Room temperature mechanical properties of electron beam welded zircaloy-4 sheet

Abstract

Resumption of operations at the Transient Reactor Test (TREAT) facility at Idaho National Laboratory was approved in 2014 to meet U.S. Department of Energy Office of Nuclear Energy objectives in transient testing of nuclear fuels. In parallel, the National Nuclear Security Administration, through the Office of Material Management and Minimization, is converting TREAT from its existing highly enriched uranium core to a low-enriched uranium core. This effort entails designing, fabricating, and qualifying a new TREAT low-enriched uranium fuel assembly, while maintaining TREAT’s experimental performance capabilities. Zircaloy-4 is being evaluated as TREAT low-enriched uranium assembly material. A preliminary study on the room temperature mechanical properties of as-received and electron beam welded Zircaloy-4 sheet (1.6mm) is presented. The sheet was high-vacuum electron beam welded using a three-pass process with varying heat input: (1) tack welding (10.5J/mm), (2) seams welded (36.7J/mm), and (3) sealed (15.7J/mm). As-received and electron beam welded specimens show comparable properties. Zircaloy-4 displays anisotropy between the transverse and longitudinal directions. Tensile properties measured for the transverse direction display higher yield strength, reduction of area, and slightly lower tensile strength and ductility than for the longitudinal (i.e., rolling) direction. Weld and base metal hardness are comparable, while hardness at the heat-affected-zone is slightly higher. Microscopic examinations show distinct microstructure morphology and grain size from weld to base metal. A correlation between welding parameters, mechanical properties, and microstructural features was established for electron beam welded Zircaloy-4 sheet.