Wachs Technical Services, Inc. was awarded the contract for the girth cutting and machining for the Steam Generator Replacement Project at North East Utilities, Mill stone Unit 2 Nuclear Power Plant in Waterford, Connecticut.

Millstone Unit 2 is an 825 MEW (Megawatt) pressurized water reactor utilizing a CE Nuclear Steam Supply System. The two Steam Generators were scheduled for replacement.

PROJECT SCOPE
The scope of work included; machine cutting the shipping caps off of the new Steam Generator sub assemblies, establishing the special designed weld prep configuration, performing the inside containment cuts on the existing Steam Generators and establishing the weld preps on the Steam Drums which were to be welded to the new Steam Generator sub assemblies.

THE WTS SOLUTION
Wachs Technical Services, in conjunction with the E. H. Wachs Company, designed and manufactured two complete machines to perform the Steam Generator girth cuts and preps.

Each “Girth Machine” was fabricated in four quadrants. When assembled, the Girth Machine is 21 feet in diameter and weighs approximately four tons. The Girth Machine attaches to the Steam Generator O.D. with 12 clamp pads, each of which has axial and radial adjustment mechanisms which allow for the fine adjustment needed for location to the cut line and machining radius.

The Steam Generator sub assembly cuts and preps were performed outside of containment where the Girth Machines could be installed on the Steam Generator sub assemblies in one piece.

After the shipping caps were cut off and removed, the Girth Machines were aligned to the axis of the Steam Generator by use of a Theodolite System which provided the required information regarding machining radius finished length and machine location. Both machines were operated simultaneously to complete the weld preps and counterbore. Each lower assembly prep required the removal of over 2,000 lbs. of material.

Inside containment, the Steam Generators are located inside concrete structures, called Block Houses. The Girth Machines had to be disassembled, lowered into the Block Houses, re-assembled, mounted to the Steam Generator and aligned to the cut line in very close quarters. After the Steam Generators were cut, the Steam Drum was lifted out of the Block House, inverted and placed on stands so that the Girth Machines could be installed to perform the Steam Drum preps. The Steam Drums were then machined to match their respective Steam Generator sub assembly.