Top nun’s urge to tour Brazilian port (8)
I believe the answer is:
prioress
'top nun's' is the definition.
(head of a priory)
'urge to tour brazilian port' is the wordplay.
'urge' becomes 'press' (synonyms).
'to tour' is an insertion indicator (to tour can mean to go around).
'brazilian port' becomes 'rio' (Rio de Janeiro).
'press' placed around 'rio' is 'PRIORESS'.
(Other definitions for prioress that I've seen before include "A senior member of a female religious house" , "Religious leader" , "Superior nun" .)