Treasury Secretary Janet Yellen on Thursday said the swelling national debt is manageable as long as it stays around where it is relative to the rest of the economy. In a CNBC interview, Yellen also noted that high interest rates are adding to the burden as the U.S. manages its massive $34.7 trillion debt load. "If the debt is stabilized relative to the size of the economy, we're in a reasonable place," she told CNBC's Andrew Ross Sorkin during a "Squawk Box" live interview. "The way I look at it is that we should be looking at the real interest...