The media sometimes uses "China Syndrome". A nuclear meltdown is a catastrophic failure of the reactor core from overheating caused by a failed cooling system. The nuclear fuel assemblies overheat to a temperature of over 4000 degrees Fahrenheit (2000 degrees Celsius) and melt either completely or partially. A completely or largely molten core has the potential to release widespread radioactivity into the environment, if the reactor's core catcher does not work as intended.