Which gundam did you say? The earliest rx782 was of course powered by the energy of the core fighter. Nuclear energy needs a radiator. Gundam radiators are mostly in the chest, while miscellaneous valleys are in the head and mouth. Gundam's nuclear power is certainly more advanced, because Gundam doesn't need so many tubes, its face doesn't need to be as wretched as Zagu, and its power is getting lighter and lighter. One gundam is worth ten Zagu!