Yes, breaching a containment layer is worse than meltdown, though it’s pretty much what would be expected after a full meltdown of a typical power reactor. I don’t know how bad a situation like Fukushima could get. Whether, for example, the core material could burn its way right out of all containment and start contaminating ground water or the ocean. Apparently that’s not happening and just capping them over will contain them, like Chernobyl. Officially, they were declared to be in “cold shutdown” in December 2011 – somewhat ironic as no one can get near enough to take a proper look. Here are some reports from 2017 onwards:
https://en.wikipedia.org/wiki/Timeline_of_the_Fukushima_Daiichi_nuclear_disaster#20_June
I don’t like water cooled reactors. Water is an unsuitable coolant because its boiling point is far too low; it explodes at nuclear reactor temperatures. It was a steam explosion that blew the 1000 tonne lid off the Chernobyl reactor.
But the Fukushima power stations were over forty years old, and they’d even been re-licensed beyond their design lifetimes. There are much safer reactor designs now. I’d like to see some molten salt and other designs prototyped, but for half a century power reactor development has stagnated, often due to public opposition.
These days, wind and solar electricity are cheaper. In particular, the growth rate of installed solar capacity is exceptionally high. But massive, international expansion of the grid is needed to take advantage of wind and solar. Nuclear power’s natural place is probably heavy industry’s centralised, continuous requirements – replacing coal for smelting steel, for instance.