Monday, September 25, 2006

Nuclear Fusion Remains a Distant Expensive Dream.

The International Thermonuclear Experimental Reactor (ITER) is due to be constructed in Cadarache, France, rather than in Japan, the other contender location. The project is not cheap since it is expected to run-up a bill of 10 billion Euros ($12.1 billion) over its 30 year lifetime, and even then, if all goes well, there will be no electricity produced from it. It is an experimental reactor (as its name states) and is intended to iron-out the practicalities of nuclear fusion, before any commercial exploitation is sought for the technology. Put another way, ITER is expected to take 10 years to build, run for another 20 years, and if all goes well, a more advanced (still research) machine will then be constructed. After another 30 years, if all still runs smoothly, the first commercial fusion-based electricity "might" come on stream. (60 years in all, and even then it is still "might").
Among the partners in the project are the E.U., France, Japan, South Korea, China, India, Russia and the U.S. In the case of the latter contributor, there has been some internal friction over the funding (1/11 th of the total, or just over £1 billion), because there is in effect competition for the funds with existing U.S. fusion science. This is "big science" in anyone's book, and ITER is the most expensive project after the International Space Station. I have explained in outline the essential principles underlying "nuclear fusion" in an early posting ("Feasible Fusion Power - I doubt it", which I wrote last December). In effect, two atomic nuclei (cores of atoms - in German the word for nucleus is "Kern", as in kernel) both carrying a positive charge must be made to collide with sufficient force to overcome the electrostatic repulsion between the charges, and get them close enough together so they "fuse", releasing a lot of energy in the process. Most of that energy is taken-up by neutrons, which are accelerated ("super-fast"), and then the trick will be to extract the neutrons into a heat exchanger made of some suitable material (no-one knows what, as yet), so and to ultimately generate steam to drive electric-turbines, rather as fission-based nuclear power stations do (and indeed, coal or gas-fired power plants).
The physics of handling such highly energetic neutrons remains another challenge to be met, and although nuclear fusion is hailed as the ultimate "green" power source (just like the Sun!), it isn't since the neutrons will activate the nuclei of the various materials used to construct the reactor itself, which will hence require disposal as radioactive waste. Agreed, these materials will be so intensely radioactive that they will not require disposal over hundreds of thousands of years, but handling such "hot" stuff will need robots not people, and any routine maintenance of the system will also need to be done by robots (another challenge, probably, since developments in robotics may be required?).
Extremely high temperatures are required to achieve fusion, the lowest being around 45 million degrees C, which is enough to bring a deuterium and a tritium nucleus close enough to fuse. To make two deuterium nuclei fuse requires around ten times that at 400 million degrees C. Under such conditions, any matter present exists in the form of a plasma, which is confined in a magnetic bottle arrangement, where the charged bits of atoms and electrons are held in the lines of force of a suitably engineered magnetic field. However, there are crucial difficulties to be overcome in achieving such "confinement", and still, no self-sustaining fusion reaction has so far been demonstrated - i.e. where the plasma can be confined for long enough to reach the "break-even" point, where as much energy is generated by the plasma as is used to produce it.
In view of so many uncertainties, the fact that even according to the best-outcome scenario there will not be any likelihood of a suitable commercial fusion device for 60 years, and the fantastic costs (probably another $100 billion to bring electricity on stream from it - even if it does work, of which there is no guarantee), it is more worthwhile to turn the huge resources involved to more immediate, and better demonstrated, technologies.
Sure, we must break our oil-dependency, but nuclear fusion is not going to do that for us. There must be more emphasis placed upon deriving a realistic plan for renewables (and to what extent they are indeed feasible: see my previous three postings on the subject of "bio-fuels"), and more immediate nuclear technologies (e.g. liquid fluoride thorium reactors, and other uranium-based nuclear programmes). I have commented before that if we were to use the "known" reserves of uranium for nuclear fission, it would probably be used up in about 50 years. However, there are alternative "fast-breeder" programmes possible, which could in principle eke that out for hundreds of years, just so long as we are happy with dealing with the attendant plutonium fuel this inevitably incurs.
Ultimately, small communities ("pods" I have called them), with their energy-needs met by electricity, and which require 90% less transportation fuel, may be our means for sustainable living. At the same time, all means to achieve a more efficient use of whatever energy we do end up with ultimately, should be explored. However, all means for the production of that electricity must be investigated thoroughly too, and there are so many technologies ahead of "fusion" to do that, certainly given the budget set aside for the latter. We are going to run out of fossil-fuel well ahead of any putative nuclear-fusion powered nirvana, and so must act in swift accordance with that inescapable reality.

1 comment:

Anonymous said...

Agree with your logic especially looking at using Thorium refer

So given that fusion reactors are probably for the next century how relevant would Helium 3 be refer