There is something with very wealthy people and unproven technology. Numerous experimental nuclear reactor types have been developed, tested, and found lacking. A new reactor type that will fix all of nuclear's problems isn't a novel idea. So why would this reactor to be built by Gates and Buffett be any different? What do they know that the rest of the scientific community has missed? Same thing with Elon Musk and the Hyperloop; what does he know that thousands of people who have tried to improve mass transportation doesn't?

It's their money, of course, but I can't help think that it would be better spent on improving renewable technology. Wind, solar, and hydro are already beating nuclear on a cost-per-watt basis and we are very close to a situation in which a grid based on renewable energy complemented by battery storage is the most cost efficient way to generate electricity.