## Fission-Fusion Hybrid Calculations

It may be difficult to separate "theory" from "application," but let''s see if this helps facilitate the discussion.
Caleb Winder
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### Fission-Fusion Hybrid Calculations

I am nearing my first fusor operation, probably within a week or two. The goal with my fusor is to get a neutron measurement and power input measurement in order to calculate the efficiency of a fission-fusion hybrid. In order to calculate the efficiency however, I will need to calculate the "K" factor of U-233. I have all of the calculations in place, except for that. Would anyone be able to help walk me through this calculation? I believe the "six factor formula" must be used.

Thanks,
Caleb

JakeJHecla
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### Re: Fission-Fusion Hybrid Calculations

What geometry, what moderator, what enrichment? It's not a straightforward calculation. You'll need access to MCNP or OpenMC at least.

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### Re: Fission-Fusion Hybrid Calculations

Not sure there is any point in using U-233 in a fission-fusion hybrid...why build a hybrid? If the fusion device has a high neutron flux you could use it to breed U-233 from thorium, and then use that U-233 in a reactor, preferably a molten salt reactor, or something. But the latter can actually then breed it's own fuel, in it's thorium blanket, bathing it in plenty of neutrons. The neutron flux from a fusor is VERY low, and it would take hell of a lot of time to breed meaningful amounts of U-233. You'd need about 30-40 kg for a MSR. You can actually fission U-238 with fast neutrons by the way, about the same energies D-D produces, if I recall correctly. If you search a bit on these forums you'll even find a fusion-fission hybrid idea, that uses boron as fissile material.

And as said above you can find the cross sections for most materials in online databases. I forgot the URL for the database I used a lot...I'll need to look it up.

Here is that fusion-boron fission hybrid thing I mentioned. I based my design on what Larry Leins came up with. He came up with the idea of using a pulsed neutron source to induce fission in boron, or other fissile materials.

viewtopic.php?f=14&t=6556&p=44431&hilit=hybrid+boron

Caleb Winder
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### Re: Fission-Fusion Hybrid Calculations

JakeJHecla:
Do you know where I would be able to find the OpenMC software? I am having trouble finding a place to download it. My reactor design is unlike most as instead of fuel rods, it uses hexagonal and pentagonal pellets with an area of 2-3cm and a width of 1cm to make a spherical casing (much like a soccer ball) around the fusor chamber. This is the fission blanket. In between the pellets are tubes containing water to act as the moderator and heat exchanger. In between the fusor and the shell is a water moderator to slow the neutrons to thermal speeds and to act as a secondary heat exchanger. Around the outside of the fuel blanket is a spherical layer of beryllium that reflects some of the neutrons back into the fuel. I will try to make a diagram, do you know of any good programs for reactor design? Also, is there any simpler formula to use? I do not need to much accuracy with my calculations, just an approximate estimate.

My design actually uses the thorium-232 as fuel, I was just going by the uranium-233 which is the material undergoing the fission for an easier calculation. It is a breeder reactor design (more specific description in the message above). I figured I would preform the calculations with the neutron count from my fusor and the count from the highest operating fusor ever (3X10^11). With the use of a moderator to slow the neutrons I figured the fusor could adequately drive a small sub-critical breeder reactor. For the design of your boron fission reactor, what program was used? I feel like my design would make more sense if I could give a visual representation.

Thanks,
Caleb

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### Re: Fission-Fusion Hybrid Calculations

It will breed, but as said above, quite slowly.

Your design is pretty much the same then, but with a spherical geometry. I chose cylindrical because it's simpler to do from an engineering standpoint.

Note that typically the total number of neutrons you get from the reactor per unit time is given when it comes to fusors. I assume that figure is no different (those here who actually know their fusor history , please do correct me if I'm wrong).

Neutron FLUX is the number of neutrons going through a unit area per unit time. That figure you cited might sound high (and it is, for a fusor) but it's actually not (the actual flux would be quite a bit lower still), and it's only achievable with a pulsed fusor (to my knowledge). Commercial fission neutron sources produce fluxes in the range of 1e15 n/cm^2s which is 10 thousand times greater per square cm than that pulsed fusor pushed through Its complete surface area!

A rapid pulsing, high flux fusor is probably possible, but i doubt it would be commercially viable. Is simpler to use U-235, or Pu-239 to start a thorium based reactor.

Royce Jones
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### Re: Fission-Fusion Hybrid Calculations

There is one potential application for a Fusion/Fission breeder and that would be when Space Launch is required. Not having radioactive material on-board the launch vehicle would be a big plus.

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### Re: Fission-Fusion Hybrid Calculations

U-235 has very low activity (very long half life), it's fairly harmless (apart from being a heavy metal, hence toxic). Pu-239 (high grade) is an alpha emitter, not particularly dangerous in that regard if handled correctly, but it's poisonous to the body, and if a Pu-239 contaminated dust particle sits into your lungs for example, it can cause localized damage over a long period of time, resulting in cancer. So yea, the fuel of choice would be U-235 to start a thorium (or any) reactor in-space (orbital or lunar), so if the rocket fails and falls apart, it has a lower potential to cause any ill effects in people who might be exposed (although they usually launch rockets over the ocean/sea, for safety reasons, so...). I'd say that a lunar nuclear station to breed U-233 for Mars or other space-missions would make a lot of sense....We'd just need to supply it with thorium (once the reactor is up and running), which is quite safe to haul around.

Dennis P Brown
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### Re: Fission-Fusion Hybrid Calculations

Your idea has merit (for uncontrolled re-entry safety issues) but there are zero applications for a nuclear reactor in space - at least inside Mars orbit since the Sun provides ample power via solar cells and the energy lasts without refueling.

As for propulsion - host of problems that no one has come close to solving; the high temps will erode/destroy any reactor matrix;, for human crews, the shielding for a reactor is prohibitive unless one uses a stand off - which has acceleration issues.

Fusion-fission hybrids have been looked at and are useless for direct power generation; indirect is an other mater but proliferation will kill any power application; can't change that issue so not worth pursuing.

Andrew Robinson
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### Re: Fission-Fusion Hybrid Calculations

Caleb,

Not to discourage you, but you are vastly over simplifying this process. Reactor theory/design is an immensely complex process. Even homogeneous reactor calculations can make your head spin. Jake makes all excellent points. You are missing many variables in this process. If you are dead set on continuing down this path, I highly recommend you start at the bottom and build a strong foundation. A lot of us got our start in nukie using the big green Lamarsh book (As we so affectionately called it). More specifically, Introduction to Nuclear Engineering by John R. Lamarsh

ISBN-13: 978-0201824988
ISBN-10: 0201824981

I would start there so you can grasp the basics. Do some homogeneous reactor designs to get your feet wet (there should be examples in that book). That will at least get you started and give you an idea of where you have to go.

Goodluck!
Andrew
I can wire anything directly into anything! I'm the professor!

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### Re: Fission-Fusion Hybrid Calculations

Dennis,

" there are zero applications for a nuclear reactor in space"

Even if you add "at least in Mars orbit" , this is a very ...bold statement...one with which I strongly disagree. I'll assume you mean "right now", but quite honestly the status quo in space exploration, while absolutely astonishing considering the funding, is saddening...

Here is my opinion:
Solar panels, while having their rightful place, are simply not the way to go if we ever dream to colonize or even thoroughly the rest of our solar system (and doing so in less than a century)...Their power density is pathetic, they are fragile, dust and radiation deteriorates them, and obviously when in shade, they don't produce any power. Energy storage (battery) is costly, bulky, heavy, has low specific capacity and has reliability issues.

Why do you think Curiosiry has an RTG? Even with its low efficiency,and high cost, it was a viable alternative to putting more solar panels and batteries on that rover.

Sticking with solar panels would absolutely prohibit using high power ion drives (200 kW to multi-MW range and beyond) for fast inter-planetary travel, unless you put several football fields worth of them on that craft...I'm sure we agree that is not practical. I haven't even got into cultivating crops in space, especially beyond Mars orbit... Even at Mars solar irradiation is less than half of what we have here, a measly 600 W/sq m... No serious colony could be based on solar panels unless we are willing to haul hundreds upon hundreds of cubic meters worth of panels there at extreme cost, or are willing to compromise a LOT when it comes to power usage...A single heavy lift rocket could probably get a 100 MWth reactor there. Maybe you'd need two for the complete plant.

Radiation protection of a manned nuclear-electric craft could be resolved rather easily by simply placing the core away from the crew module. This would greatly reduce the amount of shielding needed. I'd say you could position the water tanks in between. Just make sure there is a neutron shield around the reactor. Such a craft could be assembled in orbit, just like ISS was, delivering the power module, crew module, etc, separately.

Lets see...oh right, if the ISS had a nuclear power module the scope of possible experiments aboard would be greatly broadened...what else...lunar mining operations, colonies on the moons of Jupiter, deep space exploration...should I go on...?

Nuclear power IS the only known future (right now) for any large scale space exploration or colonization. Period. What we are doing today, while amazing, is just sploshing around in a pool. A lot more was promised, and a lot more is indeed possible with the technology we have today.

And, at the risk of being called a heretic...we don't need fusion. We need to do fission properly first, and quite frankly (prepare to throw those stones) that is what the funding going into ITER should've been spent on....

I typed this on my phone so excuse the typos.