Toshiba Corp faces a day of reckoning on Friday, when it is expected to offer an initial estimate of the multibillion-dollar charge it must take on its U.S. nuclear business, but this will be only a step in a series of tough choices on the Japanese conglomerate’s survival. Toshiba’s board meets to approve plans to spin off its semiconductor business as a separate company, hoping to raise more than 200 billion yen ($1.74 billion) by selling as much as a fifth of the core money-making unit, a person with direct knowledge of the matter said. But as the proceeds would be just a fraction of the hole from cost overruns in its Westinghouse nuclear business – which local media put at 680 billion yen ($6 billion) […]