RC-94-0152, Forwards Annual ECCS Evaluation Model Revs Rept for Vsns,Per 10CFR50.46

Forwards Annual ECCS Evaluation Model Revs Rept for Vsns,Per 10CFR50.46

ML20069G578
Person / Time
Site:	Summer
Issue date:	06/06/1994
From:	Skolds J SOUTH CAROLINA ELECTRIC & GAS CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
RC-94-0152, RC-94-152, NUDOCS 9406100078
Download: ML20069G578 (16)

Text

,

. , 10CFR50.46  ;

. South Carolina Electric & Gas Company John L. Sholds l' P O. Box 88 Senior Vee President

> Jenkinsville, SC 29065 Nuclear Operations

, (803) 345-4001 l SCE&G '

Ascr.wom l

June 6, 1994 I Refer to: RC-94-0152 'l i

Document Control Desk U. S. Nuclear Regulatory Commission l

Washington,DC 20555 l

Gentlemen:

Subject:

VIRGIL C. SUMMER NUCLEAR STATION  ;

DOCKET NO. 50/395 I OPERATING LICENSE NO. NPF-12  :

ECCS EVALUATION MODEL REVISIONS REPORT (ANN 2300)

Attached is the annual Emergency Core Cooling System (ECCS) Evaluation Model Revisions Report for the Virgil C. Summer Nuclear Station (VCSNS). This report is submitted pursuant to 10CFR50.46 which requires licensees to notify the NRC on at least an annual basis of errors or changes in the ECCS Evaluation Models.

Tables 2 - 5 in the attachment summarize the changes in peak clad temperature from the previous analysis of record. None of the model changes is considered significant under 10CFR50.46.

I declare that the statements and matters set forth herein are true and correct to the best of my knowledge,information, and belief.

If you have any questions, please call.

I Very truly yours,

[Jtht John L. Skolds ARR:lcd Attachment c: O. W. Dixon J. B. Kn otts, J r.

R. R. Mahan (w/o att.) L. R. Cartin l R. J. White NSRC  !

5. D. Ebneter RTS (ANN 2300)  !

G. F. Wunder Central File System '

General Managers File (813.12-4,818.02-17)

NRC Resident inspector I i 1

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~O NUCLEAR EXCELLENCE- A SUMMER TRADITIONI I 9406100078 940606 k PDR ADOCK 05ooo395 j I

R PDR m _I

CHANGES TO THE WESTINGHOUSE ECCS EVALUATION MODELS INTRODUCTION Provisions in 10CFR50.46 require the annual reporting of corrections to or changes in the ECCS Evaluation Model (EM) approved for use in performing safety analyses for the loss of coolant accident (LOCA). This report describes corrections and revisions to the Westinghouse ECCS EM which are applicable to V. C. Summer Nuclear Station (VCSNS). The current Westinghouse ECCS ems are listed in Table 1 and consist of several computer codes with specific functions.

Westinghouse has completed the evaluation of several items related to the Westinghouse ECCS Evaluation Models listed in Table 1. Each of these items is discussed in the following sections, which include a description of the item, the assessment which was performed, the resulting change to the Evaluation Model, and the effect of the change on the Peak Clad Temperature (PCT).

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TABLE 1

SUMMARY

OF WESTINGHOUSE ECCS EVALUATION MODELS FOR VCSNS l

NAME: 1981 MODEL WITH BASH i APPUCATION: Analysis of Large Break LOCA CODES USED: PURPOSE:

SATAN-VI Blowdown hydraulic transient BASH Reflood hydraulic transient LOCBART Hot assembly thermohydraulics and fuel rod thermal transient  !

WREFLOOD/ COCO /LOTIC Containment pressure transient NAME: 1985 SBLOCA MODEL APPLICATION: Analysis of Small Break LOCA CODES USED: PURPOSE: I NOTRUMP System Hydraulic transient SBLOCTA Fuel rod thermal transient l

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Vessel and Steam Generator Calculation Errors in Lucifer

Background

The LUCIFER code is used to generate the component databases, from raw input data, to be used in the small and large break LOCA analyses. Errors were found in the VESCAL subroutine of the LUCIFER code. These errors were in the geometric and mass calculations of the vessel and steam generator portions of the needed data. All LOCA analyses using the LUCIFER code outputs are affected by these error corrections. The errors were corrected in a manner to maintain the consistency of the LUCIFER code.

The errors were determined to be a Non-Discretionary Change as described in Section 4.1.2 of WCAP-13451 and were corrected in accordance with Section 4.1.3 of WCAP-13451.

Affected Evaluation Models 1985 SBLOCA Evaluation Model 1981 ECCS Evaluation Model with BASH Estimated Effect Representative plant calculations indicate a net PCT effect of -16 F for small break LOCA and a -6 F for large break LOCA.

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15Hil DRIFT FLUX ERROR

Background

An error was discovered both in WCAP-10079-P-A and the relevant coding in NOTRUMP 5UBROUTINE ISHilA which led to an incorrect calculation of the drift flux in NOTRUMP when a laminar film annular flow was predicted. The affected equation in WCAP-10079-P-A is Equation G-74 wherein a factor of 'g', the g ravitational constant, was inadvertently omitted from both the documentation and ibe equivalent coding. The correction of this error returned NOTRUMP to consistency with the ultimate reference for the affected correlation.

This was determined to be a Non-discretionary Change as described in Section 4.1.2 of WCAP-13451 and was corrected in accordance with Section 4.1.3 of WCAP-13451.

Affected Evaluation Models 1985 Small Break LOCA Evaluation Model Estimated Effect Representative plant analyses were used to estimate a generic PCT effect of 0 F.

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CORE NODE INITIAllIATION ERROR Backaround An error was discovered in how the p perties of CORE NODE components were  !

initialized for non-existent regions in the adjoining FLUID NODE. In particular this led to artificially high core temperatures during the timestep when the core mixture level crossed a node boundary, conservatively causing slightly more core mixture level depression than appropriate during this timestep. Correction of this error allows for a smoother mixture level uncovery transient during node crossings.

This was determined to be a Non-discretionary Change as described in Section 4.1.2 of WCAP-13451 and was corrected in accordance with Section 4.1.3 of WCAP-13451.

Affected Evaluation Models 1985 Small Break LOCA Evaluation Model Estimated Effect The nature of this error led to an estimated generic PCT effect of 0 F.

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NOTRUMP HEAT LINK POINTER ERROR

Background

An error was discovered in how NOTRUMP initialized certain HEAT LINK pointer variables at the start of a calculation. Correction of this error returned NOTRUMP to consistencywith the originalintent of this section of coding.

This was determined to be a Non-discretionary Change as described in Section 4.1.2 of WCAP-13451 and was corrected in accordance with Section 4.1.3 of WCAP-13451.

Affected Evaluation Models 1985 Small Break LOCA Evaluation Model Estimated Effect Representative plant analyses were used to estimate a generic PCT effect of 0 F.

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l FUEL ROD MODEL ERRORS IN SBLOCA Backaround A number of minor programming errors were corrected in the fuel rod heat up code used in SBLOCA analyses. These corrections were related to:

1. Individual rod plenum temperatures

2. Individual rod stack lengths

3. Clad thinning logic

4. Pellet / clad contact logic

5. Corrected _ gamma redistribution

6. Including ZrO2 thickness at t=0 initialization

7. Numerics and convergence criteria of initialization.

These changes were determined to be Non-Discretionary Changes in accordance with Section 4.1.2 of WCAP-13451 and were implemented in accordance with Section 4.1.3 of WCAP-13451.

Affected Evaluation Models 1985 SBLOCA Evaluation Model Estimated Effect The cumulative effect of the error corrections and convergence criteria change was found to be less than approximately'+4 F. This chang,e is thereforejudc ed to have a ne ligible effect on PCT and on a generic basis the estimated effect will'ae reported as F.

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LARGE BREAK LOCA FUEL ROD MODEL ERRORS

Background

Minor errors in the rod heat up code used in Large Break LOCA analyses were corrected. These errors concerned conditions which exist during periods of peilet th,mn/ clad contact and the internal bookkeeping logic associated with clad ing.

These changes were determined to be Non-Discretionary Changes in accordance with Section 4.1.2 of WCAP-13451 and were implemented in accordance with Section 4.1.3 of WCAP-13451.

Affected Evaluation Models 1981 ECCS Evaluation Model with BASH Estimated Effect Representative plant calculations have shown that these corrections have a negligible effect on PCT for near Beginning-of-Life (BOL) fuel rod conditions (i.e. <

2000 MWD /MTU). These effects become evalent as burnup increases, but are not expected to be of any significance until let/ clad contact is predicted for steady-state operating conditions (typically > 000 MWD /MTU). These corrections therefore result in a negligible PCT impact for large Break LOCA licensing basis PCT's which are calculated with near BOL conditions. This impact is being reported generically as 0 F.

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HIGH TEMPERATURE FUEL ROD BURST MODEL

Background

A model for calculating the prediction of zircaloy cladding burst behavior above the previous limit of 1742 F was implemented. This model was described to the NRC in:

Letter ET-NRC-92-3746, N. J. Liparulo @ to R. C. Jones (NRC),

" Extension of NUREG-0630 Fuel Rod Burst Strain and Assembly Blockage Models to High Fuel Rod Burst Temperatures", September 16, 1992.

This was determined to be a Non-discretionary Change as described in Section 4.1.2 of WCAP-13451 and was corrected in accordance with Section 4.1.3 of WCAP-13451.

Affected Evaluation Models 1981 ECCS Evaluation Model with BASH Estimated Effect The effect of the extended burst model has been directlyincorporated in the Analysis of Record for VCSNS.

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HOT ASSEMBLY AVERAGE ROD BURST EFFECTS

Background

The rod heat up code used in Small Break LOCA calculations contains a model to calculate the amount of clad strain that accompanies rod burst. However, the methodology which has historically been used is to not apply this burst strain model to the hot assembly average rod. This was done so as to minimize the rod gap and therefore maximize the heat transferred to the fluid channel, which in turn would maximize the hot rod temperature. However, due to mechanisms governing the zirc-water temperature excursion (which is the subject of the SBLOCA Limiting Time-in-Life penalty for the hot rod), modeling of clad burst strain for the hot assembly average rod can result in a penalty for the hot rod by increasing the channel enthalpy at the time of PCT. Therefore, the methodology has been revised such that burst strain will also be modeled on the hot assembly average rod.

I This was determined to be a Non-discretionary Change as described in Section 4.1.2 l of WCAP-13451 and was corrected in accordance with Section 4.1.3 of WCAP-13451. l Affected Evaluation Models 1985 SBLOCA Evaluation Model Estimated Effect Representative plant calculations have shown that this change introduces an approximately 10% increase in the SBLOCA Limiting Time-in-Life penalty on the hot rod. However, this penalty is beina offset in affected plants PCT Summary Sheets by the Revised Burst Strain Limit Mod'el described on Page 11. These models will be implemented concurrently in the Small Break Evaluation Model rod heat-up code in 1994.

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REVISED BURST STRAIN LIMIT MODEL

Background

A revised burst strain limit model which limits strains is being implemented into the rod heat up codes used in both Large Break and Small Break LOCA. This model which is identical to that previously approved for use for Appendix K analyses o,f lants with WCOBRA/ TRAC, as described in WCAP-10924-P-Upper Plenum Injection Vol.1, Add. 4, p'Westincihouse Large Break LOCA Best Estimate A, Rev.1, logy:Volume 1: Mode ~ Description and Validation, Addendum 4: Model Methodo Revisions," 1991.

This has been determined to be a Non-Discretionary Change as discussed in Section 4.1.2 of WCAP-13451 and is being implemented in accordance with Section 4.1.3 of WCAP-13451.

Affected Evaluation Models 1985 SBLOCA Evaluation Model 1981 ECCS Evaluation Model with BASH Estimated Effect The estimated effect on large Break LOCA PCT's ranges from negligible to a moderate, unquantified benefit which will be inherent in calculations once this model is implemented. In Small Break LOCA, representative plant calculations indicate that the magnitude of the benefit is conservatively estimated to be exactly offsetting to the penalty introduced by the Hot Assembly Averac e Rod Burst issue documented on Page 10. This model will be implemented in bot 1 Large Break and Small Break Evaluation Models during 1994.

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SMALL BREAK LOCA LIMITING TIME IN LIFE - ZlRC/ WATER OXIDATION TEMPERATURE EXCUR510N Backaround Westinghouse recently finalized an evaluation of a potentialissue with regard to burst / blockage modefing in the Westinghouse small break LOCA evaluation model.

This potential issue involved a number of synergistic effects, all related to the manner in which the small break model accounts for the swelling and burst of fuel rods, modeling of the rod burst strain, and resulting effects on clad temperature and oxidation from the metal / water reaction models and channel blockage.

Fuel rod burst during the course of a small break LOCA analysis was found to potentially result in a significant temperature excursion above the clad temperature transient for a non-burst case. Since the methodology for SBLOCA analyses had been to perform the analyses at a near beginning ofhfe (BOL) condition,where rod internal pressures are relatively low, most analyses did not result in the occurrence of rod burst, and therefore may not have reflected the most limiting time in life PCT. In order to evaluate the effects of this phenomenon, Westinghouse has developed an analytical model which allows the prediction of rod burst PCT effects based upon the existing analysis of record.

Affected Evaluation Models 1985 SBLOCA Evaluation Model Estimated Effect The PCT effect of this item was previously reported to the NRC as a temporary penalty in the June 8,1993, annual ECCS Evaluation Model Revision Report (Reference RC-93-0158) thereby meeting the intent of 10CFR50.46 reporting requirements. The Burst and Blockage / Time in Life penalty is a function of base PCT plus permanent mar allocation changes. gin allocation SCE&G will reportand this as suchunder aenalty will decrease the "Other/ increase Margin with margin Allocations" category and will include any 'CT change from the base penalty of i 115 F t reportingo newly identified model assessments when considering 10CFR50.46 requirements.  !

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l TABLE 2 Small Break Peak Clad Ternperature Margin Utilization

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Revision Date: 1/24/94 Plant Name: Virgil C. Summer (CGE) Eval. Model: NOTRUMP Fuel: Vantage +

Utility Name: South Carolina Electric & Gas FQ = 2.45 F AH = 1.62 SGTP = 20%

i Reference

• Clad Temperature Notes  !

A. ANALYSIS OF RECORD (2/93) 1 PCT = 19487 '

B. PRIOR PERMANENT ECCS MODEL ASSESSMENTS 2 APCT= -13T 1 C. 10 CFR 50.59 SAFETY EVALUATIONS Table 4 APCT= 17 D. 199310 CFR 50.46 MODEL ASSESSMENTS ,

(Permanent Assessment of PCT Margin)  :

1. Average Rod Burst Strain APCT= 127  !

2. Fuel Rod Burst Strain Limit APCT= -127 .

3. LUCIFER Error Corrections APCT= -164 E. TEMPORARY ECC5 MODELISSUES

1. None APCT= OT  :

I F. OTHER MARGIN ALLOCATIONS  ;

1. Burst and Blockage / Time in Life 1 APCT= 1157 i

LICENSING BASIS PCT + MARGIN ALLOCATIONS PCT = 2035'F References for the Peak Clad Temperature Margin Utilization summary can be found in Table 5.

Notes:

1. Reference 2 provided a 10 CFR 50.46 thirty day report on the following assessments: "Effect  !

of 51 in Broken Loop," "Effect of Improved Condensation Model," and " Drift Flux Flow l Regime Errors."

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TABLE 3 Large Break Peak Clad Temperature Margin Utilization l

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Revision Date: 1/24/94  :

Plant Name: Virgil C. Summer (CGE) Eval. Model: BASH Fuel: Vantage + l Utility Name: South Carolina Electric & Gas FQ = 2.45 FAH = 1.62 SGTP= 25%

Reference

• Clad Temperature Notes  !

A. ANALYSIS OF RECORD (3/93) 1 PCT = 2195'F 1

B. PRIOR PERMANENT ECCS MODEL ASSESSMENTS APCT= 0*F t

C. 10 CFR 50.59 SAFETY EVALUATIONS Table 4 APCT= 2*F i

D. 199310 CFR 50.46 MODEL ASSESSMENTS -

(Permanent Assessment of PCT Margin)

1. Lucifer Error Corrections APCT= -6*F .

E. TEMPORARY ECCS MODELISSUES

1. None APCT= 0*F l

l F. OTHER MARGIN ALLOCATIONS l

1. None APCT= 0*F [

LICENSING BASIS PCT + MARGIN ALLOCATIONS PCT = 2191*F References for the Peak Clad Temperature Margin Utilization summaries can be found in Table 5.

Notes: ,

None {

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TABLE 4 - 10 CFR 50.59 Safety Evaluations

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Revision Date: 1/18/93 -

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Plant Name: Virgil C. Summer (CGE)

Utility Name: South Carolina Electric & Gas ,

Reference Clad Temperature Notes ,

l. SMALL BREAK ECC5 5AFETY EVALUATIONS A. Fuel Reconstitution APCT= 1'F 1 TOTAL 10 CFR 50.59 SMALL BREAK ASSESSMENTS PCT = 1*F

11. LARGE BREAK ECCS SAFETY EVALUATIONS A. Fuel Reconstitution APCT= 2*F 1  !

TOTAL 10 CFR 50.59 LARGE BREAK ASSESSMENTS PCT = 2*F Notes:

1. This penalty is due to a fuel assembly reconstitution in assembly J64 for Cycle 8. The penalty  ;

will be removed when assembly J64 is removed from the core.

i TABLE 5 - References l

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1. RC-93-0158, "ECCS Evaluation Model Revisions Report (ANN 2300)," dated June 8,1993.  !

2. ' RC-93-0279, "10 CFR 50.46,30 Day Report," dated November 3,1993.  !

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