ML20085D317

Ro:On 721220,leak Detected Inside Containment Vessel in Joint Where Auxiliary Feedwater Pipe B,4-FW-23 Joins Main Feedwater Pipe B,16-FW-10.Caused by Saddle Welds Not Designed as Pressure Boundary.Boundary Rewelded

ML20085D317
Person / Time
Site:	Robinson
Issue date:	02/09/1973
From:	Utley E CAROLINA POWER & LIGHT CO.
To:	Oleary J US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20085D315	List: ML20085D317
References
NUDOCS 8307210137
Download: ML20085D317 (4)

Text

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February 9, 1973 Mr. John F. O'Icary, Director /

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I Directorate of Licensing U. S. Atomic Energy Commission ( 6 U'-

50-261 i M 14 , t. pt#13' g )--

Washington, D. C. 20545

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E y s' H. B. ROBINSON UNIT NO. 2 LICENSE DPR-23 ND , ,

"~g IEAK IN FEEDWATER SYSTEM Q>//{jTj N

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Dear Mr. O'Icary:

In accordance with paragraph 6.6.3 Technical Specifications, the circumstances associated with repairing veld leaks in the feedwater i system are reported.

On December 20, 1972, a leak of approximately one-half gallon per minute was detected inside the containment vessel. The leak was in the joint where the "B" auxiliary feedwater pipe (4-W-23) joins the "B" main feedwater pipe (16-W-10) (Figure 1). The unit was shut down on December 21, 1972, a repair effected on December 22, 1972 and the unit returned to service on December 23, 1972.

/Y W The repair made on December 22, 1972 consisted of plug welding g- a drilled hole in the weld saddle. At the time,it was thought that the l/ hole was a construction error that had not been properly repaired. Further 4 tgp, investigation into the cause of the leak raised questions concerning the

,, correctness of the repairs. It was determined that the drilled hole was

[b a telitale vent hole in the weld saddles and that a leak through the vent g hole indicated that the pressure boundary weld was leaking. Furthermore, gg welding up the vent hole had resulted in the saddle welds becoming the pressure boundary. Ebasco, the architect engineer during construction, N and B. F. Shaw Co., the fabricator of the feedwater pipe sections, were consulted and agreed that the saddle welds were not_d.esigned as a pressure boundary. Both recommended that a repair to the pressure boun_dary weld, j VO und D the saddle, be made. It was also determined that approximately one l year ago an identical improper veld repair had.been made on the "A" feed-water piping.

The plant was shut down on January 4,1973 to make repairs,to the pressure boundary welds on A and B feedwater piping. The Plant Nuclear Safety Comittee had met to discuss the situation in detail and had recommended that appropriate repairs be made to the pressure boundary welds. It was also determined that the joint design on "C" feedwater piping was not similar to l "A" and "B".

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COPY SENT REGION ~~,o1 1078 5

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Mr. O'Le2ry O O Fabru2ry 9, 1973 The repair consisted of grinding out the original shop welds and , rewelding the pressure boundary (Figure 2). A B. F. Shaw Co. ,

engineer was engaged to provide technical direction to the welding, inspection and heat treating of the affected piping. The plant was returned to power on January 9, 1973 after the repairs had been reviewed by the Plant Nuclear Safety Comnittee.

The leaks in the pressure boundary welds were caused by small cracks in the welds. These cracks could have been caused by a combination of vibration, thermal shock, or small defects in the original welds. It is the opinion of the Plant Nuclear Safety Committee, Ebasco engineers, and B. J. Shaw engineers that the veld repair has improved the strength of the joint above the original weld. Ebasco is conducting a thorough engineering study of the weld failure to determine the cause of the original failure and to determine if additional steps are required to prevent recurrence. Should this study indicate that additional changes are prudent, they will be accomplished during the refueling outage begin-ning in mid-March, 1973.

Very truly yours, ff

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Y E. . Utley c)

Vice President Bulk Power Supply NBB/za Enclosures cc: Mr. C. D. Barham Mr. N. B. Bessac Mr. B. J. Furr r . D. V.

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