Hirsch-Farnsworth Fusor as trigger for thorium fission?

[Gandalf]

I've not seen this topic discussed here before, so forgive my obvious lack of homework or understanding of the physics involved, or if this has already been discussed.

So, with that disclaimer, the subject contains my question: Might it be possible to initiate a thorium fission reaction using the neutrons from a fusor? With the appropriate selection of fuels it seems from my armchair hand-waiving assumptions that sufficient neutron energy might be reached. Even if this Swiss-cheeses the fusor, if it initiates a stable thorium reaction, it might be worth it.

If possible, this would have obvious advantages over using a traditional U or PU fission as the trigger, and would allow non-nuclear nations to engage in fission power without the environmental and political fallout.

-Gandalf

[D Tibbets]

Yes, a single neutron could theoretically push a fission pile to criticality. The statistical nature of radiation though makes this completely unmanagable. For a neutron source to provide good control over fission criticality, I suspect the neutron flux would need to be at least several orders of magnitude higher than any IEC device to date. The geometry, moderation, etc all have their roles. The point is mostly moot though until the fusion neutron production can be so high that control rods become much less significant. Also, most if not the vast majority of power would becoming from the fission fuel near criticality. The plutonium production, radioactive isotopes production would also generally be unchanged. Thorium fuel would only work if the neutron source was very powerful and could work within the geometry of a fission reactor. In this case things may change significantly. There would be enough excess neutrons to not only keep the fission chain reaction going, but to also burn up the fission products. There has to be enough excess power from the fission process to provide the considerable power to run the fussion side. The closer the fusion reactor can come to break even the better. This is where a DPF type device might excel. Also, a Polywell or FRC might serve, though I don't think a large Tokamak would work.

Dan Tibbets

[Skipjack]

Helions FRC fusion engine would work very well for that.
http://www.helionenergy.com/

[chrismb]

I've not seen this topic discussed here before, so forgive my obvious lack of homework or understanding of the physics involved, or if this has already been discussed.

So, with that disclaimer, the subject contains my question: Might it be possible to initiate a thorium fission reaction using the neutrons from a fusor?

This has indeed, been often mooted here, fusor.net, and just about everywhere and anywhere that has ever argued for fusion!!

The 5th claim of Thompson and Blackman's patent, which I believe is the first ever fusion energy patent [1946] reads;

5. Apparatus...wherein said vessel is surrounded ..by uranium or thorium wherein plutonium or u-233 may be bred by neutrons emanating from the vessel.

OK, so as written that addresses breeding, per se, but the fission reactions follows breeding, of course.

[KitemanSA]

I've not seen this topic discussed here before, so forgive my obvious lack of homework or understanding of the physics involved, or if this has already been discussed.

Yes it has been discussed quite frequently. Neutron augmented reators don't much care where the neutron comes from. One path is an accelerator/spallation neutron source (frequently called "accelerator driven") and others include any number of sub-Q=1 fusion sources. Some folks call these setups fusion amplifiers.
I am pretty fond of the fusion driven Molten Salt Reactor with only fission product removal as the fuel reprocessing. Leave the Pa and higher actinides in there and overcome the poisoning with fusion neutrons. But that is just me.