Freeman Spogli Institute for International Studies Center for International Security and Cooperation Stanford University

North Koreans attend a rally celebrating the country's third nuclear test at the Kim Il-Sung square in Pyongyang February 14, 2013
Photo credit: Reuters

February 14, 2013 - CISAC, FSI Stanford In the News

Hecker takes hard look at North Korea's nuclear test

By Beth Duff-Brown

North Korea conducted an underground nuclear test on Feb. 12, prompting President Barack Obama to call the detonation of a nuclear device a “highly provocative act” that threatens U.S. security and international peace. It is the third nuclear test by Pyongyang since 2006 and is escalating concern that the isolated Stalinist state is now closer to building a bomb small enough to be fitted on a missile capable of striking the United States and its allies. The test was conducted hours before Obama’s annual State of the Union speech. 

North Korea’s official Korean Central News Agency said the test was conducted, “in a safe and perfect way … with the use of a smaller and light A-bomb, unlike the previous ones, yet with great explosive power.” The statement said the nuclear device did not impose “any negative impact” on the environment. 

North Korea said the atomic test was merely its “first response” to what it called U.S. threats and said there would be unspecified “second and third measures of greater intensity” if the United States remains hostile to the North. Washington had led the call for more U.N. sanctions against Pyongyang after the North launched its first rocket and put a satellite into orbit in December. While the North said the launch was for its civilian space program, the Obama administration believes it was part of a covert program to develop ballistic missiles that can carry nuclear warheads.

We ask Siegfried Hecker, former CISAC co-director and now a senior fellow at CISAC and the Freeman Spogli Institute, as well as one of the world’s leading experts on plutonium science, to dig deep into the technical and political aspects of the nuclear test. Hecker has been invited seven times to North Korea and he made international headlines when he returned from his last trip in November 2010 and announced the isolated North Asian nation had built a modern uranium enrichment facility.


Q: Why did North Korea conduct a nuclear test at this time? What from a technical standpoint were they trying to achieve? 

Hecker: With its limited nuclear test experience, North Korea needed a third test to demonstrate that it can miniaturize a nuclear device; that is, make it sufficiently small and light to mount on one of its missiles. This test may have given them the confidence to do so for one of their shorter-range missiles. The 2006 and 2009 tests demonstrated that North Korea can build a nuclear device, but that its nuclear arsenal is likely restricted to bulky devices that would need to be delivered by plane, boat, or van, thereby greatly limiting their deterrent value. With a missile capable nuclear device, Pyongyang enhances the credibility of its deterrent.

Perhaps the greatest impact of this nuclear test is that it will signal that the Kim Jong Un regime, like its predecessors, has chosen bombs over electricity."


 Q: What do we know about the test? 

Hecker: As anticipated, North Korea conducted its third nuclear test in the northern mountains of the Punggye-ri region on February 12, 2013 at 11:57 a.m. local time. Based on analysis from the U.S. Geological Survey (USGS), we know the test was conducted in proximity of the previous two nuclear tests, with the current estimated epicenter almost directly under Mount Manthap, which is very close to the epicenter of the 2009 blast.


Q: Do you consider the test to have been successful? 

Hecker: The USGS and the Comprehensive Nuclear Test Ban Treaty Organization’s International Monitoring System reported seismic signals with a magnitude of 5.0 to 5.1, with characteristics typical for underground nuclear explosions. This is roughly twice as large as the 2009 test, which recorded seismic magnitude of 4.52 and estimated yield of 2-7 kilotons. Hence, I would call the third test successful. An accurate explosion yield estimate will have to await more detailed analysis by the scientific community. The 2006 test was likely only partially successful since it had an estimated explosion yield of less than 1 kiloton.


Nuclear facility in Yongbyon, North Korea. Fuel fabrication facility. Siegfried Hecker examining machining lathes removed from machine shop.
Photo Credit: John Lewis


Q: Is it possible to tell what kind of a nuclear device the North Koreans tested? 

Hecker: Not so far. The seismic signal only indicates the size of the explosion yield, nothing about the physical size of the device or its sophistication. Pyongyang's official Korean Central News Agency announced the day of the test that the blast "was conducted in a safe and perfect way on a high level with the use of a smaller and light A-bomb unlike the previous ones, yet with great explosive power." Taken at face value, this would indicate that the first two were primitive Nagasaki-like bombs, much as we had suspected. It makes sense for them to attempt to miniaturize the nuclear device to fit on one of their missiles.


Q: Can we tell if they used plutonium or highly enriched uranium? Did the North Korean government reveal what it used? 

Hecker: No, they did not specify whether the device was a plutonium or HEU device, and yes, it is possible to differentiate, although we do not know at this point. If the nuclear blast carried out in the tunnel deep underground causes sufficient fissures in the overburden rock, then gaseous fission products can escape and may be detected by airborne instruments or radiological monitoring stations around the world. There are different telltale signatures for HEU and plutonium devices, but they must be detected and analyzed very rapidly to allow conclusive identification. Radioactive signals were detected after the 2006 event, but not after the 2009 event. The 2006 signals were apparently not picked up in time to allow discrimination between plutonium and uranium. So far, China and South Korea have failed to pick up radioactive signals from this event.


Q: Do we know then that they used plutonium for the first two tests? Why would they switch to HEU for the third test? 

Hecker: We have no definitive evidence that they used plutonium. However, during my 2008 and 2009 visits to North Korea, their nuclear specialists and government officials told me they used plutonium. In fact, the director of the Yongbyon Nuclear Center told me that the plutonium used for the first test was made in the plutonium laboratory that they showed me in 2008. The most likely choice for this test is an HEU device. Pyongyang had recently threatened to increase the size of its nuclear arsenal; it can only do so with HEU.  North Korea has a limited plutonium inventory and decided to suspend plutonium operations in 2007. One can only speculate why it made that choice. Its plutonium facilities could have continued to produce one bomb’s worth of plutonium per year. It is possible that the North Koreans believe they can develop a significantly larger HEU production capacity. In addition, the reactor operations necessary to produce plutonium are fully visible from satellite imagery because the reactor’s cooling tower emits a visible steam plume, whereas the location and operations of uranium centrifuge facilities cannot be monitored from a distance, as was clearly demonstrated when Professor John Lewis and I were shown the previously undiscovered Yongbyon centrifuge facility during our November 2010 visit.

If Pyongyang were to share its test data with Iran, it would negate Iran’s need to test its own device and allow Iran to get even closer to a nuclear bomb without detection."


Q: But why switch to uranium when the modern nuclear arsenals of the nuclear powers use plutonium? 

Hecker: The apparent decision to pursue HEU devices is puzzling because plutonium bomb fuel is more suitable for miniaturized nuclear devices than HEU. Yet Pyongyang may have decided it would require too many tests and too much plutonium, which is in short supply, to demonstrate a miniaturized plutonium device. And, it is likely that Pakistan’s A.Q. Khan sold the North Koreans a Pakistani HEU design that could be mounted on some of North Korea’s short or medium-range missiles. If Khan provided both design and test-performance data, Pyongyang may have decided that HEU, albeit less effective than plutonium, was a quicker and more certain route to miniaturized nuclear devices.


Q: In an article in the Bulletin of the Atomic Scientists last August, you and former CISAC Visiting Scientist, Frank Pabian, speculated North Korea might detonate two nuclear devices simultaneously. Did they? 

Hecker: It does not appear that they detonated two at once. They did not claim to have done so and the seismic signals were indicative of one detonation (although it would be difficult to discriminate if the two were in close physical proximity). We believed that one more plutonium test would help to provide valuable information on the yield-to-weight ratio, critical for miniaturized designs. An HEU test would allow them to move to a possibly expanded future arsenal. We speculated about the possibility of multiple simultaneous tests because such have been conducted by the United States and the Soviet Union, and most recently in 1998 by India and Pakistan. Such tests have some technical limitations and are more challenging to conduct, but they have the huge advantage of not incurring additional political cost -- in other words, they can get two for the price of one.


Q: Is it possible that Pyongyang will follow the third test with another in short order? 

Hecker: Yes, the rationale for multiple tests is still there. And they are technically prepared to do so. We had previously reported that a third test tunnel, known as the south tunnel, was ready to go. We even predicted the epicenter of the next test under the mountain ridge in that test tunnel. However, a flurry of recent activity at the 2009 west tunnel portal made us suspect that they may use that tunnel for this test instead. The greatest security was evident around that portal prior to the test. It is too early to tell which tunnel they used, but it may well have been a second drift off the west tunnel. In that case, they have the south tunnel ready to go for another test. And, if they test soon, they may still get two tests for the political price of one. Moreover, the Kim Jong Un regime threatened unspecified “second and third measures of greater intensity” if provoked by further sanctions following this test. Perhaps the second and third measures refer to additional nuclear tests, or a combination of nuclear tests and missile launches. 


Q: What does this test tell us about the future of Pyongyang’s nuclear program and the threat it poses to the United States and its allies? 

Hecker: With every additional test, North Korea’s deterrent appears to be more credible. But, one more test does not fundamentally change the security threat North Korea poses. This test makes Pyongyang’s nuclear arsenal appear more threatening by taking it one more step closer to possessing a missile-deliverable nuclear weapon. With every nuclear test – failed or successful – North Korea’s nuclear specialists learn something. This test may indicate North Korea will expand its arsenal by stepping-up production of HEU and possibly, but not likely, restarting its suspended plutonium production. Pyongyang may now have more confidence in the deterrent value of its arsenal thereby making North Korea more provocative and aggressive in its dealings with South Korea, Japan, and the United States. Yet, it is important to remember that even if North Korea can threaten a country with their arsenal, Pyongyang can only use its nuclear weapons if it is prepared to face the destruction of the regime.


Q: Does this test mean North Korea can threaten the United States with nuclear warheads? 

Hecker: No, they have yet to demonstrate that they have developed an intercontinental ballistic missile (ICBM). To do so would require much more flight-testing of their long-range missiles. In addition, the nuclear device would have to be very small and light, which would require additional nuclear tests. The nuclear warheads would also have to survive the demanding mechanical and thermal stresses of re-entry into the atmosphere. Hence, they are many years away from threatening the United States; besides why would they want to strike the United States? It would be suicidal and the regime is not suicidal.

They are many years away from threatening the United States; besides why would they want to strike the United States? It would be suicidal and the regime is not suicidal."


Q. What reverberating effects could this test have on global nuclear proliferation? 

Hecker: North Korea has consistently been shown to be a proliferating state, often selling nuclear technologies to other countries in exchange for much needed currency. They allegedly sold natural uranium hexafluoride to Libya in February 2001, and they assisted Syria in building a covert nuclear reactor at al-Kibar, which was destroyed by an alleged Israeli airstrike in September 2007. I am most concerned that North Korea will use this test data as currency and could potentially sell it to Iran. North Korea and Iran have a long history in sharing missile technology, and it is quite possible that this cooperation could extend to Pyongyang sharing its nuclear test data with the Iranian regime. This would significantly increase the threat of Iran’s nuclear program, particularly if North Korea tested an HEU device. Iran now has the capacity to enrich uranium to weapons grade and to amass a sizable stockpile, although Iranian officials claim that its uranium has only been enriched to low levels for peaceful purposes. It would be very difficult for Iran to continue this claim if it tested a nuclear device on its soil. However, if Pyongyang were to share its test data with Iran, it would negate Iran’s need to test its own device and allow Iran to get even closer to a nuclear bomb without detection.


Q: Following this test, what can be done to solve the North Korean nuclear threat? 

Hecker: The test will spur the UN Security Council to likely impose a new round of economic sanctions again the North Korean regime. However, looking at the history of the nuclear crisis on the Korean peninsula shows that previous sanctions have not worked in stopping or reversing North Korea’s nuclear program. Imposing sanctions is a tried and failed approach so long as China refuses to implement them seriously. This test creates a new reality and requires a different strategy than previously pursued. We must find common ground with China in limiting the North Korean nuclear program. The international community should now adopt a strategy of “Constrain, Contain, and Be Prepared” to manage the North Korean nuclear threat:


  • Constrain: The first priority must be to constrain imports of certain dual-use technologies to limit North Korea’s ability to expand its HEU production. To be successful, this requires cooperation from China, North Korea’s biggest trading partner and ally in the region. We must also focus on limiting North Korea – Iran nuclear collaboration.

  • Contain: In partnership with its allies, the United States must work to contain the North Korean missile and nuclear threat by working with South Korea and Japan to develop more extensive regional ballistic missile defense capabilities, and helping South Korea increase its missile capabilities to offset North Korea’s threats.

  • Be Prepared: The United States and the international community should be prepared for more provocations by the North Korean regime, and be prepared to appropriately retaliate. 

Q: You indicate this test is not a security game changer. Then what is its greatest impact? 

Hecker: It certainly increases regional instability in Northeast Asia, so we can’t downplay its significance. But, perhaps the greatest impact of this nuclear test is that it will signal that the Kim Jong Un regime, like its predecessors, has chosen bombs over electricity. It will now be difficult to look for resolution of long-standing enmities on the Korean peninsula by focusing on issues beyond the nuclear dispute. Normalization of relations, a peace treaty, access to energy and economic opportunities – those things that come from choosing electricity over bombs and have the potential of lifting the North Korean people out of poverty and hardship – will be made much more difficult, if not impossible, for at least the next five years. This is particularly unfortunate in light of President-elect Park Geun-hye’s previously stated desire to promote better North-South relations through “trustpolitik” once she assumed office.


Topics: Nuclear nonproliferation | Nuclear safety and security | North Korea