Reuters: apan will turn over hundreds of kilograms (pounds) of sensitive nuclear material of potential use in bombs to the United States to be downgraded and disposed of, the two countries' leaders said as a nuclear security summit began on Monday. China had voiced concern earlier this year about regional rival Japan's holding of plutonium but Washington and the United Nations nuclear agency have made it clear they are not worried about the way Tokyo is handling the issue. Still, U.S. President Barack Obama...