Michael, I haven’t looked into the situation at Fukushima for some years; there’s only so much bad news I can take, you know? There were four power stations at Fukushima; one was already shut down for maintenance when the tsunami occurred. When I last looked, it was generally accepted that all three running reactors had melted down. Investigations were proceeding trying to locate the melted core masses, but the radiation kept frying the camera robots they were sending in. It was widely assumed that the melted cores had melted their way out of the reactor vessels and into the ground beneath, but confirmation had been impossible to obtain.
Yes, that could be called a “meltthrough”, or three meltthroughs, though the term hadn’t been coined at the time.
As Pigeon English stated (August 20, 21:56 above), there are over 400 power reactors worldwide, most of which are on the coast and near sea level, to use seawater for cooling. But sea level is rising and weather events are becoming more extreme. Additionally, due to lunar orbit cycles, we have a decade of extreme coastal flooding approaching:
https://www.nasa.gov/feature/jpl/study-projects-a-surge-in-coastal-flooding-starting-in-2030s
I wonder how many of them should be de-fuelled? I think nuclear power may soon incur an enormous unforeseen cost.