Nuclear is so ridiculously energy dense that there's no near future where we're in danger of running out

Fissile material is not everywhere. A lot of it comes from Kazakhstan. I'll let you check the map to see why that might be an issue. I also think you might be overestimating how much fissile material is economically feasible to extract.

I'm not saying we shouldn't be also building up renewables but every powersource has its limitations and making a mix of all of these to cover each of the downsides is our best bet.

Nuclear is a bad addition to that mix. It's too expensive, relies on rare materiald but most of all, it's deeply, fundamentally inflexible. The variability of the cheapest energy sources (solar/wind) makes nuclear a bad idea because you can't quickly turn a reactor on or off in an economically feasible way. These reactors are already so subsidized, they'd need to be running almost 24/7 to make it profitable. And with cheaper energy coming from solar and wind, we're just not going to need that. And once a nuclear reactor needs to be turned off repeatedly, it's profitability disappears into thin air.

Even a gas-powered power plant is a better idea at that point. It has some emissions unfortunately, but it is very quick to power and scale up when needed.