Whatever the question, fusion is not the answer…

At least at first glance this is a different technology without many of the drawbacks of the the fission route and is one that does not rely on uranium. Bizarrely though there is still a uranium dependency. The physics of the process is complicated and will only be described very briefly. For a full explanation seek online resources or see (1). If you take two isotopic forms of hydrogen (deuterium and tritium) and heat them to 100 million degrees centigrade they release an enormous amount of energy. Currently in all fusion experiments a small pellet of both of these hydrogen forms has either a very powerful laser fired at it (USA) or is ionised then heated (Europe). Either way no net return on the energy in has so far been obtained. Deuterium occurs naturally at a low concentration in water and is non radioactive, tritium is radioactive with a half life of 12.3 years (2). Its short half life means it does not occur in nature and has to be made. This is carried out in fission reactors from uranium (hence the uranium dependency) and its probably the most expensive isotopic element on earth.

There are a number of unsolved problems with fusion. Many of these are highly technical physics problems and will only be very briefly alluded to. The first problem is the high temperatures generated. Obviously the heat is to be used to heat water to steam and drive turbines, cooling the core, however no known material will withstand these temperatures. A second major problem is that of the intense neutron radiation generated as a side product of the process. Neutron radiation causes huge problems in conventional fission reactors since again there is no known material that is resistant to it. The neutron radiation also “transmutates” elements in the reactor making them into radioactive isotopes. Proponents of fusion state that the elements formed are ones with a short half lives and are small in number. However, this ignores the fact that if fusion works the number of fusion reactors built worldwide (eventually? see below) would be huge, leaving a significant nuclear waste problem. It should also be noted that tritium is radioactive with identical chemical properties to hydrogen therefore being explosive, leaking easily and could be also used to make a hydrogen bomb.

Perhaps the biggest problems are not those of material science but of the tritium breeding. Making the initial tritium in conventional reactors is both very expensive and not sustainable in the long term for reasons outlined earlier (uranium stock depletion). In addition existing stocks of tritium are decaying meaning if uranium stocks are depleted there may be insufficient tritium to start the first fusion reactor up in the first place. In theory the fusion process breeds tritium in the reactor using another element lithium coating the vessel’s walls. It is then somehow recovered and some directed both to the centre of the reactor and for use in other reactors. This recovery of the tritium is yet another unsolved technical problem. In practice tritium has to be bred at quite a rate per fusion reactor in order to account for decay/losses and to seed new reactors (3). There are significant scientific questions over whether this is possible (4).

To achieve all the above, the fusion process has to run continuously (not just for a few seconds) at 100 million degrees, this after decades of research and vast amounts of taxpayers cash it has failed to do. Once again claims it seems are being made that in practise cannot be fulfilled. Already costs are rising on the ITER experimental reactor (5). Even if the many technical problems can be solved not even fusion’s most ardent adherents could legitimately claim it as the answer to peak oil. The generally accepted figure before a 1GW fusion reactor is up and running is 30 years (many would say this figure is optimistic). Even then tritium would have to be bred for additional reactors (if this possible). An optimistic but scientifically plausible doubling time is five years (6), meaning after another thirty years (sixty years time) there would be 32 1GW reactors up and running, hardly the solution to an energy crisis. The ITER experimental reactor in France is not scheduled to start its first experiment until 2026!

1) “Fusion illusions by M. Dittmar” in “The Final Energy Crisis” edited by S. Newman. This is a nuclear physicist’s (works at EPH and CERN) criticism of Thermonuclear research.

2) This means if you have 1kg initially after 12.3 years you will have half a kilo as the element decays to a completely different element.

3) http://www.technologyreview.com/blog/arxiv/24414/

4) Interested readers are directed to this site http://www.fusion.ucla.edu/abdou/ and in particular the paper “Physics and technology conditions for attaining tritium self-sufficiency for the DT fuel cycle” Sawan and Abdou, Fusion Engineering & Design, 81:(8–14), 1131–1144 (2006).

5) http://news.bbc.co.uk/1/hi/sci/tech/6158040.stm and http://news.bbc.co.uk/1/hi/sci/tech/8103557.stm

6) Ibid. 3)

This was a first draft from our book.  Due to space reasons we had to shorten this section in the final printed version.

Neil

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