Cleric finds box with uranium (6)
I believe the answer is:
curate
'cleric' is the definition.
(thesaurus)
'box with uranium' is the wordplay.
'box' becomes 'crate' (crate is a kind of box).
'with' is an insertion indicator.
'uranium' becomes 'u' ('U' can be a synonym of 'uranium').
'crate' placed around 'u' is 'CURATE'.
'finds' is the link.
(Other definitions for curate that I've seen before include "He didn't really want an egg" , "Assistant to a parish priest" , "Parish priest's assistant" , "His egg is said to be good in parts." , "A truce for the church minister" .)