Preliminary study on calcium aluminosilicate glass as a potential host matrix for radioactive 90Sr—An approach based on natural analogue study

Abstract

Given the environmental-, safety- and security risks associated with sealed radioactive sources it is important to identify suitable host matrices for 90Sr that is used for various peaceful applications. As SrO promotes phase separation within borosilicate melt, aluminosilicate bulk compositions belonging to anorthite–wollastonite–gehlenite stability field are studied in this work. Tests for their homogeneity, microstructural characteristics and resistance to phase separation narrowed the choice down to the composition CAS11 (CaO = 35 wt%, Al 2O 3 = 20 wt%, SiO 2 = 45 wt%). We find that up to 30 wt% SrO can be loaded in this glass without phase separation (into Ca, Sr-rich and Sr-poor, Si-rich domains). Leaching behaviour of the glasses differs depending on the content and distribution of Sr. In general, the elemental leach rates determined from conventional PCT experimental procedure yield values better than 10 −7 g cm −2 day −1 for both CAS11 base glass as well as SrO doped glass. It was noted that leach rates calculated on the basis of Ca 2+ and Sr 2+ were of the same order and bit higher compared to those calculated on the basis of Si 4+ and Al 3+. During accelerated leaching tests, zeolite and zeolite + epidote were found to have developed on CAS11 base glass and SrO doped glasses respectively. The Sr bulk diffusion coefficients is found to vary from ∼10 −15 to 10 −13 cm 2/s at temperature intervals as high as 725–850 °C. Based on the experimental observations, it is suggested that CAS11 glass can be used as host matrix of 90Sr for various applications of radioactive Sr-pencils.