Corrosion investigations on metal waste form alloys of titanium-modified type 316 stainless steel-zirconium in simulated groundwater media

Abstract

Corrosion assessment of metal waste form (MWF) alloys was carried out in two possible geological repository environments, simulated Kalpakkam groundwater (KGW) and Rajasthan groundwater (RGW). The corrosion resistance properties, passive film stability, and surface morphologies were evaluated by electrochemical and microscopic techniques. Studies were done in two main parts. First, different MWF alloys with varying Zr content from 5 wt% to 17 wt% were compared in KGW to evaluate better corrosion-resistant alloys. All the alloys exhibited a wide range of passivation potential, indicating passive film stability and fairly higher breakdown potentials. However, the alloy with 8.5 wt% Zr showed optimum open-circuit potential (OCP), nobler breakdown potential, optimum passive current, highest polarization resistance, and lowest capacitance; therefore, it was selected as the better alloy. In the second part of the study, the corrosion properties of this better alloy were compared in two simulated RGW media and KGW media. Results showed that because of the lower concentration of chloride in RGW media, the passive film stability was excellent. Scanning electron microscopic observation of surface morphologies after electrochemical studies in both groundwater media showed insignificant corrosion attack. Therefore, this study has clearly shown excellent corrosion performance and good applicability of MWF alloys for geological disposal.