Environmental impact of p-B11 fusion?

If polywell fusion is developed, in what ways will the world change for better or worse? Discuss.

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chazmataz
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D-D or D-T polywell

Post by chazmataz »

JoeStrout wrote:
jlumartinez wrote:I try to be realistic. Enthusiasm is fine and is a powerful engine for this enterprise. The equilibrium between being enthusiastic and rational is the key point. In my opinion too many people try to see a far future ahead. Although p-b11 may be reachable the first generation of Polywell (if successful- we hope that-) will be with D-D fusion reaction.
I doubt that. D-D fusion is easier energetically, but if the Polywell approach works at all, then that won't matter much — power scales as the 7th power of the reactor size, so if your reactor can't burn p-B11, you just need to make it a little bigger.

And the trouble with D-D is that the fusion products are neutral — in fact they're mostly neutron radiation, which is nasty stuff, and extremely hard to actually extract energy from. This quickly takes you down that rat-hole of lithium blankets, your reactor quickly becoming radioactive as you use it, a thermal cycle with moving parts, and so on. By comparison, p-B11 fusion with a deceleration grid for extracting the energy is much simpler. For this reason, I doubt D-D fusion will ever be used as a power source (though it makes a dandy neutron source).
D-D fusion is not as bad as you claim, and the feasibility of p-B11 net power reactors is far from a 'given' at this point. There are many factors which might limit the maximum size of the polywell reactor, such as cooling limits, that might allow polywell to work successfully with D-T, D-D, and D-He3, but still leave it impractical with p-B11.

D-D fusion releases only 1/3rd of its output energy as neutrons - the rest as charged particles. If you can avoid fusing the tritium in the reaction product, and feed the He3 from the reaction back into the polywell, then a full 90% of the fusion energy is released as charged particles. If you can store the tritium you produce until it decays and feed the resulting He3 back into the reactor, then you end up with only 5.5% of the total energy output released as neutrons.

I have actually been contemplating the possibility that the first net-power polywell reactor should burn D-T, and dismiss the neutrons produced from the reaction as waste heat. Even though this means throwing away 80% of the energy from the reaction, it could still be a net win, because the D-T reaction is so easy, and the alphas that will be produced will all be 3.5Mev exactly. Because the reactor would use a very simple grid array to tap the energy from the alpha particles, it could be cheaper per watt of electricity than any steam turbine based powerplant.

Zixinus
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Post by Zixinus »

have actually been contemplating the possibility that the first net-power polywell reactor should burn D-T, and dismiss the neutrons produced from the reaction as waste heat.
There are problems with neutrons, one of them is that you have to shield the grids againts them. I recall that boron shielding is the best solution when you don't need tritium.

You also have to modify the power reactor walls so they won't transmutate much and won't cause to release of particles that may touch the plasma.

As for environmental impact, remember that we are not using heavy, unstable isotopes. Most elements will decay back into stable elements quickly enough. I recall that with tokamaks, neutron irradiated equipment can be used after a century. Making a nuclear cemetary to last a hundred years is much easier then for it to last millions of years.
Even though this means throwing away 80% of the energy from the reaction, it could still be a net win, because the D-T reaction is so easy, and the alphas that will be produced will all be 3.5Mev exactly.
I recall that most of the energy released goes into neutrons.

chazmataz
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Post by chazmataz »

Zixinus wrote:
have actually been contemplating the possibility that the first net-power polywell reactor should burn D-T, and dismiss the neutrons produced from the reaction as waste heat.
There are problems with neutrons, one of them is that you have to shield the grids againts them. I recall that boron shielding is the best solution when you don't need tritium.

You also have to modify the power reactor walls so they won't transmutate much and won't cause to release of particles that may touch the plasma.

As for environmental impact, remember that we are not using heavy, unstable isotopes. Most elements will decay back into stable elements quickly enough. I recall that with tokamaks, neutron irradiated equipment can be used after a century. Making a nuclear cemetary to last a hundred years is much easier then for it to last millions of years.
Even though this means throwing away 80% of the energy from the reaction, it could still be a net win, because the D-T reaction is so easy, and the alphas that will be produced will all be 3.5Mev exactly.
I recall that most of the energy released goes into neutrons.
The D-T reaction produces a 3.5Mev alpha and a 14.1 Mev neutron - almost exactly a 20 - 80 split. These neutron are moving REALLY fast, and should fly straight through the grid and the chamber walls with very few of them interacting in any way. Outside of the vacuum chamber, you would have shielding - a couple of meters of a boric acid/lithium carbonate solution should suffice.

I don't actually think a D-T polywell reactor would be cost effective. BUT -

If you build a 10MW net power D-T polywell and operate it for an hour, you would kill ITER, and attract investment money for building a commercial prototype D-D-He3 reactor, and for researching the p-B11 reactor. It would prove the superiority of the polywell over the tokamak conclusively.

MSimon
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Post by MSimon »

Solo wrote:Taking a sociological look at energy and other limits on human population, it seems that if energy becomes cheap/plentiful enough to do insanely energy-intensive things like watering deserts and making up enough ethanol to run the world's cars, trucks, ships etc, our population will go up again, as it did in the industrial/green revolutions. However, there will be yet some other limit. Perhaps we will liberate enough heat thru fusion to generate global warming directly, w/o the greenhouse effect!
So far demographics show that as people get above a subsistence level of economics birth rate goes down. At around $4,000 per capita pollution starts declining. At around $8,000 per capita birth rates go below replacement.

BTW plants that evolved in 4,000 ppm of CO2 are CO2 starved at 400 ppm.

It is amazing the number of people who think that starving plants is a good idea.

Boron is rather abundant in the earth's crust. We have enough at current electrical use rates to last us 100,000 years. It should buy us enough time to figure out what we want to do next.

MSimon
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Post by MSimon »

Zixinus wrote:
There may well be trade restrictions on which countries the technology could be sold to, which could have a dramatic effect on who has it, and who does not.
Not likely. Unlike fission, you cannot use fusion reactors to make weapons. Well, as a neutron source, maybe.
Once you have a good neutron source Pu is not hard to come by.

MSimon
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Post by MSimon »

Nanos wrote:Thats very interesting, and might explain why fusion research isn't being given the funding it could otherwise have, if indeed as you say, if it was developed, it would only increase the worlds arms race ability.

Though thats not necessarly a bad thing, as if everyones got a big stick, it might make countries behave better towards each other..

MAD anyone :-)


You are a victim of mirror image thinking.

You are leaving out religion; a force more irrational than nationalism by far.

Jihadis claim to love death. MAD might not be a deterrence in such a case. It might be an incentive.

We got in a lot of trouble by not taking a certain Austrian Corporal seriously in the 30s. I see no reason to repeat the exercise.

MSimon
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Post by MSimon »

Zixinus wrote:

I recall that most of the energy released goes into neutrons.
66% of the reactions lead to neutrons according to wiki given the burn up of all reaction products.

Given the lower energy per reaction c. 20 Mev vs 200 Mev. You get a lot more neutrons out of a fusion reactor than you do from a similar gross power fission reactor. If you use D-D.

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Post by MSimon »

chazmataz,

My proposal for a test reactor will prove D-D and p-B11.

If it works for D-D it will work for pB11.

After that you build your 100 MWth pB11 test reactor followed by actual power producing plants.

IEC Fusion Technology blog http://iecfusiontech.blogspot.com/

Scroll down.

Zixinus
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Post by Zixinus »

Once you have a good neutron source Pu is not hard to come by.
And you still need reprocessing technologies, and testing.

chazmataz
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Post by chazmataz »

MSimon wrote:
Zixinus wrote:

I recall that most of the energy released goes into neutrons.
66% of the reactions lead to neutrons according to wiki given the burn up of all reaction products.

Given the lower energy per reaction c. 20 Mev vs 200 Mev. You get a lot more neutrons out of a fusion reactor than you do from a similar gross power fission reactor. If you use D-D.
Actually, the 66% number for D-D fusion means: 66% of the energy from the fusion is released as neutrons when you assume that all the tritium burns up but that none of the He3 burns up.

In the Maxwellian plasma of a tokamak, that is a reasonable assumption. In a D-D polywell, there are a few things you can do to reduce the probability of having your tritium fuse. The most significant of these is to dilute your deuterium with plain hydrogen. It would not be unreasonable to assume that in a well designed D-D polywell, you can allow the 1Mev tritium to escape the reaction zone without fusing more than 99% of the time. This will reduce the neutron flux from the D-D reactor to 33% of the released energy (consisting of 2.45 Mev neutrons). The rest of the energy is released as charged particles - 2.5 Mev protons and 1 Mev He3 and tritium.

Once you are operating a D-D fusor with particle deceleration, you will have a source of He3. With a dependable source of He3, you will want to build a D-He3 fusor. If you use spin polarized D and He3, you will be able to completely avoid D-D reactions in your D-He3 fusors. If you cannot spin-polarize your nuclei, you can still reduce the D-D reactions by running highly He3 rich, to the point where less than 0.5 % of the fusion energy is released as neutrons.

If you have the means to store large amounts of tritium for a decade or two, it will decay into He3 - and then become useful fuel for aneutronic reactors.

Yes, normal D-D reactors will produce slightly more neutrons per watt than a fission powerplant. So what? They could still be much cheaper and less polluting. The neutron flux from a D-D reactor could actually be used to reduce the half-life of some types of fission-plant high-level nuclear waste.

chazmataz
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Post by chazmataz »

MSimon wrote:chazmataz,

My proposal for a test reactor will prove D-D and p-B11.

If it works for D-D it will work for pB11.

After that you build your 100 MWth pB11 test reactor followed by actual power producing plants.

IEC Fusion Technology blog http://iecfusiontech.blogspot.com/

Scroll down.
Yes, I have been following your Open source reactor design on the NASA forum's thread with interest.

You claim:

If it works for D-D then it will work for p-B11.

And you don't actually provide any justification for that assertion. There are many loss mechanisms in heavier atom fusion that are clearly not quantified at this point, and I feel it is much too early to make a blanket assertion like that without, you know, proof.

I would be very pleased if p-B11 turns out to be as straightforward as you and Dr. Bussard seem to think it will be. However, I don't think we should take the position that some pB11 fanatics have that 'D-T and D-D fusion are worse than fission and should be dismissed completely.'

If it would take ten years to build an experimental polywell pB11 reactor, and only a year to build an experimental D-T net-power reactor, then I think that it would pay to build the D-T reactor first.

Personally, I think it would make sense to run your hypothetical test reactor on 'natural isotope ratio' hydrogen, just to work out the kinks in steady-state operation and the scaling on the loss mechanisms. You would still get some fusions/neutrons , but only about a hundred millionth of what you would get running straight D-D.

Zixinus
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Post by Zixinus »

You are leaving out religion; a force more irrational than nationalism by far.

Jihadis claim to love death. MAD might not be a deterrence in such a case. It might be an incentive.
I know a few people that think that on that claim, the USA shouldn't have atomic weapons either. He wasn't serious, but it makes some sense.
And you don't actually provide any justification for that assertion. There are many loss mechanisms in heavier atom fusion that are clearly not quantified at this point, and I feel it is much too early to make a blanket assertion like that without, you know, proof.
How about you get more details? Yes, it can do both D-D and p-B11, however not at breakeven and only for experimental purposes.

How well it will do p-b11, is what needs to be determined. I recall that Mr.Simon's work would only barely do p-b11.
I would be very pleased if p-B11 turns out to be as straightforward as you and Dr. Bussard seem to think it will be. However, I don't think we should take the position that some pB11 fanatics have that 'D-T and D-D fusion are worse than fission and should be dismissed completely.'
I agree. However, p-b11 is much more ideal then D-T or D-D.

And there is D-He3. Yes, yes, Moon and all, but it could still work.
If it would take ten years to build an experimental polywell pB11 reactor, and only a year to build an experimental D-T net-power reactor, then I think that it would pay to build the D-T reactor first.
Agree. However, what makes you think that a D-T reactor can be built under one year?
Personally, I think it would make sense to run your hypothetical test reactor on 'natural isotope ratio' hydrogen, just to work out the kinks in steady-state operation and the scaling on the loss mechanisms. You would still get some fusions/neutrons , but only about a hundred millionth of what you would get running straight D-D.
I don't know what exactly Mr.Simon has in mind, but I think he does want to work out some smaller stuff too, and make the first runs at low level.

Also, that is the idea EMC2 has. WB-7 and WB-8 was to study more about the fusion process and confirm scaling laws, among other things.

Zixinus
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Post by Zixinus »

Does anybody know about about the by-products of getting either deuterium or boron?

Zixinus
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Post by Zixinus »

Another thing: I've heard that you can use the waste heat generated by, say, fission plants to heat houses or induce heat-based chemical reactions? A IV generation fission design (with super-critical water I recall) could be used as such, one reaction would be able to produce pure hydrogen. Since we are talking about waste heat, we get the stuff for practically free and also minimize any impact hot water vapour would put in the surrounding environment.

Do you guys think we can do the same with the waste heat of Polywell?

Zixinus
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Post by Zixinus »

Oh and here is a document on the effects on highly energetic neutrons (from D-T). While the document uses Tokamaks, it may be applicable to Polywell to some degree.

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