9.3 – Material selection, the options and the challenges

The IFMIF experimental setup, neutrons being supplied by a particle accelerator

Indeed ITER is in fact two projects rolled into one. ITER in France will work on the reactor, while IFMIF in Japan will focus on the issue of materials research. One of the problems that results from the D-T fusion method is the high neutron flux generated. You will recall the diagram above, showing the D-T reaction. You will note, not only that neutron shooting out but the very high kinetic energy attached to it. The result is that any D-T reactor will have a neutron flux at least 100 times that of a similar sized LWR (at around 1×1018 n/m2-s) or about 14-25 times more than a Fast neutron reactor generates (4 – 7 x1018 n/m2-s) . The goal of IFMIF is to develop some new material capable of withstanding these high neutron fluxes, as well as the high radiant heat loads and yet still give a reasonable service life. The smart money is currently on either Tungsten or Molybdenum (both expensive, brittle and difficult to form) or in all likelihood an alloy of either (or both) and possibly Graphite (fire risk).

Of course the critics already have a name for this new material, Unobtainium! As was discussed in the materials section, the sort of material needed to construct a working Fusion reactor, at least one with a decent service life and that’s cheap and easy to put together, simply may not exist. We could, I suspect compromise, use a graphite blanket around the core to reduce neutron fluxes with the rest of the reactor built out of a mix of Tungsten alloys, and where possible, ceramics. However, such a reactor would have a number of draw backs. Some exposed parts that can’t be shielded (it is integral to the design that they be exposed to the core) and would need to be regularly replaced, eating into capacity factors and making for an expensive operation. Alternatively we could simply build our Fusion plants with a short operating life, say 20 years rather than the current 50 years standard at present for the nuclear industry. Unfortunately, this would obviously depreciate the economics of Fusion power. And as it is, building a complex machine out of the materials I’ve suggested isn’t going to be cheap.

Worse still, all of that material, particularly the graphite, will now be mildly radioactive and need to be put into ILW storage, with some parts likely requiring HLW storage. So such a plan would mean our Fusion power program producing some quantities of radioactive nuclear wastes, a fraction of what we currently generate yes, but certainly not zero.

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