Obviously I have net access here in Madison, though it's excruciatingly slow.

Rand's post below reminds me of an idea I had a while back, and which has a little bit of traction in the fusion community (though I think it's had multiple independent inventors). The basic idea is to make a virtue of the neutrons produced in D-T or D-D fusion by using them to transmute nuclear waste into short lived (high radioactivity) isotopes. The isotopes could then be stored while they decay into something (relatively) stable. The benefits are many. First of all it deals with fission waste, helping to remove one of the obstacles to widespread deployment of fission power. Secondly, it doesn't require break-even from the fusion reactor, which makes everything a heck of a lot easier. The net transmutation plant power balance is now the sum of the fusion power and the power produced by the decay of the transmuted isotopes. A transmutation plant might plausibly be fully self sustaining. Once fusion reactors are in the hands of capitalist captains of industry, they will get better, cheaper, and more reliable.

A more exciting option is a mature fission-fusion hybrid cycle in which there are multiple passes of fission fuel through the reactor wall, to generate power using a set of reactions which spits out very low activity waste, cutting the initial fission reactor part entirely out of the cycle. This, it seems to me, is the logical long-term consequence of getting the evolutionary driving force of the markeplace to bear on the problem of commercial fusion. In the very long term, of course, we will likely see pure fusion power plants, but the path there must be along a sequence of evolvable reactor designs, each of which is at least marginally profitable.

More tomorrow, when the conference proper starts.

It'll never happen (at least no time soon). You're not thinking clearly. We already have plentiful neutron sources in the form of fission reactors. We could be transmuting our radioactive waste now, or twenty years ago. Why aren't we? For the same reason there are so few breeder reactors, even though they make more efficient use of the fuel cycle. The answer is that it's "dangerous", and the public is already squeamish about the safest and most straightforward nuclear power designs, dabbling in more advanced "nuclear technologies" would drive them over the edge, I guess. Though there is also a legimitate concern over nuclear fuel reprocessing in general and such things as plutonium extraction. The point is that if nobody's going to jump at the chance to do it now with existing technology they're not going to go for it in the future with unproven technology either.

When the sonofusion thing came out, I thought that one could use the neutrons to transmute nuclear waste. Somebody put me in my place when he said the first thing to do with nuclear waste is to PROCESS it. It's got lots and lots of Pu and that stuff can be "burned" in a reactor.

For what's left over. I don't know. Fusion neutrons are certainly more energetic than thermal ones and may be less capturable.

Actually, there's no need to go to such heroic lengths. The technology is pretty much well in hand, doesn't require any fission or fusion plant, could be implemented at current nuclear power plants to avoid transporting the waste, and produces energy as a byproduct. The answer is the accelerator driven system. Currently Sandia is researching this. In one configuration, it is used to produce tritium. But the really sweet prospect is to use the accelerator to induce fission of nuclear waste (or even naturally occurring thorium, of which the Earth AND moon have an abundance I believe), transmuting the waste and releasing energy.

However, the DoE leadership, various Congresscritters and others suffer from a collective case of cranio-rectal syndrome. The US is spending, what, $50 billion (or thousand million for you Brits) on a somewhat dubious scheme to "sequester" gigantic amounts of nuclear waste underground in Nevada, when for a tiny fraction of that (IIRC, $2-4 billion) the research into accelerator driven systems could be completed and we could be using that waste as fuel.

- Eric.

Robin - There are important differences in the fusion neutron spectrum compared to the fission neutron spectrum. Whether they are important enough to tilt things in favor of fusion isn't clear to me, since I haven't worked out all the details. Your point about proliferation concerns is good, though - this is not widely publicized, in part because the ~14 MeV neutrons from D-T fusion are good for making plutonium, so widespread use of D-T fusion would pose a significant proliferation risk. It's bad PR. Unfortunately the fusion community is highly politicized, so anything that's bad PR is hard to really tackle head-on.

Eric - accelerator driven systems are an interesting possibility, but there are quite a few bugs to work out (as there are with fusion). I'm as hostile as you are to the glassify and bury policy currently being pursued. The appropriate way to view nuclear waste IMO is as an ore we don't yet understand how to profitably exploit, but which we likely will be able to make use of in the future.

Another proliferation concern that isn't much mentioned would come from a 'renewable' hydrogen economy. This imagines huge numbers of wind turbines and PV fields producing hydrogen by electrolysis of water.

It turns out that electrolysis has a very large isotope effect -- protons are reduced to H2 much more quickly than deuterons are reduced to HD (or D2). As a result, the water in the electrolysis cell becomes enriched in deuterium at equilibrium.

Now imagine tapping off some of that enriched water and feeding it into a second rank of electrolysis cells. Repeat again if necessary. In a very large H2 production plant this side stream could produce highly enriched water that could be polished to pure heavy water in a rather small finishing plant.

Heavy water moderated reactors are one of the easier ways to make small amounts of plutonium. The Israelis produce their Pu this way, as did the Indians (IIRC). The reactor can be much smaller than a graphite moderated reactor, and can use natural uranium.

Interesting. Good ole CANDO (or CANDO like). Happily, I doubt much hydrogen will be produced electrolytically until most of our electricity is nuclear and solar generated. (Actually I have serious doubts about the "hydrogen economy" but that is another discussion.)

I remember they USED to talk about fusion-fission breeder reactors. Fast breeder fission reactors are trickier to build than conventional reactors. For a number of reasons, they probably are riskier than conventional reactors. A fusion-fission breeder could be a safer choice, but currently isn't politically acceptable.

Actually, you could build such a transmutation plant now. There is a very well known, reliable fusion device out there called a Farnsworth fusor (or a Electrostatic Inertial Confinement fusor, if you want to be fancy) It (obviously) soes not hit power break even, but it is simple to construct (High school students have built these as science projects). There is even a company which commercially manufactures these devices for us as neutron sources.

Monsyne,

I don't think the current crop of IEC devices put out a neutron flux anywhere high enough to consider industrialized transmutation.

Andrew,

While accelerator-driven systems have engineering details to work out, I *think* we have a better idea of how to build such accelerators than we do fusion reactors. IF all you want to do is deal w/ nuclear waste, then perhaps break-even isn't as much of a concern. Then you could pretty much build your transmutation plant with the present-day state-of-the-art. I agree that, if you want to surpass break-even, you'll need to research some more.

- Eric.

Eric - I think you hit the nail on the head. If net power is an issue then there is a case for fusion, if not, probably accelerators are better.

I recall seeing somewhere (no idea where) an idea for an accelerator driven fission plant using a fuel that fissions with absorption of a proton. The big plus is that it's passively safe and easily controllable, since it does not involve a chain reaction.

Yes, do a google search on "accelerator subcritical reactor" - one example page is http://www.uic.com.au/nip47.htm. The idea is to have the reactor a few percent subcritical with the accelerator making of the rest. The same idea has also been proprosed to burn up waste as mentioned in other comments. Of course, there is additional complexity and political hostility to research reactors. It might make nuclear just too attractive ... can't have that.

Well, from a quick look around it seems this scheme is getting a lot of interest around the world. Maybe I shouldn't have been so quick with my snide comment ... ah, well.

Andrew, there is no way to safely reprocess nuclear fuel. The entire goal of the exercise is to make the waste MORE dangerous in the short term so that it will be much less dangerous in the long term. At the very least any waste reprocessing process will produce materials in an intermediate step which would make excellent radiological "dirty" bombs. Additionally there is the nearly inevitable problem of tracking materials which could be a weapons proliferation concern. I mentioned fission because it's the easiest, most energy efficient, and most cost effective system that is technologically feasible right now. It is not the only process that "works", but if we aren't willing to accept the cheapest and easiest processes then we aren't going to try anything else in the same realm that's unproven and likely more costly.

Personally, I'd like to see a lot more work put into nuclear energy, fission and fusion alike. Because those are the most likely candidates for providing the energy needs of humanity in the long term. But the public still has problems with accepting nuclear technologies so until we get over that hump we'll be stalled out for a while.

"there is no way to safely reprocess nuclear fuel."

If you define "safe" as "with zero risk," well of course. Nothing can be done with zero risk. But in comparison to the risk posed by the waste put in the air, water and ground by fossil fuels, the risk is tiny. People die on a regular basis due to fossil fuel pollution. The volume of nuclear waste is tiny by comparison and can be handled with far more care than is possible with fossil waste. Compared to the alternatives, it is "safe."