|
Physics seems to require that a practical fusion reactor be very large. Complex technology is involved, it is hard to believe it is going to beat solar, hydrocarbons, fission, geothermal. etc. in economics. The problem is like that with fission -- uranium and uranium processing, and even plutonium processing are not expensive, but the reactor is. For a Deuterium-Tritium cycle, half of the fuel will be in the form of Lithium because you will breed Tritium from it in the reactor blanket. Lithium is a relatively rare element in the universe because it gets burned up in stars. It's not clear that the Lithium resource is bigger than the Uranium-in-seawater resource or the terrestrial Thorium resource. Another issue is thermal dissipation. It is already challenging to get rid of 2-3 GW worth of heat from a nuclear power plant. You could dissipate that heat by evaporating a modest amount of water, but that water could then condense and cause dangerous fog and icing on nearby roads, for instance. If fusion plants are scaled much bigger, say 50 GW thermal, getting rid of the heat is more difficult (most practically it could be disposed of in the ocean.) The plants have to be cited further away from cities, power has to be sent further, all that adds to the cost. It would be beautiful if fusion could support human life beyond the "frost line" where small bodies are rich with volatiles such as water, ammonia, carbon monoxide, etc. Imaginably you could cut up something like Pluto into small ringworlds that provide more living area than the Earth. At some distance solar energy gets weak but a practical fusion cycle (possibly D-D based) might make it possible to hop to the nearest star from comet to comet over a time scale of 20,000 years or so. The trouble is that people used to the Oort Cloud lifestyle probably won't be too interested in stars if they've managed to live that way for 20,000 years. |