Effect of Heat on the Soundness of Zircaloy-4 End Cap Closure Using a Resistance Upset Welding

Abstract

The objective of this study is to investigate the effect of main heat on the soundness of Zircaloy-4 end cap welds and the process of weld line elimination in resistance upset welding for a Direct Use of spent PWR fuel In CANDU reactor (DUPIC) fuel fabrication. The weld current and amount of upset increased linearly with the main heat, from which two relations between them were derived. It was found that the threshold to obtain sound welds was 50% of the main heat in terms of upset size, mechanical strength, and weld line elimination. A microstructure of resistance upset welds of Zircaloy-4 comprised basketweave, Widmanstätten, and martensite depending on the alteration of the main heats. Dimples on the uniaxially fractured surface at the weld line in Zircaloy-4 welds were larger and deeper than those on a biaxially fractured surface. It was also found that the process of weld line elimination in the resistance upset weld of Zircaloy-4 could be divided into three stages in terms of the presence of many pores, their shrinkage and elimination, and the shrinkage of the original weld interface with increasing weld current.