The Transport of Radioactive Corrosion Products in High-Temperature Water—III. The Interaction of Dissolved Cobalt with Heated Surfaces

A once-through loop containing pressurized water at 300°C and constant chemistry conditions of high pH (with LiOH) and dissolved hydrogen has been used to study the deposition and release of ⁶⁰Co at heated Zircaloy surfaces. The activation of the surfaces proceeds by a mechanism involving dissolved species. The mechanism is affected little by heat flux, but a great deal by the type of oxide film formed by corrosion on the Zircaloy. To take account of the mechanism, a mathematical model has been developed. It describes first-order processes, such as adsorption/desorption or ion exchange occurring at a continuously changing surface. The model has furnished deposition and release coefficients for ⁶⁰Co on thin black and thick white ZrO₂ films for operation with and without heat flux.