Max Neutron Output from Fusion: Power Requirements & Comparisons

[Cypher49]

Basically as the title says, what type of fusion would give the highest number of neutrons for a given amount of power.

Also am I correct in assuming that most fusion methods will always produce more neutrons than other neutron sources such as americium-beryllium?
(There are probably some obvious sources of neutrons that I'm not thinking of, so let me know)

For example is it possible to make something like 1x10^18n/s using fusion or some other source and how much power would it actually take?

 

[Kritmiss]

Basically as the title says, what type of fusion would give the highest number of neutrons for a given amount of power.

The reaction between deuterium (D) and tritium (T) is the easiest to ignite and at any given temperature (up to a point) proceeds about ten times faster than the next fastest fusion reaction.


Also am I correct in assuming that most fusion methods will always produce more neutrons than other neutron sources such as americium-beryllium?
(There are probably some obvious sources of neutrons that I'm not thinking of, so let me know)

Gram for gram I think this would be the case.


For example is it possible to make something like 1x10^18n/s using fusion or some other source and how much power would it actually take?

1x10^18 is about the number of fissions which would take place in a typical criticality accident. It doesn't require any power, merely the right amount of fissile material in the right configuration. For example, a change in the chemistry of a plant process may increase the concentration of fissile material in solution resulting in criticality.

Hope this helps

 

[Cypher49]

What I would like to know is how much power do you need to produce 1x10^18n/s if you were fusing deuterium and tritium and it doesn't have to break even or be even close to breaking even, I just want to know how much power it would take to produce that many neutrons per second and because D-T fusion is the easiest does that mean it takes the least amount of power to produce the 10^18 neutrons compared to other methods of neutron production?

What about D-D fusion where there's a 50-50 chance of producing a neutron but when the tritium from the other branch is burned you get a neutron from that as well don't you?

So can both sources of fusion produce the high number of neutrons and if so, watt for watt which one is better?

 

[Drakkith]

T-D fusion is MUCH easier to create and sustain and will give the most bang for the buck. However, as tritium isn't readily available, D-D fusion may be a better choice.

 

[Kritmiss]

I have done a search for you, this article gives useful information about the various fusion reactions and their cross sections, hopefully it will help.
http://fds.oup.com/www.oup.co.uk/pdf/0-19-856264-0.pdf

 

[Dmytry]

Isn't americium/beryllium a form of fusion reaction? Helium 4 (alpha particle) - beryllium reaction, to be exact.
What do you mean exactly? Electrical power required vs thermal power of radioactive isotope? Or something else?
Well in theory if you electrically accelerate helium 4 into beryllium target, that would be more efficient than americium, in practice it would depend to apparatus.

 

[Bob S]

Isn't americium/beryllium a form of fusion reaction? Helium 4 (alpha particle) - beryllium reaction, to be exact.
What do you mean exactly? Electrical power required vs thermal power of radioactive isotope? Or something else?
Well in theory if you electrically accelerate helium 4 into beryllium target, that would be more efficient than americium, in practice it would depend to apparatus.

I used to use a PuBe (plutonium + beryllium neutron source, similar to the americium beryllium) neutron source. It was a fine powder mixture of plutonium and beryllium, inside a 1" diameter solid brass cylinder, and it emitted about 50 neutrons per million plutonium decays. It was not warm to the touch.

See http://adsabs.harvard.edu/abs/1955PhRv...98..740S

Bob S

 

[Cypher49]

I think I need to be more specific, and I'll split it into 2 parts.

What is the best/easily achievable way of producing 1x10^18n/s (fast)?

For the above 'best way' how much power would you need?

 

[Dmytry]

I think I need to be more specific, and I'll split it into 2 parts.

What is the best/easily achievable way of producing 1x10^18n/s (fast)?

For the above 'best way' how much power would you need?

lol, 10^18 fast? How fast, 2 MeV will do? The neutrons alone have power of 320 KW
http://www.wolframalpha.com/input/?i=2+MeV+*10^18+%2F+second

From the poster above's method, 50 neutrons per million decays, that's 5E-5 , so you have 10^18/5E-5 = 2*10^22 , i don't know which plutonium he used, I'll assume 5 MeV so i get 16 gigawatts lol.
http://www.wolframalpha.com/input/?i=5+MeV+*+2+*+10^22+%2F+second

the cheapest way at the moment probably is - nuclear reactor, idk how many megawatts power.
Fusion, IDK. A very high flux accelerator? What is the question for? Accelerator driven nuclear reactor? I'd hazard a guess that you'd need at least several megawatts to power this.

 

[Bob S]

( from Cypher49) For example is it possible to make something like 1x10^18n/s using fusion or some other source and how much power would it actually take?

Using "Typical fission events release about two hundred million eV (200 MeV) of energy for each fission event" and "2.5 neutrons per fission" from

http://en.wikipedia.org/wiki/Nuclear_fission

gives 80 MeV per neutron, which is 1.28 x 10^-11 joules per neutron.

So 1 x 10¹⁸ neutrons per sec ≡ 12.8 MW (thermal).

Bob S

 

[Dmytry]

he wants fast neutrons, and reactor itself uses most of neutrons it makes. so he'd need way more than 13 MW.
edit: for DT fusion, its 17.6 MeV per fusion, so go multiply by 10^18 to get about 3MW . Various fusion reactor crap was at verge of breaking even, so it'd be about 3..10MW electrical required.

 

[Cypher49]

Yes I only would like to know about neutron production methods that is not fission based, as in a fission reactor a lot of the neutrons are consumed in the reactor itself.

What about D-D fusion to make the neutrons, it's more difficult to do but you don't have to have an extra layer for lithium and to then collect the tritium that's produced.

So if a DT reactor can produce the high number of neutrons for ~12MW how much more power will you need for DD reactions.

Lastly, what type of fusion reactor would you need for this sort of thing, could something like a large fusor with enough power produce the high number of neutrons?

 

[MisterX]

Lastly, what type of fusion reactor would you need for this sort of thing, could something like a large fusor with enough power produce the high number of neutrons?

I have read people report 10^6 n/s from fusors. Fusors would be a poor way to produce 10^18 n/s, I think. For D-T, 10^18 n/s corresponds to megwatts in the form of neutron kinetic energy! Fusors are inefficent because of grid collisions. Also, fusors (except possibly very large devices) would not withstand the required power level needed to produce 10^18 n/s because the grids would melt or disintegrate due to grid collisions. How large the fusor needs to be to do 10^18 n/s is hard for me to say; I'm not sure of fusor scaling.

Regardless, 10^18 n/s should be possible with a tokomak of a non-absurd size.

 

[Cypher49]

As someone asked in one of the previous posts, this thread is regarding a subcritical reactor using an added source of neutrons. I'm just doing research for an upcoming 4000 word essay that I will have to write about power.

In one part of the essay you're meant to come up with a plan to do R&D and then build a prototype power plant with an output of at least 750MWe, all with $2 billion.
This is the reason that I started this thread because I was and still am not sure on what the source of neutrons will be.

So I'll put it out to you guys, if someone gave you $2 billion how would you build a sub critical reactor? (or an idea for another source of energy that could produce baseline power because the essay doesn't have to be about nuclear power it can be about any source)

 

[Dmytry]

As someone asked in one of the previous posts, this thread is regarding a subcritical reactor using an added source of neutrons. I'm just doing research for an upcoming 4000 word essay that I will have to write about power.

In one part of the essay you're meant to come up with a plan to do R&D and then build a prototype power plant with an output of at least 750MWe, all with $2 billion.
This is the reason that I started this thread because I was and still am not sure on what the source of neutrons will be.

So I'll put it out to you guys, if someone gave you $2 billion how would you build a sub critical reactor? (or an idea for another source of energy that could produce baseline power because the essay doesn't have to be about nuclear power it can be about any source)

I wouldn't. It'd cost more than $2 billion. Look at the cost of nuclear reactors using established technology:
http://en.wikipedia.org/wiki/Econom...wer_plants#Recent_construction_cost_estimates

Plus there is no reason to build a sub-critical reactor any more. Before certain recent developments in the empirical data regarding reactor safety, one could have sold sub-critical as 'inherently safe', but now everyone got a fresh demonstration of what decay heat is, and this marketing simply won't work.

Sub-critical designs have so much appeal due to the notion that chain reaction is unstable and dangerous (could result in a nuclear explosion) - but it is actually not so hard to keep in check, given delayed neutrons, Doppler broadening, and so on.

 

[minerva]

I really do not see any merit in accelerator-driven reactors.

You need to add a very large, powerful proton synchrotron (typically on the order of 10 mA proton beam at 1 GeV) to the reactor, so you're adding non-trivial extra complexity and cost. And for what? What does it give you, relative to any other advanced, modern fission reactor design like an IFR or LFTR?

The ability to immediately, rapidly shut down criticality, trip the reactor and put all the rods in is engineered into essentially every fission reactor ever built... and you certainly don't need to create an accelerator-driven reactor to create that functionality.

And anyway, in terms of management of the fission-product decay heat in the fuel after criticality has been stopped - in a contingency situation like Three Mile Island or Fukushima - the accelerator makes absolutely no difference to anything at all.