Nuclear has never been particularly affordable. It's always been more expensive than coal or gas, even in France in the 70s-80s and China in the 2010s.

Here's how much it cost to build nuclear in France during its golden age: https://ifp.org/nuclear-power-plant-construction-costs. Adjust for inflation and draw your own conclusion.

China's nuclear costs are more opaque, but are estimated at $3B per GW. Again, not competitive.

Ontario produces a majority of its electric power from nuclear (https://en.wikipedia.org/wiki/Nuclear_power_in_Canada) and manages to sell it at competitive rates (https://www.oeb.ca/consumer-information-and-protection/elect...) similar to those in Alberta (https://ucahelps.alberta.ca/your-utilities/rates/historic-ra...) where electricity comes mainly from natural gas after a recent transition from mostly coal. A 2021 report cited at https://www.cns-snc.ca/learn-nuclear/basics-of-nuclear/how-m... finds that nuclear power in Ontario was more cost effective than everything else except hydroelectric power (granted, solar has become much cheaper in just the last few years). And this is in spite of multiple reactor shutdowns.

Yes, running a nuclear power plant is pretty cheap, if you ignore the cost of building and decommissioning it.

why is it different like that?

Mainly because regulators got scared and started adding line items for bogus safety reasons (like expecting to see background radiation levels far below those seen at coal plants due to the fly ash).

Coal plants are dead, partly due to the fly ash. I'm not sure you want to put nuclear in the same boat?

I'm not doing so. I'm pointing out that coal plants were allowed to produce more radiation than nuclear plants were allowed to out of fear of that radiation. Because the public is ill-informed about what "radiation" actually is.

I'm broadly supportive of nuclear fission, but I completely understand more nervousness of it than coal, particularly in the days before we cared much about climate change or industrial pollution. the worry about nuclear isn't low-level day to day pollution, it's disasters. coal disasters are essentially local incidents, and while they can have a big impact politically (f.e., Aberfan), they don't strike fear into people's hearts on a national or international level because the only people at risk to a disaster live very near a coal plant. when Chernobyl surged, half of Europe was affected. yes coal plants can have fallout too, but it's nowhere near as dangerous, even if the standard pollution is worse over time

coal plants were allowed to produce more radiation than nuclear plants because nuclear plants are nuclear plants and radiation management is an intrinsic part of the process. although they undoubtedly should have been, no one was paying attention to coal plants' radiation output, because they were invented before radiation was even discovered, and it's just not the star of the show there, nor is it the first consideration people have when considering coal pollution