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Biggest Obstacle of Nuclear Fusion Overcome?
Yetihehe writes "Nuclear fusion could become a more viable energy solution with the discovery of way to prevent super-hot gases from causing damage within reactors. The potential solution, tested at an experimental reactor in San Diego, US, could make the next generation of fusion reactors more efficient, saving hundreds of millions of euros a year."
I think maybe you're confused between fusion and fission. Environmentalists generally don't mind fusion, as it is a safe, and very eco-friendly way of producing energy. Which is, you know, what they like.
;-) ) being the second biggest.
Fission, on the other hand.. is problematic. It might be the only viable alternative at the moment (well actually I'm just saying that to not get flamed) but nobody can say it doesn't have its share of problems. Waste being the biggest, safety (yeah yeah I know, pebble reactors, yada yada
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Fission also produces neutrons.
Fusion produces orders of magnitude more neutrons.
In a fission plant, excess neutrons are bad. You want the pile to be barely critical, a stable, but not runaway, chain reaction. So you actually don't have a lot of neutrons flying out of the pile. You moderate the ones you do produce, and use them to fission additional fuel atoms.
But in a D-T fusion scheme, the bulk of the liberated energy is produced in the form of a very energetic 14 megaelectron-volt neutron. And this neutron doesn't participate in additional reactions, DT fusion isn't a chain-reaction process like fission is. The neutron will leave the plasma. Heck, ideally, that's how you get energy out of the reactor, by trapping that neutron in a surrounding blanket, causing that blanket to heat up so you can use that heat to boil water. Every single D-T fusion generates one of these neutrons, so the neutron flux will be many many times that of a fission plant.
But that's not an issue because of "radioactive waste." The wastes we're concerned about from fission aren't neutrons, they're from fission fragments and decay daughters. Some of those might emit neutrons themselves, but really, that's not the primary concern; neutron-induced radioactivity is actually pretty short-lived.
The reasons neutrons are a concern in a fusion plant is that continuous high-energy neutron bombardment does very bad things to all known materials that you might want to build a reactor vessel out of. When a neutron strikes an atom, it displaces it within the crystal lattice. If that happens once, no big deal, but in a commercial fusion reactor, the reactor vessel will experience 300 to 500 displacements per atom over the lifetime of the device. That means that, right now, we don't even know what to build one of these things out of. Austinitic steels start to swell, crack, and degrade after only about 30dpa, and the very best candidate materials we know of can only handle about 150; those might be acceptable, if the cost of changing the inner wall out isn't too high, but we just don't know.
And ITER won't even begin to explore those issues. ITER's flux will only generate 3 displacements per atom.
Fusion is very very hard. My money says that we'll never use commercial fusion power.