Rate assessment for Callaway was estimated to result in a +140 F PCT penalty for Large Break LOCA (LBLOCA) using the difference between the PCTs from LOCBART calculations with and without the error correction.

2. BASH PELLET VOLUMETRIC HEAT GENERATION RATE The BASH code has been modified to correct an inverted term in the calculation of the pellet volumetric heat generation rate. This change affects the steady-state and transient heat generation for the core average rod prior to bottom-of-core recovery and could result in either an increase or decrease in the cladding temperatures at the beginning of reflood. This change represents a Non-Discretionary Change in accordance with Section 4.1.2 of WCAP-13451.

Sensitivity calculations using BASH and SMUUTH indicate a negligible effect on the core inlet flooding rate during reflood, leading to an estimated LBLOCA PCT impact of 0°F for 10 CFR 50.46 reporting purposes.

3. ERRORS IN REACTOR VESSEL NOZZLE DATA COLLECTIONS Some minor errors were discovered in the reactor vessel nozzle data collections that potentially affect the vessel inlet and outlet nozzle fluid volume, metal mass, and surface area. The corrected values have been evaluated for impact on current licensing-basis analysis results and will be incorporated into the plant-specific input databases on a forward-fit basis. These changes represent a closely-related group of Non-Discretionary Changes in accordance with Section 4.1.2 of WCAP-13451.

The differences in the vessel inlet and outlet nozzle fluid volume, metal mass, and surface area are relatively minor and would be expected to produce a negligible effect on large break and small break LOCA analysis results, leading to estimated LBLOCA and Small Break LOCA (SBLOCA) PCT impacts of 0°F for 10 CFR 50.46 reporting purposes.

4. LOCBART SPECIFIC HEAT MODEL FOR OPTIMIZED ZIRLO CLADDING An option has been added to the LOCBART code to model the specific heat of Optimized ZIRLO TM cladding. The model is described in the response to Request for Additional Information (RAI) #21 in Section D of WCAP-12610-P-A and CENPD-404-P-A, Addendum 3

to ULNRC-05475 1-A, "Optimized ZIRLOTM, July 2006, and will facilitate compliance with Condition and Limitation #9 of the Safety Evaluation Report for plants with a peak cladding temperature that occurs during blowdown or early reflood. Note thatthe extrapolation algorithm described in the RAI response was replaced with an error message and code abort for temperatures below 73°F or above 2400'F. This change represents a Non-Discretionary Change in accordance with Section 4.1.2 of WCAP-13451.

No domestic plant with a BASH-EM analysis maintained by Westinghouse has both Optimized ZIRLOTM cladding and a peak cladding temperature that occurs during blowdown or early reflood, so there is no impact on any existing LBLOCA analysis results.

5. PUMP WEIR RESISTANCE MODELING A review of the reactor coolant pump data collections identified instances of either including a weir resistance for a design without a weir or double-counting the weir resistance for a design with a weir. The corrected resistances have been evaluated for impact on existing analysis results and will be incorporated into the plant-specific input databases on a forward-fit basis.

This change represents a Non-Discretionary Change in accordance with Section 4.1.2 of WCAP-13451.

Resolving the identified discrepancies has been evaluated as having a negligible effect on existing results, leading to estimated LBLOCA and SBLOCA PCT impacts of 0°F for 10 CFR 50.46 reporting purposes.

6. LOCBART OXIDE-TO-METAL RATIO An option has been added to the LOCBART code to convert the user-specified zirconium-oxide thickness to equivalent cladding reacted. This adjustment is made during problem initialization, and the cladding outside diameter is modified accordingly. This change represents a Discretionary Change that will be implemented on a forward-fit basis in accordance with Section 4.1.1 of WCAP-13451.

This change is expected to produce a minimal effect on the limiting peak cladding temperature, leading to an estimated LBLOCA PCT impact of 0°F for 10 CFR 50.46 reporting purposes.

7. LARGE BREAK LOCA EVALUATION FOR INCREASED SUMP SCREEN METAL MASS The containment sump screens were changed during Refuel 15 (spring 2007) from carbon steel to stainless steel, which resulted in an increase in containment metal mass. This change affects the LBLOCA analysis performed in support of the replacement steam generators approved via Callaway License Amendment 168. SBLOCA, post-LOCA, and LOCA hydraulic forces 4

to ULNRC-05475 calculations do not model containment parameters of this detail and are, therefore, unaffected by this change.

The sump screen modification resulted in an increase in containment metal mass. Westinghouse was asked to evaluate the effects of an increase of approximately 35,000 lbm. A LBLOCA PCT penalty of +3°F was calculated for an 82,500 ibm increase in containment metal mass that will be conservatively applied to this scenario. This change is small enough that it has negligible effects on maximum local oxidation and core-wide oxidation as calculated in WCAP-16265, the RSG topical report submitted to NRC in September 2004 to support Callaway License Amendment 168.

8. 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, units, and defaults; improving the input diagnostic checks; enhancing the code output; optimizing active coding; and eliminating inactive coding. 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 LBLOCA and SBLOCA analyses of record for Callaway.

5 to ULNRC-05475 ATTACHMENT TWO ECCS EVALUATION MODEL MARGIN ASSESSMENT FOR CALLAWAY 1

to ULNRC-05475 LARGE BREAK LOCA A. ANALYSIS OF RECORD (AOR) PCT = 1939 0 F B. PRIOR ECCS MODEL ASSESSMENTS + 00 F C. CURRENT LOCA MODEL ASSESSMENTS - + 17 0F March 2008 (see items 1 and 7 of Attachment 1)

LICENSING BASIS PCT + MARGIN ALLOCATIONS 1956 0 F ABSOLUTE MAGNITUDE OF MARGIN ALLOCATIONS 170 F SINCE LAST LBLOCA 30-DAY REPORT 2

to ULNRC-05475

. SMALL BREAK LOCA A. ANALYSIS OF RECORD (AOR) PCT = 1043'F B. PRIOR ECCS MODEL ASSESSMENTS + 0°F C. CURRENT ECCS MODEL ASSESSMENTS - + 0°F March 2008 LICENSING BASIS PCT + MARGIN ALLOCATIONS 1043 0 F ABSOLUTE MAGNITUDE OF MARGIN ALLOCATIONS 0°F SINCE LAST SBLOCA 30-DAY REPORT 3