Pressure Tube-to-End Fitting Roll-Expanded Joints in a CANDU PHWR

Abstract

A fuel channel in a CANDU reactor consists of a zirconium alloy pressure tube that is roll-expanded into a stainless steel end fitting at each end. The pressure tube contains the fuel bundles and forms the in-core portion of the fuel channel. The end fittings provide connections to interfacing components. This paper is a summary of the technology of pressure tube-to-end fitting roll expanded joint used in CANDU reactors. The design and operational requirements are identified. The codes and standards applicable to the design are reviewed. The design philosophy and the details of design assurance by component testing are presented. This paper examines the effects of variables in the design of the joint on the performance parameters. The deformation characteristics of the pressure tube and the end fitting at the roll-expanded region, and their significance, are reviewed. The residual stresses in the pressure tube and the end fitting affect joint integrity. The techniques for measuring residual stresses in the respective components and the effect of reactor operation on residual stress levels are discussed. This paper describes the mechanisms of failure of the rolled joints under axial tension. The tests to measure the axial strength of the rolled joint are described. The effect of reactor operation on the joint strength is also addressed.