U.S. to Rejoin the ITER Fusion Project

spiro_killglance writes: "BBC news is reporting here, that the USA may be about the rejoin the International Thermonuclear Experiment Reactor project. The USA left the ITER consortinum in 1999 when it bulked at the 10 Billion dollar price tag. Canada, Europe and Japan continued in the project, downscaling it to a cheaper 4.5 Billion dollars. The project claims to be the final step before commcercial reactors are possible, although the price tags might still be daunting to utility companies. ITER is designed to generate bursts of fusion energy, producing over 10 times the ammount of energy used to generate the fusion reaction (a Q factor >10), will not quite reach ignition (a self sustaining fusion reaction, or Q=infinity), but should pave the way for devices that will."

Comments

Yes, I think we do.

[Spamalamadingdong]

As you run up Q, doesn't the radioactive output also rise?

Depends what the reactants are. If you are burning deuterium with tritium (or D-D) you are emitting neutrons (D-D yields He-3 and a neutron, D-T yields He-4 and a neutron). Whether you create radioactives or not depends what those neutrons hit. You can get some neutron spallation (neutron hits something in a nucleus and tosses it out, transmuting the nucleus into something radioactive) or just neutron capture; however, you could control the results by selecting the composition of the materials exposed to the neutron flux. In a D-T burner you are going to have to replace the tritium you burn, which is usually done by capturing the neutrons with lithium. IIRC, Li-6 + n -> He-4 + tritium.

The antinukes would have to be crazy to be worried about neutrinos; their favorite energy source (old Sol) streams countless numbers of them through their bodies every second. This is not to claim that some of these people aren't crazy...

Fusion plasma won't melt a hole in the ground. By the time you dump air into the vacuum of the tokamak torus, the plasma will have been quite thoroughly quenched; you might have a few micrograms of tritium to worry about, but it has a half-life of about 12 years so it isn't much of a concern except over a relatively short term.

Over-simplification

[Spamalamadingdong]

A common misconception about fusion reactor is that there are no negative byproducts of its use. this is simply not true.

Is there any technology which has no negative byproducts?

The tokamak fusion reactor would have extremely dangerous core due to neutron and proton radiation. You would have to have one heck of a system of shielding for this to be useful.

You could say the same thing about a solar furnace; the focus would be extremely dangerous due to thermal radiation. It doesn't mean that it isn't trivial to keep yourself safe from it. Direct neutron and proton radiation is simply not a problem. Indirect exposure, say from leakage of tritium or corrosion of used reactor parts, is another issue. Lots of chemical processes have nasty intermediate products, so it's not like industry doesn't have plenty of experience managing such things.

Any thoughts on what would work best in the fuel?

The easiest fuel to ignite is deuterium-tritium. If you are concerned about radioactive byproducts and you don't mind building a much bigger and more expensive reactor, you could use boron-11 and protium; B-11 + p -> 3 He-4 + . This would give you a neutron-free reaction, at the cost of very high temperatures required to ignite the plasma and very rapid heat loss due to X-rays from the multiply-ionized boron nuclei.

Re:Fusion reactor

[Yarn]

Deuterium/Tritium is the easiest to get fusing, but some people have suggested using helium-3. The reasons for this is that although you get less energy out, you also get far less neutron radiation. Mostly gamma rays.

Gamma rays matter less than neutrons because they don't cause what they hit to become reactive.