Evaluation of radium and caesium containment performance of palm oil fuel ash-supplemented cementitious backfill for borehole disposal: Kinetic investigations

Abstract

Radium and caesium have been identified among the major radionuclides found in disused sealed radioactive sources (DSRSs) and these DSRSs are potentially planned to be disposed in borehole disposal. In borehole disposal, cementitious backfill is commonly used as engineered barrier for containment of radionuclides. Present study evaluates the potential use of palm oil fuel ash (POFA)-supplemented cementitious backfill to contain radium and caesium radionuclides. In this respect, kinetic investigations were carried out to understand the nature of the sorption process onto both Ordinary Portland Cement (OPC) and POFA- supplemented cementitious material. The results showed that the sorption process for both cementitious backfill materials reached equilibrium within 48 hours and 24 hours for radium and caesium, respectively. For both backfill materials, results from kinetic analysis of radium and caesium indicated that the sorption process followed pseudo-second order model thus suggesting chemisorption reaction. Meanwhile, pore diffusion and film diffusion were identified as the main mechanisms controlling the sorption process. It was also found that the sorption capacity was higher for POFA-supplemented cementitious material (6 – 60 Bq g-1) compared to OPC (1 – 44 Bq g−1) indicating valuable containment of radium and caesium by POFA-supplemented cementitious backfill.