North Korea may be preparing another atomic bomb test, Stanford experts say

Scientists from Stanford and Los Alamos analyze nuclear device activity against backdrop of nation's new leadership.

Reuters/KCNA North Korean leader Kim Jong Un arrives to take pictures with officials and employees of the Mansudae Art Studio in Pyongyang

North Korean leader Kim Jong Un arrives to take pictures with officials and employees of the Mansudae Art Studio in Pyongyang on April 19, 2012. Photos of the smiling young leader suggest a far different personal style than that of his reserved father, according to Stanford's Siegfried Hecker.

Stanford nuclear scientist Siegfried Hecker and Frank Pabian, a geospatial information analyst at the Los Alamos National Laboratory, used open-source technology to recalculate the epicenters of two nuclear tests by North Korea. They believe Pyongyang is capable of carrying out a third within a matter of weeks. Whether the North is willing to pay the political costs of another test remains open to debate.

Their study was published in the Bulletin of the Atomic Scientists. Pabian was a recent visiting scholar at Stanford's Center for International Security and Cooperation, where Hecker is a co-director.

In an interview, Hecker answered questions about the current state of nuclear affairs in North Korea:


Following the failed launch of a satellite by North Korea in April, a third nuclear test appeared imminent. Yet more than three months have passed and there has been no test. Why?

We make the case in the article that Pyongyang has much to gain technically and militarily from another test, but the political costs may be too high. That was also the case in 2006 and 2009, but Kim Jong Il decided to pay the price, which turned out not to be that great in the end because China did not want to destabilize the regime despite its displeasure with the tests. Now we have a young new leader, Kim Jong Un, and a more assertive China trying to guide the regime toward market reforms. So the equation has changed.

Does that mean Kim Jong Un may take a less confrontational stance on the nuclear issue?

It's too early to tell, but the country is clearly under new management. Photos of the young leader on rides in Pyongyang's version of Disneyland and photos with his new wife in modern dress – and both of them mingling with the ordinary public – are a far cry from his father's style. 

You believe that you have done the most accurate job to date in locating the epicenters of the two underground North Korean nuclear tests, and that leads you to the best estimate of what the explosion yields were. Yet there are still significant variations in yields between your analysis and the official U.S. government estimate released by the director of national intelligence. Why?

We have done the most precise analysis of locating the epicenters by combining results from seismic signals and Google Earth 3D maps of the test area. Taking our understanding of standard nuclear test practices, we were able to determine accurate depth-of-burial for the nuclear devices. We then took these new results and refined the calculations of Los Alamos National Laboratory researchers, who use a model in which yield depends on depth-of-burial.

However, researchers at the Lawrence Livermore National Laboratory use a model that does not depend on depth-of-burial within the range in question. Their model predicts a yield close to two kilotons, as expressed by the director of national intelligence. Our new analysis, based on the Los Alamos technique, suggests a yield between four and seven kilotons. The jury is still out as to which of the models is more accurate, but we believe we have the best estimate of the location of the epicenters to date.

What have recent satellite images shown around the Punggye-ri nuclear testing site?

Right after the missile launch, satellite imagery showed significant new activity at what has been identified as a likely third nuclear testing tunnel, which is why we believe it's important to re-examine North Korea's past nuclear tests to learn what we can about its future test capabilities.

Why are you so concerned about another nuclear test? 

I believe that North Korea has the bomb, but not much of a nuclear arsenal. With its limited testing success to date, Pyongyang likely does not have the confidence to field a miniaturized nuclear weapon on one of its missiles. If it can't mount a nuclear weapon on a missile, its bombs are more like a terrorist's threat – that is, they would have to be delivered by van, boat or plane. North Korea needs more nuclear tests to demonstrate it can build a miniaturized warhead.

Does that mean if it tests a weapon, it may attack the United States or its allies with nuclear-tipped missiles?

I don't believe another test would lead to that – but it greatly increases the threat that North Korea poses to all of us. That's exactly what Pyongyang is trying to convey when it says it will strengthen its deterrent. The deterrent is meant to warn the United States and putting warheads on missiles makes the deterrent more credible.

Does North Korea have missiles that can reach the United States?

No – the failed missile launch showed it still has a long way to go in improving its rocket technology. In addition, for a space launch the payload (a satellite) needs to reach orbit, whereas for a missile attack the payload (a nuclear warhead) also has to survive the enormous temperatures and stresses of re-entry. We have no indication that it has developed and tested the required re-entry vehicles to do so.

In the Bulletin article you speculate that the North may simultaneously test a plutonium bomb and one fueled by highly enriched uranium (HEU). What brings you to that conclusion? 

Plutonium production has ceased in the North, so it only has enough for four to eight bombs. When officials showed Stanford Professor John Lewis, Bob Carlin and me their new centrifuge facility during our November 2010 visit, they served notice that they can produce HEU if they so choose. So from a technical standpoint, a plutonium test gives them one more important data point for plutonium bombs and an HEU test opens up another line of possible bombs.

Why not just do two separate tests instead of complicating the containment challenges?

North Korea has to pay a political price for each test. Beijing may be getting very impatient with Pyongyang. If North Korea conducts two simultaneously, it would only have to pay the price for one test, not for two. That may be enough incentive to do multiple tests simultaneously. It can't do five like the Pakistanis, because each test depletes the meager supply of fissile materials.

What should Washington be doing to make sure that a third test does not take place?

Working with Beijing to make sure the political price for North Korea conducting another test is too high for the new regime to bear.

How were you able to gather and present the information in your study using open-source material? How does this work fit into the broader context of open-source nonproliferation work being done today by researchers and bloggers?

This is a great example of how the new information technology tools like Google Earth and social media are revolutionizing the intelligence world. Even for a country as reclusive as North Korea, there is an enormous amount of information available for a great number of socially networked analysts around the world. Some of the information comes from satellite imagery, some from what the state puts out in propaganda and some from Track II visits such as those made by my Stanford University colleagues and me.

Beth Duff-Brown is public affairs manager for the Center for International Security and Cooperation.

Siegfried Hecker, CISAC (650) 725-6468,

Beth Duff-Brown, CISAC: (650) 725-6488,

Dan Stober, Stanford News Service: (650) 721-6965,