Intermediate level nuclear waste could be stored safely and efficiently using technology usually reserved for high level waste, according to research from the University of Sheffield. Currently, the UK encapsulates “ILW”, which accounts for more than 75 % of nuclear waste, in a cement-like material, seals the composite in steel drums and stores it pending burial deep underground.
Sheffield's Neil Hyatt and colleagues in Sheffield and at the J. Stefan Institute, in Ljubljana, Slovenia and the University of Manchester's Dalton Cumbrian Facility in Moor Row, have now published two papers outlining how ILW might be turned into a durable glass material. Studies in The Journal of Nuclear Materials and European Journal of Glass Science and Technology A show that turning this kind of waste into glass, a process called vitrification, produces a material for safer long-term storage, transport and disposal [Hyatt, N.C. et al., Eur J Glass Sci Technol A(2012)53(3) 83-100; J Nucl Mater (2012) doi: 10.1016/j.jnucmat.2012.04.007]. Vitrification is already used to reduce the reactivity and volume of HLW. But there are greater volumes of ILW, which until now were not thought amenable to this process.
The researchers have tested mock ILW materials having a similar physical and chemical makeup to radioactive waste but containing none of the hazardous radio-isotopes. The vitrification process itself is relatively straightforward involving drying of the material, mixing with glass-forming compounds including iron oxide or sodium carbonate, and then heating to produce a glass that can be poured into a container. For some nuclear waste, including contaminated sand, the waste itself is its own glass-forming material.
Critically for the development of vitrification of ILW, the researchers have demonstrated that the products are highly resistant to damage from energetic gamma rays that would be produced in situ as the radioactive materials decay.
“We found that gamma irradiation produced no change in the physical properties of these glasses, and no evidence that the residual radiation caused defects,” explains Professor Hyatt. “We think this is due to the presence of iron in the glass, which helps heal any defects so they cannot damage the material.” Hyatt suggests that vitrification could offer improved safety and cost effectiveness over earlier approaches to handling ILW from decommissioned nuclear sites.