Sorption of several safety relevant radionuclides on granite and diorite – a potential repository host rock in the Taiwan area

Abstract

Summary The geological survey of natural barriers plays a critical role in determining the suitability of a site for the final disposal of high-level radwaste. This study focused on the characterization of sorption and the determination of distribution coefficients of several safety relevant radionuclides. Both batch tests and polar-microscopy/autoradiography were employed for analyzing and estimating of the sorption of nuclides on one potential host rock in the Taiwan area, which is composed of mostly granite and little diorite. Nuclides investigated were Co, Sr, Cs, U, I, and Am. De-ionized water and synthetic seawater were applied to study nuclide sorption at various concentrations. The distribution coefficients obtained based on the two-week batch tests indicated that the sorption of Co, Sr, Cs, and U on each rock sample was greater in de-ionized water than in synthetic seawater. In addition, sorption onto a specific host rock depended on microscopic heterogeneity. The photos obtained from polar-microscopy/autoradiography showed that biotite is the principal mineral component that is responsible for the sorption of 137 Cs and 90 Sr onto granite and diorite.