Heavy metal, you said? (7)

I believe the answer is:

uranium

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'heavy metal' is the definition.
(I've seen this in another clue)

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(Other definitions for uranium that I've seen before include "Radioactive metal used as fuel in nuclear reactors" , "Radioactive metal, atomic number 92" , "Radioactive element of atomic number 92" , "Radioactive metallic element" , "Fissile element" .)

I've seen this clue in The Independent.

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