Nuclear reactor (7)
I believe the answer is:
breeder
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">nuclear reactor</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for breeder that I've seen before include "Red beer (anag)" , "Type of nuclear reactor - a rabbit is a fast one!" , "One producing offspring" , "Siring horse" , "Stud owner" .)