Axil wrote: I do not intend to offend anyone; this is only a devils advocate argument.

A sub-national group steals an unguarded FF reactor from an unattended site. They then modify it to burn deuterium instead of boron. In this conversion process they replace the multi-layer foil electric generator with a beryillium/U238 blanket. They then operate this reconfigured reactor covertly for three months. They then chemically reprocess the Be/U238 blanket to extract plutonium.

Is this not possible?

What design provisions are necessary to preclude this scenario?

They’re gonna rack up a heck of an electric bill doing it that way (effectively, due to the energy budget of the process and the fact that no electrical energy is being made here, you are basically supplying all the energy for the reactions from the wall socket in a brute-force sort of way)…and 3 months is really quite, quite generous considering the amount of plutonium needed for a crude base-line implosion fission weapon (~10kg) with this sort of transmutation technique :p Unless this group also owns their own power plant and thus has access to unlimited free electrical power (how many did they steal? These things are small but they’re not THAT small!), you are probably looking at 30 years rather than 3 months if this is supposed to be done “on the sly” in some warehouse in the industrial district. The mechanics of fusion pinch reactors has been known for a long time (assuming your goal is not to have net positive energy production but instead just want to make high-energy fusion products)…yet everybody still makes their plutonium pit material (of those who are making them..N Korea for example) from breeder reactors. There’s a reason why. Plutonium can be made in particle accelerators too…but there’s no outcry about regulating those by the IAEA for non-proliferation issues. And the efficiency rate would be about the same as the modified FF device you’ve proposed from what I can surmise.

And I’m far more concerned that the sub-national group has obtained a large amount of refined U238 with which to attempt Pu239 production without drawing attention to themselves. Perhaps they went on a scavenger hunt in Serbia digging up expended A-10 round fragments from the soil? Creating a neutron source is relatively trivial these days for a group with a decent amount of financing…you don’t need a FF device to do that. What you are effectively asking is what design provisions are necessary in the manufacture of kitchen knives that will prevent violence in a world where an AK-47 can be had for under $100. A valiant goal yes..but not likely to make a difference in the big scheme of things.