Volume of nuclear waste could be reduced by 90 per cent says new research

Engineers from the University of Sheffield have developed a way to significantly reduce the volume of some higher activity wastes, which will reduce the cost of interim storage and final disposal.

The researchers, from the University’s Faculty of Engineering, have shown that mixing plutonium-contaminated waste with blast furnace slag and turning it into glass reduces its volume by 85-95 per cent. It also effectively locks in the radioactive plutonium, creating a stable end product.

The approach could also be applicable to treating large volume mixed wastes generated during the eventual clean-up of the damaged Fukushima plant.

"The overall volume of plutonium contaminated wastes from operations and decommissioning in the UK could be upwards of 31,000 m3, enough to fill the clock tower of Big Ben seven times over," says lead researcher, Professor Neil Hyatt.

"Our process would reduce this waste volume to fit neatly within the confines of just one Big Ben tower."

The current treatment method for non-compactable plutonium contaminated wastes involves cement encapsulation, a process which typically increases the overall volume. Professor Hyatt says: "If we can reduce the volume of waste that eventually needs to be stored and buried underground, we can reduce the costs considerably. At the same time, our process can stabilise the plutonium in a more corrosion resistant material, so this should improve the safety case and public acceptability of geological disposal."

Although the ultimate aim for higher activity wastes is geological disposal, no disposal sites have yet been agreed in the UK.

Plutonium contaminated waste is a special type of higher activity waste, associated with plutonium production, and includes ﬁlters, used personal protective equipment (PPE) and decommissioning waste such as metals and masonry.

Using cerium as a substitute for plutonium, the Sheffield team mixed representative plutonium contaminated wastes with blast furnace slag, a commonly available by-product from steel production, and heated them to turn the material into glass, a process known as vitrification.

A key element of the research, funded by Sellafield Ltd and the Engineering and Physical Sciences Research Council (EPSRC), was to show that a single process and additive could be used to treat the expected variation of wastes produced, to ensure the technique would be cost effective.

"Cerium is known to behave in similar ways to plutonium so provides a good, but safe, way to develop techniques like this," explains Professor Hyatt. "Our method produces a robust and stable final product, because the thermal treatment destroys all plastics and organic material. This is an advantage because it is difficult to predict with certainty how the degradation of plastic and organic materials affects the movement of plutonium underground."

Professor Hyatt is now working on optimising the vitrification process to support full scale demonstration and plans future investigation of small scale plutonium experiments.

Additional information The estimated minimum UK PCM inventory is 31,140 m3, http://www.hse.gov.uk/aboutus/meetings/iacs/nusac/131005/p15.pdf ‘Thermal treatment of simulant plutonium contaminated materials from the Sellafield site by vitrification in a blast-furnace slag’, N.C. Hyatt et al, is published in the January 2014 issue of the Journal of Nuclear Materials : http://www.sciencedirect.com/science/article/pii/S0022311513010313 Engineering in Sheffield The Faculty of Engineering at the University of Sheffield - the 2011 Times Higher Education’s University of the Year - is one of the biggest and best engineering faculties in the UK. Its seven departments include over 4,000 of the brightest students and 900 staff, and have research-related income worth more than £50M per annum from government, industry and charity sources. Its research income recently overtook the University of Cambridge, confirming its status as one of the best institutions in the world to study engineering. The 2008 Research Assessment Exercise (RAE) confirmed that two thirds of the research carried out was either Internationally Excellent or Internationally Leading. The Faculty’s expertise is extensive – its academic departments and two interdisciplinary programme areas cover all the engineering disciplines. They are leaders in their fields and outstanding contributors to the development of new knowledge, with world-leading academics linking their research to the teaching of the engineers of tomorrow. The Faculty has a long tradition of working with industry including Rolls-Royce, Network Rail and Siemens. Its industrial successes are exemplified by the award-winning Advanced Manufacturing Research Centre (AMRC) and the new £25 million Nuclear Advanced Manufacturing Research Centre (NAMRC). The Faculty of Engineering is committed to ensuring students studying at Sheffield continue to benefit from world-class labs and teaching space through the provision of the University's new Engineering Graduate School. This brand new building, which will become the centre of the faculty´s postgraduate research and postgraduate teaching activities, will form the first stage in a 15 year plan to improve and extend the existing estate in a bid to provide students with the best possible facilities while improving their student experience. Engineering in Sheffield