The pressure vessels weren't compromised?
“The pressure vessels weren’t compromised?”
According to this article, and several others, the pressure vessels were indeed compromised, hence the references to 7cm and 10cm holes in them in this article.
Presumably, the melted puddle of fuel rods in the bottom of the pressure vessel melted those holes and then at least some of the puddle continued to leak out the holes into the bottom of the containment vessel, which by the way, is a large, hollow concrete structure that houses the much smaller stainless steel pressure vessel.
Now it’s also looking like the containment vessel is compromised too, though I haven’t seen any details as to the nature of the damage, e.g., cracks from the earthquake, broken pipe fittings, and/or melted-down fuel rods melting through the bottom of the containment vessel.