Some countries have formally committed to eliminating power from nuclear fission. Most have not. Most countries have at least some regions that would be happy to accept the good, stable employment and tax base offered by a nuclear power plant in exchange for the very slight risk of accidents. So why aren't more fission power plants getting built in countries where they are not formally excluded? I believe the single greatest factor is that they take too long to build and require too large a lump of money, because a single modern reactor is too big.

Modern Generation III/III+ reactor designs have actually made this "chunkiness" worse; there's no modern reactor design under 500 MWe that's certified in the US, Canada, Japan, South Korea, or the EU. Designs in that lower power range were built decades ago, and a few still run, but now it's big-or-nothing. AP1000 and EPR are 1117 and 1600 MWe, respectively, and all projects using them are behind schedule/over budget. And since these large projects are leading to such poor outcomes for involved companies, it will be difficult to get follow-on orders that will benefit from the hard earned lessons of their initial builds.

Even if all the technical problems are solved and fusion proves capable of producing net electricity, fusion power risks hitting this same too-big-to-build problem afflicting fission if it can't scale down. If the only approaches that work are enormous tokamaks with an entry level price of $10-billion-or-more, then they'll be engineering marvels that hardly anyone builds. Maybe they'll someday supply 10% of China's electricity.