Immobilization of a simulated high-level waste in an yttrium aluminosilicate glass. Self-heating assessment

Abstract

In this article we experimentally explore the immobilization of a simulated high-level waste (s-HLW) in an yttrium aluminosilicate (YAS) glass by sintering. A suspension containing more than 20 different atomic species was prepared, simulating a HLW coming from a pressurized heavy-water reactor (PHWR). The chemical and thermal process carried out in this work produces a waste form with 10 wt% waste loading. Sintering was done in a heating microscope from room temperature up to 1250 °C. During sintering, evolved gases were characterized by mass spectrometry. The final product exhibits a porous vitroceramic structure with about 30% crystalline fraction. Crystalline phases with high density values (4.12 g/cm3 for Y2Si2O7, 3.16 g/cm3 for Al2Si2O7) were identified through XRD. The uniformity of the incorporated s-HLW and it distribution into the glass was characterized through SEM/EDS mappings. The aqueous corrosion resistance of the obtained waste form is better than other values found in the literature for borosilicate glasses used in the immobilization of nuclear wastes. We also present the results from numerical calculations, which show the thermal evolution of the waste form due to the thermal energy provided by the beta decays of 137Cs and 90Sr. Bearing in mind the physicochemical behavior of the matrix during the whole process, YAS glass can be considered as a potential host for HLW immobilization.