If you get a runaway reaction, it has a fail-safe described in the article that drains the reactor into containment vessels underground.
[1] https://www.technologyreview.com/2015/09/04/166330/meltdown-...
Any reactor in use today will have a negative void coefficient. Which means, if you don't put power into it, the reaction naturally stops. Then you've got control rods and neutron moderators that will fall back upon the core if there's no power. Then Gen3+ includes a core catcher in which, should it breach its reactor, it just falls in there and cools down.
and radioactive material is like a fraction of the problem with coal. they have much worse health impact in other areas. they're linked (directly or indirectly) to 10000s of thousands of deaths a year.
That would mean around 10 quadrillion tons of coal would need to get burned to emit the same amount of radiation. China is currently burning 4 trillion tons of coal per year, which is a 2500th part of it.
https://pubmed.ncbi.nlm.nih.gov/20005612/
https://en.wikipedia.org/wiki/Chernobyl_disaster#Release_and...
https://www.scientificamerican.com/article/coal-ash-is-more-...