On January 5, 2016, reports of an unusual seismic event close to a known nuclear test site in North Korea (Punggye-ri) were followed by official Korean news statements that North Korea had successfully tested a hydrogen bomb. Kim Jong Un, North Korea’s leader, described his country in December as “a powerful nuclear weapons state ready to detonate a self-reliant A-bomb and H-bomb to reliably defend its sovereignty and the dignity of the nation.”

Q1: Was the test truly a hydrogen bomb and if so, what does this mean for North Korea’s nuclear weapons?

A1: When North Korea joined the Nuclear Nonproliferation Treaty in 1985 it already had elements of a nuclear weapons program in place: a plutonium production reactor and a reprocessing plant. It froze its plutonium program from 1994 under an agreement negotiated with the United States (Agreed Framework) but kicked out international inspectors in 2002 and resumed its nuclear weapons activities, adding uranium enrichment capabilities. It has negotiated with China, Russia, the United States, Japan and South Korea on and off again under the Six Party Talks, but these halted in 2008. Its first nuclear test in 2006 fizzled: the yield was below 1 kiloton. In 2009, North Korea tested again, with a yield of somewhere between 2 and 7 kilotons, and in 2013 it achieved a higher yield in a third nuclear test (estimated between 7 and 25 kilotons).

Seismic readings can provide some estimation of nuclear weapon test explosions and a 5.1 Richter scale reading is slightly higher than the 2013 test at 5.0. So, this test was on par with the 2013 event. It’s possible that North Korea tested another fission device or a fusion-boosted fission device (single stage). We tend to think of thermonuclear devices as having huge explosive power (in the megaton range) because they have at least two stages and are not as limited in size as fission devices, but they can also be small. A two-stage device generally uses a primary (fission reaction) to ignite a secondary (fusion reaction) explosion. We are unlikely to get much more detail unless there was some environmental contamination from the test.

Regardless, each test provides new data to the North Koreans, enabling them to improve their designs. A fusion-boosted fission device is primarily a fission weapon that uses fused tritium to produce neutrons that increase the efficiency of the fission reaction. If so, this would suggest that North Koreans are working to make their weapons more efficient, which will widen their options for delivery on missiles.

Q2: How does this test affect the security of the United States and those of its allies?

A2: North Korea’s possession of nuclear weapons has been very destabilizing in the region and some observers have suggested that it has emboldened North Korea to act more aggressive conventionally. For the time being, a fourth nuclear test doesn’t change the military equation, but the real issue is North Korea’s ability to mount a nuclear warhead on missiles and this test is a step further in that direction. The United States has strong alliances with Japan and with South Korea and provides extended deterrence (both conventional and nuclear) to both those countries. North Korea is obviously working to develop intercontinental ballistic missiles with ranges sufficient to reach the continental United States, which would be a very significant threat.

Q3: How have the United States, Japan, South Korea and China responded so far?

A3: Secretary of State Kerry stated that “We do not and will not accept North Korea as a nuclear-armed state.” Other officials condemned further violation of UN Security Council Resolutions (which ban North Korea testing nuclear weapons and ballistic missiles) and stressed that the United States will continue “to protect and defend allies in the region… and will respond appropriately to any and all North Korean provocations.” Prime Minister Abe told reporters that the North Korean test was a grave threat to Japanese security and South Korean officials quickly condemned the test. President Park told the press that she would work “in close cooperation with the international community to ensure that North Korea will pay the price for conducting a new nuclear weapons test.” China strongly urged North Korea to honor its commitment to denuclearization and “stop taking actions that worsen the situation.”

Q4: What are the next steps in responding to the test?

A4: The UN Security Council is meeting to discuss a response but whether any actions will have a significant impact on limiting the North Korean nuclear program is questionable. Additional sanctions are likely but again, their impact could be limited. Undoubtedly, the United States will be consulting with its partners Japan and South Korea and with China about increasing pressure on North Korea to abide by its international commitments.

Sharon Squassoni is a senior fellow and director of the Proliferation Prevention Program at the Center for Strategic and International Studies (CSIS) in Washington, D.C. Victor Cha holds the Korea Chair at the Center for Strategic and International Studies (CSIS) in Washington, D.C.

Critical Questions is produced by the Center for Strategic and International Studies (CSIS), a private, tax-exempt institution focusing on international public policy issues. Its research is nonpartisan and nonproprietary. CSIS does not take specific policy positions. Accordingly, all views, positions, and conclusions expressed in this publication should be understood to be solely those of the author(s).

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Victor Cha
Senior Vice President for Asia and Korea Chair

Sharon Squassoni