Terrible strain claims atomic technician (7)
I believe the answer is:
artisan
'technician' is the definition.
(I've seen this before)
'terrible strain claims atomic' is the wordplay.
'terrible' indicates anagramming the letters.
'claims' means one lot of letters goes inside another.
'atomic' becomes 'a' (eg in A-test, atomic test).
'strain' with letters rearranged gives 'artisn'.
'artisn' going around 'a' is 'ARTISAN'.
(Other definitions for artisan that I've seen before include "Journeyman" , "Skilled workman" , "Handy worker" , "Skilled worker or craftsman" , "Skilled worker by hand" .)