Momentum slows on Obama's nuclear security agenda

By Matt Spetalnick and David Brunnstrom WASHINGTON (Reuters) - Just as fears of nuclear terrorism are on the rise, President Barack Obama's U.S.-led drive to lock down all vulnerable atomic materials worldwide risks losing momentum. Obama will convene a global summit in Washington this week in the aftermath of deadly militant attacks in Brussels that have fueled concern that Islamic State could eventually target nuclear plants and develop radioactive “dirty bombs.” But despite signif