L-PI-13-086, Revised Heat Transfer Multiplier Distributions - Error Identified in ECCS Evaluation Model, 10 CFR 50.46

Revised Heat Transfer Multiplier Distributions - Error Identified in ECCS Evaluation Model, 10 CFR 50.46

ML13248A246
Person / Time
Site:	Prairie Island
Issue date:	08/29/2013
From:	Jeffery Lynch Northern States Power Co, Xcel Energy
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
L-PI-13-086
Download: ML13248A246 (14)

Text

fl Xcel Energy AUG 2 9 2013 L-PI-13-086 10 CFR 50.46 U.S. Nuclear Regulatory Commission ATIN: Document Control Desk Washington DC 20555-0001 Prairie Island Nuclear Generating Plant, Units 1 and 2 Dockets 50-282 and 50-306 Renewed License Nos. DPR-42 and DPR-60 Revised Heat Transfer Multiplier Distributions- Error Identified in ECCS Evaluation Model, 10 CFR 50.46 As required by 10 CFR 50.46(a)(3)(ii), Northern States Power Company, a Minnesota corporation, doing business as Xcel Energy (hereafter "NSPM"), is submitting this 30-day report of an error discovered in an emergency core cooling system (ECCS) evaluation model for Prairie Island Nuclear Generating Plant (PINGP) Units 1 and 2.

The affected evaluation model is the 2004 Westinghouse Realistic Large Break Loss of Coolant Accident (LOCA) Evaluation Model using Automated Statistical Treatment of Uncertainty Method (ASTRUM), Application to Pressurized Water Reactors (PWRs) with Upper Plenum Injection.

The errors occurred in the code WCOBRA!TRAC. The errors affected the heat transfer multiplier uncertainty distributions. The errors were due to incorrect grid height specifications, and errors in processing test data used to develop the reflood heat transfer multiplier distributions.

A calculation representative of Prairie Island was performed by Westinghouse using the latest version of WCOBRAffRAC. Using the transient output, a matrix of HOTSPOT calculations was performed to estimate the effect of the changes in the heat transfer multiplier distributions. The limiting cases produced an estimated penalty of -2 °F for Unit 1 and -16 °F for Unit 2. The current analysis retains considerable margin to the 2200 °F limit. The conservative nature of the Peak Cladding Temperature (PCT) penalty coupled with the large amount of margin remaining provides assurance that compliance with 10 CFR 50.46 has been met, and that no reanalysis is necessary. The technical summary of this condition and updated PCT rack-up sheets are provided in the enclosure to this letter.

Summary of Commitments This letter contains no new commitments and no revisions to existing commitments.

1717 Wakonade Drive East

• Welch, Minnesota 55089-9642 Telephone: 651.388.1121

Document Control Desk Page 2 I j/_

~'£_,;'/! (/{___

0ame0/ Lynch Site Vice-President, Prairie Island Nuclear Generating Plant Northern States Power Company - Minnesota Enclosures (2) cc: Regional Administrator, Region Ill, USNRC Project Manager, Prairie Island Nuclear Generating Plant, USNRC Resident Inspector, Prairie Island Nuclear Generating Plant, USNRC

ENCLOSURE 1 ECCS EVALUATION MODEl CHANGES AND ERRORS Prairie Island Nuclear Generating Plant, UNITS 1 AND 2 4 pages follow

Xcel Energy Internal Correspondence PCT

SUMMARY

PilLBLOCA Pll SBLOCA PI2LBLOCA PI2SBLOCA Analysis of 11/30/07 1/21/08 11/30/07 1/21108 Record Date Analysis of 1765 959 1623 965 RecordPCT Old Changes 227 0 340 0 and Errors (absolute sum)

Last NRC 6/26/13 (1) 6/26/13 (1) 06/26/13 (1) 6/26/13 (1)

Notification Date Projected PCT 1992 959 1963 965 From the Last NRC Notification New Errors or -2 0 -16 0 Changes (from '

this Notification Only)

Total of Changes 229 0 356 0 and Errors (absolute Sum)

New Projected 1990 959 1947 965 PCT (I) These dates reflect the LBLOCA and SBLOCA 2012 annual report L-PI-13-053.

Westinghouse Non-Proprietary Class 3 to L TR-LIS-13-366, Revision 1 August 20,2013 Page2 of5 Revised Heat Transfer Multiplier Distributions

Background

Several changes and error corrections were made to WCOBRAffRAC and the impacts of these changes on the heat transfer multiplier uncertainty distributions were investigated. During this investigation, errors were discovered in the development of the original multiplier distributions, including errors in the grid locations specified in the WCOBRAffRAC models for the G2 Refill and G2 Reflood tests, and errors in processing test data used to develop the reflood heat transfer multiplier distribution. Therefore, the blowdown heatup, blowdown cooling, refill, and reflood heat transfer multiplier distributions were redeveloped. For the reflood heat transfer multiplier development, the evaluation time windows for ~ach set of test experimental data and each test simulation were separately defined based on the time at which the test or simulation exhibited dispersed flow film boiling heat transfer conditions characteristic of the reflood time period. The revised heat transfer multiplier distributions have been evaluated for impact on existing analyses. Resolution of these issues represents a closely related group of Non-Discretionary Changes in accordance with Section 4.1.2 of WCAP-13451.

Affected Evaluation Models 2004 Westinghouse Realistic Large Break LOCA Evaluation Model Using ASTRUM Estimated Effect A plant transient calculation representative of Prairie Island Unit 1 and Unit 2 transient behavior was performed with the latest version of WCOBRAffRAC. Using this transient, a matrix of HOTSPOT calculations was performed to estimate the effect of the heat transfer multiplier distribution changes. Using these results and considering the heat transfer multiplier uncertainty attributes from limiting cases for Prairie Island Unit 1 and Unit 2, an estimated PCT effect of -2°F has been established for 10 CFR 50.46 reporting purposes for Prairie Island Unit 1 and Unit 2 (future RSG AOR) and an estimated PCT effect of -16oF has been established for 10 CFR 50.46 reporting purposes for Prairie Island Unit 2 (current AOR).

Westinghouse Non-Proprietary Class 3 Attachment I to LTR-LIS-13-366, Revision 1 August20, 2013 Page 3 of5 Westinghouse LOCA Peak Clad Temperature Summary for AS'fRUM Best Estimate Large Break Plant Name: Prairie Island Unit 1 Utility Name: Xcel Energy, Inc Revision Date: 7/15/2013 Analysis Information EM: ASTRUM (2004) Analysis Date: 11/30/2007 Limiting Break Size: Split FQ: 2.5 FdH: 1.77 Fuel: 422 Vantage+ SGTP(%): 10

• Notes:

Clad Temp (OF) Ref. Notes LICENSING BASIS Analysis-Of-Record PCT 1765 1 PCT ASSESSMENTS (Delta PCI)

A. PRIOR ECCS MODEL ASSESSMENTS 1 . Evaluation of Fuel Pellet Thermal Conductivity Degradation and 227 2 (a)

Peaking Factor Burndown B. PLANNED PLANT MODIFICATION EVALUATIONS 1 . None 0 C. 2013 ECCS MODEL ASSESSMENTS 1 . Revised Heat Transfer Multiplier Distributions -2 3 D. OTHER*

1 . None 0 LICENSING BASIS PCT + PCT ASSESSMENTS PCT= 1990

• It is recommended that the licensee determine if these PCT allocations should be considered with respect to 10 CFR 50.46 reporting requirements.

References:

1 . WCAP-16890-P, Revision I, "Best-Estimate Analysis of the Large-Break Loss-of-Coolant Accident for the Prairie Island Nuclear Plant Unit 1 Using ASTRUM Methodology,

• June 2008.

2 . LTR-LIS-12-414, Prairie Island Units 1 and 2, 10 CFR 50.46 Notification and Reporting for Fuel Pellet Thermal Conductivity Degradation and Peaking Factor Bumdown," September 20, 2012.

3 . LTR-LIS-13-366, Revision I, "Prairie Island Units 1 and 2 10 CFR 50.46 Report for Revised Heat Transfer Multiplier Distributions," July 2013.

Notes:

(a) This evaluation credits peaking factor bumdown, see Reference 2.

Westinghouse Non-Proprietary Class 3 Attachment I to LTR-LIS-13-366, Revision 1 August 20, 2013 Page 4 of5 Westinghouse LOCA Peak Clad Temperature Summary for ASTRUM Best Estimate Large Break Plant Name: Prairie Island Unit 2 Utility Name: Xcel Energy, Inc Revision Date: 7/15/2013 Analysis Information EM: AS1RUM (2004) Analysis Date: 11/30/2007 Limiting Break Size: Split FQ: 2.5 FdH: 1.77 Fuel: 422 Vantage+ SGTP(%): 25 Notes:

Clad Temp (OF) Ref. Notes LICENSING BASIS Analysis-Of-Record PCT 1623 PCT ASSESSMENTS (Delta PCT)

A. PRIOR ECCS MODEL ASSESSMENTS 1 . Evaluation of Fuel Pellet Thermal Conductivity Degradation and 340 2 (a)

Peaking Factor Bwndown B. PLANNED PLANT MODIFICATION EVALUATIONS I . None 0 C. 2013 ECCS MODEL ASSESSMENTS I . Revised Heat Transfer Multiplier Distributions -16 3 D. OTHER*

I . None 0 LICENSING BASIS PCT + PCT ASSESSMENTS PCT= 1947

• It is recommended that the licensee determine if these PCTallocations should be considered with respect to 10 CFR 50.46 reporting requirements.

References:

I . WCAP-16891-P, "Best-Estimate Analysis of the Large-Break Loss-of-Coolant Accident for the Prairie Island Nuclear Plant Unit 2 Using ASTRUM Methodology," June 2008.

2 . LTR-LIS-12-414, "Prairie Island Units.! and 2, I 0 CFR 50.46 Notification and Reporting for Fuel Pellet Thermal Conductivity Degradation and Peaking Factor Bwndown," September 20, 2012.

3 . LTR-LIS-13-366, Revision I, "Prairie Island Units I and 2 10 CFR 50.46 Report for Revised Heat Transfer Multiplier Distributions," July 2013.

Notes:

(a) This evaluation credits peaking factor burndown, see Reference 2.

ENCLOSURE 2 LBLOCA and SBLOCA Peak Clad Temperature Assessment Sheets 6 pages follow

e Westinghouse Non-Proprietary Class 3 Westinghouse Electric Company Westinghouse Engineering, Equipment and Major Projects 1000 Westinghouse Drive Cranberry Township, Pennsylvania 16066 USA Direct tel: (412) 374-6663 Direct fax: (724) 720-0857 e-mail: utleyd@westinghouse.com Our ref: LTR-LIS-13-366, Revision 1 August 20, 2013 Prairie Island Units 1 and 2 10 CFR 50.46 Report for Revised Heat Transfer Multiplier Distributions

Dear Sir or Madam:

The attachment documents the 10 CFR 50.46 report for the evaluation of the revised heat transfer multiplier distributions in the Prairie Island Unit 1 and Unit 2 Best-Estimate (BE) Large-Break Loss-of-Coolant Accident (LBLOCA) analyses. References 1 and 2 remain the Analyses of Record for Units 1 and 2, respectively. Please note that for Unit 2, the Unit 1 evaluation is applicable to the future Unit 2 replacement steam generator AOR (see Reference 3). The attachment also documents the updated Peak Cladding Temperature (PCT) rackup sheets for Prairie Island Unit 1 and Unit 2.

Please contact your LOCA Plant Cognizant Engineer if there are any questions concerning this information.

Author: (Electronically Approved)* Verifier: (Electronically Approved)*

Dania! W. Utley Carmen D. Teo lis LOCA Integrated Services II LOCA Integrated Services I Approved: (Electronically Approved)*

Amy J. Colussy, Manager LOCA Integrated Services I

References:

1. WCAP-16890-P, Revision 1, "Best-Estimate Analysis of the Large-Break Loss-of-Coolant Accident for the Prairie Island Nuclear Plant Unit 1 Using ASTRUM Methodology," June 2008.

2. WCAP-16891-P, "Best-Estimate Analysis of the Large-Break Loss-of-Coolant Accident for the Prairie Island Nuclear Plant Unit 2 Using ASTRUM Methodology," June 2008.

3. WCAP-17783-P, "Best-Estimate Analysisofthe Large-Break Loss-of-Coolant Accident for Prairie Island Units 1 and 2 with Replacement Steam Generators Using ASTRUM Methodology," June 2013.

Attachment 1: Prairie Island Units 1 and 2 10 CFR 50.46 Report and Peak Cladding Temperature Rackup Sheet for Revised Heat Transfer Multiplier Distributions (5 Pages)

• Electronically approved records are authenticated in the electronic document management system.

© 2013 Westinghouse Electric Company LLC All Rights Reserved

Westinghouse Non-Proprietary Class 3 to LTR-LIS-13-366, Revision 1 August 20, 2013 Page 1 of5 Attachment 1 Prairie Island Units 1 and 2 10 CFR 50.46 Report and Peak Cladding Temperature Rackup Sheet for Revised Heat Transfer Multiplier Distributions (5 pages, including cover page)

© 2013 Westinghouse Electric Company LLC All Rights Reserved

Westinghouse Non-Proprietary Class 3 to LTR-LIS-13-366, Revision 1 August 20, 2013 Page2 of5 Revised Heat Transfer Multiplier Distributions

Background

Several changes and error corrections were made to WCOBRA!TRAC and the impacts of these changes on the heat transfer multiplier uncertainty distributions were investigated. During this investigatiqn, errors were discovered in the development of the original multiplier distributions, including errors in the grid locations specified in the WCOBRA!TRAC models for the G2 Refill and G2 Reflood tests, and errors in processing test data used to develop the reflood heat transfer multiplier distribution. Therefore, the blowdown heatup, blowdown cooling, refill, and reflood heat transfer multiplier distributions were redeveloped. For the reflood heat transfer multiplier development, the evaluation time windows for each set of test experimental data and each test simulation were separately defined based on the time at which the test or simulation exhibited dispersed flow film boiling heat transfer conditions characteristic of the reflood time period. The revised heat transfer multiplier distributions have been evaluated for impact on existing analyses. Resolution of these issues represents a closely related group of Non-Discretionary Changes in accordance with Section 4.1.2 ofWCAP-13451.

Affected Evaluation Models 2004 Westinghouse Realistic Large Break LOCA Evaluation Model Using ASTRUM Estimated Effect A plant transient calculation representative of Prairie Island Unit 1 and Unit 2 transient behavior was performed with the latest version of WCOBRA!TRAC. Using this transient, a matrix of HOTSPOT calculations was performed to estimate the effect of the heat transfer multiplier distribution changes. Using these results and considering the heat transfer multiplier uncertainty attributes from limiting cases for Prairie Island Unit 1 and Unit 2, an estimated PCT effect of-2°F has been established for 10 CFR 50.46 reporting purposes for Prairie Island Unit 1 and Unit 2 (future RSG AOR) and an estimated PCT effect of -16°F has been established for 10 CFR 50.46 reporting purposes for Prairie Island Unit 2 (current AOR).

Westinghouse Non-Proprietary Class 3 to LTR-LIS-13-366, Revision 1 August 20, 2013 Page3 of5 Westinghouse LOCA Peak Clad Temperature Summary* for ASTRUM Best Estimate Large Break Plant Name: Prairie Island Unit 1 Utility Name: Xcel Energy, Inc Revision Date: 7/15/2013 Analysis Information EM: ASTRUM (2004) Analysis Date: 11/30/2007 Limiting Break Size: Split FQ: 2.5 FdH: 1.77 Fuel: 422 Vantage+ SGTP(%): 10 Notes:

Clad Temp COF) Ref. Notes LICENSING BASIS Analysis-Of-Record PCT 1765 1 PCT ASSESSMENTS (Delta PCT)

A. PRIOR ECCS MODEL ASSESSMENTS I . Evaluation ofFuel Pellet Thermal Conductivity Degradation and 227 2 (a)

Peaking Factor Burndown B. PLANNED PLANT MODIFICATION EVALUATIONS I . None 0 C. 2013 ECCS MODEL ASSESSMENTS I . Revised Heat Transfer Multiplier Distributions -2 3 D. OTHER*

I .None 0 LICENSING BASIS PCT + PCT ASSESSMENTS PCT= 1990 It is recommended that the licensee determine ifthese PCT allocations should be considered with respect to I 0 CFR 50.46 reporting requirements.

References:

I . WCAP-16890-P, Revision 1, "Best-Estimate Analysis of the Large-Break Loss-of-Coolant Accident for the Prairie Island Nuclear Plant Unit 1 Using ASTRUM Methodology," June 2008.

2 . LTR-LIS-12-414, "Prairie Island Units 1 and 2, 10 CFR 50.46 Notification and Reporting for Fuel Pellet Thermal Conductivity Degradation and Peaking Factor Burndown," September 20, 2012.

3 . LTR-LIS-13-366, Revision 1, "Prairie Island Units I and 2 10 CFR 50.46 Report for Revised Heat Transfer Multiplier Distributions," July 2013.

Notes:

(a) This evaluation credits peaking factor burndown, see Reference 2.

Westinghouse Non-Proprietary Class 3 to LTR-LIS-13-366, Revision 1 August 20,2013 Page4 of5 Westinghouse LOCA Peak Clad Temperature Summary for ASTRUM Best Estimate Large Break Plant Name: Prairie Island Unit 2 Utility Name: Xcel Energy, Inc Revision Date: 7/15/2013 Analysis Information EM: ASTRUM (2004) Analysis Date: 11/30/2007 Limiting Break Size: Split FQ: 2.5 FdH: 1.77 Fuel: 422 Vantage+ SGTP(%): 25 Notes:

Clad Temp (0 F) Ref. Notes LICENSING BASIS Analysis-Of-Record PCT 1623 1 PCT ASSESSMENTS (Delta PCT)

A. PRIOR ECCS MODEL ASSESSMENTS I . Evaluation of Fuel Pellet Thennal Conductivity Degradation and 340 2 (a)

Peaking Factor Burndown B. PLANNED PLANT MODIFICATION EVALUATIONS I . None 0 C. 2013 ECCS MODEL ASSESSMENTS I . Revised Heat Transfer Multiplier Distributions -I6 3 D. OTHER*

I . None 0 LICENSING BASIS PCT + PCT ASSESSMENTS PCT= 1947

• It is recommended that the licensee detennine if these PCT allocations should be considered with respect to I0 CFR 50.46 reporting requirements.

References:

I . WCAP-I6891-P, "Best-Estimate Analysis of the Large-Break Loss-of-Coolant Accident for the Prairie Island Nuclear Plant Unit 2 Using ASTRUM Methodology," June 2008.

2 . LTR-LIS-I2-414, "Prairie Island Units I and 2, 10 CFR 50.46 Notification and Reporting for Fuel Pellet Thennal Conductivity Degradation and Peaking Factor Burndown," September 20, 2012.

3 . LTR-LIS-13-366, Revision I, "Prairie Island Units I and 2 10 CFR 50.46 Report for Revised Heat Transfer Multiplier Distributions," July 2013.

Notes:

(a) This evaluation credits peaking factor burndown, see Reference 2.

Westinghouse Non-Proprietary Class 3 to LTR-LIS-13-366, Revision 1 August 20, 2013 PageS of5 Westinghouse LOCA Peak Clad Temperature Summary for ASTRUM Best Estimate Large Break Plant Name: Prairie Island Unit 2 RSG Utility Name: Xcel Energy, Inc Revision Date: 7/15/2013 Analysis Information EM: ASTRUM (2004) Analysis Date: 11/30/2007 Limiting Break Size: Split FQ: 2.5 FdH: 1.77 Fuel: 422 Vantage+ SGTP (%): 10 Notes:

Clad Temp (0 F) Ref. Notes LICENSING BASIS Analysis-Of-Record PCT 1765 PCT ASSESSMENTS (Delta PCT)

A. PRIOR ECCS MODEL ASSESSMENTS I . Evaluation ofFuel Pellet Thennal Conductivity Degradation and 227 2 (a), (b)

Peaking Factor Bumdown B. PLANNED PLANT MODIFICATION EVALUATIONS I . None 0 C. 2013 ECCS MODEL ASSESSMENTS I . Revised Heat Transfer Multiplier Distributions -2 3 D. OTHER*

I . None 0 LICENSING BASIS PCT + PCT ASSESSMENTS PCT= 1990

• It is recommended that the licensee detennine if these PCT allocations should be considered with respect to I 0 CFR 50.46 reporting requirements.

References:

I . WCAP-I7783-P, "Best-Estimate Analysis of the Large-Break Loss-of-Coolant Accident for Prairie Island Units I and 2 with Replacement Steam Generators Using ASTRUM Methodology," June 2013.

2 . LTR-LIS-I2-414, Prairie Island Units I and 2, I 0 CFR 50.46 Notification and Reporting for Fuel Pellet Thennal Conductivity Degradation and Peaking Factor Bumdown." September 20, 20I2.

3 . LTR-LIS-13-366, Revision I, "Prairie Island Units I and 2 IO CFR 50.46 Report for Revised Heat Transfer Multiplier Distributions," July 2013.

Notes:

(a) This evaluation credits peaking factor burndown. see Reference 2.

(b) The reporting text and line item originally identified for Unit 1 in Reference 2 is applicable to Unit 2 with RSGs.