ML17261A131

LER 79-013/01T-0 on 790707:during Ultrasonic & Radiographic Examination of Steam Generator Feedwater nozzle-to-elbow Welds,Small Linear Indications in Elbows Were Found.Cause Not Identified.Elbows Replaced

ML17261A131
Person / Time
Site:	Ginna
Issue date:	07/23/1979
From:	Curtis A, Spector S ROCHESTER GAS & ELECTRIC CORP.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
Shared Package
ML17261A133	List: ML17261A131
References
LER-79-013-01T, LER-79-13-1T, NUDOCS 7907260596
Download: ML17261A131 (6)

Text

NRC FORM "+3 U.S.NUCLEAR REGULATORYCOMMISSION (777) 79-013/

3 ENSE E EVE NT REPORT

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~s ~LQB 0 5 0 0 0 2 4 4 7 0 7 0 7 7 9 B 0 7 2 3 7 9 QB 7 8 60 61 DOCKET NUMBER 68 69 EVENT DATE 74 I5 REPORT DATE 80 EVENT DESCRIPTION ANDPROBABLE CONSEQUENCES Q10 During ultrasonic andradiographic examinationof SG f eedwater nozzle-to-elbow weld s

)~03 required by andperformed in accordance with IE Bulletin 7 9-1 3 small linear indications in elbows were found(T.S 6 9 2.a.(9)) Pipe examination wasexpanded to 1 8 other

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welds in Containment, including penetration welds.No further problems were found.

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7 8 9 80 FACILITY STATUS OTHER STATUS Q METHOD OF DISCOVERY

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Attachment to LER 79-01 01T-0 Page 1 of 2 Rochester Gas and Electric Corporation R. E. Ginna'Nuclear Power Plant, Unit No. 1 Docket No. 50-244 Event Descri tion and Probable Conse uences In accordance with the requirements of IE Bulletin 79-13, Rochester Gas and Electric has examined the feedwater nozzle-to-elbow welds of Ginna Station's two steam generators on j'uly 9 and 10, 1979. These examinations consisted of both radiographic and ultrasonic examinations. Both the ultra-sonic and radiographic examination data revealed small linear inside diameter indications in the elbows consistent with those reported in Bulletin 79-13 for the plants listed. After confirming the feedwater nozzle cracking problem the examination scope was expanded to include other feedwater piping welds inside containment upstream from the nozzle-to-elbow welds. These examina-tions consisted of both visual and radiographic inspection of 18 additional welds. This included the welds between the steam generator nozzles and one weld past the first rigid support. Included also was the containment feedwater penetration piping welds, which represents the other terminal ends inside con-tainment. These examinations did not reveal any linear indications and con-firmed the continued structural integrity of these additional 18 welds.

The cracks were determined to be adjacent to the feedwater nozzle-to-elbow welds, in the elbow base material counter bore-taper intersection approximately 3/4 of an inch from the center line of the weld. Interpretations of the UT and RT data were made as follows:

A Steam Generator maximum depth of approximately 1/16 inch wall penetration, 300 around the circumference of the elbow.

B Steam Generator maximum depth of approximately 3/32 inch of wall penetration, 360 around the circumference of the elbow.

The preliminary metallurgical analysis has confirmed that these cracks are a result of a corrosion fatigue mechanism with maximum depth in the areas investigated to date as follows:

A Steam Gene'rator two cracks noted of 0.065 and 0.043 of an inch in depth.

B Steam Generator - one crack noted of 0.100 of an inch in depth.

This corresponds very well wi'th the ultrasonic examination flaw sizing data.

Due to the appearance of the cracks with the blunt crack tip ends, and the fact that they are completely filled with corrosion products, it is postulated that these cracks are old and have not grown recently.

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Attachment to LER 79-01 /01T-0 Page 2 of 2 Rochester Gys and Electric Corporation R. E. Ginna Nuclear Power Plant, Unit No. 1 Docket No. 50-244 Cause Descri tion and Corrective Actions The cause of these base material cracks is not known at this time.

It can only be postulated whether the cause is from original heat treatment procedural problems, a thermal fatigue phenomenon, or the synergistic effects of these two coupled with normal operating stress. In order to deter-mine the factors involved RG&E has joined a pipe cracking owners group to study and analyze the cause. This group is pursuing this investigation with Westinghouse. Recommendations for permanent corrective actions shall be considered if the repair procedures and strict heat treatment procedures implemented to date are not adequate for the final corrective action.

The corrective actions taken at Ginna have been to build up the nozzle end preps to schedule 80 and replace the carbon steel Pl elbows with schedule 80 chrome-moly (P4) elbows utilizing qualified repair procedures and very precise preheat and post weld heat treatment procedures. All corrosion pitting, cracks and surface checking inside the nozzle bore were removed by mechanical means. Any areas where minimum wall was encroached were repaired by repair welding in accordance with qualified procedures.

To gather operational data to aid in further examination of the problem, thermocouples were installed inside and outside each nozzle.

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