Bomber, working alone, starts to generate atomic yellowcake (5,3)
I believe the answer is:
enola gay
'bomber' is the definition.
(I've seen this before)
'working alone starts to generate atomic yellowcake' is the wordplay.
'working' indicates an anagram.
'starts to' suggests taking the first letters.
The initial letters of 'generate atomic yellowcake' is 'gay'.
'alone' with letters rearranged gives 'enola'.
'enola'+'gay'='ENOLA GAY'
(Other definitions for enola gay that I've seen before include "Hiroshima B-29" , "B-twenty nine that dropped the Hiroshima bomb" , "Bomber" , "B-twenty-nine that dropped Hiroshima bomb" , "Aircraft dropping Hiroshima bomb" .)