Toshiba, a fixture of Japan Inc. for more than a century, is in big trouble — to the tune of $6.3 billion. The company announced that whopping loss after the market closed in Tokyo today, and that may not be the worst yet. Some news reports say Toshiba might not survive in its current form. It is, as they say, complicated. But at the center of this is Toshiba’s big bet that turned sour on nuclear energy in the U.S.