Indigenous APR1400 PWR unit could begin commercial operation in September
The Saeul-3 nuclear power plant in South Korea has achieved first criticality with commercial operation potentially scheduled for September, state operator Korea Hydro & Nuclear Power (KHNP) said.
First criticality is the milestone moment a nuclear reactor first achieves a stable, self-sustaining nuclear chain reaction. The reactor is officially “alive” and operating at low power, although it is not yet producing electricity for the grid.
The key step came after the Nuclear Safety and Security Commission (NSSC) said its inspections at Saeul-3, near Busan in the south of the country, showed the reactor could safely achieve a sustained nuclear chain reaction.
The NSSC began pre-operational inspections after issuing an operating licence in December.
The latest checks focused on systems required before the reactor reaches criticality.
“During this process, inspections were conducted on items that must be performed before criticality, such as nuclear fuel loading inspections and high-temperature functional tests,” the NSSC said. “As a result, it was confirmed that reactor criticality can be safely achieved.”
Construction of the indigenous 1,340-MW APR1400 pressurised water reactor unit at the Saeul nuclear station, formerly known as Shin-Kori, began in April 2017, but has been delayed by changes in government policy.
State nuclear operator Korea Hydro & Nuclear Power (KHNP) applied for the licence on 5 August 2020, alongside one for the identical Saeul-4 unit, construction of which began in September 2018.
The move comes as president Lee Jae Myung pushes for renewable energy, reversing course from the more pro-nuclear stance of his predecessor Yoon Suk Yeol.
Lee said in September that building more nuclear power plants is not realistic because it takes more than 15 years to construct a new facility from scratch. However, his government has been supportive of using reactors that are already online or have started construction.
Yoon, who served from 2022 until he was impeached and removed from office in 2025, resumed construction of nuclear reactors and planned to expand nuclear output.
Moon Jae-in, who served as president from 2017 to 2022, had overseen a nuclear phaseout policy that drew fierce resistance from industry and labour unions.
According to the International Atomic Energy Agency, South Korea has 26 nuclear units in commercial operation and two, Saeul-3 and -4, listed as under construction. The 26 plants provided 31.7% of the country’s electricity production share in 2024, the IAEA said.
Apart from Saeul-3 and -4, the previous government also wanted to complete construction of two additional delayed plants, Shin-Hanul-3 and -4.
