Metal I'd coated in wonderful uranium, say (8)

I believe the answer is:

actinide

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'uranium say' is the definition.
The definition suggests a singular noun which matches the answer.

'metal i'd coated in wonderful' is the wordplay.
'metal' becomes 'tin' (tin is a kind of metal).
'coated in' indicates putting letters inside.
'wonderful' becomes 'ace' (ace can informally mean very good).
'tin'+'id'='tinid'
'tinid' put within 'ace' is 'ACTINIDE'.

Can you help me to learn more?

(Another definition for actinide that I've seen is " element of radioactivity".)

I've seen this clue in The Times.

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