ML19270F455

Followup to 790110 Interim Rept.Discusses Cause of Failure, Corrective Actions Completed, & Scheduled Repairs Re Breaks in Svc Water Reservoir Spray Header Piping

ML19270F455
Person / Time
Site:	North Anna
Issue date:	02/09/1979
From:	Brown S VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
References
720B, NUDOCS 7902130125
Download: ML19270F455 (2)

Text

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PCO VIRGINI A EL ECT RIC AND POW ER COMP ANY, RICHMOND. VIRGINI A 2 L 41 February 9, 1979 fir. James P. O'Reilly, Director Serial No. 7203 Office of Inspection & Enforcement PSE&C/JMD:mac/ wang U. S. Nuclear Regulatory Commission Region II Docket No. 50-339 101 tiarietta Street, Suite 3100 Atlanta, Georgia 30303

Dear Mr. O'Reilly:

On January 10, 1979, an interim report, serial number 720A, was made under the provisions of 10CFR50.55(e) concerning breaks in underwater portions of Unit 2A and 28 service water reservoir spray header piping. The interim report addressed the break locations, operating mode at time of f ailure, liner integrity verificatico, and repair and testing of the 2A array. This report addresses the cause of f ailure, corrective actions completed and scheduled repairs for the 2B array.

The circumferential f ailure of the 18 inch pipe occurred within a clamped pipe support which permitted axial movement but restricted vertical and lateral movement. An investigation to determine the probable mode of failure and the adequacy of the remainder of the spray array was undertaken by the fiberglass manuf acturer. The results of various tests indicates that no degradation of the fiberglass pipe occurred beyond the failed location and the pipes composition and wall thickness were within manuf acturer's tolerances.

The specific cause of f ailure was not determined, however, tests simulating the installed clamping arrangement indicated that the most probable cause of f ailure was due to an overtightening of the support clamp producing a local stress concentration, weakening the pipe laminations. The abnormal stea/y state test pressure present at the time of failure was far below the manuf acturer's surge test pressure necessary to cause a similar failure.

To establish the failure was an isolated incident caused by an improperly instailed clamp and to verify the integrity of the array, the undamaged portion of the 2B array was pressure tested and inspected. The 23 array successfully completed the structural integrity test at the systems hydrostatic test pressure during which divers inspected ehch pipe run. No additional damaged areas were found during the inspection.

An appropriate method of rejoining 1the detached porti ms of piping has been developed which will restore the full design capability of the system and reduce the complexity of underwater work. The portion of the array downstream of the 18 inch separation has been removed from the reservoir to facilitate installation of standard flanged connections in lieu of engineered mechanical joints. Additional flanges will be installed in these pipe sections to facilitate handling during underwater installation. The damaged fiberglass piping has been discarded and will be replaced.

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l' Mr. James P. O'Reilly, Director - 2'

,. m. s The underwater end of,..the 18 inch pipe has. Deen cut off-to remove damaged edges. .The. remaining fiberglass: pipe ~ will Sa joined to a metal spool piece .

using an : annular ~ expansion ~ seal inside the fiberglass pipe. Existing supports will be modified to ensure -the annular expansion seal will not be required to

-take axial pipe loadings. The seal will be retained in position by a collsr-attached to the spool piece preventing axial displacement due to hydrostatic unbalance. The replacement material and the resulting arrangement meet the original design requirements of the system. Following completion o. the 2B array repair, the system will be subjected to the system hydrostatic test pressure to verify system integrity..

The repairs to the spray headers will be completed prior to fuel load.

This submittal shall be considered a final . report under the provisions of 10CFR 50.55 (e) . - Should you require further information, please contact this office.

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and-Construction cc: Mr. ~ John G.' Davis, Acting Director Office of Inspection & Enforcement Harold R. Denton, Director Office of fluclear Reactor Regulation 4

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