Evaluation of stainless steel–zirconium alloys as high-level nuclear waste forms

Abstract Stainless steel–zirconium (SS–Zr) alloys have been developed for the consolidation and disposal of waste stainless steel, zirconium, and noble metal fission products such as Nb, Mo, Tc, Ru, Pd, and Ag recovered from spent nuclear fuel assemblies. These remnant waste metals are left behind following electrometallurgical treatment, a molten salt-based process being demonstrated by Argonne National Laboratory. Two SS–Zr compositions have been selected as baseline waste form alloys: (a) stainless steel–15 wt% zirconium (SS–15Zr) for stainless steel-clad fuels and (b) zirconium–8 wt% stainless steel (Zr–8SS) for Zircaloy-clad fuels. Simulated waste form alloys were prepared and tested to characterize the metallurgy of SS–15Zr and Zr–8SS and to evaluate their physical properties and corrosion resistance. Both SS–15Zr and Zr–8SS have multi-phase microstructures, are mechanically strong, and have thermophysical properties comparable to other metals. They also exhibit high resistance to corrosion in simulated groundwater as determined by immersion, electrochemical, and vapor hydration tests. Taken together, the microstructure, physical property, and corrosion resistance data indicate that SS–15Zr and Zr–8SS are viable materials as high-level waste forms.

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