Nuclear device's designer about to be demoted (7)
I believe the answer is:
reactor
'nuclear device's' is the definition.
(nuclear reactor)
'designer about to be demoted' is the wordplay.
I cannot quite understand how this works, but
'about' could be 'rea' (I've seen this in other clues) and 'rea' is present in the answer.
'to' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for reactor that I've seen before include "Nuclear energy generator" , "one liable to have a meltdown if things go disastrously?" , "I swing back" , "Creator (anag.)" , "Nuclear power station core" .)