United States Nuclear Regulatory Commission - Protecting People and the Environment

Bulletin 78-11: Examination of Mark-1 Containment Torus Welds

                               UNITED STATES 
                       NUCLEAR REGULATORY COMMISSION 
                    OFFICE OF INSPECTION AND ENFORCEMENT 
                          WASHINGTON, D. C. 20555 
                                     
                               July 21, 1978  

                                                         IE Bulletin 78-11 

EXAMINATION OF MARK-1 CONTAINMENT TORUS WELDS 

Description of Circumstances: 

On June 28, 1978, Vermont Yankee Power Company (VYPC) reported that five 
non-penetrating surface crack indications and one nine-inch long surface 
crack were found in the overlay weld-to-torus base metal heat affected zones
during the process of performing modifications (addition of strengthening 
gussets) to the torus support columns at the Vermont Yankee Nuclear 
Facility. These modifications were being performed as part of VYPC's overall 
program to restore the originally intended design safety margins for the 
Vermont Yankee Mark I containment system (re: Mark I Containment Long Term 
Program). 

Based upon initial indications of the depth, VYPC performed an analysis of 
the structural capability of the torus shells in the affected areas to 
support continued operation of the facility and proceeded to attempt to 
grind out the nine-inch crack. On June 30, 1978, the crack was still 
apparent after grinding to the calculated depth of 0.25 inches. The plant 
was placed in a cold shutdown condition on July 2, 1978. An evaluation is in 
progress. 

The welding operations at Vermont Yankee were performed at locations on the 
torus shell which were lower than the water level in the torus. Although the
underlying causes of the cracking have not yet been determined, the presence
of water on the opposite side of the torus shell during the welding 
operations appears to have been a primary contributor. Consequently, a 
generic concern has arisen that the potential for cracking could exist when 
welding is performed on a torus containing water. 

In view of the above, on July 7, 1978, the NRC Office of Inspection and 
Enforcement verbally requested licensee's to perform close visual 
inspections on similarly made torus weldments at Peach Bottom Unit Nos 2 and 
3, Quad Cities Unit Nos. 1 and 2, Hatch Unit No. 1 and Monticello 
facilities. These inspections revealed no apparent linear indications 
through the painted surface. However, Monticello reported 



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IE Bulletin No. 78-11            - 2 -                      July 21, 1978 

that magnetic particle examination, together with visual inspection revealed
two relevant surface linear indications, 1/2-inch long and 1-1/2 inches long
respectively, which were verified by liquid penetrant tests after removal of
the paint. Both indications were reportedly removed by grinding at less than
1/8-inch depth. 

Action to be Taken by Licensee 

Licensees for Peach Bottom Units 2 and 3, Quad Cities Units 1 and 2, Hatch 
Unit 1 and Monticello are further requested to provide the following 
information: 

Item A 

1.   Provide descriptions of the welding procedures, procedure 
     qualifications, welder qualifications and electrode controls employed 
     in strengthening the support column to torus connections (i.e., 
     addition of gussets, saddle supports, webs, etc.). 

2.   Provide a description of the preventive measures used to assure that 
     condensation did not occur on surfaces to be welded prior to and during
     the welding. 

3.   Describe the chronology of nondestructive examinations performed 
     subsequent to such welding operations. Include procedures, methods and 
     techniques, the time period of NDE application after specific welds 
     completed have been at ambient temperature, and the results of these 
     examinations. 

Item B 

Where the NDE documentation (Item A3) is not sufficiently definitive to show
that welding to the torus was nondestructively examined after the completed 
welds were at ambient temperature for a minimum period of 72 hours, the 
following measures should be taken. 

1.   Remove paint from surfaces of the overlay weld and torus base metal 
     heat affected zones (if not already done so) by rotary wire brushing or 
     equivalent means. 

2.   Examine the exposed interbead fusion zone of the overlay weld and the 
     associated base metal heat affected zones utilizing magnetic particle 
     techniques in accordance with the applicable section of the ASME Code. 



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IE Bulletin No. 78-11            - 3 -                      July 21, 1978 

3.   Any indications detected as a result of MT are to be evaluated as to 
     their acceptability in accordance with the applicable ASME code. 
     Examinations that detect relevant linear indications may be 
     supplemented by other nondestructive methods and techniques to 
     determine the character of the flaws (i.e., estimated size, shape, 
     depth, orientation, etc.). 

4.   Results of the field examination of individual weldments is to be 
     documented. 

Within ten days of the date of issue of this Bulletin, report in writing to 
the Director of the appropriate NRC Regional Office, the information 
requested in Item A, and your proposed plan of action and schedule regarding
Item B if the 72 hour minimum period described above was not met. A copy of 
your report as submitted to the Regional Office should be sent to the United
States Nuclear Regulatory Commission, Office of Inspection and Enforcement, 
Division of Reactor Operations Inspection, Washington, D. C. 20555. 

Approved by GAO, B180225(R0072); clearance expires July 31, 1980. Approval 
was given under a blanket clearance specifically for identified generic 
problems. 

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