A Description of the Kinetics and Mechanisms which Control the Release of Hlw Elements from Synroc

Leaching tests were carried out on well-characterised Synroc C specimens containing 10 wt% simulated HLW. The effect of temperature and leachant composition on the mechanisms and kinetics of leaching were investigated by leaching Synroc specimens in deionised water at 70°C and 150°C, and in silicate and bicarbonate solutions at 70°C. SEM and TEM were used before and after leaching to characterise the primary and secondary phases in and on the Synroc samples, and to describe the morphological and chemical changes which occurred. Leachants were analysed using ICP/optical emission spectroscopy and ICP/mass spectrometry. p]Titaniferous surface layers were observed on the surface after exposure to leachants. Analysis of the leaching data has established that these surface layers can reduce the release of HLW elements from Synroc and that variations in temperature and leachant composition can hinder or promote the formation of secondary phases.