ML20207A709

Responds to Item 2 in 860204 Memo Re Staff Actions Resulting from Investigation of San Onofre Unit 1 851121 Event (NUREG-1190).Water Hammer Event Did Not Result in Near Miss to Core Melt Accident

ML20207A709
Person / Time
Site:	San Onofre
Issue date:	07/07/1986
From:	Harold Denton Office of Nuclear Reactor Regulation
To:	Stello V NRC OFFICE OF THE EXECUTIVE DIRECTOR FOR OPERATIONS (EDO)
Shared Package
ML20207A713	List: IA-86-862, Rev 1 to Maint & Surveillance Program Plan ML20207A709 ML20207A715 ML20207B329 ML20207B333 ML20207G140
References
FOIA-86-862, REF-GTECI-A-01, REF-GTECI-PI, RTR-NUREG-1190, TASK-A-01, TASK-A-1, TASK-OR NUDOCS 8607160399
Download: ML20207A709 (2)

Text

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July 7, 1986 rii,0RAWDUM FOR: Victor Stello, Jr.

Executive Director for Operations FROM:

Harold R. Denton, Director Office of Nuclear Reactor Regulation .

SUBJECT:

REVIEW AND ASSESSMENT OF WATER HAMMER OCCURREhCES SINCE CY 1981 This memorandum is our response to staff action Item No. 2 enclosed with your February 4, 1986 memorandum: " Staff Actions Resulting from the Investigation of the November 21, 1985 San Onofre Nuclear Generating Station, Unit 1 Event (NUREG-1190)." The principal reason for this reassessment was the Chairman's question during the San Onofre IIT's briefing on January 22, 1986 regarding the need to reopen USI,A-1.

We reviewed the reported water hammer occurrences and find that the frequency of water hamer occurrence has decreased since last reviewed in 1981 as part i

of the resolution of USI A-1 and that no new underlying causes have emerged.

We do not expect to achieve a total elimination of water hamer occurrences (as noted previously in the resolution of USI A-1) nor do we see a stronger safety implication than was previously derived.

We find the San Onofre Unit I water hamer attributable to grossly failed check valves in the feedwater system and not a basis for reopening the water t hamer safety issue. Moreover, the resolution of USI A-1 recognized that water hamer events, such as that which occurred at SONGS-1, would continue to occur, and that such events would not produce unacceptably high contributions to core melt frequency or public risk. The water hamer event at SONGS-1, in and of itself, did not result in a "near miss" to a core melt accident.

Finally, we reconfirm our original conclusion that the imposition of new requirements related to further reducing water hammer events is not supportable by current cost-benefit guidelines.

A brief review and assessment of such water hamers has been prepared by A. W. Serkir of my staff, with assistance from Eric Leeds (AEOD), and is ranclosed.

OriginalSigned l1

_J&95!I85J Harold R. Denton, Director

! Office of Nuclear Reactor Regulation

Enclosure:

Review & Assessment of Water cc: See next page Hamer Occurrences - CY 1981 through CY 1985 Distribu ion: See next page

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