Posted on 05/17/2011 1:33:00 PM PDT by ckilmer
they can be made small enough to power an aeroplane
As it happens, I was involved with the nuclear powered aircraft project in the late 1950s (guidance, not propulsion), so I'm familiar with the problems of putting a reactor in an airplane. To begin with, reactors must be shielded, and shielding is heavy. Most of the designs for nuclear powered aircraft had a heavily shielded crew compartment, and just enough shielding on the reactor that, when it was on the ground, you could approach it in a shielded tractor. However, that meant that the airframe was bombarded by lots of neutrons, which created dislocations on the crystal structure. That would rapidly lead to crack growth, meaning the airframe would have a short useful life, and would be radioactive. Big disposal problem. Another problem was that the temperature possible in a nuclear reactor is limited by the properties of the reactor structure. No matter what you do, this is going to be lower than the gas temperature in a fossil-fueled jet engine. Lot of power in the reactor, but transferring that to a jet exhaust is tough. The laws of thermodynamics work against you (nuclear powered rockets have the same problem).
In short, a nuclear powered airplane was a loser back then, and I don't think going to a thorium reactor is going to change that.
For stationary power plants, though, and possibly for ship-board power plants, we ought to be investigating the thorium reactor. If necessary, we need to get away from the not-invented-here types in the Department of Energy.
How does a thorium reactor compare with a modular pebble bed reactor?
Who does one pay for the fuel cost of wind and solar?
....
The costs for solar and wind are capital costs and maintenance costs
Fuel costs for thorium are a tiny $0.00004/kWh versus...wind appx. 14 cents /kWh; solar thermal about 26 cents/kWh and solar photovoltaic a hefty 40 cents/kWh.
Why would you compare "fuel costs" of thorium to capital costs of solar and wind? Does thorium not have any capital cost?
Of course, this is one of the reasons the Greenies cite when they're smearing coal (radioactive elements...).
The pebble bed reactor uses uranium that's encapsulated in "pebbles." I'm not sure about the exact size, but think of them as tennis balls or softballs. In operation, an inert gas such as helium is passed through the "bed" to transfer the heat to a turbine or heat exchanger. I don't know whether thorium can be used in place of uranium. In any case, the "pebble bed" refers to a structure, not to the fissile material used.
All the discussion of thorium reactors revolves around liquid thorium fluoride. That's probably not the only way to utilize thorium in a reactor, but that's the way it's been looked at in the past. This approach seems to have many advantages over the way we now build uranium-fueled reactors, so should be investigated.
Meanwhile, the scientifically illiterate, sentimental Gaia-worshipping lawyers and career politicians are locking America into their fantasy of wind and solar power.
It is. The Chinese have been buying up mineral rights across the mountain west.
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