An American seized in Yemen in a sweep of suspected al-Qaida members had been a laborer at six U.S. nuclear power plants, and authorities are investigating whether he had access to sensitive information or materials that would be useful to terrorists. Sharif Mobley, 26, worked for contractors at plants in New Jersey, Pennsylvania and Maryland from 2002 to 2008, mostly hauling materials and setting up scaffolding, plant officials said. Nuclear Regulatory Commission spokesman Neil Sheehan said Friday that investigations are under way into which areas Mobley entered. But he noted that areas containing nuclear fuel are tightly controlled, and that...