Current understanding of pitting and crevice corrosion and its application to test methods for determining the corrosion susceptibility of nuclear waste metallic containers

A review of crevice and pitting corrosion mechanism and testing techniques is given to understand the fundamental problems involved in determining corrosion rates of alloys to be used as nuclear waste containers. The mechanisms are broken down into two sections, initiation and propagation of the crevice or pit. Theories of initiation include the absorbed ion displacement model, ion migration or penetration model and the breakdown-repair model. Experimental results concerning the initiation period include a discussion of the kinetics of initiation, the critical potential for breakdowns, and experimental factors affecting the initiation. The theories of pit and crevice corrosion propagation are mentioned as well as factors affecting propagation. Several experimental techniques are discussed that are useful in determining the probability of pitting and/or crevice corrosion of alloys. In assessing the lifetime of the metallic container accelerated tests are required. With this in mind the testing techniques concentrate on electrochemical techniques and various modifications of these basic techniques. Although susceptibility of alloys to pitting and crevice corrosion can be determined readily, initiation time and propagation rates are not as straightforward particularly over 1000 years. Nevertheless several testing techniques exist that may be used to determine these important values