Progress Energy Florida asked federal regulators on Friday for approval to operate its planned Levy County nuclear plant. It is one of several regulatory hurdles the St. Petersburg utility must clear before it can rev up the two Westinghouse AP1000 reactors it plans to build in Levy County, several miles north of Crystal River. The utility has already won approval from the Florida Public Service Commission. It will come before the commission again in September to determine how much it can start charging customers for the project. Customers could start footing the bill for the $17-billion project as early as January. The utility also has to win site approval from the Florida Department of Environmental Protection. The federal review by the Nuclear Regulatory Commission could take close to three years.