The first payment under the new agreement is due from Toshiba in October.
According to Toshiba, the $3.68 billion is the maximum payment required under its contract with Southern Company.
"We are pleased with today's positive developments with Toshiba and Westinghouse that allow momentum to continue at the site while we transition project management from Westinghouse to Southern Nuclear and Georgia Power", said Paul Bowers, chairman, president and CEO of Georgia Power.
Construction work at Vogtle and Summer has been continuing under interim assessment agreements with the plants' respective owners since Westinghouse's bankruptcy filing. But the company promised Saturday it will pour up to $3.68 billion into the project to finish it.
"We are happy to have Toshiba's cooperation in connection with this agreement which provides a strong foundation for the future of these nuclear power plants", Tom Fanning, Chief Executive of Southern Company, said in a statement.
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The move comes after Georgia Power took over the plant's project management from Westinghouse Electric Corp, which filed for Chapter 11 bankruptcy in March. And even before Westinghouse went bankrupt, the project was plagued by delays and unexpected costs.
"Toshiba aims to finalise the total maximum amount of the parent company guarantee for all four nuclear reactors under construction in the USA, and will ensure prompt disclosure of information related to this matter as and when it becomes available", it said.
To stay afloat, Toshiba has been trying to sell its lucrative computer chip business.
Toshiba's earnings reports have failed to get endorsements from its auditors, given the company's precarious finances over the US projects. According to Toshiba, the agreement specifies that the agreed maximum can not be subjected to any further increases or claims by the plant's owners "even in the event of future increases in construction costs". It also produces extremely unsafe radioactive byproducts, which was at the core of the nuclear power disasters in Fukushima in 2011 and Chernobyl in 1986.
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