Defy consequences of nuclear incident, stealing aluminium (5)
I believe the answer is:
flout
'defy' is the definition.
(thesaurus)
'consequences of nuclear incident stealing aluminium' is the wordplay.
'consequences of nuclear incident' becomes 'fallout' (nuclear fallout, radiation).
'stealing' indicates named letters should be taken away.
'aluminium' becomes 'al' ('Al' can be a synonym of 'aluminium').
'fallout' with 'al' taken away is 'FLOUT'.
(Other definitions for flout that I've seen before include "Show contempt for, defy" , "Ignore (rule)" , "Show blatant disregard for" , "Disobey openly and scornfully" , "Treat with contempt" .)