Earlier this week, a small earthquake was noted in North Korea, and Twitter speculation turned to another North Korean nuclear test. It turned out not to be, but Robert Farley (@drfarls) made an interesting point.
North Korea has a limited amount of fissile material, the enriched uranium or plutonium that is necessary for nuclear bombs. How significant is the amount used in a test? Are they depleting this limited supply?
Marcy Wheeler (@emptywheel) asked what that supply was and how many bombs they might make from it.
I went to a talk today by Siegfried Hecker, former director of Los Alamos, who has visited North Korea several times and seen parts of their nuclear program. He knows those numbers better than anyone, although North Korea is so secretive that even his numbers are estimates verging on guesses.
Hecker’s estimates for North Korea’s current inventory is 30-40 kilograms of plutonium and a “couple hundred” kilograms of highly enriched uranium. The Nagasaki bomb contained 6.2 kilograms of plutonium; the Hiroshima bomb, sixty-some kilograms of highly enriched uranium. Hecker said that modern designs use less, so let’s say 4 kilograms of plutonium or 40 of enriched uranium.
That is enough material for maybe 10 plutonium bombs and maybe 5 uranium bombs. Probably enough, depending on how the North Koreans judge such things, to spare for an occasional test. That material also has to be formed properly and fitted with conventional explosives, detonators, and electronics. North Korea’s capacity, in personnel and facilities, to build such things would also limit their numbers of nuclear weapons.