ML20214P378

Requests Review & Approval of Revised Steam Cooling Modeling Approach & Implementation for Application to LOCA Analysis. New Model Will Be Used for Generating LOCA Limits to Support Operation.Supportive Info Encl.Fee Paid

ML20214P378
Person / Time
Site:	Maine Yankee
Issue date:	05/21/1987
From:	Whittier G Maine Yankee
To:	Nerses V Office of Nuclear Reactor Regulation
Shared Package
ML20214P379	List: ML20214P378 ML20214P396
References
8650L-HFJ, GDW-87-118, MN-87-59, NUDOCS 8706030348
Download: ML20214P378 (6)

Text

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MAIRE HARHEE M0MioPOWER00MPARUe ,uav,,,y,in"gy, h (207) 623-3521

$ May 21, 1987 MN-87-59 GDH-87-118 Director of Nuclear Reactor Regulation United States Nuclear Regulatory Commission Washington, D. C. 20555 Attention: Mr. Victor Nerses, Acting Director PHR Project Directorate I-3 Division of Licensing

References:

(a) License No. DPR-36 (Docket No. 50-309)

(b) MYAPCo Letter to USNRC dated September 15, 1986 (MN-86-118) Maine Yankee LOCA Analysis

Subject:

Maine Yankee 10CA Analysis Gentlemen:

Representatives of Yankee Atomic Electric Company (YAEC) and Maine Yankee Atomic Power Company met with members of the NRC staff on October 22, 1986 to provide additional information on the proposed method changes planned to regain the lost margin to LOCA limits reported in Reference (b). During that meeting we described and provided a proposed schedule for a two-phase program which. involved the following elements:

Phase I -

Implementation of a more realistic delta P injection penalty for reflood.

! Phase II - Implementation of a revised steam cooling model.

l l Phase I of this prograin was completed in December 1986 with the issuance I of a Safety Evaluation Report (SER) by your staff. This letter provides l

justification for a revised steam cooling model which constitutes Phase II of the program.

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! The proposed model will be used for calculating heat transfer coefficients i

used during the reflood phase of LOCA analysis. Attachment A demonstrates that the proposed model is conservative with respect to the FLECHT heat

! transfer correlation and meets the Appendix K steam cooling criterion. The I model was developed by Intermountain Technologies, Inc. (ITI), and was reviewed by YAEC to ensure its applicability to LOCA licensing analysis for Maine Yankee. A summary of the model change and benchmarking program and a description of the model implementation work at YAEC is given in Attachment A. A more detailed discussion of the model is provided in Attachment B. a V$

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MAINE YANKEE ATOMIC POWER COMPANY

-b United States Nuclear Regulatory Commission Page Two Attention: Mr. Victor Nerses, Acting Director NN-87-59 He request your review and approval of the revised steam cooling modeling approach and implementation for application to the Maine Yankee LOCA analysis. He plan to use the new model for generating LOCA limits to support operation as soon as the changes are approved.

An application fee of $150.00 is enclosed. If you have any questions, please do not hesitate to call.

Very truly yours, MAINE YANKEE ATOMIC POWER COMPANY Eh G. D. Whittier, Manager Nuclear Engineering and Licensing GDH/bjp Attachments cc: Mr. Hilliam T. Russell Mr. Pat Sears Mr. Cornelius F. Holden i

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M AINE Y ANKEE ATOMIC POWER COMPANY i

2 ATTACHMENT A MN-87-59 Summary of Justification for A Revised Steam Cooling Model for Maine Yankee LOCA Analysis t

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..- 1 ATTACHMENT A MN-87-59 1 Summary of Justification for a Revised Steam Coolina Model for Maine Yankee LOCA Analysis INTRODUCTION 10CFR, Part 50, Appendix K(l) states that:

"During refill and during reflood, when reflood. rates are less than one inch'per second, heat transfer calculations shall be based on the assumption that cooling is only by steam, and shall take into account any flow blockage calculated to occur as a result of cladding swelling or rupture as such blockage might affect both local steam flow and heat transfer."

The currently approved ECCS evaluation model(2) for Maine Yankee meets these .

, requirements by incorporating a steam cooling model which is invoked when the reflood rates are less than one inch /second, and cladding rupture is -

' calculated'to have occurred. The main features of this model are:

' 1. The YAEC version of FLECHT(3) heat transfer coefficient correlation is used for calculating the coefficient below the rupture plane and the

. Dittus-Boelter correlation is used at and above the rupture plane.

2. Steam flow equal to the product of the inlet flow, the carry-over rate fraction and an empirical coefficient is used in the fluid energy equation. . The empirical coefficient is defined to assure conservative results. An equivalent steam flow is used for calculating the heat transfer coefficient in the Dittus-Boelter(4) equation. . The equivalent steam flow is defined such that the Dittus-Boelter and FLECHT correlation l heat. transfer coefficient are equal at the node immediately below the -

blockage plane.

l 3. The cladding swelling and rupture is assumed to divert part of the flow away from the rod. To account for the postulated flow diversion, the steam flow for both the fluid energy equation and the Dittus-Boelter-equation is reduced by a fraction which varies with distance from the l

rupture location.

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-This model was developed when the understanding of reflood heat transfer was

. incomplete. Specifically, heat transfer at low flooding rates and the effects of clad swelling and rupture on the heat transfer were not clearly

- understood. Several experimental programs were initiated to improve the-understanding in this area and to develop more sophisticated analysis techniques. The results of experimental programs have becin.e available in recent. years, thereby providing impetus for improved models.

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MAINE YANKEE ATOMIC POWER COMPAMY f ATTACHMENT A HN-87-59 PROPOSED MODEL Since the development of the currently licensed steam cooling model, a-substantial data base pertinent to these issues has been developed through the

.FLECHT-SEASET test program (5). These data indicate that 1) no discontinuity in heat transfer as a function of flooding rate occurs at one inch /second as stipulated by Appendix K, and 2) the core heat transfer is not degraded under blockage situations expected for a PHR LOCA. The requirements of Appendix K-are, however, still in effect. A new steam cooling model is developed, Reference (6), which takes advantage of the new experimental findings and yet meets the intent of Appendix K. The features of the new steam cooling model are discussed below.

1. Dominant heat transfer is derived using the FLECHT correlation.

This is a reasonable assumption in light of the FLECHT-SEASET data base.

These data indicate that core heat transfer is not degraded under blockage conditions expected for a PHR. Hence, the FLECHT correlation may be used to calculate the heat transfer coefficient both above and below the blockage plane.

2. Steam temperature is assumed to be the saturation temperature.

In the current licensing methodology, when the FLECHT correlation is used, the sink temperature is assumed to be the saturation temperature.

This approach is consistent with the derivation of FLECHT correlation and has resulted in conservative prediction of the behavior of a fuel rod during reflood.

3. Clad swelling and rupture is assumed to have a two-fold effect on local heat transfer.

(a) Degradation of heat transfer due to flow diversion as postulated by Appendix K, and (b) Heat transfer enhancement due to single phase turbulence, as observed in the FLECHT-SEASET(5) tests.

The existing YAEC flow diversion model is used in calculating the local steam flow. This model conservatively satisfies the Appendix K criteria.

To model the single phase turbulence, a heat transfer enhancement factor has been developed from the experimental data. Details of this model are discussed in Attachment B of this document.

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MAINE YANKEE ATOMIC POWER COMPANY

.c ATTACHMENT A MN-87-59 IMPLEMENTATION OF NEH STEAM COOLING MODEL The new steam cooling model was developed by Intermountain Technologies, Inc.

(ITI) and was directly incorporated into YAEC's version of the T000EE2 code.

The new integral model was assessed by ITI via comparison of model predictions for the Maine Yankee reactor to corresponding results predicted utilizing the FLECHT correlation. Additionally, six FLECHT tests were simulated using the T000EE2 code and the results were compared to the data. The purpose of.

simulations was to demonstrate the adequacy of the YAEC FLECHT correlation.

The model assessment results indicate that the.new steam cooling model is conservative with respect to FLECHT correlation and predicts the results of FLECHT tests in a conservative fashion. Additional information regarding the revised steam cooling model is provided in Attachment B, Reference (6).

The model development, implementation, and benchmarking results have been reviewed in detail at YAEC. Several of the ITI calculations were repeated at YAEC to further develop an in-house understanding of the new model and to assess-the impact of modeling techniques on the simulation of FLECHT tests.

These calculations employed input decks which were derived independently at YAEC. The. sources of minor differences in the YAEC and ITI results were identified and modeling differences were resolved. Through this effort, YAEC has developed and demonstrated full working knowledge of the new model and its implementation into the T000EE2 code.

SUMMARY

AND CONCLUSION It is proposed that the current steam cooling model be replaced by the new steam cooling model. The new model is based on experimental data, is conservative with respect to FLECHT correlation and satisfies the intent of Appendix ~K to 10CFR, Part 50.

REFERENCES

1. "ECCS Evaluation Models", 10CFR, Part 50, Appendix K.

2. YAEC-1160, " Application of Yankee HREM-Based Generic PHR ECCS Evaluation Model to Maine Yankee", July, 1978.

3. XN-75-41, Volume 1, " ENC HREM-Based Generic PHR ECCS Evaluation Model",

July 25, 1975

4. F. H. Dittus and L. M. K. Boelter, University of California (Berkley),

Pub. Eng., Volume 2

5. L. E. Hochreiter, "FLECHT-SEASET Program Final Report",

NRC/EPRI/Hestinghouse-16, November 1985

6. R. T. Jensen, " Revision to YAEC Steam Cooling Model for Reflood Rates Less than 1 In/Sec", April, 1987 i

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