Understanding activity transport in the coolant system in a water-cooled reactor is important for nuclear reactor safety and operation. As the coolant circulates through the reactor core, it is exposed to ionizing radiation. Radiolysis of water produces strong redox species, ranging from highly oxidizing (e.g., ·OH) to highly reducing (e.g., ·e_(aq)~-, ·O_2~-), that can alter the oxidation state of dissolved radioactive metallic species. Since metal solubility depends strongly on its oxidation state, ionizing radiation can convert more soluble to less soluble species. This may promote precipitation or colloid formation within the irradiated solution. To develop a better understanding of the effect of radiation-induced colloid formation on metal ion transport in coolant systems a comprehensive study of the effect of γ-irradiation on metal ion solubility is being performed for Fe, Cr, Co and Mn. Water containing dissolved metal ions is irradiated in a ~(60)Co γ-cell which provides a dose rate of 6.7 kGy/h and the concentrations of species present are measured as a function of irradiation time by UV-Vis spectrophotometry and gas chromatography. The radiation-induced formation of colloids is studied by Transmission Electron Microscopy (TEM), UV absorption, fluorescence and Fourier Transform Infrared (FTIR) spectroscopy. The work reported here focuses on the formation of iron-oxide colloids.
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