(Bloomberg) -- Southern Co.’s beleaguered Vogtle nuclear project is getting pushed back again after the company discovered documentation issues that will delay completion by as much as six months, prompting a $920 million charge.

The Unit 3 reactor may not go into service until March 2023 and Unit 4 may not be complete until the end of next year, Chief Executive Officer Thomas Fanning said in an interview Thursday.

The delays are yet another setback for the only nuclear plant under construction in the U.S. The Vogtle project in Georgia is now about seven years behind schedule and costs have doubled. The project will be the first new nuclear units built in the country in the last three decades.

“I’m frustrated,” Fanning, 64, said. “Every day when I get up I have Vogtle on my mind.” 

Shares of the Atlanta-based utility owner fell 1.8% to $63.68 at 9:39 a.m. trading in New York, its lowest intraday price in more than two months.

About half of the $920 million pretax charge stemmed from construction issues, with the rest related to a cost-sharing agreement with the company’s partners. The charge caused Southern to swing into the red in the fourth quarter, with the company posting a net loss of $215 million compared with earnings of $387 million a year earlier, according to a statement.

Southern discovered in December that there were significant lapses in inspection reports for Unit 3. This will delay some needed approvals from the Nuclear Regulatory Commission and prompted the company to push back its estimated completion date by three to six months, Fanning said. 

“We started seeing this at the very end of 2021, and it just got bigger,” he said.

(Updates shares in fourth paragraph.)

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