Final answer:
The metallic element used in nuclear power plants and NiCad rechargeable batteries is cadmium.
Step-by-step explanation:
The metallic element used in nuclear power plants and in NiCad rechargeable batteries is cadmium. Cadmium is a toxic heavy metal that is commonly used as the anode in NiCad batteries. It is chosen for this purpose because it has good electrochemical properties and can be easily recycled.