7th November 2013
Volume of nuclear waste could be reduced by 90 per cent
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 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," says lead researcher, Prof. Neil Hyatt. "Our process would reduce this waste volume to fit neatly within the confines of just one Big Ben tower."
The current method for treatment of non-compactable plutonium contaminated wastes involves cement encapsulation – 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 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 United Kingdom. Plutonium contaminated waste is a special type of higher activity waste, associated with 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 of 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. His study is published in the January 2014 edition of Journal of Nuclear Materials.