In the present work, the author examined the corrosion behavior of copper, which is one of the candidate metals as overpack. In particular, stress corrosion cracking and the growth of corrosion products were focused.

   Specimens were prepared from oxygen-free pure copper sheets. The surface was ground with SiC papers up to #2000 and then mirror-finished with alumia suspensions. The Slow Strain Rate Testing (SSRT) of copper tensile specimen was performed in the bentonite slurries consisting bentonite cray and deionized water with and without some salt solutions. SSRT clearly demonstrated that the tarnish-cracking type SCC occurred on pure copper even without ammonia in the bentonite slurries, that is, cracks propagated in the corrosion products consisting of copper oxide and sulfide. The frequency and propagation of crack were affected by the presence of ammonia and its concentration in the bentonite slurries. The constant strain SCC test was also performed using U-bend type specimen under same environment. As SCC susceptibility under such static loading like U-bend test is quite low compared to SSRT, some initiation of cracks was confirmed.

   The cathodic stripping voltammetry of specimens immersed in bentonite slurries showed two peaks derived from copper oxide and copper sulfide. The thickness of copper oxide was not changed if the immersion was prolonged whereas the thickness of sulfide increased with the immersion period. Furthermore, the growth of sulfide was apparently delayed when the dissolved oxygen concentration of the deionized water used for the bentonite slurries was reduced. In this presentation, correlation between properties of corrosion products and SCC susceptibility will be discussed.