TL;DR: Combining a particle accelerator and a nuclear reactor to turn Uranium-238 into Plutonium-239, which then fissions. The reactor itself is subcritical, so if the proton accelerator turns off then the reaction stops.

The main advantages of the system claim to be ‘increased efficiency of fuel use’ since the uranium doesn’t need to be enriched, the ability to burn long-lived nuclear waste, as well as the system being passively safe.

The first point strikes me as an odd thing to focus on, since all nuclear reactors are already very fuel efficient, and if you want maximum efficiency then breeder reactors exist already, which produce more fissile material than they consume - you can’t get much more efficient than that. Fast breeder reactors are also great for burning up nuclear waste too, but they never really took off because, well, there isn’t actually much nuclear waste to use, precisely because typical reactors are already very efficient: A reactor might consume one ton of fuel per year. You could fit all the spent nuclear fuel humanity has ever used into a single swimming pool. I mustn’t be too critical though - any attempt to close the fuel cycle is good, I just don’t think it’s a really pressing issue. Lastly, being passively safe is cool and all, but almost all new reactor designs are, and attaching a particle accelerator to a nuclear reactor sounds like an expensive way of doing it.

All of that being said, I’m always interested to hear about new reactor designs, so I guess we’ll see how it goes.