Greek character with clarinet and Corea playing fusion? (7,8)

'fusion?' is the definition.
(fusion is a kind of nuclear reaction)

'greek character with clarinet and corea playing' is the wordplay.
'greek character' becomes 'nu' (letter from the Greek alphabet).
'with' says to put letters next to each other.
'and' says to put letters next to each other.
'playing' indicates anagramming the letters.
'clarinet'+'corea'='clarinetcorea'
'clarinetcorea' anagrammed gives 'clearreaction'.
'nu'+'clearreaction'='NUCLEAR REACTION'