The development of deterministic models for predicting the accumulation of corrosion damage to zirconium and Zircaloys in boiling water reactor coolant environments requires the acquisition of values for various model parameters. In the present work, the point defect model ͑PDM͒ was further developed to account for the properties of passive films comprising oxide barrier layers and porous oxide outer layers that form on zirconium and Zircaloys in high-temperature, deaerated aqueous solutions. The model parameter values were extracted from electrochemical impedance spectroscopic data for zirconium in deaerated, borate buffer solution ͓0.1 M B͑OH͒ 3 + 0.001 M LiOH, pH 6.94͔ at 250 °C by optimization. The results indicate that the corrosion resistance of zirconium in high-temperature, deaerated aqueous solutions is dominated by the porosity and thickness of the outer layer. The impedance model based on the PDM provides a good account of the growth of the bi-layer passive films described above, and the extracted model parameter values might be used, for example, for predicting the accumulation of general corrosion damage to Zircaloy fuel sheath in BWR operating environments.

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The development of deterministic models for predicting the accumulation of corrosion damage to zirconium and Zircaloys in pressurized water reactor ͑PWR͒ coolant environments requires the acquisition of values for various model parameters. In the present work, the point defect model ͑PDM͒ was further developed to account for the properties of passive films comprising hydride barrier layers and porous oxide outer layers that form on zirconium and Zircaloys in high-temperature, hydrogenated aqueous solutions. The model parameter values were extracted from electrochemical impedance spectroscopic data for zirconium in hydrogenated, borate buffer solution ͓0.1 M B͑OH͒ 3 + 0.001 M LiOH, pH 6.94͔ at 250°C by optimization. The results indicate that the corrosion resistance of zirconium in high-temperature, hydrogenated aqueous solutions is dominated by the outer layer, as was found to be the case for nonhydrogenated solutions where a defective oxide barrier layer forms. The impedance model based on the PDM provides a good account of the growth of the bi-layer passive films described above, and the extracted model parameter values might be used, for example, for predicting the accumulation of general corrosion damage to Zircaloy fuel cladding in PWR operating environments.

The physical and chemical effects of ultrasound on polypropylene (PP) melts in extrusion were investigated. By applying ultrasound vibration to the entrance of the die, apparent pressure and viscosity of PP can be obviously decreased under the appropriate ultrasound power. Ultrasound has both physical and chemical effects on the polymer melt. In our study with specific polymer and ultrasound system, we determined that the chemical effect makes up 35-40% of the total effect of ultrasound on the apparent viscosity reduction of PP melts at most of the studied intensities. The physical effect plays a more important role in the ultrasound-applied extrusion than the chemical effect. This chemical effect is an irreversible and permanent change in molecule weight and the molecular-weight distribution due to ultrasound. As the ultrasound intensity increases, the molecular weight of PP reduces and its molecular-weight distribution becomes narrower; the orientation of PP molecules along the flow direction reduces (in melt state) and the crystallinity of PP samples (in solid state) decreases by applying the ultrasound vibration. Ultrasound vibration increases the motion of molecular chains and makes them more disorder; it also affects the relaxation process of polymer melts by shortening the relaxation time of chain segments, leading to weakening the elastic effect and decreasing the extruding swell ratios. All the factors discussed above reduce the non-Newtonian flow characteristics of the polymer melt and result in the viscosity drop of the polymer melt in extrusion.

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