melt down

melt down (third-person singular simple present melts down, present participle melting down, simple past melted down, past participle melted down or (archaic) molten down)

1. (transitive) To melt fully, especially metal or glass so that it can be remade into something else.
   • 2021 December 1, Nigel Harris, “St Pancras and King's Cross: 1947”, in RAIL, number 945, page 39:

     The Great Exhibition of 1851 is also very much in King's Cross's DNA. The clock in its short, Italianate central tower came from the Exhibition and in its early years it struck the hours, but the bells were first silenced in the First World War and then melted down during the Second World War.

2. (intransitive) To lose structure by being heated to a molten state.

   The reactor core melted down.

3. (intransitive, figuratively) To have a breakdown; to collapse or fail utterly.