Supercritical CO2 carbonation of cemented radioactive waste-forms: Influence on leachability and structure

The traditional practice of cementing transuranic (TRU) low-level waste poses several technical problems, the most serious of which is that many of the legacy TRU waste-forms do not meet Department of Transportation (DOT) prohibitions on decay heat and/or free liquid. To address these problems, a treatment of cemented waste-forms with supercritical CO2 (SCCO2) has been proposed. This treatment method alters the bulk chemical and structural properties of cast cement by accelerating natural carbonation reactions, while at the same time reducing both free and bound water. Reducing the amount of the hydrogenous content of a cemented waste-form to below 30 wt% simultaneously fulfills the DOT free-liquid requirement and increases the maximum allowable decay heat of the TRU-PACT-II drums by a factor of 4. The effect of SCCO2 treatment applying different CO2 pressure and temperature conditions (8.4 MPa < p < 28 MPa, 35 C < T < 62 C) on the leachability, phase constitution, and microstructure of surrogate-doped Portland cement type I/II samples was investigated