It is my understanding that this process uses a small amount of enriched uranium to begin a chain reaction in a cylinder of depleted uranium which produces plutonium, which, with additional neutrons creates a sustainable reaction breeding more fuel and producing energy. So at the end of the life of the fuel you have a cylinder of plutonium instead of depleted uranium with some plutonium in the mix. As interesting as this concept is, and with the potential it has for great returns in the form of energy I see the potential for other issues to arise. The production of weapons grade material, the radiological control issues for handling the "spent" fuel at the end of the life of the fuel are just two that come to mind. This could get very interesting.
With enough neutron reflector like beryllium around the cylinder, the neutron flux and hard spectrum should also burn out the Pu239. My hard spot is with the lack of control, this thing will burn low and slow for years, like a large tire fire (and about as controllable). Sure, the eggheads in fuels engineering might PROMISE that the burnable poison loading and moveable neutron reflectors can be lensed, yada yada but either it would be too weak to be cost-effective, or a future MARSSIM cleanup for Content1's kids.
It makes great sense to Gates because he never finished his engineering degree, the clean-green-doesn't rust bust or collect dust and it relieves cleanly to the bilge sales pitch is all about sizzle, not the steak. Plus it is someone else's Intellectual Property, another hallmark Gates business strategy. But I digress....
If gates really wants to push safe nuclear power in futuristic designs, the pulse reactor is the way to go. Lose power to the neutron generator, and the beam stops, the target piles now have only SCM present. They are a tad more money up front and a little less out the back end, but certainly much safer than an upside-down mild steel light bulb above grade rattling until the steam lines break off of the turkey fryer propped up inside
