In-Situ Corrosion Studies on Cast Steel High-Level Waste Containers Plated with Titanium/Nickel-Alloys

Abstract

ABSTRACTPrevious corrosion studies have shown that the passive alloys Ti 99.8-Pd and Hastelloy C4 are the most promising corrosion protection materials for long-term resistant carbon-steel containers for the disposal of heat-generating wastes in rock salt formations. Consequently, these materials are subject to more detailed investigations. The influence of selected container manufacturing characteristics (sealing technique, application mode of the corrosion protecting layer on the steel) on the corrosion behaviour of Ti 99.8-Pd and Hastelloy C4was studied using in-situ experiments. The corrosion resistance of the materials was examined both in NaCI brine and MgCl2-rich brine, which might enter into an HLW borehole under certain disposal conditions. Four electron-beam welded cast-steel tubes plated with corrosion protection layers made of Ti 99.8-Pd and Hastelloy C4, respectively, were stored for 18 months in 2-m deep heated boreholes in the Asse salt mine. The annular gap between the tubes and the borehole wall was filled with saturated NaCl-brine or Qbrine (MgCl2-rich). The vertical temperature profile in the boreholes ranged from 90°C to 200°CIn the cast-steel tube with a corrosion protection of Ti 99.8-Pd, no indication of corrosion was observed on the EB-welds or on the explosion plated material in both brines. The cast-steel tube with a corrosion protection of Hastelloy C4 also was found to be resistant to any kind of corrosion in the NaCl-brine. In the MgCl2-rich brine, however, small pitting corrosion of 15 pm was observed after 1.5 years on the passive surface layer that was formed.On the basis of these results, Ti 99.8-Pd continues to be considered as a promising corrosion protection material for long-lived HLW containers.