South Korea’s Nuclear Safety and Security Commission (NSSC) has confirmed that all nine mandatory inspections required ahead of initial criticality have been successfully completed for the Saeul unit 3 reactor during its pre-operation inspection phase. This milestone marks a critical step toward bringing the Saeul unit 3 reactor into service, as regulatory scrutiny continues to ensure operational readiness following fuel loading inspections and ahead of testing.
The origins of the project trace back to January 2014, when the government approved the construction of two APR1400 units designated as Saeul units 3 and 4, previously referred to as Shin Kori 5 and 6. Although construction was initially expected to begin in September 2014, the timeline shifted, with the regulator ultimately granting a construction licence in June 2016. Site activities commenced immediately thereafter, and construction of unit 3 officially began in April 2017. However, a change in government in June 2017 prompted Korea Hydro & Nuclear Power (KHNP) to halt work for three months. Progress resumed in October 2017 following a government-organised committee vote, where 59.5% supported continuing the project, citing power supply stability as a key factor. Construction of unit 4 later began in September 2018.
Before these delays, the two units were slated for commercial operation in March 2021 and March 2022. However, the timeline has since shifted significantly. In late December 2025, the NSSC granted an operating licence for the Saeul unit 3 reactor, clearing the way for fuel loading and an estimated eight months of testing. Commercial operation is now anticipated around August 2026, while Saeul 4 is expected to come online in late 2026. The NSSC has stated it will carry out additional follow-up inspections, including power increase tests, from the point at which the Saeul unit 3 reactor achieves first criticality, defined as a sustained chain reaction, through to full commercial operation.
Once operational, the Saeul unit 3 reactor is projected to contribute approximately 1.7% of South Korea’s total power generation and meet around 37% of Ulsan’s electricity demand. South Korea currently operates four APR1400 units, including Saeul units 1 and 2 and Shin Hanul units 1 and 2, while Saeul units 3 and 4 remain under construction. Beyond domestic deployment, four APR1400 reactors have also been completed at the Barakah nuclear power plant in the UAE, where they are now fully operational.
