ML20236L814

Forwards RAI for Westinghouse TR WCAP-14565,Rev 0, VIPRE-01 Modeling & Qualification for Westinghouse Pressurized Water Reactor Non-LOCA Thermal Hydraulic Analysis

ML20236L814
Person / Time
Issue date:	06/09/1998
From:	Wen P NRC (Affiliation Not Assigned)
To:	Sepp H WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP.
References
NUDOCS 9807130187
Download: ML20236L814 (5)

Text

7 9'1998

,Mr. Hank S pp, Managsr

'Ragulatory and Licsnsing Engineering Wastinghousa Elsctric Corporation 1

Mail Stop ECE 4-07A P.O. Box 355 ~;UC,, ,.,/ l/gp Pittsburgh, PA 15320-0355 r;y ,-

~

SUBJECT:

REQUEST FOR AbQkil NF kflON FOR WESTINGHOUSE TOPICAL REPORT WCA 5i'.R@ppN 0, "VIPRE-01 MODELING l

AND QUALIFICATION FOR WESTINGHOUSE PRESSURIZED WATER I REACTOR NON-LOCA THERMAL HYDRAULIC ANALYSIS"

REFERENCE:

Letter from Charles E. Rossi (USNRC) to J. A. Blaisdell (UGRA),

l

" Acceptance for Referencing of Licensing Topical Report, EPRI NR-2511-j CCM, 'VIPRE-01: A Thermal Hydraulic Analysis Code for Reactor Cores,'

. .-. Volumes 1,2,3 and 4," May 1,1986.

Dear Mr. Sepp:

By letter dated April 21,1997, Westinghouse submitted topical report WCAP-14565, Revision 0, for NRC review. The staff has reviewed the report and determined a need for additional information. The attachment to this letter identifies the information required. Please address your response to the NRC Document Control Desk.

As discussed in the above reference, the staff has generically approved use of the VIPRE code in reactor licensing applications, but left cortain additional justifications and limitations that VIPRE users are required to address, in the final review of Westingho0se's submittal (WCAP-14565, Rev 0), the staff will evaluate compliance with each of those requirements.

If you have any questions, please contact rne at 301/415-2832 (email, pxw@nrc. gov) or Walt Jensen at 301/415-2856 (email, wij@nrc. gov).

l Sincerely,

" Original Signed By" Peter C. Wen, Project Manager ,

Generic Issues and Environment!

Projects Branch Office of Nuclear Reactor Regulation

\

Atta..:hment: RAI on topical WCAP -

14565,Rev0 cc: See next page O)

DISTRIBUYlON:

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. OFFICE PM:PGEB SRXB , g , SC:PGh g ,-

NAME PWen:aywjQ d Wldeh F/dl$ddicz DATE 06I 9 / 98 06/ ( /98 06/ hJ98 9007130187 980609 lA ONE COW PDR TOPRP ENVWEST C PDR _ - _ . . _ _ _ .-___--__ _ _ _ -

cc:

Mr. Nicholas Liparuto, Manager Regulatory and Engineering Networks Westinghouse Electric Corporation Mail Stop ECE 4-15 P.O. Box 355 Pittsburgh, PA 15230-0355 Mr. Sumit P.ay Westinghouse Electric Corporation

- ~ P.O. Box 355 Pittsburgh, PA 15230-0355 Jack Bastin, Director Regulatory Affairs Westinghouse Electric Corporation 11921 Rockville Pike, Suite 107 Rockville, MD 20852 Mr. Andrew Drake, Project Manager Westinghouse Owners Group ,

Westinghouse Electric Corporation Mail Stop ECE 5-16 P.O. Box 355 ,

Pittsburgh, PA 15230-0355 4

l

p- a REQUEST FOR ADDITIONAL INFORMATION ON WCAP-14565, REV 0

1. We understand that Westinghouse plans to use VIPRE-01 in conjunction with the RETRAN code to model core response to Chapter 15 non-LOCA transients and accidents. Please provide a list of those transients and accidents that Westinghouse plans to analyze with VIPRE and RETRAN. If other computer codes will also be used in conjunction with VIPRE, for example, to calculate coce power distributions discuss how these codes will be utilized in conjunction with VIPRE.

2. The NRC generic safety evaluation report for VIPRE-01 (Ref. 4 to WCAP-14565) includes five conditions for use of the code. Discuss how Westinghouse will meet each of these conditions in using VIPRE-01.  ;

3. The NRC generic safety evaluation report for VIPRE-01 (Ref. 4 to WCAP-14565) includes the results from sensitivity studies to determine the effect of the input parameters. The code was found to have significant sensitivities in the following areas:

a. Axial noding - Present the results from axial noding studies done by Westinghouse to select axial noding detail for VIPRE. Show the effect of axial noding on minimum DNBR. Is the core noding detailincreased in the region of minimum DNBR. What noding studies will be performed for new fuel designs? What is,the minimum axial noding length that will be provided? '

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b. Turbulent mixing - The hot channel, flow conditions and DNBR are sonsitive to cross '

channel mixing. An empirical turbulent mixing coefficient is !nput. Section 3.5 of WCAP-14565 discusses typical values of the empirical mixing coefficient. Discuss how this value will change as a function of Westinghouse fuel type and how it is experimentally determined.

j c.' Time step - The VIPRE code was found to be particularly sensitive to time step in the subcooled boiling region. Provide resulis from sensitivity studies of fuel element DNBR  !

in subcooled boiling to demonstrate that the appropriate time step has been selected.

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4. Documentation for VIPRE-01 (EPRI NP-2511-CCM Vol.4) recommends that two phase friction be calculated using the Columbia /EPRI correlation with the EPRI void model. This option produced the best correlation of test data and is the default option. Section 3.8 of WCAP-14565 states that the homogeneous two-phase friction model will be used. This  ;

option was shown to significantly under predict two phase friction in the EPRI  ;

documentation. Increased frictinn in the hotter regions of the fuel bundle might act to '

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redistribute flow and result in a lower calculated DNBR. Provide sensitivity studies showing j the effect of using the Columbia /EPRI model to calculate two phase friction on DNBR.

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5. Section 3.8 of WCAP-14565 states that core void fractions are calculated using the Levy 1 l subcooled model and the homogeneous model for bulk boiling. The NRC staff's SER for h

VIPRE (Ref. 4 to the WCAP) listed only the EPRI void model as acceptable. However, the SER also stated that in some applications other correlations might give better results. The  !

l ATTACHMENT l

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2 SER recommended that users review the EPRI benchmark resulti. to determine which correlation would give the best results for a particular application. Please provide justification that the void fraction models that you selected are conservative for the various applications of VIPRE which you listed in response to Question 1. One application of VIPRE is to correlate DNBR test data for determining the allowable limit for critical heat flux correlations (95% of rods not in DNBR with a 95% confidence). Justify that your selection of models to determine core void fraction is conservative for calculating the minimum DNBR (95/95) limit.

- 6. Section 3.3.2 of WCAP-14565 discusses the Bishop-Sandberg-Tong heat transfer correlation that is used to calculate film boiling heat transfer. This correlation was accepted {

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by the NRC staff for use in the FACTRAN code (Ref.16 to WCAP-14565). Please provide a list of the transients and accidents for which you will use VIPRE in the post CHF heat j transfer region and discuss the licensing requirement that the calculation is designed to meet. As stated in the NRC generic SER for VIPRE-01, " Post CHF analysis and aspects of l l

the code dealing with post CHF phenomena were excluded from this review," the use of VIPRE for this type of analysis will thorefore require additional justification. Please provide justification that VIPRE can conservatively model the mechanical, physical and chemical changes that might occur in the fuel rods at elevated temperature including comparisons with applicable reactor fuel rod test data.

7. Section 3.3.4 states that in VIPRE the metal-water heat generation in the cladding is assumed to be uniform. Justify that this assumption is conservative in comparison with the  !

assumption that all the rea.ction heat is deposited at the cladding surface.

8. Describe and justify assumptions made for heat distribution of any cladding metal-water i reaction between the cladding and the gaseous reaction products that are released into the coolant channel.

9. Section 3.6 states that the coefficient of cross flow resistance "A" is determined based on the pitch and rod diameter of a typical cell. Provide and justify the methodology for performing this determination. Present any applicable experimental data.

10. Section 3.7 provides the equations used to calculate the axial friction in laminar and turbulent flow. The reference, number 21, states that the laminar equation is for circular channels and the turbulent equation is for isothermal flow in commercially available smooth tubes. Justify that these equations are appropriate for calculating the frictional pressure drops in reactor fuel rod bundles. Present comparisons to experimental rod bundle data.

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11. Following the NRC staff review of the Westinghouse mixed core methodology the staff concluded the methodology to be acceptable subject to four conditions. Discuss how these conditions will be met using Westinghouse VIPRE methodology. (See Ashok Thadani (NRC) letter to W. J. Johnson ( Westinghouse), " Technical Evaluation of Extension of l

Methodology for Calculating Transition Core DNBR Penalties Westinghouse Electric Corporation WCAP-11837", October 12,1989.) '

12. Comparisons of local flow rate and local equilibrium quality in the hot channel between THINC-IV and VIPRE are provided for cases 2,10 and 12 of Table 4-1. Provide these comparisons for cases 1,5 and 8.

. _ . . . ., 13. For a typical Westinghouse PWR, provide comparisons of predicted DNBR as a function of time between VIPRE and THINC-IV/FACTRAN for each proposed application of VIPRE listed in your response to Question 1. Discuss and justify the cause of differences between the predictions.

14. Describe the Westinghouse user training and qualification program for VIPRE. Discuss features of the program that are designed to promote proper implementation of the code .

and reduce user error. Describe Westinghouse quality assurance procedures for control of ,

the various code input options which may be modified by the user. l l

15. To enable the staff to perform additional sensitivity studies, please provide electronic  !

vensions of the VIPRE-01 code and the plant model utilized in responsa to Question 12.

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