Powerful explosive with nuclear particles? (9)
I believe the answer is:
herculean
'powerful' is the definition.
(powerful like Hercules)
'explosive with nuclear particles?' is the wordplay.
'explosive' becomes 'he' (abbreviation for high explosive).
'with' means one lot of letters go next to another.
'particles?' is an anagram indicator (the same parts or particles in a new order).
'nuclear' with letters rearranged gives 'rculean'.
'he'+'rculean'='HERCULEAN'
(Other definitions for herculean that I've seen before include "Powerful" , "Showing great strength" , "Enormously demanding (task)" , "Colossal" , "for Poirot?" .)