May 25, 2006

The future is coming

Writing about web page http://news.bbc.co.uk/1/hi/sci/tech/5012638.stm

Following an announcement nearly a year ago that a site in France has been chosen for ITER (International Thermonuclear Experimental Reactor), the news came yesterday lunchtime that the go–ahead has been given for work to start. This represents a long term security for clean energy supply, and is the successor to the JET fusion reactor in Culham, Oxford. It is expected for work to begin in 2007 and for construction to take 8 years. If all goes to plan we should see a full scale demonstration reactor being set up by 2040, with commercial availability around 2050. About time I say. Sequestration of clean coal won't keep us going forever, and gas is fast running out. Other nuclear fission alternatives, such as fast breeder reactors or thorium reactors, aren't yet here either and would I suspect prove unpopular with the public, just as conventional fission is currently. I even doubt the inherently fail–safe pebble bed systems being developed and built in South Africa will prove acceptable to the NIMBY brigade.

For those who are unaware with the background, Fusion is a nuclear process involving the joining of small atoms as opposed to current nuclear technology based on fission, which splits large atoms into smaller ones. For anyone who wants the physics, it releases energy because atomic stability (measured in binding energy per nucleon) increases for small elements up to Iron, which is the most stable element in nuclear terms. Beyond this, binding energy per nucleon decreases (due to electrostatic repulsion from protons in the nucleus becoming more significant than the powerful but short–ranged strong nuclear force). Reactors on earth use two hydrogen isotopes (usually deuterium and tritium) to make a helium nucleus and a free neutron, which most of the energy goes to. The high speed neutron is then absorbed by a blanket around the reactor, and heats up. This can then be converted to steam and power extracted from turbines. Radioactive products from the reactor are only the helium atoms, which have a radioactive half–life of 10 minutes. In order to overcome the strong electrostatic repulsion of two protons, immense energy is required, and so temeratures in excess of 100 million degrees centigrade have to be reached, with up to 300 million degrees reached at JET. The process takes place in a vacuum, and obviously at these temperatures the material cannot come into contact with any non–reaction material so is magnetically confined. In any case, contact between the reaction material and the reactor walls (or any impurities in the vacuum) would result in massive temperature loss and bolts shooting through the reactor pressure vessel. Because the products have such a short half–life, and because any failure of the vacuum or magnetic confinement results in immediate massive temperature loss and therefore reaction ceasing, the process is inherently safe and there is no possibility of the reaction becoming unstoppable.

With regards to fuel availability, deuterium is readily extractable from water (which is not exactly in short supply), and enough deuterium exists in 500 litres of seawater to supply a person's electricity needs for a lifetime. One kilogram of fuel for a fusion reactor has the same energy content as 10,000 tonnes of fossil fuel.

So basically, the future of energy supply draws ever closer. Watch this space!


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  1. One kilogram of fuel for a fusion reactor has the same energy content as 10,000 tonnes of fossil fuel.

    But how much of that energy is USED to keep the fusion process going? Not an insubstantial amount I suspect, maybe even 80% of it or more. Now fair enough that's still a sizeable advantage but it's slightly manipulating the figures to portray it in the best light.

    25 May 2006, 09:44

  2. You mean with sustaining the reaction through ohmic, RF and beam heating? Not as much as you think. The thing about JET is it's not full size, so people get misconceptions about the process. It's exactly the same as a fission reaction in that there's a critical size below which the reaction is not self sustaining; at larger sizes the reaction will be self–sustaining and not require external heating. I quote directly from the JET website (www.jet.efda.org) :

    bq.ITER is an international collaboration with seven partners (EU, Japan, USA, South Korea, Russia, China and India) – and is a more advanced, larger version of JET. It will be capable of producing 500MW of fusion power (ten times that needed to heat the plasma). In comparison, JET can only produce fusion power that is ~70% of the power needed to heat the plasma

    Are you familiar with the concept of ignition of plasmas? Essentially you get to a point where the energy from the alpha particles (Helium nuclei) transfers sufficient energy to the Deuterium and Tritium particles that the reaction becomes self heating, i.e. you don't need external plasma heating. This is referred to as ignition. Check out this page to learn more about plasma heating.

    25 May 2006, 10:31

  3. From the JET FAQ, here's a direct response to your point.

    25 May 2006, 10:33

  4. With regards to fuel availability, deuterium is readily extractable from water (which is not exactly in short supply)

    Try telling that to Thames Water et al.

    25 May 2006, 10:57

  5. Heh. Thankfully we can extract deuterium from any water, it doesn't have to be fresh drinking water standard! And according to climate change people we're going to be swamped with the stuf it's so overabundant (already covers some 80% of the earth's surface as you well know).

    As an aside, water shortages were a subject reported on in PE earlier this month. Apparently there's some 3.6 billion litres a day leaked (source: Environment Agency). Solutions posed (aside from the obvious of plugging the leaks) include the formation of a national water grid. PE suggested that a 150 million litre a day desalination plant coupld be built in Barking by using water from the Thames, which has a lower salt content, which would supply a reported 400,000 homes (giving a 375 litre/day per household figure, which compares to a quoted use of 150 litres/person/day). Using that 375 litre/day/household figure it can be seen that by plugging all the leaks we'd have enough water to supply an extra 9.6 million homes. We could also dredge current resevoirs and build a few new ones. But to my knowledge I've yet to hear of a single increase in storage/production measure that hasn't been blocked by planning councils.

    25 May 2006, 11:50

  6. according to climate change people

    You may side with the (increasingly loony) fringe that maintains there's no connection between human activity, the rate & magnitude of change of atmoshpheric CO2 and the rate of change of global climate over the last 250 years (when viewed relative to the last 500,000)... but I've yet to hear anybody argue that global climate is not changing. Therefore, "climate change people" means everyone, or everyone but you.

    Various models have suggested various possibilities for the myriad local effects of global change, but most of them for the UK strongly predict a pattern of increased floods and increased dry periods. The two often go hand–in–hand – viz subtropical regions.

    25 May 2006, 12:49

  7. Allow me to clarify that Simon – by climate change people I mean those who study it in depth (i.e. climate change scientists), not those who agree with the consensus that it is happening.

    25 May 2006, 12:53

  8. PhD in Nuclear Fusion anyone? :D

    25 May 2006, 13:10

  9. Oliver Ford has a PhD lined up with Imperial/JET. Personally I'd love to do something with fusion, but the work is all done by external contractors so it's relatively difficult to set yourself up working there directly.

    25 May 2006, 14:38


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