CARACAS, Venezuela (Reuters) - Venezuela's President Hugo Chavez is approaching his wary South American neighbors about developing a nuclear energy program, raising questions in Washington about his atomic ambitions. ADVERTISEMENT Chavez, a self-described socialist revolutionary fiercely opposed to the U.S. administration, says he wants to cooperate with Argentina, Brazil and possibly Iran to develop nuclear energy as part of his drive for regional integration. But energy experts estimate it will take his government at least five years of studies, training and investment to develop a sustainable nuclear energy project in Venezuela, the world's No. 5 oil exporter. "Nuclear energy is...