Scientist is away during scrap (6)
I believe the answer is:
boffin
'scientist' is the definition.
(I know that boffin is a type of investigator)
'is away during scrap' is the wordplay.
'is away' becomes 'off' (I've seen this in another clue).
'during' means one lot of letters goes inside another.
'scrap' becomes 'bin' (I've seen this in other clues).
'off' going inside 'bin' is 'BOFFIN'.
(Other definitions for boffin that I've seen before include "Military scientist" , "Technical expert" , "Scientist (in the back room?)" , "Research scientist" , "Brainbox" .)