South Korea took the 950MW Kori reactor 4 off line on Tuesday, ahead of the expiry of its operational permit.
The permit expires on 6 August, operator Korea Hydro and Nuclear Power (KHNP) previously said. KHNP has not commented officially on the halt, but company data show output began falling early on Tuesday, and that it had stopped altogether by the end of the day.
KHNP has been seeking to extend the licence and minimise output curtailments after former president Yoon Seok-Yeol reversed his predecessor's plans to phase out nuclear energy. The halt might indicate that the administration of Lee Jae-Myung, which took office in June, is taking a different stance. That said, KHNP lists the reactor as being off line for maintenance, rather than retired.
Without Kori 4 and based on KHNP's maintenance schedule for other plants, South Korean nuclear availability is at 18.9GW this month, against 20.8GW of actual nuclear output a year earlier. Weaker nuclear output is likely to boost coal-fired generation this month, as the Korea Power Exchange (KPX) seeks to reduce the wholesale electricity price, a market participant said. KPX wholesale power prices averaged 128 won/kWh in January-June, supported by government restrictions on coal-fired generation that boosted the call on gas. Wholesale prices averaged W125/kWh a year earlier, KPX data show.
KHNP wants to extend life of the 650MW Kori reactor 2 and 950MW Kori reactor 3, which were taken off line in April 2023 and September 2024, respectively, when their permits expired. Neither has yet secured an extension, with South Korea's recent political instability muddying the picture.

