The reactor being built by TerraPower, a start-up, won’t be finished until 2030 at the earliest and faces daunting obstacles. The Nuclear Regulatory Commission hasn’t yet approved the design, and the company will have to overcome the inevitable delays and cost overruns that have doomed countless nuclear projects before.
This is the kind of high-risk project where it makes sense to have somebody with really deep pockets financing it. There’s a good chance that it’s not competitive with the improved storage technologies which are likely to be available when the demonstration reactor is completed.
There are other low-probability-of-success-but-amazing-if-it-works things he’s put money into, notably some of the enhanced rock weathering studies.