Nuclear accident (8)
I believe the answer is:
meltdown
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">nuclear accident</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I know that meltdown is a type of nuclear accident)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for meltdown that I've seen before include "Disastrous collapse - nuclear accident" , "Sudden disastrous failure (of nuclear reactor)" , "Total disaster" , "Disastrous event as to overheated nuclear reactor" , "Serious nuclear accident" .)