Georgia Power has said the unit is now expected to reach initial criticality during February and to be in service in April, a slight delay from the company's previous projections that the AP1000 unit would be in service during the first quarter of this year.

A view inside Vogtle 3's containment in December 2022 (Image: Georgia Power)

The delay is due to vibrations associated with certain piping within the cooling system, which were discovered during start-up and pre-operational testing at the unit, the Georgia Power parent Southern Company said in a filing to the US Securities and Exchange Commission (SEC) on 11 January. The plant's licensee, Southern Nuclear Operating Company, Inc, is in the process of remediating the vibrations.

The two AP1000s under construction at Vogtle near Waynesboro in Georgia are the first new nuclear units to be built in the USA in over three decades (two units that were also under construction at the VC Summer site in South Carolina were subsequently cancelled). Construction of Vogtle 3 began in March 2013 and unit 4 in November that year. Southern Nuclear and Georgia Power, both subsidiaries of Southern Company, took over management of the construction project in 2017 following Westinghouse's Chapter 11 bankruptcy.

Fuel loading at unit 3 was completed in October, and the projected schedule now depends primarily on the progression of start-up, final component and pre-operational testing, the company said. "New challenges also may arise which may result in required engineering changes or remediation related to plant systems, structures, or components (some of which are based on new technology that only within the last few years began initial operation in the global nuclear industry at this scale). These challenges may result in further schedule delays and/or cost increase," it told the SEC. AP1000s are already in operation at Haiyang and Sanmen in China.

Extending the in-service date for Vogtle 3 beyond the first quarter 2023 is estimated to result in additional base capital costs for Georgia Power of up to USD15 million pre tax per month, the company said.

Vogtle 4 is expected to begin hot functional testing by the end of the first quarter of this year.