Concerned with someone offered part for nuclear device (7)
I believe the answer is:
reactor
'for nuclear device' is the definition.
(nuclear reactor)
'concerned with someone' is the wordplay.
'concerned with' becomes 're' (re can mean regarding, concerning).
'someone' becomes 'actor' (actor is a kind of someone).
're'+'actor'='REACTOR'
'offered part' acts as a link.
This may not be right. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for reactor that I've seen before include "Atomic pile" , "See 3 Down" , "Nuclear energy generator" , "Heart of a nuclear power station" , "(Nuclear) powerplant" .)