In-Process Control of Welding During CANDU Reactor Maintenance Operations

Abstract

Current rolled joint design and fabrication procedures produce a step change (burnish mark) in the inside diameter of the pressure tube inboard of the rolled joint. This can result in abnormal fuel support at the inlet rolled joint of a Bruce-type (with fuel latch-type fuel changing process) fuel channel. It has been recommended that the burnish mark step be reduced between the rolled and unrolled regions of the pressure tube for inlet rolled joints. The flush rolled joint concept involves the use of a pressure tube with a thick end, achieved by decreasing the inside diameter. Dimensions of the thick end are chosen so that when rolled into the inlet end fitting, the rolled joint bore will be flush with the unrolled region of the pressure tube. This paper details the program to develop and qualify the flush rolled joint design for installation in a commercial power reactor. Specific attention has been given to the material properties of the thick-ended pressure tube, the geometry of the inside surface of the pressure tube at the rolled joint, pressure tube residual stresses in the roll expanded region, pullout strength, and helium leak rate across the rolled joint. The above results are evaluated using the database on CANDU pressure-tube-to-end-fitting rolled joints as the frame of reference.