North Korea's decision to restart its 5 megawatt electric (MWe) reactor at the Yongbyon nuclear scientific research complex threatens Northeast Asia with a disaster potentially worse than Chernobyl, according to nuclear experts.
"This reactor comes from another world. The Yongbyon site has a concentration of so many nuclear facilities that if there was a fire in one building it could lead to a disaster worse than the Ukrainian one," said Seo Kyun Reul, a professor at the nucleonic department of Seoul National University.
Yongbyon's 5 MWe reactor uses obsolete magnox technology that, combined with the reuse of old graphite moderators, greatly increases the risk of a fire, Seo said.
Magnox technology uses graphite instead of water to moderate neutrons. It was held responsible for the 1957 accident in the UK when the Unit 1 reactor at Windscale (now Sellafield) caught fire and released radioactive contaminants into the surrounding area. Similarly, it was an explosion and subsequent fire at Chernobyl that helped release large quantities of radioactive particles into the atmosphere.
"Graphite loves to burn. All the countries that used it faced a fire issue at some point," said Peter Hayes of the Royal Melbourne Institute of Technology. "The safety issue in Yongbyon is straightforward - the graphite moderator catches fire, and you have a perfect storm: a fire with powerful thermal plume carrying contents high into the sky."
Seo said that in a fire engineers were likely to lose control of the reactor, triggering a disastrous chain reaction. Rising temperature and pressure would lead to an explosion, projecting radioactive particles high into the atmosphere, as happened in Chernobyl.
Soviet doctrine is thought to have informed much of North Korea's capabilities and although the North Koreans are likely to have examined the Chernobyl disaster, it is unclear whether they have incorporated any lessons learned into current doctrine, training and operations. Most analysts think it is unlikely that they have the resources to effectively control a fire or any subsequent radiation.
Depending on the wind direction, the radioactive plume could threaten the population of Pyongyang, which is only 85 km away, or Siberia and northern Japan. Seoul, which is only 300 km south, could also be impacted.
Pyongyang announced in April 2013 that it would restart the 5 MWe reactor, which had been closed under an agreement reached at the six-party talks in 2007. Satellite imagery published in August 2013 suggested that operations had resumed at the site. This was confirmed by Nam Jae-joon, the director of South Korea's National Intelligence Service, on 8 October 2013.