All entries for Thursday 25 May 2006
May 25, 2006
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!