Physical and welding metallurgy of Gd-enriched austenitic alloys for spent nuclear fuel applications -Part II: Nickel-based alloys

The physical and welding metallurgy of gadolinium- (Gd-) enriched Ni-based alloys has been examined using a combination of differential thermal analysis, hot ductility testing, Varestraint testing, and various microstructural characterization techniques. Three different matrix compositions were chosen that were similar to commercial Ni-Cr-Mo base alloys (UNS N06455, N06022, and N06059). A ternary Ni-Cr-Gd alloy was also examined. The Gd level of each alloy was ∼2 wt-%. All the alloys initiated solidification by formation of primary austenite and terminated solidification by a Liquid → γ + Ni ₅Gd eutectic-type reaction at ∼1270°C. The solidification temperature ranges of the alloys varied from ∼100° to 130°C (depending on alloy composition). This is a substantial reduction compared to the solidification temperature range of Gd-enriched stainless steels (360° to 400°C) that terminate solidification by a peritectic reaction at ∼1060°C. The higher-temperature eutectic reaction that occurs in the Ni-based alloys is accompanied by significant improvements in hot ductility and solidification cracking resistance. The results of this research demonstrate that Gd-enriched Ni-based alloys are excellent candidate materials for nuclear criticality control in spent nuclear fuel storage applications that require production and fabrication of large amounts of material through conventional ingot metallurgy and fusion welding techniques.