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 2 ]z0?223 mol [OH 2 ] at various temperatures up to 80uC. The study focused on the stability of the passive oxide film, the susceptibility to crevice corrosion and cracks in the titanium hydride (TiH 2 ) layer. General corrosion depth for sustained passivation may be determined as i pass times the evaluation period of 10 4 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 d c of 10 mm. The crack depth becomes as much as 100 mm at 2000 years.

Anticipated Degradation Modes of Metallic Engineered Barriers for High-Level Nuclear Waste Repositories

“…Equation 15 represents the corrosion rate of grade 17 titanium as a function of [OH À ] (mol/L) and the temperature (K), for [OH À ] < 1 mol/L. 114 According to Eq. 15, the corrosion rate of this Ti alloy increases with increasing temperature and pH.…”

“…General corrosion is not a main concern for these alloys in repository environments. 6,7,45,74,75,[112][113][114][115][116][117] CR lm=year ½ ¼3:04 Á 10 6 OH À ½ 0:25 exp…”

“…The processes included in the fabrication of containers, namely TIG welding, 20% of cold work, and a heat treatment of 4 h at 600°C, do not compromise the crevice corrosion resistance of the alloy. 114…”

“…This process continues as long as the hydride layer keeps growing. 114 Nakayama et al 45,114 performed the assessment of HIC on Ti alloys based on the thickness and mechanical properties of the hydride layer, which cracks above a critical thickness. Figure 10 shows the growth of titanium hydride phase and the formation of cracks.…”

A critical appraisal of laser peening and its impact on hydrogen embrittlement of titanium alloys

“…Titanium is alloyed with molybdenum, aluminium, iron, vanadium, among other elements, to produce lightweight alloys as well as strong alloys for aerospace, 4,5 marine, medical implants, 6,7 chemical process industry, 8,9 nuclear industry, 10 desalination unit, hydrogen storage devices, 11,12 heat exchanger systems, transuranic waste containers and seawater-cooled piping. 13,14 However, the interface between hydrogen-carrying environment and titanium alloys leads to harsh and severe problems. 15–20…”