Characteristics of Cs pollucite synthesized at various Cs loadings for immobilization of radioactive Cs

Radioactive Cs is an important fission product known for the generation of a large amount of heat. Several ceramic matrices have been proposed to effectively immobilize radioactive Cs. Among them, pollucite stands out owing to its exceptional thermal and structural durability, low solubility in water, and high Cs retention. This investigation focused on the preparation and assessment of an appropriate precursor for a waste form tailored to the disposal of Cs-loaded silica–alumina (SA) filters. We synthesized simulated Cs-loaded SA filters and transformed them via calcination into a Cs pollucite (CsAlSi2O6) phase. To investigate the influence of Cs loading, five samples with different ratios of the Cs precursor and matrix were synthesized and subsequently subjected to characterization and chemical durability assessment. Depending on the Cs content, the calcination process led to a phase transformation, resulting in the formation of CsAlSiO4 and/or Cs pollucite (CsAlSi2O6). Following calcination, the degree of crystallinity of the samples increased, and in certain instances, their surfaces were covered with agglomerated particles. Building upon prior research, chemical equations elucidating the phase transformation of both the matrix material and Cs pollucite (CsAlSi2O6) were formulated. The chemical durability of the samples was evaluated via the product consistency test-A method. The lowest Cs leaching rate was 3.86 × 10−4 g/m2·day for the sample comprising a Cs2O/matrix ratio of 0.2 and calcined at 1200°C. The high leaching rates observed in certain P-1200 samples can be attributed to the presence of CsAlSiO4. The leaching behavior of Al resembled that of Cs. The leaching rate of Si remained consistent across the samples heat treated at 1200°C (P-1200), and it was lower than those of samples calcined at 1000°C (P-1000). P-1200 is expected to be a suitable precursor of the waste form tailored to Cs immobilization. [Display omitted]