Cesium transport behavior through engineered and natural barriers in a fixed-bed column system.

Radionuclides stored for extended periods in radioactive waste repositories can leach through engineered (concrete) and natural (granite) barriers. Isosaccharinic acid (ISA), a cellulose degradation product generated under high-alkaline conditions, can form stable complexes with radionuclides, adsorb onto rock surfaces, or reduce pore sizes, thereby accelerating radionuclide release. This study employs continuous fixed-bed column reactors packed sequentially with concrete and granite to evaluate the effects of various environmental conditions on cesium transport. The hydraulic properties of the two rock columns were determined by tracer tests using bromide, and the effects of initial cesium concentration, flow rate, bed depth, and ISA concentration on cesium mobility were examined. The breakthrough data were well described by the advection-dispersion equation (R2 = 0.994-0.999). The retardation factors (R) for cesium were 5.24 in concrete and 12.41 in granite. Results showed that increasing the initial cesium concentration, flow rate, or initial ISA concentration, as well as decreasing the bed depth, reduced the R value, indicating enhanced cesium transport. Overall, this study provides new insights into cesium behavior in both engineered and natural barriers, offering a basis for predicting its mobility under various environmental conditions.