University official holding a dangerous part of plant (7)
I believe the answer is:
reactor
'dangerous part of plant' is the definition.
'university official holding a' is the wordplay.
'university official' becomes 'rector'.
'holding' indicates putting letters inside.
'rector' enclosing 'a' is 'REACTOR'.
(Other definitions for reactor that I've seen before include "chemical substance!" , "Atomic pile" , "Nuclear installation" , "Producer of nuclear power" , "See 3 Down" .)