Shares of Usec (NYSE USU) rocketed up more than 27% on Thursday.

"We are not hearing any rumors or news responsible for the bullish activity. But obviously people are betting that USEC shares might be running to fill the gap left on the charts created when they warned on Feb. 26 that their outlook would not match street estimates," said Jon Najarian, a founder of Web information site optionmonster.com in Chicago.