Former Los Alamos National Laboratory director Siegfried Hecker assesses North Korea’s claim to have detonated a hydrogen bomb in an underground nuclear test this week. Hecker is one of the world’s top experts on the North Korean nuclear program. He has visited North Korea seven times since 2004, and is the only Western scientist known to have ever been inside a North Korean uranium enrichment facility. He is currently a senior fellow at Stanford’s Center for International Security and Cooperation, and a research professor of Management Science and Engineering.

Do you believe that North Korea actually detonated a hydrogen bomb in its latest nuclear test?

I don’t believe it was a real hydrogen bomb, but my greatest concern is not so much whether or not they actually tested a hydrogen bomb, but rather that they tested at all. Since this test worked, they will have achieved greater sophistication in their bomb design – that is the most worrisome aspect. This is their fourth test – with each test they can learn a lot.

What makes a hydrogen bomb a more threatening weapon than a conventional atomic bomb?

A hydrogen bomb can be a hundred or a thousand-fold more powerful than a fission bomb. Certainly a blast of a megaton will be much more destructive than the Hiroshima bomb, but the more important part is the ability to deliver at long range and to do it accurately. That is what would threaten the United States and its allies most; even with the size of nuclear blasts they have already demonstrated.

White House officials say that initial data from nearby monitoring stations are not consistent with a hydrogen bomb test. How will we know for sure whether it was a hydrogen bomb or not?

The short answer is that we may never know. The telltale signs of a hydrogen bomb are very difficult to pick up in a deeply buried test. Typically hydrogen bombs have greater explosive power or yield. This test is currently believed to have resulted in a seismic tremor of 5.1 on the Richter earthquake scale. That would make it roughly equivalent to the third nuclear test in February 2013. At that time, North Korea claimed it tested a miniaturized atomic bomb – there was no mention of a hydrogen bomb. My estimate of the yield for the 2013 test is roughly 7 to 16 kilotons – which is in the range of the 13-kiloton Hiroshima blast. As far as destructiveness, a Hiroshima-scale explosion is bad enough. Detonated in Manhattan, it may kill as many as a quarter million people. The power of the 2013 and the current explosion is more consistent with fission bombs than hydrogen bombs.

Can you rule out the possibility that it was a hydrogen bomb?

I find it highly unlikely that the North tested a real hydrogen fusion bomb, but we know so little about North Korea’s nuclear weapons design and test results that we cannot completely rule it out. A modern hydrogen bomb is a two-stage device that uses a fission bomb to drive the second stage fusion device. A two-stage device is very difficult to design and construct, and is likely still beyond the reach of North Korea today. However, by comparison, China’s early nuclear weapon program progressed rapidly. It tested its first fission bomb in 1964 and less than three years later demonstrated a hydrogen bomb – and that was 50 years ago. North Korea has now been in the nuclear testing business for almost 10 years, so we can’t rule anything out for certain.

If it wasn’t a hydrogen bomb, what kind of bomb might it have been?

What may be more likely than a two-stage hydrogen bomb is that they took an intermediate step that utilizes hydrogen (actually hydrogen isotopes) fuel to boost the explosive yield of the fission bomb, a sort of turbocharging. Such a device has a fusion or “hydrogen” component, but is not a real hydrogen bomb. It allows miniaturization – that is making the bomb smaller and lighter. Moreover, it would be the first step toward eventually mastering a two-stage hydrogen bomb.

The most important aspect then is to miniaturize, whether it is a fission bomb, a boosted fission bomb, or a hydrogen bomb. The Nagasaki bomb weighed 5,000 kilograms. It was delivered in a specially equipped B-29 bomber. North Korea wants to demonstrate it has a deterrent. To do so, it needs to be able to credibly threaten the U.S. mainland or our overseas assets. For that, you have to make the bomb (more correctly, the warhead) small enough to mount on a missile. The smaller and lighter, the greater the reach. At this point, what makes their nuclear arsenal more dangerous is not so much explosive power of the bomb, but its size, weight and the ability to deliver it with missiles.

How close is North Korea to being able to credibly threaten a nuclear strike against the mainland United States?

North Korea is still a long way off from being able to strike the US mainland. It has only had one successful space launch. It needs a lot more, but it has a large effort in that direction.

Do you think North Korea conducted this test for political or technical reasons?

North Korea had very strong technical and military drivers for this test, as well as follow-on tests. The political environment is mostly what has constrained it from testing earlier and more often. However, this test demonstrates that Pyongyang is willing to weather the political storm this test will bring. It has done so for all previous tests.

What are your current estimates on the size of North Korea's stockpile of nuclear weapons and materials?

Much like in the area of sophistication of the bomb, we have little information of what North Korea actually possesses. The best we can do is to estimate how much bomb fuel, plutonium and highly enriched uranium, they may have produced and estimate how many bombs they can produce from that stockpile. My best estimate at this time is that they may have enough bomb fuel for 18 bombs with a capacity to make 6 to 7 more annually. That, combined with the increased sophistication they surely achieved with this test, paints a troublesome picture.

How should the U.S. respond?

I am concerned about we haven’t done to date. Washington has lost many opportunities we have had since North Korea began its nuclear weapon production in earnest in 2003. One thing that’s clear is that doing what we and the rest of the world have done so far – half-hearted diplomacy, ultimatums, and sanctions – have failed, so these are not the answer. I have previously argued that we should focus on three “No’s” for three “Yes’s” – that is no more bombs, no better bombs (meaning no testing) and no export – in return for addressing the North’s security concerns, its energy shortage and its economic woes. This could have worked when I first proposed it 2008 after one of my seven visits to North Korea. It will be more difficult now.

South Korea and the United States are “completely aligned” on North Korea strategy, the chief American diplomat in South Korea said to a Stanford audience on Monday.

Mark Lippert, who assumed the role of U.S. ambassador to the Republic of Korea in 2014, delivered remarks at a public seminar, “Perspectives on the U.S.-Korea Alliance,” organized by the Korea Program at the Walter H. Shorenstein Asia-Pacific Research Center.

Arriving from the Washington summit of President Obama and Korean President Park Geun-hye, Lippert spoke of the success of the state visit. The U.S.-Korea relationship is in “as good a shape as it’s ever been,” and that secure foundation is allowing the two countries to forge ahead on shared challenges, including North Korea, trade and global health.

Mark Lippert expressed optimism about the U.S.-ROK alliance at a Stanford talk on Oct. 19, 2015.

He said the United States and South Korea are invested in getting to a place where the North Koreans will “come back to the table” for discussions on ending their nuclear program, noting the continuing viability of the Six Party Talks mechanism which has been stalled for more than five years.

Lippert also cited U.S.-Korea strategic cooperation on sanctions against North Korea, and defense capabilities aimed to deter the threat of a North Korea with nuclear and long-range missile capacity.

Looking ahead, “The United States strongly supports calls for reunification of the Korean Peninsula,” he said. Human rights, a free economy and a democratically elected government in the North would be a priority in that pursuit.

Lippert said the United States is supportive of inter-Korean talks and reunions for families separated by the Korean War, both announced earlier this year. On Tuesday, hundreds of South Koreans crossed the border to meet with North Korean relatives, who have been separated for more than six decades.

Partnering on the economic level was another key aspect of the summit, Lippert said, and the Trans-Pacific Partnership (TPP) was among items discussed. The United States, as one of 12 TPP member nations, would welcome an application from South Korea should they choose to pursue it, he said.

Lippert acknowledged that South Korea already has bilateral trade agreements with 10 out of the 12 TPP member nations, including one with the United States. The U.S.-Korea Free Trade Agreement (KORUS) came into force in 2012 and is moving toward full implementation, he said. The United States’ sixth largest trading partner is South Korea.

Following his formal remarks, Lippert took questions from the audience.

Michael Armacost, a Shorenstein Distinguished Fellow, asked Lippert how Japan and China figured into the summit discussions following recent developments. In September, President Park attended a military parade in Beijing that marked the 70^th anniversary of the end of World War II. She was the only leader from a democratic country at the event.

Responding on China, Lippert said the United States is supportive of South Korea engaging with China. “We don’t view this as a zero-sum game,” he said, likening South Korea’s regional relationships to a situation where “all boats rise” together.

Dafna Zur, a professor of Korean culture and literature, asked Lippert to talk about how his education informed his career in public service.

Lippert attended Stanford and studied political science and international policy studies.

His education, he said, was invaluable in preparing him for the diverse situations and people that a diplomatic career brings.

Lippert encouraged students to savor conversation and debate in the classroom. Participating in that kind of forum not only “makes you a more informed person” but also “sharpens your analytic skills,” he said.

Prior to becoming ambassador, Lippert held senior positions in the Department of Defense and the White House and served in the U.S. Navy.

Following the event, Lippert met with faculty members of Shorenstein APARC and the Freeman Spogli Institute for International Studies for a roundtable discussion, chaired by Kathleen Stephens, a distinguished fellow at Shorenstein APARC and former U.S. ambassador to the Republic of Korea (2008-11).

Embedded photo: Mark Lippert speaks at Stanford on Oct. 19, 2015. Photo credit: Heather Ahn.

In a recent interview with Voice of America, David Straub, associate director of the Korea Program at the Shorenstein Asia-Pacific Research Center, said that "Washington and Seoul will press China and Russia harder to use their influence to bring North Korea to genuine denuclearization talks."

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In an NK News' series of interviews with a panel of U.S. experts on North Korea policy, David Straub, associate director of the Korea Program and former State Department Korea director, analyzes the U.S. approach toward Pyongyang. With NK News' permission, downloadable PDF versions of the interviews are available below.