In reply to Steven Krivit's message of Sat, 11 Mar 2006 16:18:52 -0800: Hi, [snip]
I quote:- "This is a volume of 3400 m3, which, at an average density of about 3 g/cm3,would weigh 10,000 metric tons. A conservative cost would be ~$180/kg, for a total blanket-shield cost of $1.8 billion. This amounts to $1800/kWe of rated capacitymore than nuclear fission reactor plants cost today (8)." What is wrong with this is that the fusion reaction in question produces mono-energetic neutrons. This means that the expensive blanket/shielding can be replaced by a cheap 4 layer shield/blanket. 1) Inner layer - thin vacuum wall. 2) Thick layer of (cheap;heavy?) water, acts as neutron moderator, and removes heat. 3) Thin metal layer that chemically separates water layer from the Lithium layer. 4) Thin (and hence cheaper) Lithium layer that absorbs neutrons, slowed by the water layer, and produces Tritium. This layer can now afford to be much thinner , because the neutrons have already been slowed in the moderator (water) layer. This sort of arrangement should work, because the neutrons are mono-energetic, and hence the thickness of the water layer can be pre-determined such that it removes most of the energy from the neutrons, but allows e.g. 95% them to pass, leaving them free to enter the Li layer and react at thermal energies, where the reaction cross section is much higher, and hence the layer can be much thinner. Furthermore, this design has built in heat removal in the form of the water layer, which means that the heat removal per square meter of surface area can be much higher, and therefore the overall size much smaller, resulting in a far cheaper design. Furthermore, the heat created in the Li layer is also easily conducted back to the water layer as well, such that the water layer easily cools the entire reactor. Some of the hydrogen in the water will absorb a neutron and eventually convert to Tritium which can then be removed and used in the reactor. Regards, Robin van Spaandonk http://users.bigpond.net.au/rvanspaa/ Competition provides the motivation, Cooperation provides the means.
