The U.S. Nuclear supervision commission says a quarter of the country\'s nuclear plants fall short of safety levels, and need to be upgraded to withstand natural disasters. The commission launched an investigation of all 104 U.S. nuclear plants, following the Fukushima crisis in Japan. 27 were found to have a lower than expected ability to withstand natural disasters, such as earthquakes. Some parts of the U.S. have been shown to be more earthquake prone than was thought at the time the nuclear plants were built.