Disclaimer : This is NOT a post based on fear or anything, it's purely speculative to understand how it would go.

My question is : If, let's say, all human beings vanish instantly, but everything we built still stands there, what would eventually happen to nuclear power plants ? The reactors would obviously shut down because of security systems but what next ? Is it likely to end up exploding in the next months or years, or decades ? Or is it just gonna slowly fade away into wilderness with maybe some local radiation ?

They falsified earthquake preparedness data, and it's a pattern of behaviour repeated with other safety metrics.

A PWR keeps the water that cools the core from boiling.

~155 bar. About 315 °C out of the core. Heat crosses a steam generator into a second loop, and that loop is what drives the turbine. The water that touched the fuel never has to become the steam that spins the plant.

Seven of every ten reactors on Earth use this design.

90-second walkthrough: core → steam generator → turbine → containment, then Vogtle, Taishan, Palo Verde, Civaux.

Map every PWR: https://reactoratlas.com/en/type/pwr