ML20135H356

Forwards Request for Addl Info Re EPRI NP-2511-CCM,Vols 1-4, VIPRE-01:Thermal Hydraulic Analysis Code for Reactor Cores. Response Requested by 851015

ML20135H356
Person / Time
Issue date:	09/17/1985
From:	Thomas C Office of Nuclear Reactor Regulation
To:	Blaisdell J ELECTRIC POWER RESEARCH INSTITUTE, NORTHEAST UTILITIES SERVICE CO.
References
TAC-57644, TAC-57645, NUDOCS 8509230096
Download: ML20135H356 (7)

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. September 17, 1985 tir. John A. Blaisdell, Chaiman UGRA Executive Cemittee Northeast Utilities Service Company Post Office Box 270 Hartford, Connecticut 06141-0?70

SUBJECT:

RE0l!EST ML't'PER ONE FOR ADDITI0flAL IllF0Ft'AT10N ON EPPI NP-2511-CCM, VOLT'PFS 1 THROUGH 4 Ve are currently reviewing the Electric Power Research Institute Licensing Topical' Report, EPRI t'P-2511-CCM, Volumes 1 through 4 entitled "VIPRE-01:

A Thermal-Hydraulic Analysis Code for Reactor Cores".

The initial review reveals the need for the additional infemation indicated in the enclosure. In order to complete this review within the currently scheduled tire, responses to all questions should be received by NPC by October 15, 1985 Please advise H. Bernard at (301) 492-9709 f f you cannot neet this date.

The reporting and/or recordkeeping requirerents contained in this letter affect fewer than ten respondents; therefore, OPP clearance is not required under P.L.96-511.

Sincerely, Original signed by Cecil 0. Thomas, Chief Standardization & Special Projects Branch Division of Licensir.g ,

Enclosure:

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% ,,,,,+ September 17, 1985 Mr. John A. Blaisdell, Chairman UGRA Executive Committee Northeast Utilities Service Company Post Office Box 270 Hartford, Connecticut 06141-0270

SUBJECT:

REQUEST NUMBER ONE FOR ADDITIONAL INFORMATION ON EPRI NP-2511-CCM, VOLUMES 1 THROUGH 4 k'e are currently reviewing the Electric Power F.esearch Institute Licensing Topical Report, EPRI NP-2511-CCM, Volumes 1 through 4 entitled "VIPRE-01:

A Thermal-Hydraulic Analysis Code for Reactor Cores".

The initial review reveals the need for the additional information indicated in the enclosure. In order to complete this review within the currently scheduled time, responses to all questions should be received by NPC by October 15, 1985. Please advise H. Bernard at (301) 492-9799 if you cannot meet this date.

The reporting and/or recordkeeping requirements contained in this letter affect

- fewer than ten respondents; therefore, OMB clearance is not required under P.L.96-511.

Sincerely, p o. A === -

Cecil 0. Thomas, Chief Standardization & Special Projects Branch Division of Licensing

Enclosure:

As stated ,

ENCLOSURE Request for Additional Information on the Review of the VIPRE Computer Code (EPRI NP-2511-CCM, Volumes 1 through 4)

1. Approval of VIPRE document does not permit use of VIPRE for licensing applications. Each user should first submit a document with (a) Proposed uses (including postulated transients, accidents and setpoint calculations, etc.)

(b) codes with which it will interact.

(c) which options will be used with justification (seequestion2).

- (d) the source of each input (e.g. another code, design value, as-fabricated value, engineering judgement)withjustificationforitsuse. This includes selected correlations or correlation constants used when the default option is not selected.

(e) justify that all models and correlations used are

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used within their applicable ranges.

2. Use of VIPRE with an approved DNBR correlation to obtain safety limits ,

should be justified by showing that, given the correlation data base, _

VIPRE gives the same or a conservative safety limit.

3. Flow distribution, two-phase pressure drop and void fraction calculations presented in Section.2 & 3, Volume 4, are not in the range of PWR operating conditions. Justif'y the range of applicability in view of these model qualification calculations. .

4. Code Configuration Control A. Describe the quality assurance program to be used in the application of VIPRE-01 in safety analysis. That is, explain what steps are taken to maintain consistency in safety analysis applications.

(a) What steps will be taken to assure that only the approved versions of VIPRE will be used by UGRA?

(b) How will future modification to VIRPRE be implemented?

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5. ' (a) In the UPFLOW model, whengK is made proportional to the

- distance between the centroids, what proportionality constant is used? Does the choice of this constant affect stability?

(b) The default damping factor D =0.8R was suggested for updating the lateral pressure difference in upflow. Was this used for all problems tested? How does the adjustment of D R affect stability?

(c) In COBRA III-C, the equation [A]W =B is solved. It is 3 _

known that reducing a x and a t in the equation adds more ,

diagonal dominance to the A matrix and thus, more stability to the numerical solution. On page 2-65, Volume I, it is claimed that the matrix A in equation (2.5-14) is more diagonally dominant than the A matrix in the ab'ove equation. Is this true in general?

6. The critical heat flux correlations and their respective' minimum DNBR limits are generally developed with the steady state CHF test data and steady state thennal hydraulic codes. Though it appears to have been a comon perception that transient CHF can be predicted by using the l

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steady state CHF data from rod bundles having the same geometry and tested under the same local fluid conditions, a review of the open literature appears to show that this conclusion is not applicable to all transients and all CHF correlations. The analysis performed in Section 6.7 of Volume 4 of VIPRE, provides the following observations.

(1) The use of steady state CHF correlations become more question-able as the transient becomes more rapid and complex.

(2) The transient response of DNBR is dependent upon the CHF correlations used.

Therefore, in order to validate the VIPRE code with a steady state CHF correlation for licensing transient calculations, the following questions should be addressed.

(a) The safety analysis application af VIPRE in the transient mode will be for analysis of Anticipated Operational Occurrences (A00s) and accidents in which DNBR is the safety limit. Regulatory Guide 1.70, Revision 3 classifies these A00s and accidents into general categories (see Table 15-1). For the following categories, discuss why the VIPRE transient analyses are sui.tably conservative for licensing calculations. Provide '

comparisons of VIPRE with data from tests appropriate to each category to ,

demonstrate that conservative results are obtained. -For example, for

" Decrease in Reactor Coolant System Flow Rate", provide data from tests which simulate a loss of flow along with calculations to demonstrate that either the predicted heat flux is' lower than the measured value or the time to CHF'is earlier than measured.

CATEGORIES Decrease in Reactor Coolant System Flow Rate Reactivity Anomalies (power increases)

DecreaseinReactorCoolantInventory(depressurization) 3

(b) Justify why a steady state 95/95 safety limit, as specified in the Standard Review Plan Section 4.4 is applicable to transient analyses in view of the comparisons with data shown in Section 6.7 of Volume 4 and the discussion in Section 6.7.4 concerning the validity of steady state correlations for transient calculations.

(c) For a representative transient or accident in each of the categories under question (a), provide a comparison of the minimum DNBR for both the quasi-steady state and transient solutions.

7. Supply the input and results of a VIPRE calculation of a postulated PWR locked rotor accident from full power and another transient or accident to be agreed to by UGRA and NRC.

Identify the choices made for all cptions in the calculations including two-phase flow models, Dh8 correlations, turbulent mixing coefficient, turbulent momentum factor, etc.

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8. The NRC review was confined to the following documentation:

EPRI NP 2511-CCM, Volumes 1-4 Letter from J. A. Blaisdell, UGRA, to A. Gill, NRC,

July 26, 1985 If any other documentation is intended to be part of the documentation l for this licensing review, please list it and provide the documentation, i

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