Development of welded joints for steel and zirconium tubes at nuclear power plants

The design of transition joints and the technique of joining dissimilar materials by solid-phase vacuum diffusion welding are discussed, using as an example joints between tubes made of stainless steel 06X18H10T and tubes of zirconium alloy with 2.5% (mass) of niobium (transition joints of RBMK pressure tubes). The results of tests demonstrating the performance of diffusion-welded joints and of studies on the transition joints are presented, and the results of calculating the stressed-strained states of a transition joint are described, covering the range from the fabrication stage (residual stresses) through operation (residual and operational stresses). Detailed structural analysis has been performed for the zirconium-steel bonding layer. The long operation history of transition joints in RBMK reactors is summarized. (authors)