Check uranium in mine entrance (5)
I believe the answer is:
audit
'check' is the definition.
(an audit is an examination or check)
'uranium in mine entrance' is the wordplay.
'uranium' becomes 'U' (U is the chemical symbol for uranium).
'in' is an insertion indicator.
'mine entrance' becomes 'adit' (an adit is a passage leading to a mine).
'u' going inside 'adit' is 'AUDIT'.
(Other definitions for audit that I've seen before include "Check of books" , "Official inspection of company accounts" , "Financial investigation" , "Verify accounts" , "Formally examine" .)