Long-Term Chemical Alteration of 238Pu-Doped Borosilicate Glass in a Simulated Geological Environment with Bentonite Buffer

Chemical degradation of borosilicate glass doped with 238Pu was modelled in conditions of a failed underground radwaste repository in granite host rock with bentonite buffer material after penetration of aqueous solutions at temperature of 90 °C. The total duration of the experiment exceeded two years. It is shown that wet bentonite preserved its barrier function and prevents migration of plutonium to the solution. The total amount of plutonium adsorbed on bentonite clay during the experiment did not exceed 0.02% of the initial amount of plutonium in the glass sample. Estimated accumulated dose of self-irradiation of the glass sample after the experiment varies from 3.16 × 1015 to 3.39 × 1015 α-decays per gram, which is equivalent to more than 1000 years storage of 239Pu doped sample with the same Pu content. Beishan granite remained intact, with no evidence of Pu penetration into the granite matrix along mineral grain boundaries.