Stress Corrosion Cracking of Copper in Humid Bentonite Powder

Abstract

Copper is one of the candidate materials for over pack of nuclear waste geological disposal. Overpack would be exposed to hot oxygenated humid atmosphere in the initial stage of disposal, because air introduced during burying operation. In the present work, the authors examined the corrosion behavior of copper, which is contact with bentonite powder in humid environment. Specimens were prepared from oxygen-free pure copper sheets. The surface was groundwith SiC papers up to #2000 and then mirror-finished with alumina suspensions. Bentonite powder (Kunigel VI; Kunimine Ind., Co., Ltd.) was exposed to an air of 63, 75 and 80 % relative humidity at 60 ℃. Th bentonite power absorbs water, but is still keeping powder fluidity. The cupper specimens was buried in the humid bentonite power to observe behavior of corrosion, and also the Slow Strain Rate Testing (SSRT) was performed in the humid bentonite powder. Cathodic stripping voltammetry of specimens immersed in the humid bentonite power showedtwo peaks derived from copper oxide and copper sulfide to reveal thickness of corrosion products. Tarnish rupture type SCC of cupper was also confirmed by SSRT in the humid bentonite powder. In this presentation, correlation between properties of corrosion products and SCC susceptibility will be discussed.