Stanford nuclear experts said they were skeptical of North Korea’s claim that it had detonated a hydrogen bomb this week.

However, they said the test was an important step forward for North Korea’s nuclear program and would have a destabilizing effect on the entire region.

“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,” said Siegfried Hecker, former director of Los Alamos National Laboratory and senior fellow at Stanford’s Center for International Security and Cooperation.

North Korean dictator Kim Jong-un has “a track record of exaggerated statements, hyperbole and outright lies,” according to Scott Sagan, Caroline S.G. Munro professor of Political Science.

“The propaganda machine in North Korea has made all sorts of claims about Kim Jong-un’s personal prowess and his history, and it is totally unsurprising that he might make exaggerated claims about North Korea’s military prowess,” Sagan said.

Former U.S. Secretary of Defense William J. Perry said he also doubted that North Korea had detonated a two-stage hydrogen bomb.

“Whether it’s a hydrogen bomb or not, it’s very dangerous, destabilizing development,” said Perry.

“It’s obvious they’re working to increase the capability and size of their nuclear arsenal and that represents a huge danger to the region and creates major instability and major concerns on the part of South Korea and Japan.”

Many North Korea watchers had been anticipating another nuclear test.

“We’ve thought that the North Koreans could test at any time – that the tunnels were ready, that they could do this at any time – so it would be a political decision, not a technical decision,” said Thomas Fingar, senior fellow at the Freeman Spogli Institute for International Studies.

Hecker said North Korea’s latest nuclear test would move the country closer to being able to miniaturize a nuclear warhead and mount it on a missile, extending the reach of their nuclear weapons.

“They will have achieved greater sophistication in their bomb design – that is the most worrisome aspect,” Hecker said.

“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.”

On the diplomatic agenda, the U.S. and its allies will likely push for stronger sanctions in the wake of the tests, according to Kathleen Stephens, a former U.S. Ambassador to the Republic of Korea and William J. Perry fellow at Walter H. Shorenstein Asia-Pacific Research Center (APARC).

“In the UN the U.S., Japan and South Korea will likely look for another, and stronger, UN Security Council resolution, presumably with some efforts to attach to it some teeth and strengthen sanctions,” Stephens said.

The U.S. Congress is currently considering financial sanctions that would cut of all access to U.S. banks for any banks dealing with the North Koreans.

But financial sanctions would likely be less effective in dealing with North Korea than they had been with Iran, according to Fingar.

“It’s like hitting a masochist,” said Fingar.

“North Korea is relatively insulated from the external economy, where Iran wasn’t. Iran had a middle class, you could make sanctions hurt, they could have a real effect. You could make it hard for the North Koreans to buy luxury goods, but at the end of the day, is that going to bring down the regime?”

Financial sanctions against North Korea could have the unintended consequence of also hurting China, said David Straub, associate director of the Korea program at APARC.

“This could be problematic for China because many of the transactions that North Korea conducts would be going thorough Chinese banks, and the Chinese, understandably might not be happy about the US financial sanctions on them, in effect,” Straub said.

Perry recommended that the U.S. reinvigorate diplomatic talks with North Korea in collaboration with China, South Korea, Japan and Russia.

“I would not give up on negotiations with North Korea yet,” Perry said.

“What could have been done many years ago was following through on negotiations with North Korea at the turn of the Century, which were proceeding robustly in the last years of Clinton’s second term, but were abandoned by the Bush Administration...That was a geo-strategic error.”

But Hecker said those negotiations would be harder now.

“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,” said Hecker.

“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."

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.

The United States and Russia should keep working together to stop the spread of nuclear weapons even while disagreeing on issues like Ukraine, Stanford scholars say.

In a recent article in the Bulletin of the Atomic Scientists, Professor Siegfried Hecker and researcher Peter Davis advocate continued U.S.-Russia collaboration on nuclear weapon safety and security.

"The Ukraine crisis has exacerbated what had already become a strained nuclear relationship," Hecker said in an interview. "As one of our Russian colleagues told us, nuclear issues are global and accidents or mishaps in one region can affect the entire world."

Hecker is a professor in the Department of Management Science and Engineering and a senior fellow at CISAC and the Freeman Spogli Institute for International Studies. Over the past 20-plus years, he has worked with Russian scientists to help stop nuclear proliferation. He and Davis returned from a trip this spring to Russia, where they met with nuclear scientists.

"We agreed that we have made a lot of progress working together over the past 20-plus years, but that we are not done," they wrote in the journal essay.

Hecker and Davis described Moscow as a reluctant partner in talks on nuclear proliferation. As for the United States, it actually backed away from cooperation first. A House of Representatives committee recently approved legislation that would put nuclear security cooperation with Russia on hold. And though the White House has opposed this, the Energy Department has issued its own restrictions on scientific interchanges as part of the U.S. sanctions regime against Russia.

But, Hecker said, "Cooperation is needed to deal with some of the lingering nuclear safety and security issues in Russia and the rest of the world, with the threats of nuclear smuggling and nuclear terrorism, and to limit the spread of nuclear weapons."

Washington does not have to choose between the two. It still can pressure Moscow on Ukraine while cooperating on nuclear issues, Hecker and Davis wrote.

They called for further nuclear arms reductions between the two countries, rather than a resumption of the nuclear arms race that took place in the mid-20th century.

Changing relationship

Hecker and Davis acknowledged that the U.S.-Russian relationship overall is changing.

"We realize … that the nature of nuclear cooperation must change to reflect Russia's economic recovery and its political evolution over the past two decades," they wrote.

For example, due to the strained relationship, nuclear proliferation programs must change from U.S.-directed activities to more jointly sponsored collaborations that serve both countries' interests.

As they noted, one huge problem is that Russia still has no inventory or record of all the nuclear materials the Soviet Union produced – or where those materials might be today.

"Moreover, it has shown no interest in trying to discover just how much material is unaccounted for. Our Russian colleagues voice concern that progress on nuclear security in their country will not be sustained once American cooperation is terminated," Hecker and Davis said.

Iran is a flashpoint

America needs Russia to help in its effort to stop Iran from building a nuclear weapon, Hecker and Davis wrote. Russia is a close ally of Iran: "Much progress has been made toward a negotiated settlement of Iran's nuclear program since President Hassan Rouhani was elected in June, 2013. However, little would have been possible without U.S.-Russia cooperation."

In a June 2 interview in the Tehran Times, Hecker said that the only way forward for Iran's nuclear program is transparency and international cooperation. He suggested that the country follow the South Korean model of peaceful nuclear power.

"In my opinion, South Korea will not move in a direction of developing a nuclear weapon option because it simply has too much to lose commercially. That is the place I would like to see Tehran. In other words, it decides that a nuclear program that benefits its people does not include a nuclear weapons option," he told the interviewer.

Hecker said that it is not in Russia's interest to have nuclear weapons in Iran so close to its border.

"Washington, in turn, needs Moscow, especially if it is to develop more effective measures to prevent proliferation as Russia and other nuclear vendors support nuclear power expansion around the globe," Hecker said.

In February, the Iranian government republished an article by Hecker and Abbas Milani, the director of Iranian Studies at Stanford University. The story ran in Farsi on at least one official website, possibly indicating a genuine internal debate in Tehran on the nuclear subject. Hecker and Milani described such a "peaceful path" in another essay on Iranian nuclear power.

Hecker is working with Russian colleagues to write a book about how Russian and American nuclear scientists joined forces at the end of the Cold War to stymie nuclear risks in Russia.

Media Contact

Siegfried Hecker, Freeman Spogli Institute: (650) 725-6468, shecker@stanford.edu

Clifton B. Parker, Stanford News Service: (650) 725-0224, cbparker@stanford.edu

Siegfried Hecker and his research assistant, Peter E. Davis, write that South Korea's nuclear energy program has become model that countries aspiring to obtain nuclear energy should emulate.

CISAC Senior Fellow Siegfried Hecker and his research assistant, Peter E. Davis, write in this Bulletin of the Atomic Scientists article that South Korea's nuclear energy program has become model that countries aspiring to obtain nuclear energy should emulate.

CISAC and FSI Senior Fellows Siegfried Hecker and William J. Perry write in this New York Times OpEd that Iran has little to show for its 50-year pursuit of a nuclear program. They argue Iran should forego its attempts to build the bomb and concentrate on learning how to build better nuclear power plants, which would aid the country's beleaguered economy and promote international cooperation.

"Japan and South Korea became leading global reactor vendors by doing so," they write. "This could constitute a pragmatic and honorable choice. Such a solution offers the best opportunities for technical and industrial development with greatest economic gain and and least danger of proliferation."

Nuclear energy is an essential engine that has helped to power South Korea’s industrialization and economic miracle. South Korea has become a world leader in both the domestic utilization of nuclear energy and its export potential. That journey began 40 years ago with the U.S.–South Korea Peaceful Nuclear Cooperation Agreement (the so-called 123 Agreement). 

Despite its meteoric rise in nuclear power, South Korea faces serious challenges: It must demonstrate that nuclear power remains safe; that the government can convince the public to accept interim spent fuel storage and long-term geologic disposal; and that its choices of nuclear fuel cycle technologies do not compound global nuclear proliferation concerns. 

Because South Korea’s ascendency in nuclear power was built on close cooperation with American companies and was initially based on American technologies, its nuclear fuel-cycle choices remain in large part dependent on U.S. concurrence. 

The extent of U.S. control and influence of South Korea’s nuclear choices is the crux of the current negotiations for the renewal of the 40-year old agreement, which has been extended for two years until 2016. The position of the U.S. government appears to have been forged primarily on the pillar of nonproliferation. South Korea, on the other hand, views energy security, competitiveness of the industry, and its national security as equally important. The politics and symbolism of the negotiations appear to have obscured a rational analysis of South Korea’s nuclear future and its cooperation with the United States. 

A team of researchers led by me and others here at the Center for International Security and Cooperation (CISAC) collaborated with a team from South Korea’s East Asia Institute, led by Professor Ha Young-Sun. Together we co-wrote a report, designed to look at these issues from both South Korean and American points of view.  

The CISAC team stepped back from the political stalemate and analyzed South Korea’s nuclear future based primarily on technical and economic considerations, but informed by the political situation. It conducted a TEP (technical, economic and political) analysis of the entire fuel cycle, which includes the front end (uranium mining and conversion; enrichment), the middle (fuel fabrication; reactor fabrication and construction; spent fuel storage) and back end (fuel reprocessing; spent fuel disposal; high-level waste disposal).

South Korea’s strategy of building a nuclear industry by focusing on the middle of the fuel cycle during the past several decades was brilliantly conceived and executed. Its nuclear industry is now among the best in the world. However, South Korea is advised to move to the construction of a centralized, away-from-reactor, dry-cask storage capability as quickly as possible. The TEP analysis finds it inadvisable for South Korea to pursue domestic enrichment in the short term because of the low technical and economic benefits, the ready global availability of enrichment services, and the substantial political downsides of pursuing such an option. In the longer term, if South Korea finds it needs enrichment capabilities as a hedge against supply disruption, large price fluctuations, or to enhance its reactor export potential, then it should pursue these strictly through international cooperative ventures.

South Korea’s strategy of building a nuclear industry by focusing on the middle of the fuel cycle during the past several decades was brilliantly conceived and executed."

 The TEP analysis also indicates that reprocessing spent fuel, either by the conventional PUREX process or by pyroprocessing, is not critical to South Korea’s short-term domestic program or its export market. Even if pyroprocessing can be shown to be technically and economically viable, its commercial development cannot be achieved rapidly enough to deal with South Korea’s near-term spent fuel accumulation problem. Moreover, the deployment of pyroprocessing faces considerable U.S. opposition. 

The best short-term option is to continue a robust pyroprocessing research program, preferably in cooperation with the United States as it is currently envisioned in the 10-year joint R&D program. In the longer term, the best prospects for the application of pyroprocessing are as a part of a fast reactor development program. The South Korean research team believes that pyroprocessing is an economically attractive alternative even for their current once-through fuel cycle; that is, it need not await the development of fast reactors because of the high cost of spent-fuel storage and eventual disposition in South Korea. 

Regardless of future fuel cycle choices, it is essential for South Korea to take immediate actions to restore the public’s trust in the nuclear industry. The government must deal resolutely with the industry’s alleged corruption problems and strengthen the government’s regulatory organizations dealing with all aspects of South Korea’s nuclear industry, as well as instill greater transparency and attention to quality matters in the Korean nuclear industry. This issue is closely tied to nuclear safety, which must remain the nuclear industry’s highest priority. 

Although the prospective terms for renewing the 123 Agreement were not a direct part of this study, we offer some overarching observations. First, the renewal should strive to develop a South Korea–U.S. partnership that reflects the enormous progress made in South Korea’s economic, political and industrial standing in the world since 1974. 

Second, Washington should not insist on the so-called nonproliferation “gold standard” adopted for the United Arab Emirates, in which countries developing nuclear energy pledge not to enrich uranium or reprocess plutonium. Instead, the United States should strive for a criteria-based standard that better reflects a country’s technical, political, regulatory, and industrial capacity, as well as its nonproliferation record. 

Third, the agreement should not be constrained by the North Korean nuclear problem. Pyongyang has clearly violated the letter and the spirit of the 1992 North-South agreement. The nature of South Korea’s civilian nuclear capabilities has little, if any, influence on North Korea’s nuclear weapons program. 

Finally, we should not allow the controversies over the terms of renewal for the 123 Agreement to overshadow what we view as the most important domestic and international consequence of South Korea’s meteoric rise as an industrial and nuclear energy power: It has emerged as a model state for future nuclear power aspirants by focusing on the middle of the nuclear fuel cycle.