The Tennessee Valley Authority yesterday approved plans to produce nuclear weapons material in a commercial reactor for the first time in U.S. history, breaching the wall between civilian and military nuclear power. The TVA board voted unanimously to allow the Watts Bar plant in Tennessee to produce tritium as early as 2003, while continuing to supply electricity to the TVA. Activists were none too happy about the deal between the TVA and the Energy Department, saying it runs counter to efforts to get other countries to reduce their nuclear weapon arsenals and not mix civilian and military uses of reactors.