Thermal vitrification could reduce waste volumes by 90%

NDA says thermal treatment of Plutonium Contaminated Material (PCM) at Sellafield could save US$1.3 billion.

UK-based Costain has been awarded a contract by Sellafield to demonstrate its plasma vitrification technology.

The six-month trial is to demonstrate thermal treatment of Plutonium Contaminated Material (PCM) drums. Costain and its technology partner Tetronics will deploy the technology capabilities on simulated materials in a bespoke test environment, with the longer-term aim of minimizing the costs and risks associated with reducing and disposing of nuclear waste.

Costain says benefits of the technology include volume reduction of up to 90%, final stable product, high throughput for faster decommissioning, and the ability to handle a variety of wet waste types. These benefits can lead to significant cost savings.

The UK’s Nuclear Decommissioning Authority (NDA) says significant savings could potentially arise from technologies that are able to immobilize diverse kinds of radioactive waste, especially those that exist in large quantities. Such technologies include vitrification and other kinds of thermal treatment. NDA empasises that various research projects are underway but yet to conclude successfully.

A case study previously published by NDA says economic modelling shows that lifetime savings across just a single Sellafield waste, PCM, could reach more than 1 billion pounds (US$1.3 billion). NDA's cost estimates are based on reduced waste volumes, meaning fewer packages and stores would be required. Additional savings could result from stabilizing waste and destroying chemically reactive species.

“Costain has been working with Tetronics, a specialist in plasma furnaces, to develop plasma vitrification as a technology to treat nuclear waste,” Costain Project Director Leigh Wakefield told Nuclear Energy Insider.

“Plasma vitrification combines the versatility of a plasma furnace and the radionuclide retention characteristics of vitrification to volume reduce low and intermediate level nuclear waste, producing a stable product for long-term storage.

“This is a cost-effective alternative to the more established methods of supercompaction and/or grouting, which often result in volume increases and a product which has limited long-term stability.”

The conventional treatment for most low to medium level radioactive waste is cement encapsulation. This is established internationally but cement grouting and packaging significantly increase the volumes needing storage, pending development of a disposal facility.

Proven Plasma

Plasma furnaces have been in existence for more than 50 years, and primarily used for treatment of hazardous materials, melting of metals and recovery of materials from waste streams.

Vitrification is a recognized method of encapsulating (mostly high level) nuclear waste to form a stable product for long-term storage and disposal and is widely used for other hazardous but non-nuclear waste streams – such as incinerator ashes, asbestos-containing materials, contaminated soils and wastes from the mining and metallurgical industries.

Sellafield Ltd. is assessing the suitability of thermal treatment processes to treat a range of higher activity wastes currently under storage on the Sellafield site.

“This particular contract is to demonstrate the potential benefits offered by thermal treatment for the conditioning of PCM – a challenging and diverse waste stream currently stored in 200-litre steel drums,” said Wakefield.

“Over the next six months, we aim to show that plasma vitrification can effectively process a range of PCM material.”

The Vitrification Process

Source: Tetronics

The most immediate application is treatment of existing and arising PCM drums. The lifetime PCM waste arisings requiring to be processed are estimated to be between 160,000 to 243,600 equivalent drums.

Costain claims its solution can provide waste volume reduction of up to 90%, depending on the nature of the material being treated.

“The 90% volume reduction is achieved for wastes with high levels of volatile and/or organic material that can be decomposed and treated in the offgas and where low levels of glass are needed to retain the residual radionuclides,” said Wakefield.

“Innovations in thermal treatment will be key to helping the industry deliver against the Nuclear Sector Deal target of 20% reduction in UK decommissioning costs by 2030.”

Scott Birch