Electrochemical Corrosion Rates of Waste Container Materials

摘要

The degradation rate of spent oxide fuel in a disposal facility will depend on the surface potential, which may be strongly affected by the concentration of dissolved H_2 within a breached waste container. The H_2 generation rate due to anoxic metal corrosion is a key variable in the fuel degradation model being developed for use in performance analyses of waste disposal facilities. We are using electrochemical methods to measure the corrosion rates of low alloy steel, stainless steel, and Zircaloy-4 to represent H_2 generation rates under solution redox (Eh) and pH conditions spanning the ranges that could occur in disposal systems. Potentiostatic tests are conducted to measure corrosion rates at fixed Eh and pH conditions and Electrochemical impedance spectroscopy is performed periodically during those tests to quantify changes in the surface electrical properties as the material attains a constant corrosion rate. The corroded surfaces are examined with scanning electron microscopy after the test to relate the electrochemical measurements to physical changes. Results of tests with 4320 steel in acidic and alkaline brine solutions at an imposed potential of 0.25 V_(SCE) are presented as an example of the experimental method and how the fuel corrosion rate varies with the H_2 generation rate.