Influence of noble metal fission products and uranium on the microstructure and corrosion behaviour of D9 stainless steel-zirconium metal waste form alloy

Metal waste form (MWF) alloys of composition D9SS-8.5Zr, D9SS-10Zr-1NMFP and D9SS-10Zr-1NMFP-10U were prepared by casting of D9SS (Ti-modified austenitic 316 stainless steel), zirconium, NMFPs (noble metal fission products) and uranium for evaluating the influence of NMFPs and U on the microstructure and corrosion resistance of MWF alloys. Gradual increase in the hardness value was observed with the addition of NMFPs and uranium. Microstructural characterisation revealed the formation of Zr-rich intermetallic phases in these alloys which act as hosts for NMFPs and U. Fe-Zr and Ni-Zr based intermetallics were identified in D9SS-Zr and D9SS-Zr-NMFP alloys by XRD technique. In the U added alloy, UZrO2 and NiU2 were observed along with Fe-Zr and Ni-Zr intermetallics. Electrochemical corrosion monitoring confirmed active corrosion potential and higher passive current density with the addition of NMFPs and U. The MWF alloy with NMFPs showed higher break down potential with high polarization resistance revealing stable passive film.