Last edited Thu Feb 15, 2018, 02:10 PM - Edit history (1)
...in connection with the wonderful The Ronald E. Hatcher SCIENCE ON SATURDAY Lecture Series, and occasionally other lectures open to the public.
The Science on Saturday series covers a broad range of topics, but usually every year - I've been going for close to ten years now - one or two lectures are scientific marketing on the benefits and prospects of fusion.
As a fission advocate I've been somewhat skeptical but they have convinced me and I do believe that the money spent on researching fusion is money very well spent, not just as potential source of significant energy, which it may well be someday - but certainly not soon enough to address the immediate problem of climate change - but also because of the basic science implications.
The ITER project being built in France will not produce energy for the grid, but it will show, for the first time, a net energy gain over the energy invested, a critical step that's been a holy grail for more than half a century.
Even after the accomplishment of this important milestone there are huge hurdles to address. One is materials science. The neutrons released by fusion are extremely high energy, an order of magnitude higher than fission neutrons. I was told by one of the scientists there that they have demonstrated materials that maintain integrity to 100 dpa (displacements per atom), but I believe they're tungsten carbide based.
Tungsten is a critical element, one subject to depletion. This said, fusion reactors have a very high energy to mass ratio, the highest known, orders of magnitude higher than fission reactors, and it is possible to imagine that not much tungsten would in fact be required.
Neutrons cannot be steered like charged particles, and they do, with most elements in the periodic table result in induced radioactivity. (However they can also cause long lived radioactive isotopes to be transmuted into much shorter lived radioactive isotopes that rapidly decay into stable isotopes.) Since neutrons cannot be steered, they must be shielded, and shielded in such a way to recover their energy. This is a non-trivial problem.
Much of the energy released by fusion will be, in fact, contained in these neutrons and that has its own set of difficulties. Some will be in the form of helium ions, effectively alpha particles, also at very high energy, although some heavy atoms do produce alpha particles at roughly comparable energies.
This represents the biggest hurdle to fusion to my way of thinking, heat exchange, the conversion of dense amounts of energy into electricity or other forms of energy that can provide useful work. It is an extension of the materials science problem.
Heat exchange issues are the very issues that lead to the trivial, but disastrous in a purely marketing sense, failure at Fukushima.
Although a fusion reactor cannot practically melt down in the sense that a nuclear reactor of historical design can, components can be destroyed in such a way as to incur huge expense. It's not clear how easy it will be to cross that barrier or what the economic implications will be.
The joke about fusion is that it's been twenty years away from practicality for more than half a century. Again, I think this is a reasonable investment nonetheless, the research into seeing if or when it can become a practical source of energy. It has suffered, I think, from being over hyped. Fusion is certainly superior to solar research, since any nuclear system of any type will clearly and unambiguously superior to any diffuse and material intense system, which solar, and to a slightly less, but insufficiently less, wind systems are.
Nevertheless, this is not the cultural decision that has been made worldwide. The decision has been made to sink vast sums of money into solar and wind, more than two trillion dollars in the last ten years, and the results, written in the planetary atmosphere, are trivial and have had no meaningful effect. I am sure that if just ten percent of that money had been invested in fusion energy, with the balance invested in fission, the world would be a better and safer place.
Thanks for asking. I hope you find these comments useful.
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