ML20083A971

Forwards Annual Rept of ECCS Model Changes & Errors for 1994,per 10CFR50.46

ML20083A971
Person / Time
Site:	Prairie Island
Issue date:	05/02/1995
From:	Richard Anderson NORTHERN STATES POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NUDOCS 9505110215
Download: ML20083A971 (17)

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1 Northem States Power Comporty 414 Nicollet Mall Minneapolis, Minnesota 554011927 Telephone (612) 330-5500 May 2, 1995 U S Nuclear Regulatory Commission 10 CFR part 50 Attn Document Control Desk Section 50.46 Washington, DC 20555 Prairie Island Nuclear Generating Plant Docket Nos. 50-282 License Nos. DPR-42 50-306 DPR-60 Annual Report of Corrections to ECCS Evaluation Models Attached is the annual report of corrections to Westinghouse Emergency Core Cooling System (ECCS) Evaluation Models for the calendar year of 1994. This report is being submitted in accordance with the provisions of 10 CFR 50, Section 50.46.

The applicable corrections noted in Attachment I have been applied to Northern States Power's current ECCS analyses of record, and all analyses were found to be in compliance with the applicable acceptance criteria (Attachment 2).

Please contact Mel Opstad (612-295-1653) if you require further information related to this submittal.

T* O Co< Roger O Anders.'n Director Licensing and Manegement Issues 95o5110215 950502 PDR ADOCK 05o00282 P

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V L*:9-USNRC May 2, 1995 Page 2 c:

Regional Administrator - Region III, NRC

. NRR; Project Manager, NRC

- Senior Resident Inspector, NRC State of Minnesota Attna Kris Sanda J_E Silberg Attachments:

1. 1 50.46 Summary Report of Emergency Core Cooling System Evaluation Model Changes and Errors for the 1994 Calendar Year

1. 2 Prairie Island Units 1 & 2 LOCA Peak Clad Temperature-(PCT) Margin Utilization Sheets References Westinghouse ESBU Nuclear Safety Advisory Letter NSAL-95-002Q, dated January 30, 1995, that was transmitted via a February 3, 1995 Westinghouse letter from T W Wallace to R L Lindsey (NSP)

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ATTACHMENT 1 50.46 Annual Report of Emergency Core Cooling System (ECCS) Evaluation Model Changes and Errors for the 1994 calendar year i

l Prairie Island Units 1 & 2 k

WCOBRA/ TRAC UPI Code Version Combinations and Error Corrections i

NOTRUMP Boiling Heat Transfer Correlation Errors

'T NOTRUMP Steam Line Isolation Logic Errors NOTRUMP Core Zirc Oxide Initialization Errors i

NOTRUMP Pressure Search Convergence Criteria NOTRUMP Friction Value Input Corrections i

NOTRUMP Automatic Containment Spray Actuation During SBLOCA SBLOCTA Revisions and Axial Nodalization Errors NOTRUMP Safety Injection in the Broken Loop Northem States Power Page 1

WCOBRA/ TRAC UPI CODE VERSION COMBINATION AND ERROR CORRECTIONS

Background

Near the end of 1993, a decision was made to combine the three UPI versions of WCOBRAfrRAC (Appendix K blowdown and reflood, and superbounded versions) into one UPI code to reduce the number of codes to be maintained. To combine the codes, some updates were included to provide flags and input options to switch on various Appendix K models. In performing the code combination, several updates that were in the superbounded version were introduced into the Appendix K version (a decision had been made previously to not include these changes in the Appendix K version because they were not considered code errors which would affect code results). In addition, several undefined variables were identified and corrected. A user convenience update was added to have the code automatically stop at the end-of-blowdown conditions. His effon was completed in 1994.

In addition, several errors were found during preparation and review of the best estimate ECOBRA/ TRAC code in 1994 which also apply to the UPI version. Dese corrections were also made in 1994. A summary of the corrections folicws:

Corrections to add additional variables to the restart file, to reduce small differences which occur when a restarted case is compared to a non-restarted tase.

Correction to lateral velocity for convection of axial momentum.

Correction to intercell drag force logic.

Corrections to two minor errors in 1-D components.

Correction to rod gap pressure calculation.

Correction of a typo in 1979 decay heat table. No effect on Appendix K results.

Correction of an error in the condensation model which was discovered earlier, but was not corrected properly.

Correction of a minor error in the 1-D/3-D junction.

Correction of an error in the Zirlo" reaction rate constant. Too high a reaction rate was being calculated.

Does not affect Appendix K results.

Correction of some errors in coding logic which improperly calculated the location of the zirc-oxide interface, and the momentum area following burst.

Affermi Evaluation Models UPI ECOBRAfrRAC Large Break LOCA Evaluation Model Northem States Power Page 2

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7 WCOBRAfrRAC UPI CODE VERSION COMBINATION AND ERROR CORRECTIONS f

(continued)

Estimated Effect An analysis was performed on a representative UPI plant to assess the effect on superbounded and

~ Addendum 3 analyses. There is no effect on superbounded results. The representative Addendum 3 Appendix K analysis shows a 35'F PCT benefit, which could be applied to any future PLT Margin Utilization Sheets.

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To assess the impact on Appendix K Addendum 4 analyses, all affected UPI plants were reanalyzed with the revised code. Individual PCT impacts are shown on the attached PCT Margin Utilization Sheets.

l For Prairie Island Units 1 and 2, the impact of the 1994.ECOBRAfrRAC UPI Code Updates is a net 120*F benefit over the analysis of record as shown on line D. However, not all of the impact is i

attributable to the code changes. Input deck modifications were included in this analysis to bring it in line with current methodology, in addition to the new code updates, yielding a licensing basis PCT of 1969'F.

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i BOILING HEAT TRANSFER CORRELATION ERRORS l

Background

r This closely related set of errors deils with how the mixture velocity is defined for use in various boiling heat transfer regime correlations. The previous definition for mixture velocity did not properly account for drift and slip effects calculated in NOTRUMP. This error particularly affected NOTRUMP calculations of heat tr:nsfer coefficient when using the Westinghouse Transition Boiling j

Correlation and the Dougall-Rohsenow Saturated Film Boiling Correlation.

In addition, a minor typographical error was also corrected in the Westinghouse Transition Boiling Correlation.

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

Affected Evaluation Model 1985 SBLOCA Evaluation Model (NOTRUMP)

Estimated Effect r

Representative plant calculations for this issue resulted in an estimated PCT effect of -6 degrees for affected plants.

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i STEAM LINE ISOLATION LOGIC ERRORS

Background

This error consists of two portions: a possible plant specific effect which only applies to analyses

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which assumed Main Feedwater Isolation (FWI) to occur on S-signal, and a generic effect applying to all previous analyses.

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t ne possible plant specific effect was the result of incorrect logic which caused the main steam line isolation to occur on the same signal as FWI. Therefore, when the S-signal was chosen through user input to be the appropriate signal for FWI, it also caused the steam line isolation to occur on S-signal.

This is inconsistent with the standard conservative assumption of steam line isolation on Loss of Offsite Power coincident with the earlier Reactor Trip signal.

The generic effect was the result of incorrect logic which always led to the isolation functions occurring at a slightly later time than when the appropriate signal was generated.

His 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 Model 1985 SBLOCA Evaluation Model (NOTRUMP)

Estimated Effect Representative plant calculations for this issue resulted in an estimated PCT effect of +12*F for the plant specific portion, if applicable, and +18'F for the generic portion.

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CORE NODE ZIRC OXIDE INITIALIZATION ERROR

Background

NOTRUMP models two regions for each core node analogous to the two (mixture and vapor) regions in adjoining fluid nodes. During the course of a transient, NOTRUMP tracks region specific quantities for each core node. Erroneous logic caused incorrect initialization of the region specific, fuel cladding zirc oxide thickness at times prior to the actual creation of the relevant region during the core boiloff transient.

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 Model 1985 SBLOCA Evaluation Model (NOTRUMP)

Estimated Effect Representative plant calculations led to an estimated generic PCT effect of 0*F for this effect.

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PRESSURE SEARCH CONVERGENCE CRITERIA IN NOTRUMP

Background

The' convergence criteria used during the pressure search in NOTRUMP have been found to not be adequately restrictive to ensure a sufficiently accurate value for Fluid Node pressure when conditions approach the boundary between subcooled and saturated in some cases. The resulting effects on predicted pressure were more pronounced at pressures below those normally seen during standard Evaluation Model calculations. 'Ihe previously hardwired convergence criteria values have been made user input, appropriate values have been determined, and these will be implemented in 'all future analyses.

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 Model 1985 SBLOCA Evaluation Model (NOTRUMP)

Estimated Effect The nature of this error led to an estimated generic PCT effect of O'F for existing analyses.

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FRICTION VALUE INPUT CORRECTIONS

Background

j The SPADES code is used to generate input decks for the small break analysis code, NOTRUMP.

An error was found in the code which involved the values assigned to some of the friction factor input. The erroneous values had no impact on transient calculations and were corrected in order to maintain the consistency of the SPADES code with the relevant documentation.

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ne errors were considered to be discretionary changes as described in Section 4.1.1 of WCAP-13451 and were corrected in accordance with Section 4.1.3 of WCAP-13451.

l Affected Evaluation Model e

1985 SBLOCA Evaluation Model (NOTRUMP)

Estimated Effect i

Representative plant calculations indicate no effect on PCT analyses.

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t AUTOMATIC CONTAINMENT SPRAY ACTUATION DURING SBLOCA.

Background

Automatic containment spray actuation during a small break LOCA had not previously been addressed I

in the Westinghouse small break LOCA evaluation model. 'Ibe containment pressure transient is not modeled because the small break PCT is not directly sensitive to this effect. While investigating this issue, however, Westinghouse concluded that containment spray actuation early in the small break transient is possible for a variety of containment types. Containment spray actuation could result in draindown of the RWST prior to conclusion of the small break transient. Switching to cold leg i

recirculation during the transient may reduce or briefly internipt the modeled ECCS injection flow in some plants and elevate the enthalpy of ECCS injection water. Furthermore, an alternate single failure scenario could result in earlier draindown for the RWST and subsequent switchover to cold leg recirculation.

i Future small break LOCA analyses will explicitly consider these issues.

Affected Evaluation Models 1975 SBLOCA Evaluation Model (WFLASH) 1985 SBLOCA Evaluation Model (NOTRUMP)

Estimated Effect Plant specific evaluations of affected plants currently indicate no PCT effect due to SI interruption or reduction following switchover to cold leg recirculation. A generic evaluation for the increase in ECCS enthalpy with an alternate single failure has yielded a PCT penalty of 20*F for some plants.

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SBLOCTA REVISIONS AND AXIAL NODALIZATION ERRORS Reference Letter NTD-NRC-94-4343, " Interim Report of an Evaluation of a Deviation or Failure to Comply Pursuant to 10CFR21.21(a)(2) - Closecut 94-002", NJ Liparulo (20, November 15, 1994 Backrround Westinghouse has completed an evaluation of issues concerning the SBLOCTA code which is a part of both the NOTRUMP and WFLASH SBLOCA ECCS Evaluation Models. The potential issue originally identified was a deficiency in the amount of detail used for the axial nodalization of the fuel rod, as it affected the solution of the channel fluid equations. Further investigation identified several additional related issues associated with nodalization and the overall solution of the fluid conservation equations which have subsequently been corrected. As a separate, but related issue, a revised model for calculating transient fuel rod internal pressure was implemented in the SBLOCTA code. The NRC was informed of these modeling changes, which were summarized in the closeout notification of the reference.

Affected Evaluation Models 1985 SBLOCA Evaluation Model (NOTRUMP) 1975 SBLOCA Evaluation Model (WFLASH)

Estimated Errect Since all of the issues relate to portions of the SBLOCTA code and/or its associated input methodology, they were reported as a single closely-related group of changes. Evaluations were performed for all plants and the results reported to the utilities. Revised SBLOCA Margin Utilization Summary tables were transmitted containing a compilation of the net effect as item " Axial Nodalization, RIP Model Revision and SBLOCTA Error Corrections", along with sufficient information for reporting, if necessary.

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SAFETY INJECTION IN THE BROKEN LOOP Reference WCAP-10054-P, Addendum 2, "Ad'dendum to the Westinghouse Small Break ECCS Evaluation Model Using the NOTRUMP Code: Safety Injection into the Broken Loop and COSI Condensation Model," August,1994.

Background

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The referenced topical report presents a change to the Westinghouse SBLOCA methodology dealing with ECCS flows in the broken loop. It also presents a revised condensation model that will be used on the safety injection jet in future analyses.

This change is being implemented on a forward fit basis prior to formal approval in accordance with Section 4.1.3 of WCAP-13451.

Affected Evaluation Model 1985 SBLOCA Evaluation Model (NOTRUMP)

Estimated Effect This change has been shown to typically produce PCT benefits in studies presented in the reference.

Since it is being implemented on a forward fit basis, a net PCT impact of 0'F is being assessed against existing analyses.

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L-ATTACHMENT.2 1

Prairie Island Units 1 & 2 LOCA Peak Clad Temperature (PCT) '

Margin Utilization Sheets

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Small Break Peak Clad TempcInturdargia_Iltilization Revision Date: 01/26/95

^l Plant Name: Prairie Island Units I and 2 Eval. Model: NOTRUMP Utility Name: Nonhern States Power Fuel: 14x14 OFA ZIRLO(TM)

FQ =2.80 FdH =2.00 SGTP=25%

Reference *

- Clad Temperature Notes

' A. ANALYSIS OF RECORD (7/93) 1 PCT =

1195 *F 1

. B. ' PRIOR PERMANENT ECCS MODEL ASSESSMENTS 2

APCT=

-29 *F C.10 CFR 50.59 SAFETY EVALUATIONS Table A APCT=

0 'F D.199410 CFR 50.46 MODEL ASSESSMENTS (Permanent Assessment of PCT Margin)

1. Boiling Heat Transfer Correlation Error APCT=

-6 'F l

2. Steam Line Isolation legic Error APCT=

18 *F

3. Axial Nodalization, RIP Model Revision and SBIDCTA 6 PCT =

-32 'F Error Corrections Analysis E. TEMPORARY ECCS MODELISSUES" l

1. None -

APCT=

0 'F l

F. OTHER MARGIN ALIDCATIONS

1. None APCT=

0 'F LICENSING BASIS PCT + MARGIN ALLOCATIONS PCT =

1146 'F

• References for the Peak Clad Temperature Margin Utilization summary can be found in Table B.

" It is recommended that these temporary PCT allocations which address current I.DCA model issues not be considered with respect to 10 CFR 50.46 reponing requirements.

l Notes:

l. Includes annular pellet evaluation.

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.1 Large Break Peak Clad Temperature Martin Utilization -

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Revision Date: 01/26/95 -

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l Plant Names Prairie Island Units I and 2 -

Eval. Model: WCOBRA/ TRAC, Addendum 4

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Utility Name: Northern States Power Fuel: Ihl4 OFA ZIRLO(TM)

I FQ =2.40 FdH= 1.75 SGTP= 15%

Reference

• Clad Temperature Notes

. A. ANALYSIS OF RECORD (11/93) 3

. PCT =

. 2089 'F l

B. PRIOR PERMANENT ECCS MODEL ASSESSMENTS APCT=

0 *F C.10 CFR 50.59 SAFETY EVALUATIONS Table A

'APCT=

0.*F i

D.199410 CFR 50.46 MODEL ASSESSMENTS (Permanent Assessment of PCT Margin)

- 1.1994 WCOBRA/IRAC UPI Code Updates APCT=.

-120 "F 1

E. TEMPORARY ECCS MODELISSUES" i

1. None APCT=

0 *F F. OTHER MARGIN ALLOCATIONS

1. None APCT=

0 *F LICENSING BASIS PCT + MARGIN ALLOCATIONS PCT =

1%9'F l

• References for the Peak Clad Temperature Margin Utilization summaries can be found in Table B.

• • It is recommended that these temporary PCT allocations which address current IDCA model issues not be considered with respect to 10 CFR 50.46 reporting requirements.

t Notes.

1. This PCT assessment is the result of an actual analysis, which included the effect of code changes and input deck changes to bring it in line with current methodology.

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, w-4 Table A-IILCER.51515mfe4ylvaluations Revision Date: 01/26/95 Plant Name: Prairie Island Units 1 and 2

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Utility Name: Northern States Power Reference Clad Temperature Notes L SMALL BREAK ECCS SAFEIY EVALUATIONS APCT=

0. *F

.l A. None TOTAL 10 CFR 50.59 SMALL BREAK ASSESSMENTS PCT =

0 *F.

I II. LARGE BREAK ECCS SAFETY EVALUATIONS APCT=

0 *F A. None TOTAL 10 CFR 50.59 LARGE BREAK ASSESSMENTS PCT =

0 *F Notes:

None l

Tsh]c_B _Referentes f

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1. NSP-93-521, "Nonbem Power Company Prairie Island Units 1 and 2 Small Break Loss-of-Coolant Accident Final Engineering Report for the ZIRID(IM) Fuel Upgrade," July 30,1993.

2. NSP-94-204, "Nonhern Power Company Prairie Island Units 1 and 210 CFR 50.46 Notification and Reponing I

Information," Febmary 8,1994.

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3. NSP-93-529, " Northern Power Company Prairie Island Units 1 and 2 Large Break Imss-of-Coolant Accident Final Engineering Report for the ZIRID(TM) Fuel Upgrade,* November 3,1993.

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