[delt0r]

In order for a neutron source to be a proliferation risk, it also has to be a power source. At least if you want to transmute enough stuff under a few 100 years anyway.

We can run some basic numbers. Lets assume DD fusion with full T ash burn and no He3 burn. Thus we have

DD->T +p, DD->3He +n, DT->4He+n

total reaction is

5D->3He+4He+2n+p 24.9MeV (16.5 MeV in neutrons)

So if we want to get 7kgs of Pu from 238U we need about 30 moles of neutrons assuming 100% efficiency. To do this in one year you need a average power of 1.1MW. Definitely not just a neutron generator.

EDIT: i forgot the not unsubstantial power from the transmutation itself.

[delt0r]

And don’t get me started on “peer review”. ½ marginally competent volunteer editing, and ½ gatekeeping by status quo stakeholders.

I get tired of this. Of course peer review is not perfect, but just look at all the crap submitted to the the preprint archives. We need some filter. Also its mostly untrue. Not only does the DPF stuff get published, but other groups are now looking more at fusion possibilities and many in the field are taking it quite seriously. Even the polywell has had two peer reviewed papers, one very recently. ITER folk are *not* suppressing this work.

Talking about conversion, this attitude that its all “big physics” that is holding it all down is a big problem. Because they are not holding you down. If there budget is cut, so is yours. You won’t get that slice of the pie.

Personally I try to educate *if* others are interested. If not, meh. I don’t try to win over. Just facts, data, and why it is so tantalizing. A good example is that confinement time has been growing faster than Moore’s law! Yes its traditional fusion that is a dirty word here. But its is very good progress. If we keep that up for another 30 years even DD fusion becomes “easy”. Another is that boondoggles like ITER are boondoggles mostly because of politics, not science. It is very easy to show this with a little google. Next is the “dark horses”, that is Focus fusion, General fusion and a few others.

But most of all i try to point out the very low levels of funding. Even ITER is not that expensive. A 1GW coal plant cost a cool billion or so, and a plain old fission plant more like 10 billion. 1GW for a year is about 400Million of electricity. People don’t get the scale of the energy we use and the energy problem. We put more money into farm subsides than we do into solving our energy future.

My last point, if we are still on talking terms, in the long term nature of the problem. If it is going to take 50 years, so what? we are in this for the long haul. Getting fusion in 50 years is better than limping along without it for 100 because “50 years is too long”. Of course we could take our long term energy security more seriously and get it sooner if we go all “Manhattan project” on it.

Just for the record. I advocate a diverse funding portfolio. We don’t know which horse to bet on right now, or we would already have fusion.

[delt0r]

Yes i know. But since it produces 2 gammas the branching ratio is suppressed by the fine structure constant squared. So its like 10^-6 or something IIRC. Enough to detect with MW of fusion. Otherwise not worth considering.

[delt0r]

This is not the same as claiming D+D->4He by a long shot. A very long shot.

[delt0r]

And where do these neutrons come from? Sorry but after 20 years the data does not back up anything other than nothing nuclear. In one statement they claim transmutation of metals, in the next they claim D+D->4He via lattice effects to explain away the lack of neutrons, tritium or gammas. A lattice effect billions of times higher than anything proposed or measured.

[delt0r]

I didn’t read it all in detail since he misses a pretty serious detail with D+D fusion. That is he claims D+D fusion gives 4He, which it does not. A 10sec wiki search would have told him that. There are probably other equally ignorant errors throughout the rest of the text.

Remember the golden rule. Politics is not science and scientists are bad at politics. Much of the issues with ITER and there kin are from the fact that you end up with a lot of physicists trying to be good at politics.

[delt0r]

Interesting asymmertic_implosion. I would differ to your experience in the matter. I try to keep up with the literature. But it is hard when i have my own field to keep up with. Lucky my institute has most of these journals.

Honestly i would have gone for a bigger upgrade to existing facilities, like JET with more diagnostics and tritium handling facilities. I am constantly surprised by how little diagnostics many of these experiments really have. I would even include the FF in that to. I would want at least a streak camera? no? But the upgrades would have the focus of studding plasma stability under burning conditions, and lets get a better handle on ELM. IIRC there was some suggestion that controlling the burning rate is going to be very hard in such devices.

As for material choices how does some of the spallation neutron source rate for some material studies? Mitigation of these risk factors would seem cost effective even if expensive.

I don’t think DEMO is a good idea. I wanted to see how plasma behaves under long burn and then lets start working on something a big smaller? Clearly some magnet breakthrough would help… but its not given that we are going to get one.

[delt0r]

In ITER defense, 99.9% of the delays and problems are political not scientific. Its stuff like where it gets built, and who gets the magnet contract, and why should they get all the magnet contracts what about my country magnet maker..etc. The original time line is about a decade behind right now and there was much less money made available, at least in part because the US pulled out (or mostly pulled out). I mean you need to get 20 countries to agree on something each time a big decision is needed, what would you expect?

From a science perspective it think either some serious upgrade to JET (begin done) or ITER is the next logical step. Sure everyone want a slice of the pie, but the fact is that nothing else is really close. Nothing else has data that is even close and well at the end of the day… Show me the data. Sometimes i think the “not working with ITER” folk forget that when the Russian reveled the design it was 100x better than anything else at the time, so good that the west assumed they were lying. It wasn’t until a team from the west took their own measurements before they where believed. Right now they still are the best design on the table (stellarators are nice too but cost more to build).

I know that ITER is a dirty word here… but lets try and work with data, and not feelings. They are not steeling your funding. If the money is taken away from ITER it will not go into other fusion work. Most likely it will go into the banking sector and not science at all.

[delt0r]

I should also point out that just about every reactor ever built has had problems with corrosion. Its it not just a matter of a material choice, it has to be something that works with the neutron economy as well. Also the corrosion that happens in a high radiation environment is quite different and typically faster and more aggressive than plain corrosion. Even many of the Dry casket storage systems are failing due to radiation driven corrosion and that is much lower activity radiation.

[delt0r]

The huge advantage of homogeneous reactor design, That is designs where the fuel is mixed with the coolant is that it is very easy to avoid hot spots, keep reactivity predicable and even, and maintain a positive void coefficient and a negative temperature coefficient. You also get perfect even burn for free. These things are all hard to achive with solid fuel designs and tyically require a fairly compilcated fueling schedule for even burn at least. These things are all even harder to achieve with fast reactors.

For thermal designs with water and dissolved salts they have the lowest fuel inventory required by a long shot, and for fast reactors they are one of the surest ways to maintain stable reactivities with passive control. Other practical issues is you don’t need to validate fuel element design which is still a very large cost (time as much as money). Then there is a few unvalidated at this point ideas, of continuous in situ processing, which add a lot of other advantages to the complete fuel cycle. Also this can reduce the decay heat quite a bit too since thing don’t accumulate and some wastes can be pulled out when a more favorable isotope is produced. Further you can degauss it and keep out neutron poisons especially Xe which makes the designs capable of load following, or more importantly easier to make load following… ie capable of peek power production.

On planet earth keeping water out is a exercise in futility when the unexpected happens. Say like a giant wave of … Water! Note that the water in air can set liquid Na on fire. The problem is that we either have salts that are not stable with water when molten, or tend to be soluble in water when not (Chlorides). As for liquid metal designs i can’t see what we gain with Na that something like lead/Bismuth doesn’t give us? Add that the later can have enough heat capacity to passively deal with decay heat.

[delt0r]

LFTR salt is not inert and is somewhat corrosive. In fact it reacts with water and gets even more corrosive (Hydrofluoric acid is produced). This can also lead to hydrogen production…. Also LFTR still have the decay heat to contend with as well. So it still not as simple as “it drains and is off”. It needs to drain to somewhere than can still cool the salts and not melt. if you have a 1GW plant, even .1% is a lot of heat to get rid of in a passive configuration.

[delt0r]

Normal fission can be done at very small scale. There have been plans for something light enough for a man to carry. The core mass can be very low, for example water moderated homogeneous reactors can have fuel inventory in the low kg’s. However i think the only ones fielded where isotope thermal types. There are some pretty small lab reactors IIRC with outputs in the kW range.

Regulation has more to do with perceived safety than anything else. Note that when a FF is on, it is quite a potent source of radiation without proper shielding. So there will be some regulation.

[delt0r]

40x is meant to refer to the use of fuel. That is a LWR or BWR typically has a burn up fraction of 1-5% or thereabouts. While a burn and bread design can use 40% or more of both the fuel and fertile elements. Of course this is also the problem. No fuel element/pellet has ever been rated with such a high burn up fraction, where volume and gas build up can compromise the element. The cost of validating fuel elements is one of the bigger costs in terms of time and hence money for a new design.

Otherwise the design seems like a good one. Uses depleted uranium as the main stock of fuel, gives the most of the benefits of reprocessing without the reprocessing.

[delt0r]

This is unfortunately not how neutrons behave. Almost everything is nothing but space and so neutrons are quite penetrating since the don’t see the electron clouds. Then there is the prompt gammas and activation. Its not really a big deal, but it is something that will part of standard operational procedures. Water is indeed a good neutron absorber if you have a lot of it (needs lots of volume or they diffuse out). Most is absorb by hydrogen to become deuterium. The Boron will be quite dilute in gas form and will be practically transparent to neutrons.

[delt0r]

I don’t think so. The side reactions that give off neutrons are indeed rare. But once you scale up to MW its still a lot. Also the true cool down time will depend on other materials used. Neutron activation over days, weeks and years will not be insignificant. It is of course something that is reasonably easy to deal with, given proper materiel choices. Remember that we are talking about moles of neutrons here, they all get absorbed somewhere.

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