John McCain embraces it. Barack Obama wants to address its flaws. Hillary Clinton is cautious but not opposed. Nuclear power—controversial in the United States and throughout much of the world—is on the agenda of all three U.S. presidential candidates as they seek to diversify the country's energy mix and reduce dependence on foreign oil. Interviews with top policy advisers to the three White House hopefuls reveal a varied approach to the technology that some observers see as a necessary answer to fighting climate change and others view as expensive and dangerous.Update: Reuters has published a sidebar, Factbox, presenting each candidate's positions in more detail.