The news that the UK nuclear reprocessing plant at Sellafield has ‘lost’ 29.6 kg of plutonium has been accompanied by much emphasis that this doesn’t mean that the stuff has physically gone missing. It’s simply an accounting shortfall, we are reassured, and a leader in the Times on the subject is notable for being probably the most scientifically literate editorial I’ve seen in a major newspaper for some time. Nonetheless, there is a real issue here, though it’s not related to fears of nuclear terrorism. The British Nuclear Group spokesperson is reported as saying “There is no suggestion that any material has left the site. When you have got a complicated chemical procedure, quite often material remains in the plant.” In other words, in all the complex and messy operations that are involved in nuclear reprocessing, some of the plutonium is not recovered, and remains in dilute solution in waste solvent. And in that form it’s potentially another small addition to the vast tanks of radioactive soup that form such a noxious legacy of the cold war nuclear programs in the UK, USA and the former Soviet Union.
Can nanotechnology help? The idea of a fleet of nanoscale submarines making their way through the sludge pools, picking out the radioactive isotopes and concentrating them into small volumes of high level waste which could then be safely managed, is an attractive one. Even more attractive is the idea that you could pay for the whole operation by recovering the highly valuable precious metals whose presence in nuclear waste is so tantalising. Is this notion ridiculously far-fetched? I’m not so sure that it is.
A very interesting technology that gives us a flavour of what is possible has been developed at Pacific Northwest National Laboratory. Nanoporous materials, with a very high specific surface area, are made using self-assembled surfactant nanostructures as templates. This huge internal surface area is then coated with a layer of molecules a single molecule thick; functional groups on the end of each of these molecules are designed to selectively bind a heavy metal ion. Such SAMMS – self-assembled monolayers on mesoporous supports – have been designed to selectively bind toxic heavy metals, like lead and mercury, precious metals like gold and platinum, and radioactive actinides like neptunium and plutonium, and they seem to work very effectively. Applications in areas like environmental clean-up and mining are obvious, in addition to applications to nuclear processing and clean-up.