In CANDU™ (Canadian Deuterium Uranium) Reactors, the joint between the Calandria tubes to the Calandria tubesheets is achieved by roller expanded joints. This paper models a detailed account of the Calandria tube joint fabrication and deformation. Numerical simulation illustrates the mechanisms of bending and compression that cause the plastic deformation in the joint. Results show that the insert deformation must pinch the Calandria tube both axially and radially at groove edges to create leak tightness. Predicted rolling forces have been used to quantify the elastic deformation in the rollers and mandrel, and the final tool setting is seen to account for this springback as well as springback in the joint components.