ML19316B223

Forwards Westinghouse Multiple Aperture Small Break ECCS Analyses, in Response to NRC 800409 Request.Multiple Aperture Breaks Are Bounded by Analyses Performed in FSAR Where Only Single Break Location Assumed

ML19316B223
Person / Time
Site:	McGuire, Mcguire
Issue date:	06/06/1980
From:	Parker W DUKE POWER CO.
To:	Harold Denton, Youngblood B Office of Nuclear Reactor Regulation
Shared Package
ML19316B224	List: ML19316B223 ML19316B225
References
NUDOCS 8006120367
Download: ML19316B223 (2)

Text

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Acr Pets 60 tut igite=0Nt; Amte 704 S etsu PmCOvCfoO= 373-4083 June 6, 1980 Mr. Harold R. Denton, Director Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Washington, D. C. 20555 Attention: Mr. B. J. Youngblood, Chief Licensing Projects Branch I Re: McGuire Nuclear Station Units 1 and 2 Docket Nos. 50-369, 50-370

Dear Mr. Denton:

Mr. Robert L. Baer's letter of April 9, 1980 requested an analysis of a 10-inch cold leg break in combination with a 6-inch break.

The attached report demonstrates that generically, multiple aperture breaks are bounded by the analyses performed la FSARs where only a single break location is assumed. A three loop Westinghouse NSSS plant was utilized in the report. This plant was selected since,in general, three loop plants yield relatively high peak clad temperature results compared to other plant' designs. This is true because of the relatively high power rating per loop and lower safety injection rate per loop in these plants. It is believed this will maximize the sensitivity to multiple aperture breaks and this~is sufficient to enable the use of the conclusions to other Westinghouse plant designs, including four loop, UHI, plants.

The two sections of the report appropriate for this application are:

1. Section 2 which verifies that the model changes necessary to analyze multiple break scenarios have an insignificant effect on small break transient responses.

Section 3 which compares a spectrum of simultaneous hot and cold Sco/

2. s leg breaks with their equivalent size cold leg breaks and shows j /j that the equivalent cold leg break cases are limiting in terms of core uncovery and peak clad temperature. 56*DE-c/fo:

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June 6, 1980 Cold leg breaks tend to be the worst postulated break locations for Westinghouse plants, because of the necessity of clearing the loop seal of water in order to vent steam generated in the core, out the break. ,

Also, these cold leg break cases represent the greatest amount of flow path resistance and thus, more steam binding. Cold leg break analysis assumptions also include the spillage of safety injection from the line of least resietance. For simultaneous hot and crossover leg breaks or simultaneous cold and crossover leg breaks, an additional vent path for steam generated in the core is introduced. This is similar to the simultar.20us hot and cold leg break case considered in the attached report. For these cases, the loop seal uncovery is no longer as important a phenomena which leads to higher core coolant mixture levels and thus' lower peak claa temperature results. 0 Since the postulated events for McGuire are bounded by the spectrum of break sizes considered in Section 3, it may be concluded that the limiting small break case in the McGuire FSAR bounds the multiple loop break cases in question. Therefore, with the documented results of the attached report, the requirements of 10CFR50.46 are met for the McGuire units.

Very truly yours, m

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_l William O. Parker, Jr.

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