meltdown

(countable, uncountable) Severe overheating of the core of a nuclear reactor resulting in the core melting and potentially in radiation escaping.
(countable, uncountable) A situation being likened to a nuclear meltdown; a crisis.
(countable, informal, uncountable) A tantrum or emotional outburst.
(countable, uncountable) An autistic response to stress or sensory overload, in which the person is overwhelmed by intense, seemingly disproportionate emotions, behaving erratically and becoming unable to mask.