Neutron multiplying materials may help us create all the fuel we need to ensure a fusion powered future.

If a strange man were to approach you on the street and offer to sell a jar of mystic metals which would magically allow your car to create all the fuel you could possibly need – you would not be faulted for laughing. However, if a fusion scientist approaches you with a similar offer, you should hear them out. They just might be telling the truth.

TRITIUM – AN EXPENSIVE, PRODUCIBLE FUEL

Unlike a car, which constantly requires new fuel, a fusion reactor is capable of producing some of the key components of its own fuel. In fact, most reactor designs are intended to create at least as much fuel as they consume. This is a rather wise design choice, since tritium, one of the key ingredients in most nuclear fusion fuels, costs about €25k per gram (roughly $30k for my American fellows).

Making tritium can be tricky in practice, but it is straightforward to explain. The standard fusion reaction consumes one bit of tritium and releases one neutron.
We can use the neutron to make one more piece of tritium. At the end of the day, we have the same amount of tritium, some extra energy, and a little less lithium, since this is used to make the new tritium. Unfortunately, we have not yet perfected this task. Sometimes, we lose a piece of tritium (it’s a slippery one), or our neutrons hit the wrong bit of wall and are wasted. Either way, we slowly deplete our tritium supply.

Rodrigo Atunes and Paul Barron have written excellent articles in this journal discussing the details of tritium production. Both are very much worth your time.

A JAR OF MAGICAL ELEMENTS COMES IN HANDY

Particularly if that jar is full of “neutron multipliers” – substances that, when hit with one neutron, release two neutrons. If we are able to use substances like these, such as the commonly available lead, the rather exotic beryllium or the colourful bismuth, we make it much easier to create all the tritium we need. With neutron multipliers, we trade in a very high-energy neutron for two slightly less energetic neutrons. If we manage to, in turn, combine both of these with lithium – we could actually end up with more tritium than when we started. In fact, present designs suggest that we could breed roughly 20 percent more tritium than we consume! For reference on the TBR stat which discusses analysis of a breeder blanket module that utilizes beryllium as the neutron multiplier.

THE ROAD AHEAD

There are many challenges to overcome when using neutron multipliers (some are quick to melt, some are toxic, etc.), but there is also a tremendous opportunity, namely cheap, clean, and nearly limitless energy. We face a very curious future – where these beautiful and sometimes hazardous metals might help us harness the same reactions that power the stars above.

authorbox_David-TompkinsI am a marketer at Hasbro, Inc. with undergraduate degrees in Marketing and Mechanical Engineering from the University of Pennsylvania. I believe that if you want to make the world a better place, you should build something that is either for kids or for the future. The work being done by EUROfusion will make the world a better place, and I’m very thankful for the opportunity to write this piece.

David Tompkins (25) from the U.S.A. is currently based at: Providence, Rhode Island. (Picture: private)