Welding Zircaloy Thin Tubes to End Plugs

Abstract

This work aimed at optimizing parameters while welding Zircaloy-2 tubes with end plugs, as a simulation of a part of the fabrication of the nuclear fuel pins. Samples were welded by Tungsten Inert Gas arc welding (TIG) process under controlled atmosphere of pure argon. Some samples were welded using Electron Beam (EB) welding process.

For samples welded using TIG process both the design of the welding chamber (size and tightness), and the purity of the shielding atmosphere were found to have appreciable effect on the quality of the welded joint. Increasing the arc length and/or the welding current increases grain growth and extends both fusion and heat-affected zones. However, heat input (arc length and welding current) must be high enough to give complete penetration welds. Optimum arc length of 1.2 mm was found to give good welds with the smallest possible heat-affected zones.

Optimum parameters of EB welding process (vacuum, welding current and EB amplitude) were determined. Welds prepared by EB welding were found to have finer grain size and less extended fusion and heat-affected zones.

Welds prepared by both TIG and EB processes were inspected visually, metallographically and by using X-ray radiography. Welds integrity were tested using helium leak and pressure tests.