ML19322B616

Methods to Prevent Boron Precipation in Long-Term Following Postulated Loca.

ML19322B616
Person / Time
Site:	Oconee
Issue date:	12/18/1975
From:	DUKE POWER CO.
To:
Shared Package
ML19322B615	List: ML19322B614 ML19322B616
References
NUDOCS 7912040642
Download: ML19322B616 (9)

Text

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l 1 METHODS TO PREVENT BORON PRECIPITATION IN THE LONG-TERM l, FOLLOWING A POSTULATED LOSS OF COOLANT ACCIDENT

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1 METHODS TO PREVENT BORON PRECIPITATION IN THE LONG-TERM l FOLLOWING A POSTULATED LOSS OF COOLANT ACCIDENT l In Duke Power Company's April 16, 1975 submittal, it was demonstrated that if a core circulation in excess of 40 gpm following a postulated loss-of-coolant accident was maintained, the resulting boron concentration buildup would be limited to a C/Co of less than 11. This concentration buildup assures that boron precipitation does not adversely affect long term cooling capability.

In order to assure that this minimum 40 gpm core circulation can be maintained, a station modification will be made to each Oconee unit to provide a gravity flowpath from the hot leg nozzle to the Reactor Building sump through the decay heat drop line. A 2" ID, or larger, drain line with two electric motor operated isolation valves (LP-X and LP-Y) will be installed on the decay heat drop line above valve LP-1 (See attached figures.). This line will allow drainage of highly concentrated water from the top of the core for all postulated loss-of-coolant accidents, allowing dilute water to enter the core and thus promote significant core circulation. The gravity head in these lines will assure that a flow in excess of 40 gpm will exist following the postulated LOCA.

The above described drain line is not single failure proof in itself; therefore, an additional flowpath is necessary. For Unit 1, another 2" ID, or larger, drain line and electric motor operated valve (LP-Z) will be installed below valves LP-1 and LP-2. This will establish a second flowpath from the hot leg to the Reactor Building sump through the decay heat drop line and will enable the single failure criteria to be met.

For Units 2 and 3, the existing flowpath through valves LP-1, LP-2, LP-3, LP-4 (Unit 2 only) to the A LPI pump suction or to the Reactor Building sump through valve LP-19 provides an alternate gravity flowpath.

The following additional information concerning the design and required changes in procedures is provided:

(a) The gravity flowpaths for the proposed mode of boron dilution are identified in the attached PO drawings.

(b) The elevation of the 36" ID outlet nozzle is 809' 6". For Unit 1, the decay heat line begins at the bottom of the hot leg nozzle, elevation 808', and continues downward to valves LP-1 and LP-2 at elevation 798' 6",

the line then turns upward and penetrates the Reactor Building at elevation 812'. The tap for valves LP-X and LP-Y will be above LP-1, and the tap for LP-Z will be below LP-2 before the decay heat line turns upward. The sizing and location of the drain lines will be such that a minimum flow of 40 gpm, following a postulated LOCA, will be assured.

For Units 2 and 3, the decay heat line begins at the bottom of the hot leg nozzle, elevation 808', and continues downward to valves LP-1 and l-