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What to Make of North Korea’s Latest Nuclear Test?

12 September 2016

Image: Shutterstock

Image: Shutterstock

On September 9, 2016, seismic stations around the world picked up the unmistakable signals of another North Korean underground nuclear test in the vicinity of Punggye-ri. The technical details about the test will be sorted out over the next few weeks, but the political message is already loud and clear: North Korea will continue to expand its dangerous nuclear arsenal so long as Washington stays on its current path.

Preliminary indications are that the test registered at 5.2 to 5.3 on the Richter scale, which translates to an explosion yield of approximately 15 to 20 kilotons, possibly twice the magnitude of the largest previous test. It appears to have been conducted in the same network of tunnels as the last three tests, just buried deeper into the mountain. This was the fifth known North Korean nuclear explosion; the second this year, and the third since Kim Jong Un took over the country’s leadership in December 2011.

Unlike previous announcements, such as the claim of having detonated a hydrogen bomb in January 2016, the current statement can no longer be dismissed. This time, KCNA reported North Korea’s Nuclear Weapons Institute claiming:

The standardization of the nuclear warhead will enable the D.P.R.K. to produce at will and as many as it wants a variety of smaller, lighter and diversified nuclear warheads of higher strike power with a firm hold on the technology for producing and using various fissile materials. This has definitely put on a higher level the D.P.R.K.’s technology of mounting nuclear warheads on ballistic rockets.[1]

This statement brings up some fundamental questions.

How many nuclear warheads can the DPRK produce? North Korea’s capacity to produce plutonium remains limited to 6 kilograms, or approximately one bomb’s worth, per year. We estimate that it may have a stockpile of 32 to 54 kilograms (roughly 6 to 8 bombs’ worth) of plutonium now. Whereas plutonium production can be estimated reasonably accurately because of telltale signals resulting from reactor operation, production of highly enriched uranium (HEU) remains highly uncertain. However, based on what I saw at the Yongbyon centrifuge facility during my last visit in November 2010, the expanded footprint of the facility since, and our probabilistic estimates of how much it could make in covert facilities,[2] it is possible that the DPRK could add 150 kg of HEU (roughly 6 bombs’ worth) to a current stockpile of perhaps 300 to 400 kg.[3] In other words, a stockpile of sufficient fissile material for approximately 20 bombs by the end of this year and a capacity of adding approximately 7 per year makes the DPRK claim sound plausible.

Can the DPRK produce lighter, smaller warheads and as claimed by the DPRK Nuclear Weapons Institute, ones that have been “standardized to be able to be mounted on its ballistic missiles?” With the two successful nuclear tests this year, we must assume that the DPRK has designed and demonstrated nuclear warheads that can be mounted on some of its short-range and perhaps medium-range missiles. Its ability to field an ICBM fitted with a nuclear warhead capable of reaching the United States is still a long way off—perhaps 5 to 10 years, but likely doable if the program is unconstrained.

As much as a doomsday nuclear shot at the United States worries Americans, it is not what I consider to be the primary threat from Pyongyang’s unrelenting drive to more bombs and better bombs. At a minimum, the current state of the North’s nuclear arsenal is an effective deterrent to potential hostile external intervention. It has reinforced Kim Jong Un’s legitimacy as leader of what the North considers a beleaguered nation. The current situation is very different from what my Stanford colleagues and I encountered during our November 2006 visit a few weeks after the North’s first nuclear test. At each of our stops—the Ministry of Foreign Affairs, the Department of Atomic Energy, and the military—we found their pronouncements of having achieved a deterrent against the United States to ring hollow.

Nevertheless, Kim Jong Il appeared sufficiently confident of the state’s security that he accepted the Bush administration’s change of heart and new willingness to find a diplomatic solution. The years 2007 and 2008 marked significant diplomatic progress, which resulted in a rollback of operations at the Yongbyon nuclear complex, the return of international inspectors, and the presence of an American technical team. However, in the summer of 2008, the Bush administration pulled back followed by a similar response by the North in August. Kim Jong Il suffered a stroke shortly thereafter. Succession planning in the North was done in an environment greatly influenced by the hardline approach of South Korea’s new president Lee Myung-bak. All of these events likely contributed to diplomacy not getting back on track before time ran out on the Bush administration.

By the time our Stanford team visited Pyongyang in February 2009, we were told that times had changed—the North was going to launch a long-range rocket and that matters would get much worse. And, so they did. The launch was followed by UN condemnation and Pyongyang’s expulsion of the international inspectors and American team. Then in May, the North conducted its second nuclear test, which, unlike the first, appeared successful. Seoul and Washington apparently rebuffed Pyongyang’s overtures in the summer of 2009 to get back on a diplomatic track and the DPRK was off and running on a determined path for more and better bombs, combined with greatly increasing its missile threat.

The death of diplomacy, namely the Obama administration’s retreat to “strategic patience” and the demise of the Six Party Talks, opened the door to an unrelenting expansion of the North’s nuclear weapons program, as best as one can tell, unconstrained by international opprobrium and escalating sanctions.

Construction activities at Yongbyon picked up steadily in the latter half of 2009. Pyongyang made numerous claims of nuclear progress—declaring it had achieved nuclear fusion and that it was successful in enriching uranium, which it stated was now required to fuel the new indigenous light water reactor it was going to build. Most of these pronouncements were dismissed outside the DPRK, but then came its remarkable revelation of a modern, industrial-size uranium centrifuge facility during our Stanford delegation’s last visit in November 2010. Then, the curtain descended on foreign visitors to Yongbyon, while construction and testing picked up and has continued to the present.

Based on commercial satellite imagery, the 5 MWe Reactor in Yongbyon has operated off and on since August 2013. It is capable of producing up to 6 kg plutonium annually, but also is capable of producing tritium for fusion bombs if Lithium-6 targets are irradiated in the reactor. The Radiochemical Laboratory is operational again allowing plutonium to be separated from the spent reactor fuel. The North also has hot cell facilities near its IRT-2000 Reactor to recover tritium that may be produced in either reactor. It has rebuilt the fuel fabrication facilities to allow more metallic 5 MWe Reactor fuel to be fabricated. It has completed the external construction of the Experimental Light Water Reactor (ELWR), including having developed fuel fabrication facilities for its ceramic fuel. It has doubled the size of the Yongbyon centrifuge hall, enabling it to enrich uranium for ELWR fuel and produce the feed material that is likely taken to a covert facility to be enriched to weapons-grade HEU. The expansion of Yongbyon facilities, all visible from above, has been nothing short of breathtaking.

I was puzzled for many years by the slow pace of North Korea’s medium-to-long-range missile testing program. However, at about the same time as the Yongbyon expansion began, Pyongyang also mounted a major construction effort on a new launch facility on its west coast, from which it has launched three long-range rockets since 2012. Much of the world laughed as the North paraded what looked like dummy missiles through the streets of Pyongyang during military parades, but they are not laughing any more, as the pace of missile tests during the past year has been just as intense as its nuclear buildup. Beyond the satellite launches, the North has now demonstrated its capability to fire a submarine-launched ballistic missile and a solid-fuel, two-stage medium range missile.

This brings us full circle to the fifth nuclear test. This test must be viewed with great concern, not for any specific capabilities it may have demonstrated, but as part of this enormous buildup of North Korea’s nuclear arsenal. Five tests conducted over a ten-year period, sufficiently spaced that the test results can inform the next test, are deeply alarming.

What are the greatest threats from the rapidly expanding North Korean nuclear program? Left unchecked, Pyongyang will likely develop the capability to reach the continental United States with a nuclear tipped missile in a decade or so. Much more troubling for now is that its recent nuclear and missile successes may give Pyongyang a false sense of confidence and dramatically change regional security dynamics. The likely ability of the DPRK to put nuclear weapons on target anywhere in South Korea and Japan and even on some US assets in the Pacific greatly complicates the regional military picture. That situation would be exacerbated if Pyongyang decides to field tactical nuclear weapons as its arsenal expands and its confidence in its nuclear arsenal grows.

More bombs and better bombs also increase the potential of accidents and miscalculations with greater consequences as the number and sophistication of bombs increase. Rendering the nuclear enterprise safe and secure in case of internal turmoil or a chaotic transition in the North becomes more difficult. We also cannot rule out that a financially desperate leadership may risk the sale of fissile materials or other nuclear assets, perhaps to non-state actors.

So, what to do? The latest nuclear test demonstrates conclusively that attempting to sanction the DPRK into submission and waiting for China to exert leverage over Pyongyang’s nuclear program do not work. Increasing sanctions and adding missile defenses in South Korea to that mix will also not suffice and make China even less likely to cooperate. What’s missing is diplomacy as much as Washington may find it repugnant to deal with the Kim regime.



[1] “DPRK Succeeds in Nuclear Warhead Explosion Test,” KCNA, September 9, 2016.

[2] John Bistline, et al. “A Bayesian Model to Assess the Size of North Korea’s Uranium Enrichment Program,” Science and Global Security 23 (2015): 71-100.

[3] Chaim Braun, Siegfried Hecker, Chris Lawrence, and Panos Papadiamantis, “North Korean Nuclear Facilities After the Agreed Framework,” Center for International Security and Cooperation, Stanford University, May 27, 2016,

Reader Feedback

14 Responses to “What to Make of North Korea’s Latest Nuclear Test?”

  1. Andrew Cain says:

    This report if accurate,calls for immediate response as this is indeed a threat that has catastrophic potential to cause widespread destruction and harm.That this path chosen by someone who has been proven unstable is allowed to persist is beyond me.An appropriate response that would deter any further actions of this sort would have to be a military one, diplomacy has proven useless to this point.The only ones hurt by diplomacy are the north Korean people themselves but has little if any effect on the government or regime of the day.

  2. Clay Ramsey says:

    I can’t imagine modern China ever assisting any other nation in a nuclear program in any way whatsoever. Not a chance.

    Also note that having a missile and having a warhead (nuclear or not) is only a very small step from having none at all. It would be a miracle if even 10% of missiles fired could penetrate either RoK or Japanese defenses. They are very hard to get through.

  3. Ned says:

    The author describes the hollow threats of North Korea when empty missiles were paraded before the Dear Leader, but the White House statements that “a nuclear DPRK is not acceptable” ring equally hollow years later now that detonations have been successful–and across the world other adversaries also flaunt US impotence.

    What could the United States possibly offer in diplomacy at this point? Pyongyang will not let go of a nuclear arsenal capable of striking Soul–which it will have within months.

  4. Kelly Chri STENSEN says:

    Why, in all these posts, is Chinese involvement not discussed? I find it difficult
    to believe that these rapid advances in nuclear/missile technology were achieved
    solely by the DPRK/Iranian collaboration. China is the elephant in the room that no
    one wants to talk about.
    How much has China covertly contributed to the North’s recent advances?

  5. Kostadinov says:

    “If North Korean geography is limiting underground yields (makes no sense actually), it would be even more limiting to above ground testing”

    1. No sense to reduce the magnitude from 5,6 to 5,3 in the border region with China? I am not sure.
    2. Above the ground test can be at 550 km(Polaris)or 1400 km(Musudan) height. This is orders of magnitude less dangerous than underground or low above the ground tests, is visible at long range and will be done only under exceptional circumstances.

  6. Clay Ramsey says:

    Well, I have to admit, you don’t give up easily. I guess my response is, *post my earlier comment*. It’s a fact of the modern world, the internet givith, and the internet takith away. Just ask Hilary! It’s all going to come out anyway, nothing is hidden anymore. Seriously, nothing..

  7. Steven Hayden says:

    I agree that the 5th test yield was deliberately reduced .
    “The fusion cell itself wasn’t very powerful. It comes out to about 17.6MeV, but one can put as much hydrogen as needed making it as powerful as you want.[4] Fission uses heavy elements, while fusion uses the lightest elements of the isotopes of hydrogen.”

  8. Clay Ramsey says:

    If North Korean geography is limiting underground yields (makes no sense actually), it would be even more limiting to above ground testing. Actually, I agree, a full yield real live atomic bomb test is coming, and soon. I’m not saying the program is a hoax, what I’m saying is that the recent tests were a hoax. It’s just the same methodology used in making the Musudan program appear as though DPRK were awash in long range missiles. A series of ‘attempts’ (with nice photography) followed by an actual long range missile obtained elsewhere to give the appearance of success. Now the Nuclear program is a little different. The colaboration with Iran is obviously much deeper than most will admit. Iran has the money and resources to move the program forward and DPRK provides much of the intellectual input as well as a place to test the bomb. Iran would be hesitant to test in Iran itself since doing so would produce devastating and unrversable results. North Korea *wants* very much a nuclear test on its own soil. A DPRK/Iranian collaboration makes tons of sense, and judging by the rhetoric (as seen in these comments) it’s apparent that we are about to see it happen. The Musudan approach once again. Get plenty of doubting comments (like mine) then ‘show the world’ how wrong ‘we’ are! It bugs me that you are setting *me* up as being responsible for the upcoming test though. I can understand the frustration, but I didn’t really do anything wrong. It just worked out that way.

  9. Kostadinov says:

    The yield of North Korea nuclear underground tests is limited by the dimensions of the country. About 5,3 magnitude is close to the uper possible safe limit. So the yield is intentionaly reduced.
    It is reasonable that the real yield of the device is, at least, several times greater.
    But if the doubts in the public opinion remain that all this is hoax, maybe they will be compelled to full yield test in the atmosphere.

  10. John Moore says:

    I have an observation that is also a question. It is stated that it will take a decade for NK to achieve an ICBM with a workable, deliverable warhead. Presumably most of the effort will be in warhead design – a warhead that must survive re-entry and detonate at the right point.

    However, what if NK’s goal is to be able to threaten an H-EMP (high altitude electromagnetic pulse) attack?

    An H-EMP attack merely requires a nuclear warhead be detonated above the atmosphere over the target. North Korea has successfully orbited a satellite, and this weapon could be a satellite. It need not follow the normal, somewhat defended ballistic trajectory towards the US.

    A weapon of suitable size, detonated over the north central US, would likely destroy most of the nation’s power grid and communications systems, resulting in a massive disaster and large loss of life – up to 2/3rds of the population.

    This would probably require a relatively large fission or boosted fission weapon, but would not require a staged thermonuclear device.

    The US EMP Commission report shows that this is hardly science fiction. Starfish-Prime and other tests in the ’60s demonstrated the effect.

    Such an effect would certainly be suicidal, but so would a launch of a nuclear tipped ICBM to US soil.

    Why is H-EMP never discussed?

  11. Clay Ramsey says:

    I didn’t read it all (too much!) but I do get the gist.

    Regarding the centrifuges that were displayed several years back, I always assumed those were the Iranian centrifuges damaged (destroyed) by Stuxnet. I still remember, that all happened at about the same time. You would not be able to tell if a centrifuge was functional just by casual observation. Just seemed to me that would be an easy and cheap way to mislead someone and the Iranians would be more than willing to participate in just such a ploy. But, I mean seriously, U232? So now we’re talking about something like 6 bomb designs, if I read these correctly. Some requiring *a lot* of skill to pull off. My rhetorical question is, ‘how could a U-235 bomb be constructed that doesn’t work perfectly?’ The only hard part of making a Uranium bomb is getting the U-235. It’s not possible, it wasn’t Uranium. It would be no trick at all to detonate full yield Uranium bombs at your pleasure, *if* there were a source of U-235 available, therefore, there must not be. I saw the ‘Disco Ball’, I rest my case..

  12. Clay Ramsey says:

    Here is a link to an image I made describing how to fake a 10 kt atomic bomb. Since I was able to figure out a way, I’m sure you would have no trouble coming up with a method as well.

    If my Photobucket is exceeded and you have Facebook:

    But if it were real (yikes!):

    The 10 kt figure is a very revealing number. That pretty much indicates it was not a Uranium bomb, since there is almost no way to build one that would not go off with full yield.

    For a Plutonium bomb, that would be about half yield for a Fat Man design. Since none of the previous bombs came close to full yield either, the design would just simply not be there yet. Poorly triggered bombs could produce a spread like that (even full yield is statistically possible).

    The home built miniature implosion bomb (the disco ball) is not very convincing. The ‘design’ being very impractical and honestly would never exist at all if someone were to actually try and make one. The shortcomings of it would quickly become apparent and some other way would be perused. A bomb that small would be very miniaturized indeed, quite a technological step. A 1000 lb bomb would be shocking enough, and perfectly adequate for all of DPRK’s large missiles, even the fake ones. Only the KN-08 would gain a huge benefit from such a small bomb but none of the long range missiles are more fake than the KN-08, so that dispenses with that.

    As far as miniaturization goes, the same techniques that allow smaller bombs to even be possible also will produce much more powerful bombs. If the technology were in place to truly miniaturize, we should have seen some truly impressive tests.

    I’m not going to worry much over it until and unless the Air Force decides to release convincing WC-135 mass spectrometer data that shows a real atomic bomb was used.

  13. Steven Hayden says:

    Even the puny 5MWe reactor producing 30 to 60 MW thermal output was enough to almost precipitate a repeat of destruction of the Korean conflict.

  14. Steven Hayden says:

    It is an honor to have Siegfried Hecker author an article on this site. Even the DPRK would recognize that his vast experience with nuclear weapons technology gives great authority to the observations they gave him while in DPRK.
    Look through the eyes of the DPRK at the goals and methods of DPRK nuclear program.The DPRK had been reduced to rubble by US bombing in Korean conflict. The DPRK knew that if became to much of a threat it would be attacked again. Never the less the DPRK goal was to have nuclear arsenal to defend themselves against attack. However the very process of acquiring adequate fissile material could precipitate a attack by nuclear armed USA. The DPRK knew it needed fissile material in adequate amounts for fission events. Once the DPRK had enough fission devices events they could produce fusion devices .
    The DPRK pursuit could include U232, U235 , and Pu 239 as fission material. The Yongbyon reactor was built for production of fissile material at time when the protection of USSR was collapsing. Listed at only 5 MWe the thermal output was much higher. Obviously the DPRK needed a 100 MWe reactor of the same design for weapons grade fissile material but never built it because they would have been attacked before completing a larger reactor . Even the puny 5MWe reactor producing 30 to 60 MWe output was enough to almost precipitate a repeat of destruction of the Korean conflict. The DPRK learned from the near bombing of their reactor to never demonstrate the ability to produce large amounts fissile material or else they might be attacked by USA . For years the national policy of DPRK was to downplay its capacity for fissile production and keep secret any break though in fissile production that could be stopped by USA.
    Other DPRK options besides Pu 239 including pursuing U235 or U 232.The popular often quoted “gas centrifuge” method would have serious drawbacks including conspicuous substantial electrical consumption for amount of U235 produced. Lets face it the Zippe centrifuge is for losers and the Zippe patent was even declassified at one point.The DPRK knew that US surveillance would closely monitor electrical lines and transformers supplying power to centrifuge plant. After DPRK was almost destroyed again for Yongbyon minimal fissile production capacity the DPRK national policy was avoid appearance of massive fissile production. The threat of attack created the need for covert production of fissile material in large amounts. A centrifuge plant with its electrical demands can not be hidden and would stick out like a sore thumb in a country without much electrical activity.Electrical centrifuges were not and could not be the best path for long term covert fissile isotope production. The DPRK adopted goal of covert massive fissile production and rejected open massive fissile production. No doubt the search for effective covert separation technologies had gone on for decades likely all the way since the Korean conflict. The DPRK would have invested massive resources at covert technologies for producing fissile material especially U 235 . They had hundreds of internet scientists available to scour all available known methods and time to create their own technology.
    First the DPRK knew that Heckler was a wonderful humanitarian with US security clearance and was respected in US and international circles. They knew that even though he was an idealist his ultimate loyalties were with the West and Western culture.Showing him the centrifuge plant for producing fissile materials meant that he would be required to disclose it to the US authorities. He would see only what the DPRK wanted him to see . He would be required to divulge all he had seen to USA. Hecker openly and honestly disclosed what he saw in the centrifuge plant . First any large gas centrifuge plant is easily located by US intelligence so the DPRK already suspected that US knew the location of the centrifuge plant they showed him. Although it looked modern and clean it was merely a DPRK diversion from other methods of fissile production. The entire centrifuge plant was a red herring designed to convince the USA that fissile production would be small and in a manner that USA could monitor.Of coarse the DPRK based on its experience of US threats against fissile production would never show the primary means of fissile production. The DPRK did show the centrifuge plant because the US already knew about it. Think. Did Stalin ever show a US nuclear expert the principal source of fissile production in USSR…of coarse not. The DPRK needed USA to believe that its fissile production was limited , so DPRK showed Hecker a centrifuge plant that was not much of a threat. A gas centrifuge plant that is not a threat will not be attacked so no harm in disclosing it.

    Meanwhile the covert program for massive fissile production was proceeding successfully in a parallel fashion unseen by Western intelligence. The US had no way to monitor the covert fissile production. Instead the US could persuade itself that DPRK was content with production of minimal fissile material.
    Then Kim Jong Un became the Supreme leader . He had not grown up under massive bombing of the Korean conflict or the Yongbyon crisis that almost restarted the Korean war. As Supreme commander he was informed of success of covert program for massive fissile production . The Supreme leader was informed of the large stockpile of fissile material. His administration changed the rules for boasting about nuclear adequate fissile material. The DPRK began to speak of nuclear sea of fire. The goal of Kim Jong Un was to go from capacity for adequate fissile events to adequate fusion events. The policy of boasting about nuclear capacity had already changed because DPRK had already reached much of its goal for fissile production. If you raise the temperature on a frog in a pot of water you can boil him alive. The DPRK policy was not to startle the USA until after large amounts of fissile material was made.

    KCNA Sept 9 2016
    It was confirmed through ……… the nuclear material usage coefficient[ the test was effort to reduce amount fissile material blends [U233 U235 Pu 239 for explosion adequate for fusion events ]
    “The standardization of the nuclear warhead will enable the DPRK to produce AT WILL and AS MANY AS IT WANTS of SMALLER LIGHTER and diversified nuclear warheads of HIGHER STRIKE POWER [ fusion] with a firm hold on the technology for producing and using VARIOUS fissile materials [U235, U232, and Pu 239] .

    The successful test of DPRK weapon using blend of fissile material was able to efficiently reach energy necessary for hydrogen fusion using smaller warhead and with less fissile material. Now the number of critical mass explosives can be smaller use less material have higher efficiency for fusion. Likely it implies that DPRK potential arsenal has doubled or tripled to “AS MANY AS IT WANTS” . The boosted fission warheads are now small enough for artillery rockets. What is “as many as it wants? Russia maintains 1500 deliverable warheads . DPRK would want at least 500 . 500 fission events could not be achieved based on plutonium alone. DPRK knew when their reactor was almost bombed that the future fuel for hundreds of fissile events lay in U 235 and U 232. Blends of VARIOUS FISSILE MATERIALS are used to provide the energy for fusion . The bulk of the fissile material of DPRK is likely not Pu 239. Seigfried observed a small capacity U235 production system. But this was merely the deliberate distraction of DPRK. At the time of Hecker’s tour of centrifuges,the DPRK wanted USA to believe that they could not produce fissile material in large amounts. The DPRK arsenal has grown from 50 to 150 to 250 nukes. DPRK has adequate fusion fuel. KCNA is saying their goals are within reach , This is 5th nuclear test in 10 years. Pakistan tested 6 nukes and has 130 plus nukes. Likely the DPRK nuclear stockpile is over 100 already well on its way to 500.
    On the military front, the US plans to dispatch a nuclear-powered aircraft carrier to South Korea next month in a show of force to deter further military provocations……
    The USS Ronald Reagan (CVN-76), the flagship of the Yokosuka, Japan-based Carrier Strike Group Five of the US Navy, will sail to South Korea’s Yellow and South seas to participate in a joint naval exercise with South Korea, slated for Oct. 10-15, the official said.
    The US Carrier will be seen as threat to DPRK and China.The US will be tempted to attack before they think the DPRK has adequate delivery systems to USA. The USA is already using SK and Japan to receive dozens of warheads in event of war, so that these war heads will not reach USA.
    The DPRK has sixthnuclear test ready .They will add lots of hydrogen to fusion cell and raise the KT yield from 50-150 kilotons. DPRK must prove they are “full fledged nuclear power” before the new US president. They must prove their claim to be a full fledged nuclear power . If USA sees DPRK as a potential nuclear power without enough ‘full fledged nuclear” destructive power the USA will be tempted to attack.It is very important for DPRK to make complete path to nuclear power as rapidly as possible.

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