Uncle's destroyed uranium included in core (7)
I believe the answer is:
nucleus
'core' is the definition.
('nucleus' can be a synonym of 'core')
'uncle's destroyed uranium included' is the wordplay.
'destroyed' is an anagram indicator.
'uranium' becomes 'u' (U is the chemical symbol for uranium).
'included' indicates putting letters inside.
'uncles' with letters rearranged gives 'nucles'.
'nucles' placed around 'u' is 'NUCLEUS'.
'in' is the link.
(Other definitions for nucleus that I've seen before include "Tiny factor" , "Atom's core" , "Core, centre" , "Heart of the Matter" , "Centre of an atom" .)