99% of commercial reactors irl are Gen2 designs from the 70s and 80s. Basically slightly more advanced LWR (light water reactors). That’s why they use water, not to mention the water used to run the turbines. The remaining 1% are Gen3 reactors from the 90s and early 2000s, but they’re mostly experimental proof-of-concept reactors. Nobody wants to be the first to build a full scale reactor that has never been used commercially before, not to mention the bad reputation nuclear has.
Gen4 reactors are still in development, the goal is to start building them in the 2020s. The only problem is that out of 6 designs, only one can be made with currently known materials
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