A project to complete the second reactor at the Watts Bar nuclear plant received a critical environmental approval Friday.

In a supplement to the unit's environmental impact statement, the Nuclear Regulatory Commission announced it found no environmental reasons that would prevent it from issuing an operating license for the reactor. The NRC also noted that it expects to complete its update to the unit's final safety evaluation report – the second NRC document critical to the license – in May of next year.

Watts Bar 2 has the same type of 1,150 megawatt Westinghouse reactor as unit 1, which was first licensed in 1996. The second reactor was mothballed roughly 80 percent complete in 1988 until TVA resumed construction in 2007. The federal utility's current schedule calls for unit 2 to be finished at the end of 2015, with the completion project costing between $4 billion and $4.5 billion.