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

Re:Do we want Q=Infinity?

[bofh31337]

I haven't kept up with the current design iterations of ITER, but I think the thing to remember is we are talking about Q_effective and not Q_actual. The main confusion is when we talk about Q in science and in engineering, they both use a different definition. The scientific definition is only counting the power to the plasma and not the energy for the lasers, fuel injectors, and everything else.

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.

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.

Re:Fusion reactor

[emmons]

UW-Madison (which has the largest fusion studies program in the nation) seems to be rather interested in H-3, so much so that the Fusion Technology Institute here has designed a device for mining H-3 from the moon. Interesting stuff, check out the website.

If only it were that simple...

[Spamalamadingdong]

... 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.

It was my impression that He-3 + D -> He-4 + p + yielded all of its energy in the charged reactants, which further heats the plasma instead of being lost to the chamber wall (as photons and neutrons are). BTW, thanks for reminding me of He-3, I'd missed that earlier.

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

I hate to break this to you, but depending on the energy of the photon and the composition of the target, it can. If the gamma ray has enough energy to eject a nucleon from a nucleus in the target yielding a radioisotope, rest assured that some fraction (however infinitesimally small) will do so. Photons can also raise nuclei into metastable states, from which they decay some time later with the emission of some other form of radiation (usually another gamma ray, IIRC). If you go through a table of the isotopes, you'll find a bunch of curious things regarding various elements; you might want to do that on your own, just to make sure that your schooling isn't interfering with your education.

Re:If only it were that simple...

[Winged Cat]

Problem: if you have He-3 + D, you're also going to get an occasional He-3 + He-3 or D + D, the latter of which emits neutrons...and, thus, potential radioactivity (depending on what the neutrons hit).

He-3 + He-3, with no D at all, does result in purely charged reactants.