Roll Expanded Joints in the Reactor Assembly of CANDU PWHR 's

Abstract

Roll-expanded joints are used extensively in the reactor assembly of CANDU PHWRs and they have performed reliably in commercial power reactors for 25 years. They provide a cost-effective means of joining components of dissimilar materials and enhance the ease of replaceability of the respective sub-assemblies. The joints require no maintenance and they require minimal space. Each application requires a distinct joint design due to the differences in the service conditions, dimensions and materials of construction of the components, performance requirements and installation considerations. This paper describes the roll-expanded joints used in the following applications in CANDU reactor assembly: (a) the joint between the zirconium alloy pressure tube and the stainless steel end fitting in the fuel channel assembly, (b) the joint between the liner tube and the end fitting body, (c) the joint between the zirconium alloy calandria tube and the stainless steel calandria-side tube sheet in the calandria, (d) the joint between the fuel channel annulus bellows assembly/fixed-end-stop collar and the lattice tube at the fuelling machine tube sheet, and (e) the joints between the zirconium alloy guide tube and the stainless steel outer hub in the flux detector assembly. The reasons for selection of the specific roll-expanded joint design for the respective application are presented and design and performance requirements are detailed. Variables in the roll-expansion process and their effect on the properties of the joint designs are discussed. The deformation characteristics of the components and their significance are outlined. The paper summarizes the development, testing and qualification of the roll-expanded joints as well as the operating experience in the CANDU commercial power reactors.