Partial melting and recrystallization of granite and their application to deep disposal of radioactive waste: Part 2—Recrystallization

A previously published scheme for the high temperature disposal of nuclear waste in deep boreholes requires that granite host rock partially melted by the heat from the waste can be completely recrystallized on the time scale of the cooling of the waste. Experimental studies of dynamic recrystallization of a typical S-type crustal granite were therefore undertaken under the pressure (=0.15 GPa) and other conditions likely to arise during implementation of this scheme. Linear cooling experiments at 1 °C/h, 0.1 °C/h and 1 °C/day were carried out over the temperature range 800–560 °C. These demonstrate that the partially melted granite can be fully recrystallized when cooled at 0.1 °C/h or slower. Crystal growth rates for the main phases formed during cooling are linearly proportional to total H2O content and decrease from alkali feldspar through biotite to quartz. Recrystallizing the partially melted granite at 0.1 °C/h compared with 1 °C/h increases grain size by a factor of ∼2.5. On the basis of partial melting experiments reported previously by us [Lithos (2003) this issue.] for the same granite and the results presented here, it is concluded that an S-type granite similar to the one studied would be a suitable host rock for the proposed high temperature, very deep disposal scheme for radioactive waste.