Vitrification could improve safety of ILW treatment

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Studies have found that vitrifying intermediate-level nuclear waste (ILW) is a viable alternative to encapsulating waste in specially formulated cement.

ILW makes up more than three quarters of the volume of material destined for geological disposal in the UK, according to a report entitled Radioactive Waste in the UK: The 2010 Estimate of Radioactive Waste for Geological Disposal.

The UK’s preferred method is to encapsulate ILW using a method in which the waste is mixed with cement and sealed in steel drums in preparation for disposal deep underground.

Two studies, published in the latest issues of the Journal of Nuclear Materials and European Journal of Glass Science and Technology A show that vitrifying this kind of waste could be a better method for its long-term storage, transport and eventual disposal.

High-level waste (HLW) is already processed using this technology, which reduces the reactivity and the volume of the waste produced. Until now, this method has not been considered suitable for ILW because the technology was not developed to handle large quantities of waste composed from a variety of different materials.

The research programme, funded by the Nuclear Decommissioning Authority (NDA) and led by Prof Neil Hyatt at Sheffield University’s Department of Materials Science and Engineering, tested simulated radioactive waste materials — those with the same chemical and physical make-up but with non-radioactive isotopes — to produce glass and assess its suitability for storing lower grades of nuclear waste.

The process used to produce the glass waste storage packages sees the waste dried, mixed with glass-forming materials such as iron oxide or sodium carbonate, heated to make glass and finally poured into a container.

According to a statement, a key discovery made by the Sheffield team was that the glasses produced for ILW proved to be very resistant to damage by energetic gamma rays, produced from the decay of radioactive materials.

‘We found that gamma irradiation produced no change in the physical properties of these glasses and no evidence that the residual radiation caused defects,’ said 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.

‘For large volumes of waste that need to be stored securely, then transported to and eventually disposed of, vitrification could offer improved safety and cost effectiveness’ he added.

Dr Darrell Morris, NDA research manager, said: ‘We welcome this fundamental research demonstrating a possible alternative means of treating ILW. We look forward to seeing further progress on the applicability of this technology to the UK’s waste inventory.’