THE NUCLEAR OPTION

 Dick Pountain/ Idealog307/ 8th February 2020 14:49:23

Those horrific wild-fires in Australia may prove to be the tipping point that gets people to start taking the threat of climate change seriously. Perhaps IT isn’t, at the moment, the industry most responsible for CO₂ emissions, but that’s no reason for complacency. On the plus side IT can save fossil fuel usage, when people email or teleconference rather than travelling: on the minus side, the electrical power consumed by all the world’s social media data centres is very significant and growing (not to mention what’s scoffed up mining cryptocurrencies). IT, along with carbon-reducing measures like switching to electric vehicles, vastly increases the demand for electricity, and I’m not confident that all this demand can realistically be met by renewable solar, wind and tidal sources, which may have now become cheap enough but remain intermittent. 

That means that either storage, or some alternative back-up source, is needed to smooth out supply. A gigantic increase in the capacity of battery technologies could bridge that gap, but nothing on a big enough scale looks likely (for reasons I’ve discussed in a previous column). For that reason, and unpopular though it may be, I believe we must keep some nuclear power. It doesn’t mean I admire the current generation of fission reactors, which became unpopular for very good reasons: the huge cost of building them; the huge problem of disposing of their waste; and worst of all, because we’ve realised that human beings just aren’t diligent enough to be put in charge of machines that fail so unsafely. There are other nuclear technologies though that don’t share these drawbacks, but haven’t yet been sufficiently researched to get into production.

For about 50 years I’ve been hopeful for nuclear fusion (and like all fusion fans have been perennially disappointed). However things now really are looking up, thanks to two new lines of research: self-stable magnetic confinement and alpha emission. The first dispenses with those big metal doughnuts and their superconducting external magnets, and replaces them with smoke-rings - rapidly spinning plasma vortices that generate their own confining magnet field. The second, pioneered by Californian company TAE Technologies, seeks to fuse ordinary hydrogen with boron to generate alpha particles (helium nuclei), instead of fusing deuterium and tritium to produce neutrons. Since alpha particles, unlike neutrons, are electrically charged, they can directly induce current in an external conductor without leaving the apparatus. Neutrons must be absorbed into an external fluid to generate heat, which then drives a turbine, but in the process they render the fabric of the whole reactor radio-active, which alpha does not.

The most promising future fission technology is the thorium reactor, in which fission takes place in a molten fluoride salt. Such reactors can be far smaller than uranium ones, small enough to be air-cooled, they produce almost no waste, and they fail safe because fission fizzles out rather than runs wild if anything goes wrong. Distributed widely as local power stations, they could replace the current big central behemoths. That they haven’t caught on is partly due to industry inertia, but also because they currently still need a small amount of uranium 233 as a neutron source, which gets recycled like a catalyst. But now a team of Russian researchers are proposing a hybrid reactor design in which a deuterium-tritium fusion plasma, far too small to generate power itself, is employed instead of uranium to generate the neutrons to drive thorium fission.

A third technology I find encouraging isn’t a power source, but might just revolutionise power transmission. The new field of ‘twistronics’ began in 2018 when an MIT team lead by Pablo Jarillo-Herrero announced a device consisting of two layers of graphene stacked one upon the other, which becomes superconducting if those layers are very slightly twisted to create a moiré pattern between their regular grids of carbon atoms. When you rotate the top layer by exactly 1.1° from the one below, it seems that electrons travelling between the layers are slowed down sufficiently that they pair-up to form the superconducting ‘fluid’, and this happens at around 140°K, way warmer than liquid helium and around halfway to room temperature. Twisted graphene promises a new generation of tools for studying the basis of superconduction: you’ll be able to tweak a system’s properties more or less by turning a knob, rather than having to synthesise a whole new chemical. Such tools should help speed the search for the ultimate prize, a room-temperature superconductor. That’s what we need to pipe electricity generated by solar arrays erected in the world’s hot deserts into our population centres with almost no loss. Graphene itself is unlikely to be such a conductor, but it may be what helps to discover one.  

[ Dick Pountain ain’t scared of no nucular radiashun]