Utilization of recycled cement powder as a solidifying agent for radioactive waste immobilization

Abstract

Due to the uniquely high disposal cost for disposal of Intermediate/Low level radioactive waste in Republic of Korea, reduction of concrete waste by separating activated/contaminated portion of the concrete needs to be accomplished to minimize cost and environmental burden. Since the activated or contaminated portion of the concrete is on the hydrated cement paste, a 2 h heat treatment at 600 °C and 22 h milling process were applied to mortar specimens to separate recycled cement powder from fine aggregate. Separated recycled cement powder that passed 150 μm sieve was evaluated for the utilization as a solidifying agent for liquid radioactive waste immobilization. The 3 M CoCl2 and 3 M CsCl solutions were used as waste simulants containing Co and Cs, respectively. It was found that the wasteform made of 3 M CoCl2 and 3 M CsCl with recycled cement powder met the strength requirement of 3.45 MPa that was required for disposal of solid wasteform. Wasteform specimens also passed thermal cycling and water immersion requirements. Leachability indices of Co and Cs containing wasteform specimens were in the range of 17.2 ~ 18.7 and 6.7 ~ 15.3, respectively. It was found that recycled cement powder can be used for immobilization of liquid radioactive waste.