sentences:  In February 2011, a major manufacturer in the nuclear industry reported a potential "substantial safety hazard" with control rods at more than two dozen reactors around the USA.GE Hitachi Nuclear Energy said it had discovered extensive cracking and "material distortion," and recommended that the boiling water reactors using its Marathon control rod blades replace them more frequently than previously told.If the design life is not revised, it "could result in significant control blade cracking and could, if not corrected, create a substantial safety hazard and is considered a reportable condition," the company said in its report to the NRC.