Rejoicing in lab crazily interrupts project (8)
I believe the answer is:
jubilant
'rejoicing' is the definition.
(thesaurus)
'in lab crazily interrupts project' is the wordplay.
'crazily' indicates anagramming the letters.
'interrupts' indicates putting letters inside.
'project' becomes 'jut' (I've seen this before).
'in'+'lab'='inlab'
'inlab' anagrammed gives 'bilan'.
'bilan' placed into 'jut' is 'JUBILANT'.
(Other definitions for jubilant that I've seen before include "Shouting with joy" , "Cock-a-hoop" , "In transport" , "Elated" , "Overjoyed" .)