Greetings and felicitations

[Mark Stockman]

Hi!

My name is Mark Stockman, and I'm from upstate NY (not to be confused with NYC). I'm an armchair inventor, with an interest in alternate power sources for transportation. My goal is to use the KISS principle ("keep it simple, stupid!") to design prime movers that will be lower in total ownership cost per MW than the current generation of diesels and turbines.

My interest in the Farnsworth-Hirsch fusor comes from an idea I am working on for an ultra-compact subcritical fission reactor. The problem with subcritical reactor designs is generating a high enough neutron flux to initiate fission. Not incredibly difficult if you're working with a core of high-enriched fissile fuel that's only subcritical due to its shape. But for reasons such as cost, safety, non-proliferation, and NIMBYism, my plan is to start with fertile material (Uranium 238, Thorium 232, etc.) instead. Hence the interest in an inexpensive, reliable, high-flux neutron source using the D-D reaction. Needless to say, a billion dollar, mile long accelerator won't work, since I'm trying to fit the whole system within the size and weight parameters of a diesel engine of comparable output.

So, I came here to pick you folks' brains (via the forums) to research how Fusor technology can be used to produce maximum neutron flux, as opposed to maximum plasma containment. Any assistance would be greatly appreciated.

Thanks,

Mark Stockman

[Jim Kovalchick]

Welcome to the forum.

As much of a fan as I am of Thorium use in reactors, breeding U-233 from Th cannot be viewed as sensitive to non-proliferation because it is very similar to Pu 239. It also has the nasty disadvantage of being associated with U 232.
I am also unsure about non-proliferation aspects of the application of U 238 breeding since it inherently makes Pu.

So, why not just make a fission reactor? From a design standpoint, it is easier, and the safety benefits you imply don't really exist.

Either way, good luck to you. I hope you find the forum useful.

[Mark Stockman]

Thanks for the welcome. What I'm working on is essentially a "breed and burn" design. Theoretically, the fissile material will be burned at about the same rate as it's bred, so there is never a useful (from a weapons standpoint) amount of fissile material in the core, and it requires some serious chemistry to separate it.

A subcritical reactor has two advantages; First, inherent safety. Shut off the neutrons, the reactor shuts down. (You do need to design the core to deal with the decay heat after shutdown.) Second, a lot of the long-lived fission products will absorb neutrons and transmute into a heavier element and/or fission. You don't refuel until the core won't produce sufficient fission heat.

Welcome to the forum.

As much of a fan as I am of Thorium use in reactors, breeding U-233 from Th cannot be viewed as sensitive to non-proliferation because it is very similar to Pu 239. It also has the nasty disadvantage of being associated with U 232.
I am also unsure about non-proliferation aspects of the application of U 238 breeding since it inherently makes Pu.

So, why not just make a fission reactor? From a design standpoint, it is easier, and the safety benefits you imply don't really exist.

Either way, good luck to you. I hope you find the forum useful.

[Rich Feldman]

A subcritical reactor has two advantages; First, inherent safety. Shut off the neutrons, the reactor shuts down. (You do need to design the core to deal with the decay heat after shutdown.)

Welcome, Mark.

What you just described applies just as well to conventional fission reactors.
In steady state operation of a mature core, about 10% of the heat comes from decay, which you can't shut off.
In loss of cooling accidents it's the buildup of decay heat that has rendered cores on the floor,
as at Fukushima and (almost) at TMI.

Good luck with your project.

[Jim Kovalchick]

Yes Mark, I got the sense of what you are going for, but my tiny mind as yet does not compute how this works for anything but low fission rates because once you are past the point of adding heat, you will have to consider temperature dependent reactivity effects. Generally, you want your reactor to have a negative coefficient so as temperature begins to rise you will need to add reactivity to keep the reaction going. To add external neutrons to accomplish this will mean an energy input at a level that if it were viable you may as well just build a fusion reactor. Compensating for the reactivity by any other means implies having a reactor that could return to critical when it cooled off.

Subcritical multiplication is still effected by neutron eaters like poisons, leakage, and fuel configuration just like critical reactors.

I find all this very interesting regardless of my shortcomings in understanding it.

Either way, an admin will likely tell me that this is just an introduction thread and take this discussion elsewhere. Again, good luck.