This note was quite short, so Bill Gates didn't go into much details.
The details are:
* Bill believes in a new nuclear fission technology that addresses the concern of nuclear waste, traveling wave reactor [1].
* He financed a startup called TerraPower [2] to demonstrate and then to put in use this technology
* Being aware of the strong anti-nuclear sentiment in the US and of the more friendly attitude in China, he signed an agreement with China National Nuclear Corporation to build a 600MW reactor in China
* With the new US administration more hawkish approach towards China, some new restrictions on nuclear deals were announced by the Department of Energy in October [3]
* Gates' TerraPower venture found itself in the crosshairs of these restrictions, so the deal with the CNNC became for all practical purposes void [4]
[1] https://en.wikipedia.org/wiki/Traveling_wave_reactor
[2] https://en.wikipedia.org/wiki/TerraPower
[3] https://www.energy.gov/articles/doe-announces-measures-preve...
[4] https://www.rt.com/business/447910-bill-gates-nuclear-china/