Despite the description of the March 11, 2011 disaster as “outside safety expectations”, there were multiple warnings from Japanese scientists, writers, activists, and international bodies that a large earthquake and tsunami could cripple Japan's nuclear plants. This article examines how assumptions of nuclear safety remained strong in Japan from the 1950s until the 2000s, even after numerous accidents that demonstrated inadequate oversight, and ties these assumptions to technological nationalism at the heart of Japan's conservative political culture.