Effects of leachant type and initial input concentration on the leaching rate of Cs, Sr, and Co from the cement-solidified waste

Abstract

In Korea, cementation is primarily used for the treatment of low- and intermediate-level liquid radioactive waste generated during nuclear power plant operations, including spent ion-exchange resins, concentrated borate solutions, evaporator condensates, and decontamination wastewater. These waste streams are typically solidified using Portland type I cement to ensure chemical stability and structural integrity. The leaching test for cement-based solidified radioactive waste follows the ANS 16.1 guidelines. According to the test protocol, deionized water is used as the leachant although the actual disposal conditions involve high alkali levels. Most research on the leaching test of radioactive waste typically involves non-radioactive nuclides that require high concentrations for detection. However, the sorption and desorption of nuclides are influenced by the initial loading and type of leachant used. To investigate the impact of these test conditions, Cs, Sr, and Co were selected as reference nuclides. Therefore, this study investigated the variations in the leachability index based on the leachant type and initial loading. Furthermore, the presence of Cs, Sr, and Co was observed in Portland type I cement and cement-dissolved solution, which can influence the leaching rate of these nuclides. The findings of this research are expected to enhance the safety assessment of silo-type repositories employing Portland type I cement as a solidification material. Furthermore, this study will contribute to establishing conservative leaching limits by incorporating the leaching characteristics of cement-based solidified waste into safety assessments including release of radionuclides.