melt down
• melt a metal article so as to reuse the raw material.
• "beautiful objects are being melted down and sold for scrap"
• collapse or break down disastrously.
• "many expected him to melt down at the first sign of trouble"
• (of a nuclear reactor) undergo a catastrophic failure as a result of the fuel overheating.
• "if the pumps that cool the reactor core become disabled the core could begin to overheat, and the reactor could melt down"
