North Korea’s Nuclear Test: Another Fizzle?

The North Korean nuclear test on May 25, 2009, was “heard” loud and clear around the world despite its apparent limited size. Detection of small, clandestine nuclear tests seems to work.

By Hans M. Kristensen

The Korean Central News Agency reportedly has announced that North Korea “successfully conducted one more underground nuclear test on May 25 as part of measures to bolster its nuclear deterrent for self-defense.”  Several news media reported that the Russian Ministry of Defense estimating the test had a yield of approximately 10 to 20 kilotons.

Yet the preliminary seismic data published by the U.S. Geological Survey (USGS) shows that the test had a seismic magnitude of 4.7, only slightly more powerful than the 4.3 of the 2006 test.

Was it another fizzle? We’ll have to wait for more analysis of the seismic data, but so far the early news media reports about a “Hiroshima-size” nuclear explosion seem to be overblown.

Update: CTBTO’s initial findings.


21 Responses to “North Korea’s Nuclear Test: Another Fizzle?”

  1. David M. May 25, 2009 at 12:02 pm #

    The Richter scale is logarithmic, so wouldn’t this blast be 2.5 times more powerful than the previous?

    Reply: Yes, the test seems to have been more powerful than the previous, but the initial reports of 10-20 kilotons seem to have been too high. In either case, the higher yield suggests they have made some progress. HK

  2. Jim May 25, 2009 at 11:32 pm #

    [Edited] A layman question: How much yield does the weapon have to have in order for it to destroy most of Seoul or Tokyo?

    Reply: To destroy “most” of those cities, the weapon would need to have a yield of several kilotons. The Hiroshima bomb was 15 kilotons and the Nagasaki bomb 21 kilotons. Yet even a one-kiloton bomb could kill people in an area of about one square mile and partially destroy a much larger area. You can experiment with yield and blast effects on our nuclear blast simulator (although it only has US cities). HK

  3. Mark Nelson May 25, 2009 at 11:58 pm #

    Since Russia is next door, I would assume their border with North Korea is lined with an array of sophisticated seismological equipment, and that due to their close proximity they may have human intelligence sources within North Korea also. So I would tend to think the Russians would have access to the best set of data for evaluating the yield of this most recent DPRK test.

    Reply: One would think so. However, in terms of seismic stations, accurate data doesn’t require close proximity to the event. CTBTO reported that 23 primary and 16 auxiliary seismic stations registered the North Korean test. The closest IMS station to the event was at Ussuriysk, Russia, and the furthest in Texas, USA – halfway around the world. A map of these stations is available here. HK

  4. Andrew May 26, 2009 at 6:12 am #

    The Richter scale is logarithmic but the scale measures shaking not energy released. A rough estimate using the CTBTO’s figures from the difference in earthquake magnitudes from 2006 (4.1) and 2009 (4.52) would be an energy difference of about 4.25 times larger. The USGS figures differ in earthquake magnitude from CTBTO’s but the difference between the two events is the same so the estimate of increased yield would be about the same. Russia’s early estimate of the 2006 event yield was 5-15kT which was also considered an overestimate so this early yield figure could also be misleading. One theory is that these figures are taken from North Korean warnings to China/Russia and are therefore deliberately vague/misleading. If later estimates of yield for the 2006 event, of about 1kT, are more realistic it suggests this later event is around the 5kT level, which is still perhaps interestingly small for a first generation device.

  5. Christian Packmann May 26, 2009 at 6:43 am #

    Could the NK devices be intentional fizzles? I.e., you design a 30kt device, cripple the design so that you predict a 4kt fizzle, the test gives a ~4kt fizzle, so you’re pretty certain to have a working 30kt design? I find it hard to believe that NK couldn’t get a working design going (assuming they’re testing simple fissions devices and don’t try to hop to fusion immediately) with modern technology and computer simulations. After all, the first plutonium bombs were designed 64 years ago with only marginal computer assist, and simple uranium designs are pretty much a no-brainer.

    Reply: Apparently (fortunately) it is a great deal harder to design a nuclear warhead than people normally assume. A two-stage thermonuclear weapon is even more complicated. Simple uranium gun-type designs are easier than implosion warheads, but North Korea went the plutonium way. HK

  6. Vegas May 26, 2009 at 8:05 am #

    The UNSC sanctions seem to have only bolstered the North Korean resolve to test/gain nuclear materials. Will there be a revival of the Six-Party Talks, or is that scenario dead in the water?

  7. Jan Galkowski May 26, 2009 at 9:28 am #

    [Edited] Richter measures are misleading. Energy leaked from large explosions — including nuclear detonations — are a characteristic of natural sources, so Body Wave Magnitude (Mb) derived from short-period P waves is used to characterize it. If Mb is the body wave magnitude, an approximate yield in Kilotons is exp(Mb-4). Another estimate can be obtained from the Surface Moment, Ms, as exp(Ms-2) [See: Zhu, EASA-130, "Seismology and Nuclear Explosions"]. The particular coupling the North Korean test site presents makes estimates of magnitude depend upon raypaths and their takeoff bearing, especially in this locale. [See: Hong, Tae-Kyung; Baag, Chang-Eob; Choi, Hoseon; Sheen, Dong-Hoon, "Regional seismic observations of the 9 October 2006 underground nuclear explosion in North Korea and the influence of crustal structure on regional phases"]. This may be why CTBTO is being cautious. However, national interests probably know a great deal more already. If it was a stronger detonation, is it possible that North Korea simply replicated the October 2006 test, this time somewhat more successfully?

    Reply: Thanks for providing these references. As for replicating the 2006 test, yes, apart from the many things we don’t know – the intention, the designs, the results of the air samples – I agree that the 2009 test could have been a re-run of the 2006 test. HK

  8. JohnA May 26, 2009 at 12:44 pm #

    [Edited] This is a very serious wake-up call that should no longer be ignored. According to the EMP Commission, a Hiroshima sized nuclear-High-altitude Electro Magnetic Pulse weapon detonated at 250 miles above the mid-U.S. via a missile, could destroy the U.S.’s entire high-tech-based society’s devices and most of the high-tech continental military devices. We would return to the pre-electric agrarian society of 1752. In this case only 30 million lives could be supported by this agriculture and 270 million lives would expire from starvation and/or disease after one year. It currently takes a year or more to replace a few hundred large transformers for the world power grid-imagine if tens of thousands are destroyed in the U.S. alone. We are totally dependent on the power grid and other critical infrastructures that depend upon the power grid to sustain life and they are all currently totally unprotected against EMP. At perhaps 80 miles in altitude, a missile detonation above our East Coast from a submarine or freighter could take out perhaps 70% of the U.S. power grid and our key governmental and economic infrastructures. We need to harden the power grid immediately and then move on to hardening the other critical infrastructures.

    Reply: But we’ve lived under that potential threat since the Soviet Union deployed its first nuclear ballistic missile. There were even U.S. governments that believed we could “win” a nuclear war. So why is one single North Korean hypothetical (remember, they don’t have the capability to bring a nuclear warhead to detonation 250 miles above the United States) suddenly so vital that it requires hardening the power grid “harden the power grid immediately and then move on to hardening the other critical infrastructures”? HK

  9. AmberG May 26, 2009 at 12:56 pm #

    The use of the term “slightly more powerful” ( 4.7 vs 4.3 ) is a bit peculiar. As some one mentioned, the scale is logarithmic (in Amplitude – In terms of energy it is 3/2 power of amplitude), so a difference of 0.4 (4.7-4.3) translates to about a factor of 4! (not “slightly more powerful” )… Actually this ratio could be as high as 6 if you make allowance that, say 4.74 would still be written as 4.7.

    Reply: I guess, if they’re going from essentially no yield to a little yield. But the point I was trying to make was that the alleged 10-20 kilotons was a long way away from what the seismic data suggested. North Korea has made progress, but it was not a “Hiroshima-size” explosion. So far the statements made by others seem to support that conclusion. HK

  10. 3.1415 May 26, 2009 at 3:06 pm #

    The Dear Leader is enjoying his spotlight. He will get the bomb to work sooner or later at this rate. There is really no military solution to this problem. And the diplomatic solution will not work either, because everyone of the 6 parties has different agenda. China does not want NK to fail and let the Americans go beyond 38th parallel, neither does Russia. Japan and SK might want to go nuclear, but the Americans won’t let them. Any concession from the US would weaken Obama’s position and will not change the Dear Leader’s determination to be a nuclear state, declared or otherwise. The Korean War never really stopped; an armstice was called. Maybe it is time for China and US to go back to the negotiation table to finish the business. Not very pleasant, but what is the alternative? The six party talk has four parties too many.

  11. Pedro May 26, 2009 at 6:18 pm #

    If DPRK has access to tritium then their ‘feeble’ 4Kt nuke can relatively easily be boosted to 20Kt or more by incorporating a just few grams within the bomb pit. Tritium is not hard to make (given a reactor) and a few grams of tritium can be transported around the “axis of evil” in any Syrian’s lunch-box. Tritium boosting offers a ‘no-need to test’ 5-10X yield improvement if you’ve got the theory right.

    Rest assured that a ‘tested’ 4Kt device will be a ‘virtually assured’ 20Kt when it appears over your house.

  12. JohnA May 26, 2009 at 10:22 pm #

    To HK on EMP Threat: The sad fact is that during the Cold War we were all potentially expendable in the U.S. during a nuclear exchange. We were advised to build our own shelters and stock our own goods for survival and to duck and cover in public places and schools. There were some community shelters with stocked goods.

    HEMP E1 & E2 effects were details in a full nuclear exchange. However, we did not know about HEMP E3 effect until 1994 when a Russian scientist told us about it and its destructive effects in a conference. We did not know because we tested over water in 1962 and the Soviets tested over land and suffered consequences to their electrical grids and devices. This is likely why they signed the above-ground Test Ban Treaty-because we did not know about E3 and they did.

    In the Soviet Union, both the strategic weapons and critical infrastructures were protected against HEMP. Also, nuclear shelters existed in all major cities for the elites as is also the case in China-including the brand new one in Shanghai.

    We did not know the Soviets/Russians had a super HEMP weapon until 2004 when Russian generals hired by the EMP Commission told us of its existance. It delivers 200,000 volts/meter at the center of the detonation line-of-sight. We protected our strategic weapons and facilities to 50,000 volts/meter during the Cold War and up to today. Therefore, we are totally unprotected. A HEMP weapon is the perfect asymmetric weapon for a rogue state/terror group to destroy the U.S. Also, we would never know who did it. The Russian’s said this in 1999 when the head of the Russian Duma threatened us with such a HEMP attack over the Kosovo negotiations. Both Iran and North Korea have tested HEMP trajectories-Iran from submarines and NK over Japan. Next question?

    Reply: Only this: it would be interesting to see the references for all of that. HK

  13. IVAN May 27, 2009 at 2:42 am #

    Mr. Kristensen, I will ask you straight-what is the possibility of nuclear war in world by rate from 1 to 10?My rate is 9. What is yours?

    Reply: If you mean nuclear “war” then I’d estimate the possibility is 2. If you mean nuclear “use” then I’d estimate 5. I think the risk of nuclear “war” – meaning two nuclear powers fighting each other with nuclear weapons – is low because India and Pakistan are probably the greatest possibility right now, but both of them have more important issues to deal with. The risk of nuclear “use” is greater, I think, because of accidental/inadvertent launch of nuclear forces on alert or a terrorist organization getting hold of a weapon. HK

  14. JohnA May 27, 2009 at 2:14 pm #

    To HK: In reply to your other comments in my first posting above, the North Koreans can deliver such a missile to our mid-U.S. or anywhere else, for they have many submarines to bring the missiles closer to us. With regards to size of nuclear weapon in KT and physical size, remember that miniaturized nuclear weapon plans were found on the computers of AQ Kahn’s Swiss operatives in the early 2000s. AQ Kahn was an operative for China for the Libyan nuclear manufacturing equipment we recovered during the Iraq War was wrapped in Chinese newspapers and the weapon’s design was Chinese.

    During the Cold War there was only one return address, the Soviet Union. If we were attacked, massive retaliation-MAD-would be delivered to that return address. Since the end of the Cold War, the Russians and Chinese have been creating other potential return addresses-Iran, North Korea and terror groups. We will never know who attacked us with a HEMP weapon and we do not even have a retaliation policy for a HEMP attack.

    Hardening the power grid is not that expensive and the cost of hardening all the critical infrastructures is not expensive compared to the current stimulus and recovery act expenditures. Experts say perhaps 3% to 7% is the range of additional cost of hardening a device if incorporated during the design phase. One expert believes the critical transformers could be protected for only a few hundred million dollars. Compared to a potential massive loss of life, these costs are minuscule. Not protecting against HEMP is the height of irresponsibility toward protecting American life.

    Reply: There are different assessments on the need for hardening, how much needs to be hardened, and how significant the threat is. It would be good to see some references to the statements you make.

    As for the “many submarines” you say North Korea have that “can deliver [nuclear] missile” to the middle of the United States, I’m not aware they have any submarines that can do that, much less have nuclear missiles that we know currently can deliver nuclear weapons. Can you identify the submarines and missiles you’re taking about? HK

    Response from JohnA: You will find extensive materials on the EMP Commission website. Perhaps 80+% of the EMP Commission documentation/work is classified. Because of the general lack of response to this threat, and in answer to questions, the head of the EMP Commission made some comments (likely classified before this hearing) during the 7-10-08 hearing to put this horrendous asymmetric threat into proper perspective. The video of the hearing is on the HASC website (scroll down to July 10th, 2008 and to video and available transcripts).

  15. bernard behrens May 27, 2009 at 5:05 pm #

    ok, here’s another bush-league question, what distinguishes the seismic signature of a nuclear underground explosion from conventional explosives ? How would we know if the dear Leader isn’t just bluffing the whole world with a massive conventional explosion ?

    In those 56 years that have elapsed after the Korean War Armistice, the NKA has likely stockpiled hundreds of thousands of tons of ammunition in its arsenals. The dear Leader may have been persuaded by some ambitious and yet practical-minded ordnance officer that rather than horde it all, the oldest stuff is so marginal that they might as well dispose of it in one big underground detonation that would get rid of about 6000 tons / 6 kt of useless outdated ordinance, artillery shells, mortar rounds, Katyusha rockets, anti-tank gun ammunition, land mines, etc; then sprinkle it with some radioactive byproducts from their reactors so as to get enough radiation to leak out from underground, and thus dear Leader could create the impression that North Korea is a nuclear power when in fact they are not even close to it ?

  16. NoAstronomer May 28, 2009 at 2:51 pm #


    The problem with that scenario is (IIRC) the radioactive byproducts that are used to trace such tests are only produced by nuclear explosions and not during normal operation of a reactor.

  17. Duce A. May 28, 2009 at 4:28 pm #

    Could it be possible that the north given its limited amount of Pu-239 on hand, that it may be testing deliberately smaller devices to economize plutonium consumption and test certain design principals of what would be a much larger design once weaponized? Is it known if the north has access or the ability to produce tritium, deuterium gas, or solid lithium deuteride-tritide? such aids could be used to boost a fission reaction and thus yield of a Fission device, lithium deuteride could be used to even manufacture a secondary fusion stage which would require only a small primary trigger to ignite the reaction. Such a design similar to the ones in current arsenals in the US and Russia would allow small warhead designs of a few hundred kilotons. The way I see it, this depends on what we know on the capabilities the north has to produce Lithium Deuteride and other needed materials. The actual basic design principals employed in a warhead are already fairly common knowledge, and if they already have exploded a device then it seems it would be more about amassing the needed material to take the next step, rather then so much the design and construction of a proprietary warhead design, if they just copy someone else. Its also known that in the 90′s thanks largely to the lax security of the Clinton administration, Chinese espionage at Los Alamos and other sensitive sites netted them designs for the W-88 (our most advanced warhead) among others. So the notion of simply copying another nations design is not really that far flung.

    Reply: There are many “ifs” in this matter, but as for the assertion you include from the so-called Cox report, that “Chinese espionage at Los Alamos and other sensitive sites netted them designs for the W-88 (our most advanced warhead) among others,” readers should read the assessment published by Stanford University’s Center for International Security and Cooperation (CISAC) before drawing conclusions. HK

  18. Kapil May 29, 2009 at 4:26 am #

    HK: Considering the fact that US and other developed nations consider North Korea as a threat to stability of Asia and the world at large, I don’t know what practical steps can really be taken to stop the menace given by the known fact that any military operation would lead to war and South Korea and Japan will have to bear the brunt of it due to geographic proximity and alliance with US. Do you really consider the current tests by North Korea just a baby step to getting closer to build a nuclear weapon or its still some time before they can really make one?

    Reply: I don’t know if “baby step” is the right word, but the impression I get is that in two tests North Korea hasn’t been able to demonstrate convincingly that they have an effective nuclear weapon design. Granted, we don’t know what they’ve been aiming for, and even a small yield is a yield. But at least in my mind it raises some serious questions about the widespread claim that North Korea has actually built nuclear weapons. One problem is a tendency to translate plutonium into weapons. But it takes a great deal more to deploy an operational nuclear weapon than producing some plutonium and setting off an explosion inside a mountain. Are they working on the same test device (2006 and 2009)? Was the second test an actual weapon or only a test device? If it’s only a test device, then they still have to miniaturize it so it can fit under the wing of an aircraft or inside a reentry body on top of a ballistic missile. I don’t know what the intelligence community knows, but what I see in public does not convince me that North Korea has operational nuclear weapons yet. It took them three years to move from test one to test two, from less than one kiloton to less than four (so it seems) kilotons. Whether they think that is sufficient for a weapon remains to be seen. HK

  19. edward allen May 31, 2009 at 6:51 pm #

    The North Koreans are also involved in testing the other side of this matter: a long range missile. Do we have any idea of the weights involved here, and if they could install a bomb of even modest size on a rocket that could hit Japan? Do they not have a problem with second stages they have yet to resolve, and if so, is this something they can be expected to resolve soon? A nuclear bomb, even if it fizzled, would have unbelievable political and military repercussions in Japan.

  20. Albie June 3, 2009 at 9:05 pm #

    North Korea will manage to come up with a halfway decent nuclear warhead and will also improve on their long range ballistic missiles. But before the two are matched up and are ready for use, North Korea’s leadership will be decimated. Kim will have already died, his 3rd son replacement will have been assassinated from within by the “inner circle”, power struggles between the politicos and military will kill off many more.
    Left in charge will be either “crazies” which will mean No. Korea will be destroyed due to neccessity or fairly rational minded types who will see that the best bet is to unify the north with the south and become one.

  21. hiperion June 4, 2009 at 7:09 am #

    All said and done fact remains that they virtually have a nuclear bomb
    and so does Iran.They are both virtually on the ‘nuclear summit’.
    I don’t understand why everybody is going haywire over this.
    The nuclear genie is out of the bottle and consequently can’t be
    contained anymore. This will go on and on and spread more and more.
    What are you all dreaming? We are all in the water and the
    boat has sunk. People rather believe the illusion that they are in the boats

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