Reuters: Prices for credits that ethanol blenders can buy to meet U.S. biofuel requirements have risen about 9 percent since late last week on worries that producers may not be making enough of the alternative fuel to meet U.S. mandates, Rinxchange said on Tuesday. The credits are up amid shutdowns of plants owned by VeraSun Energy Corp (VSUNQ.OB) and other U.S. ethanol producers. VeraSun said on Tuesday that 12 of its 16 plants are in “hot idle,” or shut but not currently making …