Crystallisation of a simulated borosilicate high-level waste glass produced on a full-scale vitrification line

► Insufficient reaction time in the glass melter results in as-cast samples with inhomogeneous microstructures. ► Crystal phases to potentially incorporate HLW radionuclides have been identified. ► Preferential partitioning of SiO2 into cristobalite and zektzerite has been identified. ► The potential effect of crystallisation on wasteform aqueous durability has been assessed. ► The lanthanoid (Nd,Gd,La,Ce) silicate formed in heat treated samples is a potential host phase for Am and Cm.