Clergyman going round a power plant (7)
I believe the answer is:
reactor
'power plant' is the definition.
(I've seen this in another clue)
'clergyman going round a' is the wordplay.
'clergyman' becomes 'rector' (rector is a kind of clergyman).
'going round' indicates putting letters inside (some letters go around others).
'rector' going around 'a' is 'REACTOR'.
(Other definitions for reactor that I've seen before include "Nuclear energy source" , "nuclear facility" , "(Nuclear) powerplant" , "See 3 Down" , "I swing back" .)