&gt; How safe are the other reactor designs when malicious human intervention is considered is still a very open question.<p>Nothing is safe from malicious action, absolutely nothing. You can cut someone with a piece of paper, drown them with a glass of water, or stab them in the throat with a pencil. You can even simply punch someone with your hand in the back of the neck and kill them. We simply make malicious action difficult and unlikely through design and rules, exactly how we manage cars and coal plants and nuclear weapons.