An Associated Press article reporting on the collapse of a flood wall protecting the Fort Calhoun nuclear power plant against historic flood waters on the Missouri River mentions that "The berm's collapse didn't affect the reactor shutdown cooling or the spent fuel pool cooling, but the power supply was cut after water surrounded the main electrical transformers, the NRC said. Emergency generators powered the plant Sunday while workers tried to restore power." (emphasis added) If the emergency diesel generators were also to fail (as by being submerged under flood waters), the final line of defense, in terms of running vital reactor cooling systems, would be the direct current (DC) emergency batteries. At most U.S. atomic reactors, such batteries only have 4 hours of life.