Seoul, September 13

Two earthquakes that jolted South Korea last night, including the largest ever recorded in the country, prompted concerns about the safety of nuclear plants clustered in the quake-prone southeast.

Korea’s Meteorological Agency said the two earthquakes, of magnitude of 5.1 and 5.8, occurred near the city of Gyeongju. They could be felt in the capital Seoul, over 300 km to the northwest.

Fourteen people were injured but there were no reports of serious damage, a Ministry of Public Safety and Security official said.

Nonetheless, Korea Hydro & Nuclear Power Co shut down four nuclear reactors at the Wolsong complex in Gyeongju as a precaution.

South Korea’s reactors are designed to withstand a magnitude 6.5 or 7.0 earthquake, said Nuclear Safety and Security Commission.

Orders were given to upgrade old reactors to that standard after the disaster at Japan’s tsunami-crippled Fukushima Daiichi nuclear power plant in 2011. “That will be completed by next year,” said Shim Eun-jung, a spokeswoman for the nuclear watchdog.

South Korea’s 25 reactors supply about one-third of its electricity and make it the world’s fifth-largest user of nuclear power. It plans to add nine more nuclear plants by 2027, according to the nuclear watchdog.

As in many countries, nuclear power is controversial in South Korea, especially after a 2012 scandal over parts being supplied with fake certificates prompted shutdowns.

Park Jong-kwon, head of an anti-nuclear civic group in South Gyeongsang Province, said no more nuclear reactors should be built in southeastern cities like Ulsan and Gyeongju as they are close to an active fault line.

“Even though nuclear reactors are designed to withstand an earthquake of a magnitude 7.0, if they are hit by 4.5 and 5.8 magnitude earthquakes several times, they can be knocked down by a real 7.0 magnitude earthquake at a single blow,” Park said.