Advances in Appendage Joining Techniques for PHWR Fuel Cladding

Abstract

This paper describes work carried out at the BARC onthe development of a technique to join tiny appendages(spacers and bearing pads) to thin cladding (before loadingof UO pellets) by resistance welding for PHWR fuelassemblies. The work includes qualifying the process forproduction environment, designing prototype equipment forregular production and quality monitoring.In the first phase of development, welding ofappendages on UOy loaded elements was successfullydeveloped, and is being used in production.Welding of appendages on to empty clad tubes is asuperior technique for several reasons. Many problemsassociated with development of welding on empty tubes wereresolved. Work was initiated, in the second phase of thedevelopment task, to select a suitable technique to joinappendages on empty clad tubes without any collapse of thinclad. Several alternatives were reviewed and assessed suchas laser, full face welding, shim welding and shrink fittingring spacers. Selection of a method using a mandrel and amodified electrode geometry was fully developed. Resultswere optimized and process development successfully completed.-Appropriate weld monitoring techniques were alsoreviewed for their adaptation. This technique is useful tor19, 22 as well as 37 element assemblies.