meltdown vs disaster

meltdown and disaster both are nouns.

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

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

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

meltdown (noun)	disaster (noun)
a disaster comparable to a nuclear meltdown	an act that has disastrous consequences
severe overheating of the core of a nuclear reactor resulting in the core melting and radiation escaping	an event resulting in great loss and misfortune
	a state of extreme (usually irremediable) ruin and misfortune