Abstract
In safety assessments of the geological disposal of TRU waste, it is important to understand the possibility and extents of influence of hyperalkaline groundwater derived from the degradation of cementitious materials that are used as forms for the containment of waste and as constructional materials in the disposal facilities of TRU waste. In this research, reactive transport analyses of hyperalkaline plume induced by cementitious materials were performed to clarify the extent of the hyperalkaline groundwater spreading and the type of alterations occurring with or without considering the precipitation of zeolite. The effect of the groundwater velocities on the spread of hyperalkaline groundwater was also examined.
With respect to the precipitation of zeolite, both cases considering; 1) only analcime and phillipsites(two types) that are most likely observed in experiments by researchers and 2) 16 zeolites including 13 of them, being likely to precipitate（clinoptilolites(two types)，heulandite，laumontite，mordenite，erionites(two types)，chabazites(two types)，epistilbite，yugawaralite，stilbite，scolecite）, showed similar results that hyperalkaline groundwater spread only 40 meters and major amounts (> 0.1 vol.%) of secondary minerals precipitated. In these cases, dominant secondary minerals were zeolites such as analcime and phillipsite, and other minerals such as sepiolite. In the case that zeolites were not allowed to precipitate, high-pH (>11) groundwater extensively spread and only a small amount of secondary minerals precipitated. These results indicate that whether zeolites precipitate or not significantly affect extent of hyperalkaline groundwater and the amount of precipitation of secondary minerals. In the case that groundwater velocity was 10 times higher, hyperalkaline groundwater spread broader than the original groundwater velocity case. It might be due to our kinetic dissolution model of host rock minerals, which limits chemical reactions neutralizing hyperalkaline groundwater.
