The chemical durability of glass and graphite-glass composite doped with cesium oxide

The role of temp. in detg. the chem. stability of a waste form, as well as its leach rate, is very complex. This is because the dissoln. kinetics is dependent both on temp. and possibility of different rate-controlling mechanisms that appear at different temp. regions. The chem. durability of Alumina-Borosilicate Glass (ABG) and Glass-Graphite Composite (GGC), bearing Tristructural Isotropic (TRISO) fuel particles impregnated with cesium oxide, were compared using a static leach test. The purpose of this study is to examine the chem. durability of glass-graphite composite to encapsulate coated fuel particles, and as a possible alternative for recycling of irradiated graphite. The test was based on the ASTM C1220-98 methodol., where the leaching condition was set at a temp. varying from 298 K to 363 K for 28 days. The release of cesium from ABG was in the permissible limit and followed the Arrhenius's law of a surface controlled reaction; its activation energy (Ea) was 65.6 ± 0.5 kJ/mol. Similar values of Ea were obtained for Boron (64.3 ± 0.5) and Silicon (69.6 ± 0.5 kJ/mol) as the main glass network formers. In contrast, the dissoln. mechanism of cesium from GGC was a rapid release, with increasing temp., and the activation energy of Cs (91.0 ± 5 kJ/mol) did not follow any model related to carbon kinetic dissoln. in water. Microstructure anal. confirmed the formation of Crystobalite SiO2 as a gel layer and Cs+1 valence state on the ABG surface. [on SciFinder(R)]