Glass has been used as a nuclear waste disposal material for many years. Since it takes a long time (up to 106 years) for fission products to decay to a safe level, the long-term reliability of the nuclear waste disposal glass is of special concern. Fission products can diffuse through the glass due to the action of the temperature gradient caused by radioactive decay and the small thermal conductivity of the glass. Diffusion may eventually lead to crystallization. Because the densities of the products of glass crystallization may differ from that of the parent glass, crystallization causes stresses to develop, which can lead to fracture and exposure of increased surface area to environmental attack. Much attention should therefore be paid to the crystallization phenomenon of nuclear waste disposal glass.