meltdown vs catastrophe

meltdown and catastrophe both are nouns.

Word	Noun	Adjective	Verb	Adverb
meltdown	Yes	No	No	No
catastrophe	Yes	No	No	No

As nouns, catastrophe is a hypernym of meltdown; that is, catastrophe is a word with a broader meaning than meltdown:

Other hypernyms of meltdown include calamity, cataclysm, disaster, tragedy.

meltdown (noun)	catastrophe (noun)
a disaster comparable to a nuclear meltdown	an event resulting in great loss and misfortune
severe overheating of the core of a nuclear reactor resulting in the core melting and radiation escaping	a sudden violent change in the earth's surface
	a state of extreme (usually irremediable) ruin and misfortune