Long-term performance of candidate materials for HLW/spent fuel disposal containers. 1. Annual progress report (November 2000 - October 2001)

The project started on 1 November 2000 and will last three years till 31 October 2003. In the present paper the results of the investigations performed during the first year of the project are presented. The results of the investigations in MgCl2-rich (T=150 C) indicate that the welded specimens of the TStE355 carbon steel suffer from severe pitting corrosion. However, the stress relief thermal treated welds are resistant to pitting corrosion, as do so the unwelded specimens. In NaCl-rich brine, the welded steel is resistant to pitting corrosion and suffers only from general corrosion as the unwelded material. Investigations on contact specimens of the material pair Ti99.8-Pd and TStE355 steel in NaCl-rich brine at 150 C show that the coupling of these materials does not cause contact corrosion. Cu, Ni and Cu-Ni alloys (90-10 and 70-30) have between 25 C and 80 C in salt brines a large passive range, and the corrosion rates are low (8-30 mum/a). Potentiodynamic polarization tests (20 C) in granitic-bentonite water show that Hastelloy C-22, Cu-OF and Cu-Ni 70-30 are resistant to pitting corrosion. Furthermore, Hastelloy C-22 is resistant to crevice corrosion (Cl--content: 50,000 mg/l) and to stress corrosion cracking in granitic-bentonite water. Cu-OF shows a slight crevice corrosion in this medium. In clay water (anaerobic conditions) at 16 C and a Cl- content up to 50,000 mg/l, the materials Ti99.8-Pd, Hastelloy C-4, Hastelloy C-22 and the stainless steel UHB 904L are resistant to pitting corrosion. The stainless steels AISI 316L and AISI 316Ti show pitting corrosion at Cl--concentrations higher than 20,000 mg/l. At the higher temperature of 90 C, only Ti99.8-Pd remains resistant to general and pitting corrosion. The carbon steel TStE355 exhibits general corrosion, and the susceptibility of UHB 904L to pitting corrosion increases with growing Cl--content. However, no serious corrosion problems are expected for the UHB 904L steel under realistic disposal conditions in clay. The alloys Hastelloy C-4 and Hastelloy C-22 suffer from pitting only in solutions containing more than 20,000 mg/l Cl-. At 140 C and aerobic conditions in clay water, the susceptibility of the UHB 904L steel to pitting is higher than at 90 C. (orig.)