North Korea is rightly considered an international pariah that not only starves its population while pampering its dictator but also thumbs its nose at the international community’s demand that it not test nuclear bombs or continue its missile development. It is therefore, perhaps, strange to think why the DPRK tested its two nuclear bombs underground.
After all, it is much simpler and less expensive to have an atmospheric test. It also provides a cheap and accurate way of calibrating the bomb by photographing the fireball in the same frame as the sun. China used this method in at least one of its 22 atmospheric tests after the US and the Soviet Union signed the Limited Test Ban Treaty. (That treaty went into force on October 10, 1963 while China’s first nuclear test, an atmospheric one, was a year later.)
Was the North trying to maintain secrecy about the design of its bombs by containing the radioactive particles that might have been used for nuclear forensics? If that was the reason, it seems unlikely that it could successfully hide all the produced radionucleotides, including the noble gases. Of course, the West has, at least to my knowledge, remained very silent on what they have detected. Or was Kim Jun-il concerned about fallout landing on his own people? If that was the concern, they could have positioned it very close to the Eastern coast and waited for a day with a constant wind blowing out of the West.
Or was North Korea, contrary to all international expectations, succumbing to the international norm of only testing nuclear bombs underground?
If NK could test their missiles underground, they would.It is about limiting secrecy, certainly not abiding by concerns over international law or the safety of their people.
NK can do this because there are few,if any, consequences to their actions.
More importantly, what lessons does Iran learn from the U.S. response?
Think they are actually quite keen to one day be regarded as a ‘normal’ state by the rest of the world and were probably very aware that atmospheric tests would have gone too far against norms.
That said, they are now warning of ratcheting up things even more so whats to say an atmospheric test isn’t going to be the next step?
What if it didn’t occur to them to do an above ground test, simply because they were copying everyone else’s recent procedures (Pakistan, etc)?
Interesting question. But rather than concerns for its own population regarding fallout, how about concerns regarding the risk of fallout on Chinese territory (an a possible “red line” having been drawn by Beijing in this respect)? This is where a nice simulation re. prevailing winds would be interesting. We know you’re good at modelling, perhaps you should give it a try?
May be they were incertain about the quality of their blasts from the beginning? It is almost impossible to hide the failed outcome of an atmospheric blast, including the prevalence of isotopic markers for the failure to purify the plutonium sufficiently? Or too much Pu238?
How legit is this?
http://blogs.sciencemag.org/scienceinsider/2009/06/north-koreas-cu.html
“Or was North Korea, contrary to all international expectations, succumbing to the international norm of only testing nuclear bombs underground?”
I don’t know. Where are the krypton-85 and xenon-135 signatures for the last test/event?
You cannot decouple an atmospheric test. You can decouple an underground one,
leaving everyone guessing at the true yield. What if one or both NK test explosions were deliberately decoupled?
Another advantage of testing your weapon underground is that Kr-85, Xe-131m, Xe-133, Xe-133m, and Xe-135 drifting in the atmosphere will tell your enemies that the explosion was nuclear, but not much more. If solid debris has not vented into the atmosphere, they will not learn the isotopic composition of your plutonium, which would give away valuable clues on your weapons program.
On decoupling, see ‘Nuclear Testing and Nonproliferation – The role of seismology in deterring the development of nuclear weapons’ http://www.iris.iris.edu/HQ/Bluebook
Chapter 5 “Assessing Monitoring Requirements”. In the chapter’s Footnote 8:“The most credible scenario for evading a seismic monitoring system is by decoupling the explosion in a large underground cavity. The size of the seismic signal produced by such muffling can be reduced by approximately a factor of 70 based on U.S. extrapolations from small explosions and Soviet experiments.” And in the preceding body of text: “ If we assume that the Central Asian nation could fully decouple the explosion and decrease the magnitude of the seismic signal by a factor of 70, then we arrive at a monitoring threshold of around 20 kilotons”
NK has enough military underground structures expertise to excavate a large, specifically shaped underground test chamber in hard rock in order to decouple a test explosion. Published US and Soviet experiments and simulations were for spherical, cylindrical and elipsoidal cavities. Those with bettter topology skills than mine are encouraged to conceptualise other shapes. It would be hypothetically possible to fashion a large tuned resonance cavity out of rock to play merry hell with everybody’s analytical assumptions. It would be equally possible to precisely synchronise a nuclear and a large non-nuclear detonation close to each other to further confuse the picture. The equations of state for published simulations were all for salt or limestone. If anyone has developed simulations for granite or basalt, they are not saying. Specific geology of the NK test site is unknown. So, might this have been 20kt after all? Are the Russians onto something with their widely ridiculed estimate of 10-20kt? They have very good expertise on decoupling from Soviet nuclear tests, some conducted specifically to investigate these phenomena; see http://handle.dtic.mil/100.2/ADP204483
It is implausible that NK could successfully decouple a test. As I understand it and according to the 2002 NAS Report, “Only nations possessing extensive knowledge of nuclear explosive devices and with access to suitable geologic sites could expect to address the difficulties” of decoupling. The only country other than the US to successfully decouple a test was the (then) USSR, and that test was only decoupled by a factor of 15. Compared to the US and Russia, NK is an amateur at these techniques and doesn’t have the knowledge-base or the facilities to successfully decouple.
Also, why would NK want to hide a test? These tests are giving Kim the international attention and leverage he craves. He serves to gain nothing by hiding a test.
In answer to why he tested underground…I agree with Isotopic’s point that perhaps they are uncertain about the quality of the blasts (Exhibit A: 2006 test), and want to prove they have a nuclear capability but not reveal too many details about the outcome of the test or risk the international embarrassment of a fizzle. However I think it is a great proposition that it was in response to international norms. International acceptance is vital to regime survival, which is Kim’s number one priority.
My non-expert’s view is that preparations for the underground test could be at least plausibly denied and so any potential dud would not cause international embarrassment.
Alternatively it could be that their culture of secrecy has become so ingrained that placing it underground did not require any logical reasoning, it was simply automatically assumed to be the correct thing to do.
Heather:
What about decoupling requires advanced nuclear test experience?
Nearly all the critical information needed is published openly. The NAS report overstated the difficulty.
SW,thanks for the great links. The discussion about decoupling is very interesting. According to this article, the DPRK has the labor to both drill and perhaps construct a cavity.
english.chosun.com/site/data/html_dir/2009/06/03/2009060300829.html
I’m not sure the labor would be that skilled. But it is an interesting insight.
I’ve noticed a certain segment of the readership of this blog who feel that since they have read so much about nukes, and thought about them for so long, that they must know more than people like Glasstone and Dolan. Because of that “familiarity” they believe that they have an intuitive feel for things like nuclear effects and their intuition is more accurate than published information. Or in this latest case, that since they have read about decoupling, they must understand all the details much better than NAS. That is, of course, their prerogative, but I hope they don’t feel upset when I say I trust the real experts much more than I trust them.
If you take a close look at their action over the course of this year, NK has spent a lot of effort to look like they are following international norms. This is something they’ve never done before and they must calculate it will reduce the effectiveness of action against NK.
Interesting comments, especially the one perceiving the North Koreans as being subconsciously secretive; perhaps the North Koreans have maladroitly become the contemporary world’s Rorschach inkblot test. Regardless, I very much doubt the DPRK gives much thought to decoupling. They have no particular motive to down play the magnitude of their yield. Far more likely is that they detonated underground for very much the same drivers that push everyone else down that road: contain fallout and hinder airborne collection of data on internal composition of the devices.
If this is an expert-only blog and CNWDI is required to comment, say so, and I will gladly butt out. I do not have any expertise in nukes at all – express, implied, inferred, real, virtual, or self-delusional. I do not think NKs have mastered (emphasis added) the science of decoupling, nor that they design their test chambers in sophisticated simulations.
I also do not think they want to hide their tests as such. Whether they want to hide underground their actual yields, and/or the isotopic composition of their Pu, is another question altogether. How would the US react if proof were to be found, for example, that the second test was not Pu, but HEU? Any news yet on that distinctive noble gases signature?
Crude, not masterful, decoupling by NK would not necessarily require extensive indigenous knowledge of nuclear explosive devices. They could make do with a private, well-paid consultancy from any of the retired Russian physicists involved in the USSR decoupling experiments in the 60s and 70s. As to the access to ‘suitable geologic sites’, the geology of the NK test site is unknown (unknown to us, that is). NKs do not need to aim for Nevada/Semipalatinsk best practice. A modest decoupling factor of 5-10 would keep the Dear Leader happy and everyone else guessing. Quite a neat way to usher in the DPRK National Nuclear Ambiguity policy, no?
SW, all opinions are welcome at this blog (even those that say they will only believe those they consider experts) as long as it doesn’t dip into personal attack. Of course, such ambiguous rules make it difficult for moderators and I hope I have successfully navigated some of these troubled waters.
Clearly, the NKs have learned quite a bit by watching the success of the Iranians, who are much smoother and more adept negotiators.
NK diplomatic strategy is normally extreme brinksmanship, but they appear to have learned the value of disguising their actions as peaceful programs and invoking sovereign rights.
Because of China’s human rights record, and it’s history with the west, China is very vulnerable to seduction by claims of sovereignty, though it looks like the Chinese are smart enough not to buy it this time. It will be fascinating to see whether the Chinese will actually enforce the latest security council resolution.
“In this multipolar world, many issues such as nuclear proliferation, energy and climate change require a concert approach. The major powers of the 21st century have proved to be heterogeneous and without much experience as part of a concert of powers. Connecting their purposes, however, needs to be their ultimate task if the world is to avoid the catastrophe of unchecked proliferation.”
Henry A. Kissinger
“Reining In Pyongyang”