In like manner, I believe that reactors should be designed such that an earthquake of any magnitude could not destroy the reactor or its containment shell, further that if the reactor core was to start to melt down, the melt down itself would shut the reactor down and, at the very worst, the reactor would entomb itself with no potential release of radiation into the environment.

FORBES: A Year After Fukushima Meltdown, Is Nuke Power Any Safer?

In a reactor, the containment structure may melt.

FORBES: Housing's Positive Feedback Loop and the Coming Meltdown

The reactor vessels remained intact as did the reinforced concrete containment buildings, but each reactor building lost its hat due to the hydrogen explosions.

FORBES: Explainer: What Caused The Incident At Fukushima-Daiichi