We know from the seismic analysis that the explosive yield of the announced DPRK nuclear test is 1 kiloton or less of TNT equivalent.The US Director of National Intelligence confirms that the air samples collected contain radioactive xenon of greater than minimum detectable concentration and that the test was indeed a nuclear explosion.If we knew the isotopic ratios of the plutonium debris that resulted from the DPRK nuclear test, we could calculate the exact yield of the DPRK nuclear explosion, as analyzed in this study.We speculate that at this stage, it is unlikely that such information has been collected outside of the DPRK; but if it is available, that it would likely simply confirm that the range was between 0.5 and 1 kilotonne of TNT equivalent.
There are many possible reasons why the DPRK nuclear test yielded less than 1 kilotonne of TNT equivalent.The pre-detonation of the DPRK nuclear explosion could be caused by poor machining of the device, the non-simultaneity of the detonation of the explosive charges used to compress the plutonium mass, the poor shaping of these charges, the small amount of plutonium used and/or mixture of non-pure-plutonium nuclides that might lead to pre-detonation, difficulties with the neutron initiator, and other environmental factors such as the performance of a neutron reflector. (13)
Whatever the explanation, we conclude that the DPRK test was more a failure than a success in physical terms defined with respect to a usable nuclear device configured as a warhead.However, it was also a technical success in four possible respects.The first and most important is that nuclear criticality was achieved.The DPRK has likely been designing nuclear explosives of various scales for many years.The DPRK scientists and engineers working on the test program will have learned a great deal from this first exercise, and will use this knowledge to improve their design for a second test.Achieving any level of nuclear explosion is a significant technical achievement and a pre-detonated critical mass is simply one event along a spectrum of possible outcomes, all of which offer substantial learning opportunities and a basis for on-going design work.
The second is that the DPRK may be confident that it can explode larger nuclear weapons and decided to tackle small warheads at the start of its test program in order to increase the speed with which it has a deployable long-range weapon on a missile or other delivery system.This is more challenging technically and this first test would assist them in this objective even if it did not yield the desired explosive power.
The third is that the DPRK may not have much plutonium due to difficulties with operating their reactors in the last two decades and with separating it from the spent fuel, and was economizing on their use of this scarce resource.
The fourth is that the DPRK may have been trying to minimize the risk of radioactive emissions and the political reaction to its test by keeping the test very small.A combination of these four and other factors may be at play.
Nonetheless, the fact is that the DPRK is now a self-declared nuclear weapons state, but not an actual or demonstrated nuclear weapons state.This is not a domestic political problem for Kim Jong Il at this time.Indeed, on October 20, 2006, the leadership staged a “mass rally” in central Pyongyang to "welcome the historical successful nuclear test” and, as one gigantic placard stated, to “ardently congratulate the scientists, technicians, and workers who succeeded in a nuclear test.”
But for the reasons outlined above, the other nuclear weapons states know the true state of affairs.Until the test, it was possible for the DPRK to employ the “Israeli model” of nuclear opacity as the basis for nuclear threat, whatever the purpose of having such a threat capacity, and to keep everyone guessing.
Having tested and failed, the DPRK can no longer rely on opacity as the basis for having a credible nuclear force, at least sufficiently credible to threaten its adversaries with a nuclear explosion.The DPRK might believe that a half kilotonne “mininuke” still provides it with a measure of nuclear deterrence and compellence; but it could not rely on other nuclear weapons states to perceive it to have anything more than an unusable, unreliable and relatively small nuclear explosive device.
In short, the DPRK has now demonstrated that it does not yet have a nuclear capacity that enables it to threaten nuclear Armageddon against anyone but itself.