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"But to prove that it will work he has to demonstrate a self-sustaining reaction in uranium-238."

This is the rub. U238 doesn't fission, according to my references, it is a great absorber of "fast" newtrons, hence a good shielding material.

If the conditions are just right, the U238 becomes a U239 isotope and CAN, with the right conditions, become Pu239, Plutonium, which fissions quite well.

I doubt that this guy will ever demonstrate a self-sustaining reaction with the uranium left over in spent fuel. There are too many fission fragments in spent fuel acting as impurities that mess up the process.

U-238 fissions at neutron energies above 0.5 MeV. The average neutron energy from a fission is 2 MeV. The moderator, typically water, heavy water, or graphite, slows the neutrons down to thermal energy, roughly 0.4 eV (or is it 0.04 ev?, I forget), when they are absorbed by the U-235 nucleus (or Pu-239 or Pu-241).

Delayed neutrons are born in the keV (thousands of electron volt) range. They are born below the fast fission threshold of U-238.

Based on this article, I don't have a clue as to what they are trying to accomplish.

Delayed neutrons make up about 0.6% of all neutrons. Conventional thermal reactors, which include almost all of the power reactors now operating, depend on delayed neutrons for control of the reactor.