The fuel elements for CANDU reactor consist of uranium dioxide pellet enclosed into zircaloy-4 tubular segments. Segments are sealed by welding Zircaloy-4 end caps. Methods for attaching of end caps to 0.4 mm thick tube were studied.
Because of weld defect, we could not obtain satisfactory bonds by gas tungsten arc welding. In second end cap welds, weld defect was severe. weld defect formation was caused by welding method and end cap design due to welding process.
From the diffusion-type bonding standpoints, we considered that weld line, in magnetic force resistance welding, was composed of fine, discontinuous voids and/or remained original interface where grain coalescence has not occurred. But weld line has no effect on the tensile, Burst test of weld.
From the microstructual Point of view, resistance welding process due to rapid heating and cooling cycle, has the following advantages when compared with gas tungsten arc welding.
ⅰ) Smaller grain size of heat affected zone
ⅱ) Smaller size of heat affected zone
ⅲ) Smaller probability of contamination by impurities
