I just came across this article by geologist Jeffrey Park in the Bulletin of the Atomic Scientists. Park says that the seismic data indicate the latest North Korean test was another fizzle, concluding the yield was “likely 4 kilotons or smaller”.
According to the author bio in the sidebar, Park seems to be qualified to opine knowledgably on the seismic data. In my previous post, I cited a Guardian article. I failed to note that article relied exclusively on a Russian source for estimates of the device’s yield. Recall that after the 2006 test, the Russians’ estimates were way above everyone else’s, calling into question the accuracy of their seismic data and/or their analysis.
If Park is right it tends to support my view that the North Koreans produced a batch of plutonium contaminated with too much Pu-240. This, I think, is the best explanation of the documented low yield back in 2006 and the (possible) low yield last month. North Korean technology is just too primitive to solve the problem they doubtless created when they tried to increase the reactor’s plutonium output through a higher burnup. Higher burnup translates into a higher percentage of Pu-240.
For now, I’ll wait to pass judgment on the success of the North Korean test until there is some agreement on the seismic data, though I’m inclined to accept Park’s estimate of 2 to 4 kilotons.