KYIV, Ukraine (AP) – The head of the U.N.’s nuclear watchdog said Wednesday that a Ukrainian nuclear plant surrounded by Russian troops has lost all external power needed for vital safety systems for the second time in five days. International Atomic Energy Agency Director-General Rafael Grossi said agency monitors at the Zaporizhzhia Nuclear Power Plant reported the interruption and said backup diesel generators are keeping nuclear safety and security equipment operational. He said the repeated loss of power at the plant is “a deeply worrying development.”