Calandria Tube-to-Tubesheet Roll Expanded Joints in CANDU PWHR

Abstract

The calandria vessel in a CANDU reactor is a stainless steel cylindrical tank that contains the heavy water moderator. It is penetrated by 380 to 480 horizontal zirconium alloy calandria tubes that are connected to the planar end shields (tubesheets). These tubes act as stays between the calandria shell and end shields. As well, they assist in supporting the fuel channel assemblies installed inside them and provide thermal insulation of the moderator from the primary coolant.


The calandria tube is joined to the end shield (calandria tubesheet) at each end, using a "sandwich-type" roll-expanded joint. A unique sandwich-type rolled joint is necessary because of the geometry of the calandria tube (wall thickness and the inside diameter) and the design requirements.


This paper is a summary of the technology of the calandria tube-to-tubesheet joints. The joint variables and their effect on the performance characteristics, viz., axial strength and leak-tightness are discussed. Elements of the development test programs (e.g., helium leak tests, load-cycling tests and axial pull-out tests) are discussed. Operating experience (including replacement history) of the joints in CANDU commercial power


reactors is presented.