The term REACTOR MELTDOWN SITE can be summarized as a location where a nuclear reactor has experienced a meltdown. A CORE is the central and most important part of a nuclear reactor, and it is typically composed of fuel rods containing uranium or plutonium. The CORE is the area where the nuclear reaction takes place, and it is surrounded by a containment structure to prevent radiation from escaping. In the event of a meltdown, the CORE can become damaged and release dangerous levels of radiation into the environment.