Digging Deep

Science’s role in radioactive waste disposal


Last summer, the Government set out its plans for the long term management of the UK’s most highly radioactive waste. This is a pretty big deal. The government policy will determine our strategy for managing radioactive waste, and some of the radioactivity associated with this waste will take a million years to decay to safe levels. So now that we’re in it for the long haul, what can synchrotron science from Diamond do to help the UK build a storage facility capable of outlasting humanity itself?
As a result of our work in nuclear energy, industry, medicine, research, and defence, the UK generates radioactive waste. We already get rid of large volumes of this waste safely. But a small yet highly radioactive proportion— enough to fill just over half of Wembley Stadium—will need a different disposal solution. And because we’re looking at a million years for some of this radioactivity to decay, any disposal facility needs to last.  
Currently, this highly radioactive waste is stored temporarily in specially engineered facilities built to last about one hundred years. During this time, the sites need to be monitored, and then, at the end of their lifespans, rebuilt. But the more we repackage and move radioactive waste from old facilities to new ones, the more we risk exposing ourselves and our environment to unsafe levels of radiation. So what the UK really needs is a permanent disposal solution.
Disposal is no easy feat, and many ideas have been proposed in the past, from dropping radioactive waste into the ocean to sending it into space. In 2006, after extensive consultation, the UK government committed to geological disposal: meaning we’re going to bury it in rock deep underground. 
The experimental set up on B18
The experimental set up on B18
And deep means deep—somewhere between 200 and 1000 metres under the surface. To put this in context, the London Underground at its deepest is only 65 metres down. Of course, we can’t just throw our radioactive waste into a very big hole and hope for the best:  to do this properly, we need to call on science and engineering.
The formal term for an engineered geological disposal site is a Geological Disposal Facility, or GDF.   These disposal facilities combine multiple, man-made protective barriers of cement and clay with the natural underground rock environment to stop radioactivity moving up towards the surface. Once built deep into rock, the UK GDF would be open for the deposit of radioactive waste for about one hundred years. After this time, the GDF would be sealed. Then, over tens of thousands of years and buried deep underground surrounded by layers of engineered cement, clay buffers, and rock, the waste can safely decay without dangerous radiation ever reaching the surface.   
But before the UK proceeds with its disposal facility, the government needs to understand the science and engineering involved. This means looking at the GDF design, materials, and environment as well as modelling how things could change over time. The choices we make now will affect what happens far into the future, so we need to get it right. And to help make sure we do, the UK government is supporting a significant amount of GDF-related scientific research.
Enter the special science done at Diamond. Here, scientists are working hard to understand the interaction of radionuclides with environmental materials on an atomic scale and to predict how this interaction could affect the engineering and environment of a GDF over hundreds of thousands of years. This research will help to ensure that the UK’s GDF is built using the most up-to-date, cutting-edge science available. 
Principal Beamline Scientist, Fred Mosselmans, on I18
Principal Beamline Scientist, Fred Mosselmans, on I18
Using X-ray light from Diamond, Sam Shaw, Kath Morris, Carolyn Pearce, and Richard Pattrick from the University of Manchester, and Claire Corkhill and her team from the University of Sheffield are looking at different but interrelated aspects of geological disposal. 
On one of Diamond’s spectroscopy beamlines, B18, Kath and Sam work to understand radioactive contamination of the environment both inside and surrounding the disposal facility. They are studying how radionuclides, including transuranic materials, which arise from nuclear processes, combine and interact at the atomic level with natural minerals and microbes in the earth. In order to protect the surrounding environment, we have to understand the impact that radioactivity in the waste could have as the disposal facility gradually evolves over tens of thousands of years.
And that brings us to the next challenge: how can you even engineer a facility capable of containing waste safely for this long? What structures and what materials should you use? Richard, Carolyn, and Claire all study atomic-level reactions and changes in the buffer materials used in geological disposal facilities. Richard and Carolyn’s work on I18 focuses on atomic level radiation damage to the clay that goes into the buffers. They measure structural changes in the clay as the individual atoms change over time. Over on I11, Diamond’s high resolution powder diffraction beamline, Claire is working with a different buffer material: cement. She studies how this material reacts with water, but her experiment is a bit unusual. Instead of looking at her sample over a period of seconds, hours or weeks, Claire is measuring reactions and interactions in the same sample of cement as it becomes hydrated over a period of two years. Examining changes over this extended period should make it easier to predict what might happen over a much longer time.
The science that these researchers are undertaking is innovative its own right. But Kath, Sam, Carolyn, Richard, and Claire also share the excitement of knowing that they are working within a much bigger network of researchers across the country.  Together, these scientists are helping the UK get its geological disposal facility off – or should we say, under – the ground.
A disposal solution with a seriously long-term guarantee: it’s an ambitious undertaking. The range of work taking place at Diamond demonstrates the huge part science has to play in helping the UK to put the pieces of this intricate puzzle together. There’s no doubt that radioactive waste disposal is a real challenge, but science is bringing us closer to finding a solution, once and for all.

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