Abnormal radiation detected near Korean border

Yesterday the world media was abuzz with reports of abnormally high levels of xenon detected near the border between North and South Korea.  Some reports questioned whether the high radiation was a result of a successful nuclear fusion test by North Korea.  Joshua Pollack at Arms Control Wonk suspects something less nefarious:

There are a handful of other ways that some excess radioactive xenon could have found its way to South Korea’s skies.

One possibility is the production of medical isotopes. But it doesn’t appear that there’s a facility big enough and close enough to have caused the spike.

A second possibility is a reprocessing facility, like North Korea’s “radiochemistry laboratory” at Yongbyon. Pyongyang claims to have finished its last reprocessing campaign there last year, but it’s possible that they were bluffing until recently.

Unfortunately for this theory, even if the plant had been operating in May 2010, the spent fuel would have aged too much to release much xenon. The half-lives of its radioisotopes are counted in hours or days. So scratch that idea.

The last important possibility is a nuclear reactor of one sort or another. It seems that whenever a reactor is started up or the pressure vessel is opened for refueling, gases escape, including xenon. A typical light-water reactor is refueled annually. And given all the power reactors across the Far East, that probably happens around there with some regularity.

All that’s really required to explain the unusual reading at Geojin is for a reactor startup or opening to have occurred within hundreds of miles in the previous week or so. Heck, if you want a specific candidate, Japan’s Monju breeder reactor was restarted on May 6.