Corrosion of High-Level Waste Packaging Materials in Disposal Relevant Brines

Previous corrosion studies identified the materials Hastelloy C4, Ti 99.8-Pd, and carbon steels as promising for the manufacture of long-lived high-level waste containers that could act as an engineered barrier in a rock-salt repository. Here, the efficiency of the corrosion-resistant concept using surface-welded Hastelloy C4 as corrosion protection of carbon steel containers is compared with the corrosion-allowance concept using unalloyed or low-alloyed steels. The materials are examined in three disposal relevant brines (two rich in MgCl₂, one rich in NaCl) at 150°C. The results indicate that welded Hastelloy C4 is highly resistant to corrosion in the NaCl-rich brine. In the presence of sulfides or MgCl₂-rich brines, however, severe pitting corrosion occurs. The three steels investigated are resistant to pitting corrosion in all brines, and their general corrosion rates imply corrosion allowances acceptable for thick-walled containers. In view of these results, carbon steels continue to be considered promising materials for long-lived containers. Further investigations on carbon steels and Ti 99.8-Pd as alternatives to Hastelloy C4 are in progress.