Chattanooga Times Free Press: The Tennessee Valley Authority, created during the Great Depression to harness the power of the Tennessee River, is beginning the 21st century by turning to nuclear power and natural gas for additional electricity. But coal still is the primary fuel source for the electricity delivered to homes and businesses in TVA’s seven-state region. Burning coal generated more than 60 percent of TVA’s power last year. Despite concerns over air pollution and global warming caused by coal …