Long term integrity against corrosion of titanium used for TRU waste container

Abstract

Commercial grade pure titanium containing palladium (Ti-Grade 17) may be used for transuranic waste containers. The long term integrity of Ti-Grade 17 against corrosion was studied in the concrete permeated alkaline sodium water environment of 0·6 mol [Cl⁻]+0·223 mol [OH⁻] at various temperatures up to 80°C. The study focused on the stability of the passive oxide film, the susceptibility to crevice corrosion and cracks in the titanium hydride (TiH₂) layer. General corrosion depth for sustained passivation may be determined as i _pass times the evaluation period of 10⁴ years, with addition of the electric quantity for the destruction and repair of passivation film. Crevice corrosion sensitivity is not affected by processes such as welding, cold work and heat treatment. Cathodic reactions essential for maintaining the passive state produce hydrogen that, to some extent, is adsorbed to form a hydride layer. This layer subsequently undergoes cracking to cause reduction in the critical hydride layer thickness δ _c of 10 μm. The crack depth becomes as much as 100 μm at 2000 years.