Advanced corrosion studies on selected packaging materials for disposal of HLW canisters in rock salt

Corrosion studies performed until now on a number of materials have shown that unalloyed steels, Hastelloy C4 and Ti99.8-Pd are the most promising materials for a long-term resistant packaging for disposal of high-level waste (HLW) canisters in rock salt formations. To characterize their corrosive behavior in more detail, additional studies have been performed. The influence exerted by the gamma dose rate (1 Gy/h to 100 Gy/h) has been examined on the corrosion of three preselected steels and Hastelloy C4 at 900C in a salt brine (Q-brine) rich in MgCl2 which is relevant for accident scenarios in a repository. Furthermore, the stress corrosion cracking resistance has been investigated of fine-grained steel (reference steel) in this brine at slow strain rates (2.5 x 10-5 to 5 x 10-7 s-1) and temperatures of 900C and 1700C. In addition, in situ corrosion experiments were carried out at elevated temperatures (1200C to 2100C) in the absence and in the presence of a gamma radiation field of 3 x 102 Gy/h, within the framework of the US/FRG Brine Migration Test in The Asse salt mine. Under the test conditions the gamma radiation did not exert a significant influence on the corrosion of the steels investigated