What happens to a nuclear plant if you just leave it be?

>>9133396
I doing think it'll blow up but it will melt down without humans to renew the cooling process

>>9133396
Reactors blow up when the coolant becomes too hot and boils into steam, too much pressure ruptures the containment vessel and produces an explosion of steam. In the case of Fukushima it was caused by normal seawater being poured into the reactor and boiling off into a flammable gas which if I recall correctly was ignited when the fuel rods became exposed and came into contact with the gas.

Modern reactors wouldn't blow up, they have multiple backup safety systems such as liquid poisons (a liquid is injected into the reactor which damps down the reaction and stops it immediately) to kill the reaction if the reactor begins to melt down. Those safety systems are activated independently of human control or computer control. If they don't overheat and they just keep running, eventually the fuel rods will degrade and cool off, eventually rendering them dead and the reactor will stop producing power.

>>9133421
*I don't

>>9133396
They would shut down automatically after some days, or at least when some minor failure occurs

>>9133396
it depends. Nuclear power plants operate at an equilibrium the vast majority of the time.
By some means (such as a decline in power demand, a build up of radioactive poisons, you simply burn away some of the nuclear fuel, SOMETHING), a variable will change the reactivity inside of the reactor, and you'll start to see a drift. That drift will eventually shut the reactor down, or the drift will reach a safeguard setpoint and cause a reactor shutdown.
I know that about a decade ago only 3 reactors in the entire world had a positive void coefficient, so they're really the only reactors even capable of a runaway scenario without extra input(assuming those 3 reactors are even operating at all still), but I know nothing else about their system, so I can't even tell you if their safeguards aren't extra stupid-proof to arrest such a situation.

If none of the above happens, its likely that there is eventually a disruption in the power chain to critical reactor equipment that would by design also mean a shutdown of a reactor. At that point something like 50% of 50% of the world's reactors (basically older reactor designs that were running at higher levels of power before shutdown) would produce enough heat from radioactive decay that without some restored method of heat removal they would be forced to vent into a larger containment by design, and things would be fine, except a few could have a Fukushima style hydrogen buildup and explosion that could damage containment systems and could release some radioactive contaminants to the environment.

Despite involving explosions, that's still a lot different than "blow up". When reactors blow up and it always takes a concerted effort of multiple stupid people in simultaneous action to make that happen, with some dumbass job of engineering.