Person taking part from atomic pile without engineers (5)
I believe the answer is:
actor
'person' is the definition.
(actor is a kind of person)
'pile without engineers' is the wordplay.
'pile' becomes 'reactor' (term for a nuclear reactor).
'without' is a deletion indicator.
'engineers' becomes 're' (abbreviation for Royal Engineers).
'reactor' with 're' taken away is 'ACTOR'.
'taking part from atomic' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for actor that I've seen before include "I pretend" , "eg Anthony Hopkins" , "Film star" , "Theatrical performer" , "One on stage" .)