ML15314A657

Wolf Creek - Submittal of 10 CFR 50.46 Thirty Day Report of Emergency Core Cooling System (ECCS) Model Changes

ML15314A657
Person / Time
Site:	Wolf Creek
Issue date:	11/04/2015
From:	Hafenstine C R Wolf Creek
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
RA 15-0080
Download: ML15314A657 (5)

Text

W~FCREEK'NUCLEAR OPERATING CORPORATIONNovember 4, 2015Cynthia R. HafenstineManager Regulatory AffairsRA 15-0080U. S. Nuclear Regulatory CommissionATTN: Document Control DeskWashington, DC 20555

Reference:

1) Letter RA 15-0025, dated March 20, 2015, from S.R. Koenig, WCNOCto USNRC2) Letter from C. F. Lyon, USNRC, to A. C. Heflin, WCNOC, "Wolf CreekGenerating Station -Issuance of Amendment re: Revise TechnicalSpecification 5.6.5, "CORE OPERATING LIMITS REPORT (COLR),"to Add ASTRUM to the List of Analytical Methods (TAC NO.MF351 8)," dated August 28, 2015

Subject:

Docket No. 50-482: 10 CFR 50.46 Thirty Day Report of Emergency CoreCooling System (ECCS) Model ChangesGentlemen:In accordance with 10 CFR 50.46, "Acceptance criteria for emergency core cooling systems forlight-water nuclear power reactors," paragraph (a)(3)(ii), Wolf Creek Nuclear OperatingCorporation (WCNOC) is submitting the attached information to fulfill the 30-day reportingrequirement for the Wolf Creek Generating Station (WCGS).In Reference 1, WCNOC reported the WCGS peak cladding temperature (PCT), calculatedbased on an-acceptable evaluation model. A new best-estimate large break loss-of-coolant(LOCA) methodology was approved for WCGS in Reference 2, known as Automated StatisticalTreatment of Uncertainty Method (ASTRUM). The license amendment was implemented atWCGS on October 26, 2015. The new analysis resulted in changes of greater than 50 0F in thePCT from those previously reported to the NRC in the last 10 CFR 50.46 report (Reference 1).The calculated PCT for the WCGS large break LOCA remains within the acceptance criteria setforth in 10 CFR 50.46. Additional reanalysis is not required.Attachment I provides an assessment of the specific changes to the Westinghouse ECCSevaluation model for large break LOCAs.P.O. Box 41 IBurlington, KS 66839 I Phone: (620) 364-8831 P '-An Equal Opportunity Employer M/F/HCNVET RA 15-0080Page 2 of 2Attachment II provides an update of the WCGS POT margin utilization for the large break LOCAevaluation model.This letter contains no commitments. If you have any questions concerning this matter, pleasecontact me at (620) 364-4204.Sincerely,Cynthia R. HafenstineCRH/rltAttachmentI Assessment of Changes to the Westinghouse Emergency Core CoolingSystem (ECCS) Evaluation Model for Large Break Loss-of-CoolantAccident (LOCA)II Emergency Core Cooling System (ECCS) Evaluation Model Peak CladdingTemperature (PCT) Margin Utilization Rack-up Formcc: M. L. Dapas (NRC), w/aC. F. Lyon (NRC), w/aN. H. Taylor (NRC), wlaSenior Resident Inspector (NRC), w/a Attachment I to RA 15-0080Page 1 of 2Assessment of Changes to the Westinghouse Emergency Core Cooling System (ECCS)Evaluation Model for Large Break Loss-of-Coolant Accident (LOCA)GENERAL CODE MAINTENANCEBackgroundVarious changes have been made to enhance the usability of codes and to streamline futureanalyses. Examples of these changes include modifying input variable definitions, units anddefaults; ,improving the input diagnostic checks; enhancing the code output; optimizing activecoding; and eliminating inactive coding. These changes represent Discretionary Changes thatwill be implemented on a forward-fit basis in accordance with Section 4.1.1 of WCAP-13451"Westinghouse Methodology for Implementation of 10 CFR 50.46 Reporting."Affected Evaluation Model2004 Westinghouse Realistic Large Break LOCA Evaluation Model Using ASTRUMEstimated EffectThe nature of these changes leads to an estimated peak cladding temperature (PCT) impact of0°0F.ERRORS IN DECAY GROUP UNCERTAINTY FACTORSBackgroundErrors in the calculation of decay heat were discovered in the WCOBRA/TRAC code. Thedecay group uncertainty factors for each fissile isotope are provided in Table 8-14 of WCAP-16009-P-A. The uncertainty factors for 239Pu were applied to 238U, and those for 238U wereapplied to 239pu. This error causes an over-prediction of the uncertainty in decay power from239pu and an under-prediction of the uncertainty in decay power from 238U. Further, the decaygroup uncertainty factor for Decay Group 6 of 235U was erroneously coded as 2.5% instead of2.25%. Correction of these errors impacts the application of the sampled decay heatuncertainty, which may result in small changes to the decay heat power. These issues havebeen evaluated to estimate the impact on Automated Statistical Treatment of UncertaintyMethod (ASTRUM) best-estimate large break LOCA analysis results. The resolution of theseissues represents a closely-related group of Non-Discretionary Changes in accordance withSection 4.1.2 of WCAP-1 3451.Affected Evaluation Model2004 Westinghouse Realistic Large Break LOCA Evaluation Model Using ASTRUMEstimated EffectThe issues described above were evaluated to account for the correction of these errors. Theplant-specific sensitivity study resulted in an estimated PCT impact of -10°F for Wolf CreekGenerating Station (WCGS).

Attachment I to PA 15-0080Page 2 of 2WCGS CONTAINMENT COOLING CAPACITYBackgroundWolf Creek Nuclear Operating Corporation (WCNOC) identified an error in the containment fancooler capacity transmitted for use in the best-estimate ASTRUM evaluation model analysis.This issue has been evaluated to estimate the impact on existing PCT results. The resolution ofthis issue represents a Non-Discretionary Change in accordance with Section 4.1.2 of WCAP-13451.Affected Evaluation Models2004 Westinghouse Realistic Large Break LOCA Evaluation Model Using ASTRUMEstimated EffectThe estimated effect was determined for the large break LOCA evaluation model based on thechange in calculated containment, pressure resulting from the correct containment coolingcapacity. The change in calculated containment pressure leads to an estimated effect of 0°F forthe ASTRUM evaluation model analysis.

Attachment II to IRA 15-0080Page 1 of 1EMERGENCY CORE COOLING SYSTEM (ECCS) EVALUATION MODEL PEAK CLADDINGTEMPERATURE (PCT) MARGIN UTILIZATION RACK-UP FORM**LARGE BREAK LOCA PCT MARGIN UTILIZATION ***Evaluation Model:Fuel:Peaking Factor:SG Tube Plugging:Power Level:Limiting Break Size:LICENSING BASISASTRUM (2004)RFA-2FQ=2.50, FdH=1.6510%3565 MWthDEGClad Temp (0F)Ref. NotesAnalysis of Record (AOR) PCTMARGIN ALLOCATIONS (APCT)1900°F 1A. PRIOR PERMANENT ECCS MODEL ASSESSMENTS1. NoneB. PLANNED PLANT CHANGE EVALUATIONS1. Containment Fan Cooler CapacityC. 2014 PERMANENT ECCS MODEL ASSESSMENTS1. Containment Fan Cooler Capacity2. Decay Group Uncertainty Factors ErrorsD. OTHER1. None000-102 (a)230LICENSING BASIS PCT + MARGIN ALLOCATIONSPCT = 1890 0F

References:

1. WCAP-17107-P, Revision 1, "Best-Estimate Analysis of the Large-Break Loss-of-CoolantAccident for the Wolf Creek Nuclear Power Plant Using the ASTRUM Methodology,"January 2014.2. LTR-LIS-14-400, "10 CFR 50.46 Report for the Wolf Creek Large Break LOCA Evaluationof the Change in Containment Cooling Capacity," August 2014.3. LTR-LIS-14-492, "Wolf Creek Unit 1 10 CFR 50.46 Report for the Correction of the DecayGroup Uncertainty Factors Errors," November 2014.Notes:(a) This effect was estimated based on a cooling capacity intended to bound futureimplementation of replacement tube bundles in the containment fan coolers.

W~FCREEK'NUCLEAR OPERATING CORPORATIONNovember 4, 2015Cynthia R. HafenstineManager Regulatory AffairsRA 15-0080U. S. Nuclear Regulatory CommissionATTN: Document Control DeskWashington, DC 20555

Reference:

1) Letter RA 15-0025, dated March 20, 2015, from S.R. Koenig, WCNOCto USNRC2) Letter from C. F. Lyon, USNRC, to A. C. Heflin, WCNOC, "Wolf CreekGenerating Station -Issuance of Amendment re: Revise TechnicalSpecification 5.6.5, "CORE OPERATING LIMITS REPORT (COLR),"to Add ASTRUM to the List of Analytical Methods (TAC NO.MF351 8)," dated August 28, 2015

Subject:

Docket No. 50-482: 10 CFR 50.46 Thirty Day Report of Emergency CoreCooling System (ECCS) Model ChangesGentlemen:In accordance with 10 CFR 50.46, "Acceptance criteria for emergency core cooling systems forlight-water nuclear power reactors," paragraph (a)(3)(ii), Wolf Creek Nuclear OperatingCorporation (WCNOC) is submitting the attached information to fulfill the 30-day reportingrequirement for the Wolf Creek Generating Station (WCGS).In Reference 1, WCNOC reported the WCGS peak cladding temperature (PCT), calculatedbased on an-acceptable evaluation model. A new best-estimate large break loss-of-coolant(LOCA) methodology was approved for WCGS in Reference 2, known as Automated StatisticalTreatment of Uncertainty Method (ASTRUM). The license amendment was implemented atWCGS on October 26, 2015. The new analysis resulted in changes of greater than 50 0F in thePCT from those previously reported to the NRC in the last 10 CFR 50.46 report (Reference 1).The calculated PCT for the WCGS large break LOCA remains within the acceptance criteria setforth in 10 CFR 50.46. Additional reanalysis is not required.Attachment I provides an assessment of the specific changes to the Westinghouse ECCSevaluation model for large break LOCAs.P.O. Box 41 IBurlington, KS 66839 I Phone: (620) 364-8831 P '-An Equal Opportunity Employer M/F/HCNVET RA 15-0080Page 2 of 2Attachment II provides an update of the WCGS POT margin utilization for the large break LOCAevaluation model.This letter contains no commitments. If you have any questions concerning this matter, pleasecontact me at (620) 364-4204.Sincerely,Cynthia R. HafenstineCRH/rltAttachmentI Assessment of Changes to the Westinghouse Emergency Core CoolingSystem (ECCS) Evaluation Model for Large Break Loss-of-CoolantAccident (LOCA)II Emergency Core Cooling System (ECCS) Evaluation Model Peak CladdingTemperature (PCT) Margin Utilization Rack-up Formcc: M. L. Dapas (NRC), w/aC. F. Lyon (NRC), w/aN. H. Taylor (NRC), wlaSenior Resident Inspector (NRC), w/a Attachment I to RA 15-0080Page 1 of 2Assessment of Changes to the Westinghouse Emergency Core Cooling System (ECCS)Evaluation Model for Large Break Loss-of-Coolant Accident (LOCA)GENERAL CODE MAINTENANCEBackgroundVarious changes have been made to enhance the usability of codes and to streamline futureanalyses. Examples of these changes include modifying input variable definitions, units anddefaults; ,improving the input diagnostic checks; enhancing the code output; optimizing activecoding; and eliminating inactive coding. These changes represent Discretionary Changes thatwill be implemented on a forward-fit basis in accordance with Section 4.1.1 of WCAP-13451"Westinghouse Methodology for Implementation of 10 CFR 50.46 Reporting."Affected Evaluation Model2004 Westinghouse Realistic Large Break LOCA Evaluation Model Using ASTRUMEstimated EffectThe nature of these changes leads to an estimated peak cladding temperature (PCT) impact of0°0F.ERRORS IN DECAY GROUP UNCERTAINTY FACTORSBackgroundErrors in the calculation of decay heat were discovered in the WCOBRA/TRAC code. Thedecay group uncertainty factors for each fissile isotope are provided in Table 8-14 of WCAP-16009-P-A. The uncertainty factors for 239Pu were applied to 238U, and those for 238U wereapplied to 239pu. This error causes an over-prediction of the uncertainty in decay power from239pu and an under-prediction of the uncertainty in decay power from 238U. Further, the decaygroup uncertainty factor for Decay Group 6 of 235U was erroneously coded as 2.5% instead of2.25%. Correction of these errors impacts the application of the sampled decay heatuncertainty, which may result in small changes to the decay heat power. These issues havebeen evaluated to estimate the impact on Automated Statistical Treatment of UncertaintyMethod (ASTRUM) best-estimate large break LOCA analysis results. The resolution of theseissues represents a closely-related group of Non-Discretionary Changes in accordance withSection 4.1.2 of WCAP-1 3451.Affected Evaluation Model2004 Westinghouse Realistic Large Break LOCA Evaluation Model Using ASTRUMEstimated EffectThe issues described above were evaluated to account for the correction of these errors. Theplant-specific sensitivity study resulted in an estimated PCT impact of -10°F for Wolf CreekGenerating Station (WCGS).

Attachment I to PA 15-0080Page 2 of 2WCGS CONTAINMENT COOLING CAPACITYBackgroundWolf Creek Nuclear Operating Corporation (WCNOC) identified an error in the containment fancooler capacity transmitted for use in the best-estimate ASTRUM evaluation model analysis.This issue has been evaluated to estimate the impact on existing PCT results. The resolution ofthis issue represents a Non-Discretionary Change in accordance with Section 4.1.2 of WCAP-13451.Affected Evaluation Models2004 Westinghouse Realistic Large Break LOCA Evaluation Model Using ASTRUMEstimated EffectThe estimated effect was determined for the large break LOCA evaluation model based on thechange in calculated containment, pressure resulting from the correct containment coolingcapacity. The change in calculated containment pressure leads to an estimated effect of 0°F forthe ASTRUM evaluation model analysis.

Attachment II to IRA 15-0080Page 1 of 1EMERGENCY CORE COOLING SYSTEM (ECCS) EVALUATION MODEL PEAK CLADDINGTEMPERATURE (PCT) MARGIN UTILIZATION RACK-UP FORM**LARGE BREAK LOCA PCT MARGIN UTILIZATION ***Evaluation Model:Fuel:Peaking Factor:SG Tube Plugging:Power Level:Limiting Break Size:LICENSING BASISASTRUM (2004)RFA-2FQ=2.50, FdH=1.6510%3565 MWthDEGClad Temp (0F)Ref. NotesAnalysis of Record (AOR) PCTMARGIN ALLOCATIONS (APCT)1900°F 1A. PRIOR PERMANENT ECCS MODEL ASSESSMENTS1. NoneB. PLANNED PLANT CHANGE EVALUATIONS1. Containment Fan Cooler CapacityC. 2014 PERMANENT ECCS MODEL ASSESSMENTS1. Containment Fan Cooler Capacity2. Decay Group Uncertainty Factors ErrorsD. OTHER1. None000-102 (a)230LICENSING BASIS PCT + MARGIN ALLOCATIONSPCT = 1890 0F

References:

1. WCAP-17107-P, Revision 1, "Best-Estimate Analysis of the Large-Break Loss-of-CoolantAccident for the Wolf Creek Nuclear Power Plant Using the ASTRUM Methodology,"January 2014.2. LTR-LIS-14-400, "10 CFR 50.46 Report for the Wolf Creek Large Break LOCA Evaluationof the Change in Containment Cooling Capacity," August 2014.3. LTR-LIS-14-492, "Wolf Creek Unit 1 10 CFR 50.46 Report for the Correction of the DecayGroup Uncertainty Factors Errors," November 2014.Notes:(a) This effect was estimated based on a cooling capacity intended to bound futureimplementation of replacement tube bundles in the containment fan coolers.