South Korea’s nuclear regulatory authorities and operators have decided to undertake large-scale improvements to enhance reactor cooling. Rising sea water temperatures are placing eight domestic reactors at risk of halting operations within the next 10 years. The project aims to reinforce nuclear facilities and raise the operational minimum, known as the design sea temperature, which refers to the maximum temperature of seawater at which a nuclear reactor can operate safely.
The Nuclear Safety & Security Commission (NSSC) held a meeting with Korea Hydro & Nuclear Power (KHNP) to discuss current response measures and future plans related to the increase in sea temperatures. KHNP has incrementally raised the limit temperatures for reactor shutdowns within safe operational limits but will now upgrade facilities to safely operate at even higher temperatures.
Currently, following improvements to units 1&2 at the Shin-Wolsong NPP in Gyeongbuk Gyeongju, improvements to units 1-6 at the Hanbit NPP in Jeonnam Yeonggwang are set to be completed by 2029. Long-term plans include extending this to all NPPs to raise the sea temperature limits. KHNP is operating a task force to promote facility improvements in collaboration with design and supply partners.
As climate change continues to raise sea temperatures, cooling efficiency has decreased, increasing the risk of equipment failure. Recently, the average sea temperature near the Korean Peninsula has been rising by 0.087 degrees a year. If the seawater exceeds the design sea temperature, the plant must halt the reactor within six hours and complete cooling within 36 hours.
The design sea temperature at units 1&2 of the Shin-Hanul NPP near Uljin is the lowest at 31 degrees Celsius, while unit 2 at the Kori NPP in Busan Gijang is the highest at 36.1 degrees. According to KHNP’s analysis, units 1&2 at Shin-Wolsong are expected to reach the design sea temperature in 2030, Hanbit 3&4 in 2031, and Hanbit 1, 2, 5 &6 in 2034.
According to the Korea Institute of Ocean Science & Technology, the average water temperature in the East Sea has risen by 8.3°C over the past 30 years from 1980 to 2010, and has risen by 1°C over the past three years (2021-2023). Most of Korea’s NPPs have less than a 5℃ margin to design seawater temperatures.
KHNP predicts that the seawater temperature will reach the design seawater temperature at about eight NPPs within 10 years. Until now, KHNP has responded by raising the design seawater temperature reducing the safety margin. Kori and Hanul had their design seawater temperature increased a long time ago, and Saeul 1&2 went through the same process three years ago. However, there are limits to this. “When raising the design seawater temperature of the Saeul Nuclear Power Plant three years ago, some members of the Nuclear Safety Commission criticised how long they could respond by cutting the margin,” said NSSC head Lim Si-woo.
In response, KHNP has announced plans to increase cooling performance by increasing the efficiency of the heat exchangers in the plants. Shin Wolsong 1&2 have already improved cooling performance by improving the heat exchanger and KHNP plans to replace heat exchangers for Hanbit 1-6 units by the first half of 2029. Although heat exchangers vary, the improvement work is expected to cost KRW10-20bn ($7,194-14,388) for each NPP.
In addition, KHNP is experimenting with various methods to cope with seawater temperature. Recently, in order to lower the sea temperature itself, a large amount of ice was put into the sea around a NPP. However, even though the temperature temporarily drops, it has little permanent effect.
