Welding Experiments of Alloy 625 and 800h Using an Automatic Gtaw Orbital System in Support of the Canadian SCWR Fuel Concept

Abstract

A key feature of the Canadian Super Critical Water Reactor (SCWR) fuel concept is the adoption of the proven collapsible cladding concept utilized in CANDU fuel. Alloy 800H (Ni-Cr-Fe) has been selected as cladding material due to its excellent high temperature properties. The assembly of fuel elements and wire wrapped spacers requires the use of a welding technique that minimizes the Heat Affected Zone (HAZ), as this area may develope fine second–phase particles that might compromise the mechanical and corrosion-resistance properties of the alloy. In this work, welding experiments were performed to study the effect of the operating parameters of GTAW welding on the resulting HAZ and its impact on the microstructure and mechanical properties of alloy 800H. The welds were mechanically tested and characterized using various techniques. Full weld penetration was achieved using a heat input of about 2.6 kJ. Large fusion and heat affected zones were observed. A decrease in heat input to 2.4 kJ reduced the fusion and heat affected zones by more than 15% and maintained full weld penetration.