Development of a Backfill for Containment of High-Level Nuclear Waste

Abstract

ABSTRACTSodium and calcium bentonites, pressed to densities between 1.9 and 2.2 g/cm3, have hydraulic conductivities in the range of 10−11 to 10−13 cm/s. Batch sorption distribution ratios (Rd) indicate that Sr, Cs, and Am are strongly sorbed on bentonites and zeolites, that Np and U are moderately sorbed on bentonites and zeolites, and that Am, Np, U, I, and Tc are strongly sorbed on charcoal. Sorption results with basalt and tuff ground waters are similar; however, iodine in tuff ground water sorbs more strongly on bentonites Thermal diffusivity measurements for dry, compacted (p ∼ 2.1 g/cm3) sodium bentonite indicate that the thermal conductivity of a high density bentonite backfill should be roughly similar to that of silicate host rocks (basalt, granite, tuff). These results indicate that a bentonite backfill can significantly delay the first release of many radionuclides into the host rock and that by forming a diffusion barrier a bentonite backfill can significantly decrease the longterm release rate of radionuclides from the waste package.