Minister shown round a nuclear facility (7)
I believe the answer is:
reactor
'nuclear facility' is the definition.
(I've seen this before)
'minister shown round a' is the wordplay.
'minister' becomes 'rector' ('rector' can be a synonym of 'minister').
'shown round' is an insertion indicator.
'rector' enclosing 'a' is 'REACTOR'.
(Other definitions for reactor that I've seen before include "Device to produce energy by nuclear fission" , "nuclear facility" , "Creator (anag.)" , "Producer of nuclear energy" , "(Nuclear) powerplant" .)