Sir

In your Editorial about the increasing expense of the ITER fusion reactor ('The price isn't right' Nature 453, 824; 2008), you suggest that scientists might be suspected of deliberately under-quoting the price to help sell the project. Possibly. What then should one make of the projected costs of fusion energy outlined in the European Fusion Development Agency in its 2005 report (see http://tinyurl.com/5gvh5o)?

The report gives a projected electricity cost for a 1.5-gigawatt plant of conservative design of €0.09 (US$0.14) per kilowatt-hour. This is rather high compared with, say, renewables; but it goes on to state (on the basis of untested conceptual designs with less conventional materials) that this cost would be reduced to €0.05 per kilowatt-hour “in a mature fusion industry”. This figure is only a little higher than for conventional nuclear power plants. Moreover, it has been quoted by leaders in the fusion community (see C. Llewellyn-Smith and D. Ward, Nuclear Future 2, 93–100; 2006). Hidden in these projected costs is that both the €0.09 and €0.05 numbers have already been reduced by a factor of 0.65 to give the cost of 'a tenth of a kind' — that is, for the tenth reactor. The original cost estimate of nearly €0.14 per kilowatt-hour has been cleverly reduced by almost a factor of three. At a time when the economics of fusion energy needed some support, one cannot help admiring this approach.

As the costs of ITER come under further pressure on all sides and the huge technical problems become recognized, there is an urgent need for realistic and independent assessment of the costs of a practical fusion device, and even as to whether it is sensible for the programme to continue. Apart from the plasma conditions, what about the tritium breeding and reprocessing, the massive materials problems in a radiation-damage environment, the near-impossibility of maintenance and the difficulty of maintaining the integrity of superconducting magnets over long periods? The list of areas where heroic engineering is needed goes on and on.

As US physicist William Metz once said, “It sometimes seems necessary to suspend one's normal critical faculties not to find the problems of fusion overwhelming.” The fusion story is like a snowball going downhill gathering mass and momentum — impossible to stop, and at the end there will be only a pool of water to show for all the effort.