South Korea Clears Restart of 685 MWe Kori 2 Nuclear Reactor

South Korea's Nuclear Safety and Security Commission (NSSC) has completed its inspections and confirmed that the 685 MWe pressurised water reactor (PWR) Kori 2 can be restarted. The unit has been offline since its operating permit expired on 8 April 2023. In November 2025, the NSSC had already approved continued operation of Kori 2 until 2033, granting operator Korea Hydro & Nuclear Power (KHNP) the necessary regulatory clearance. Against the backdrop of South Korea's renewed nuclear ambitions, the decision is part of a broader strategy to extend the operational life of the country's reactor fleet. Kori 2 began commercial operation in August 1983.

Inspections and Restart Conditions

The NSSC verified design changes to accident management facilities, including the reactor coolant external injection path, as well as the installation of power supply systems for essential accident response equipment. The authority conducted an in-depth inspection of the accident response strategy to ensure it was effectively implemented on site. In total, 10 safety measures required prior to restart under the continued operation permit were fully implemented, along with cable replacements to ensure safety margins. Improvements stemming from fire risk analysis — including the installation of new fire monitors — were also completed.

Given Kori 2's extended shutdown period, the NSSC conducted a focused inspection of safety-related pumps and valves, confirming that test cycles and operational performance met applicable standards and that steam generator management was properly implemented. Out of 102 periodic inspection items, 94 were verified, including the replacement of the passive catalytic hydrogen recombiner for severe accidents and a steam generator tube integrity inspection. The NSSC concluded that reactor criticality can be safely achieved.

Nine Other Reactors Awaiting Regulatory Decisions

KHNP has submitted safety assessment reports for the continued operation of nine other reactors whose licences expire before 2030: Kori 3 and 4, Hanbit 1 and 2, Hanul 1 and 2, and Wolsong 2, 3, and 4. These files are currently under NSSC review. Operations at Kori units 3 and 4 were suspended in September 2024 and August 2025 respectively, after their 40-year design lives had expired. The global nuclear industry is closely monitoring these regulatory milestones, amid a broader international resurgence of interest in atomic energy.

Kori unit 1 was permanently shut down in June 2017 after 40 years of operation, becoming South Korea's first reactor to enter decommissioning. KHNP submitted its dismantling application to the NSSC in May 2021, and the regulator approved the decommissioning of Kori 1 in June 2025. The contrasting trajectories of units at the Kori plant illustrate the dual challenge facing South Korea's nuclear sector: extending the life of its more recent reactors while managing the progressive retirement of older units.