UN Secretary-General Ban Ki-moon has warned that the world must prepare for more nuclear accidents on the scale of Chernobyl and Japan's Fukushima Dai-ichi plant. He said that this grim reality will demand sharp improvements in international cooperation. UN Secretary-General Ban Ki-moon and others portrayed the growth of nuclear power plants as inevitable in an energy-hungry world as they spoke at a Kiev conference commemorating the explosion of a reactor at Ukraine's Chernobyl nuclear reactor 25 years ago.