North Korea Claims Hydrogen Bomb Test

January/February 2016

By Elizabeth Philipp

North Korea declared on Jan. 6 that it had successfully conducted a test of a hydrogen bomb earlier that day, sparking a mix of condemnation and skepticism around the world. Government officials and independent experts agreed that the event was an underground nuclear test, but cast doubt on the claim it was a hydrogen bomb.

In response to the North Korean announcement, White House spokesman Josh Earnest said on Jan. 6 that the initial evidence of the test is “not consistent with North Korean claims of a successful hydrogen bomb test” but that the blast was “provocative and a flagrant violation” of a number of UN Security Council resolutions. The test has not “caused the United States government to change [its] assessment of North Korea’s technical and military capabilities,” Earnest said.

Classic hydrogen bombs are more technologically sophisticated devices and produce a higher explosive yield because they involve two stages: a first one involving nuclear fission, the splitting of atoms, and a second one involving nuclear fusion, the combining of atoms. North Korea’s past three nuclear tests in 2006, 2009, and 2013 were of fission devices. North Korea is prohibited from testing nuclear weapons under UN Security Council resolutions.

The Jan. 6 announcement, which was relayed by Pyongyang’s state-run Korean Central News Agency (KCNA), described the test as a “spectacular success.” Pyongyang also indicated its intent to continue nuclear development, stating it “will steadily escalate its nuclear deterrence of justice both in quality and quantity.”

Punggye-ri Test Site

Seismic activity from the nuclear test was detected immediately by the Comprehensive Test Ban Treaty Organization (CTBTO), the international body that is preparing for the implementation of the Comprehensive Test Ban Treaty (CTBT) and monitors the environment for nuclear testing.

North Korea, which is not a party to the CTBT, is the only state to test a nuclear weapon in this century.

The CTBTO reported an “unusual seismic event” near North Korea’s known nuclear testing site via a statement on its website Jan. 6. The seismic data confirm that it was “indeed a manmade explosion,” said Lassina Zerbo, executive secretary of the CTBTO, at a Jan. 7 press briefing.

Although North Korea did not announce an imminent test, experts have been aware of preparations for months, tracking activity at North Korea’s Punggye-ri nuclear test site. In a Dec. 2 analysis on 38 North, an online publication of the U.S.-Korea Institute at Johns Hopkins University, Jeffrey Lewis, director of the East Asia Nonproliferation Program at the James Martin Center for Nonproliferation Studies, wrote that Pyongyang is “excavating a new tunnel for nuclear testing.” Speaking on the implications of that activity at a Dec. 16 press briefing by 38 North, Joel Wit of the U.S.-Korea Institute said digging a tunnel is “serious” and that North Korea “may want more tunnels for the future to conduct more tests.” In a Jan. 7 analysis of satellite imagery published by 38 North, Joseph Bermudez, chief analytics officer for AllSource Analysis, said the test almost certainly was conducted at an older tunnel that was used for the 2009 and 2013 tests. North Korea had been excavating this tunnel for more than a year, he wrote.

Nuclear Yield

Experts can estimate the yield of a nuclear explosion based on seismic data. Through its International Monitoring System, the CTBTO detected the test at more than two dozen detection stations around the world, Zerbo said at a Jan. 6 press briefing. The explosion was found to be similar to the 2013 test in size and location, he said.

The CTBTO analysis found the magnitude of the explosion to be 4.85, just slightly smaller than the 2013 test, which had a magnitude of 5.1, according to Zerbo. The recent event is “on the order of 10 kilotons,” said Lewis at a Jan. 7 briefing by 38 North. But that is just an estimate, given that the North Korean site is not calibrated, he said. A calibrated site would allow for a standardized and reliable seismic reading.

Zerbo said the CTBTO would monitor its radionuclide detectors, which collect gases released into the air by the nuclear explosion. The presence of certain elements, such as xenon, can confirm that the seismic event was caused by a nuclear explosion. It can take time for the gases released by the explosion to reach the surface. In 2013, it took 55 days for the CTBTO’s radionuclide detectors to pick up evidence from the February test. The 2009 nuclear test yielded no radionuclide evidence.

Test Type

The evidence indicates that the magnitude of the test was significantly less powerful than past tests of hydrogen bombs by other states, said a South Korean military official quoted by South Korea’s Yonhap News Agency.

Rather than a classic two-stage hydrogen bomb design, it is more likely that North Korea tested a “boosted fission device,” Lewis said at the Jan. 7 briefing by 38 North. A boosted device uses hydrogen isotopes to increase the explosive yield by making the fission reaction more efficient.

That may be what North Korea means when it refers to a “hydrogen bomb,” he suggested. The detonation of a boosted fission device thus would be consistent with North Korea’s hydrogen bomb claim and with the observed yield, he said. A boosted device would be a “reasonable” step for North Korea in its fourth nuclear test, he said.

The increased efficiency means that North Korea would require less fissile material for each weapon and therefore represents an “important and useful step” in developing warheads for its intercontinental ballistic missile (ICBM) program, Lewis said.

North Korea deploys a variety of short- and medium-range ballistic missiles. It has displayed an ICBM, the KN-08, but not tested it. Pyongyang is also developing a submarine-launched ballistic missile, which it most recently tested in December (see page 38).

A second important implication of the test is that a boosted device “makes an excellent first stage” of a two-stage hydrogen bomb, Lewis said.

International Responses

At a Jan. 6 press conference, UN Secretary-General Ban Ki-moon “condemn[ed the test] unequivocally” and announced that the UN Security Council would immediately begin work on a new resolution against North Korea.

The Security Council held an emergency meeting on Jan. 6 to discuss responsive measures. The United States expressed its support for new multilateral sanctions in a Jan. 6 press statement by Samantha Power, U.S. ambassador to the United Nations.

The effectiveness of additional sanctions depends on China, Joseph DeThomas, former deputy assistant secretary of state for nonproliferation, said at the Jan. 7 press conference by 38 North. Experts have criticized Beijing, which is North Korea’s primary trading partner, for being too lenient on Pyongyang.

“Sanctions alone will not leverage change in the North Korean policy in the absence of a fundamental change in the Chinese policy,” DeThomas said. The additional sanctions should eventually be coupled with a diplomatic and political track that provides North Korea a pathway to negotiated denuclearization, he said.

On Jan. 6, the Chinese Foreign Ministry published a statement, saying the Chinese government is “firmly opposed” to North Korean nuclear testing and called on Pyongyang to “honor its commitment to denuclearization.”

In a Jan. 6 statement, South Korean President Park Geun-hye called for the United States and other allies of Seoul to impose sanctions on North Korea, saying her country would work with the international community to ensure North Korea “pay[s] the price” for the “grave provocation.”

Members of the U.S. Congress from both political parties called for a variety of actions, particularly a strengthening of sanctions. Rep. Adam Schiff (D-Calif.), ranking member on the House Intelligence Committee, said on Jan. 6 that “new and more biting” sanctions on North Korea are necessary. Sen. Kelly Ayotte (R-N.H.) called for the “toughest and broadest possible sanctions against North Korea” and any entities that support Pyongyang’s illicit activities.

In separate Jan. 7 statements, Rep. Mac Thornberry (R-Texas), chairman of the House Armed Services Committee, and Sen. John McCain (R-Ariz.), chairman of the Senate Armed Services Committee, called for expanding missile defense systems to counter the threat posed by North Korean missiles.