Modeling of the protective oxide layer growth in non-isothermal lead-alloys coolant systems

Lead alloys have been determined to be potential coolant candidates in advanced reactors and accelerator driven systems (ADS) because of their favorable thermal-physical and chemical properties. However, the corrosiveness of the lead-alloys is a critical obstacle and challenge for safe applications in reactors and ADS. Furthermore, the selective dissolution of materials into lead alloys would destroy the structure and contaminate the coolant rapidly, and the deposition of corrosion product may lead to severe flow-path restrictions. One of the effective ways to protect the material is to form and maintain a protective oxide film along the structural material surface by active oxygen control technology.;The goal of this research is to provide basic understanding of the protective oxide layer behaviors and to develop oxide layer growth models of steels in non-isothermal lead-alloys coolant systems in order to provide useful information for active oxygen control technique.;First, a theoretical kinetic model based on the boundary layer theory was developed to investigate the corrosion/precipitation in non-isothermal lead alloy coolant systems. The analytical expressions of the local corrosion/precipitation rate and the bulk concentration of the corrosion products were obtained by considering a turbulent core region and a laminar sub-layer. Numerical solutions were also accomplished together with considering the effect of the eddy mass diffusivity in lead alloy systems. Second, a diffusion controlling oxide layer growth model with scale removal was built in oxygen containing lead alloys. Scale removal effect was considered and the formation mechanism of duplex oxide layer structure was investigated in the model. Finally, the oxide layer growth process, together with the transport of oxygen and ionic metal, was studied at a mesoscopic level based on an improved stochastic cellular automaton (CA) model.;Results from the developed models were compared with the available experimental data and previous work, and good agreement was attained. Moreover, the extended applications of the developed models were analyzed.