This project will focus on determining how the degree of crystallinity would affect cracking of vitrified High Level Waste (HLW). Radiation is known to affect glass in a variety of ways, for example causing a volume change. This volume change can induce strain which can lead to cracking. Historic work on active glass showed that crystalline inclusions could halt crack propagation. The new glass formulation being used to vitrify HLW is known to form Ca-Mo crystals although there is little information on how radiation affects the growth of these crystals.