Officials and analysts in South Korea cast doubt Wednesday on the North’s claim that it had detonated a hydrogen bomb for the first time, saying seismological data from the impact was more in keeping with that of an atomic device.
The North Korean announcement was immediately condemned by Britain, China, France, Japan, the United States, the European Union and NATO, among others, even as experts cautioned that the North might have exaggerated its claims, as it did with its three previous nuclear tests, in 2006, 2009 and 2013.
For one thing, they said, the estimated yield, or energy, from the explosion appeared to be too small to be that of a hydrogen bomb. The North might instead have tested a so-called boosted-fission bomb — which involves placing a tiny amount of tritium, a radioactive form of hydrogen, at the core of an atomic bomb, but is more destructive than a traditional nuclear weapon.
Lee Cheol-woo, a member of the intelligence committee of the South Korean National Assembly, said his country’s National Intelligence Service had estimated the explosive yield that was equivalent to 6 kilotons of TNT. (By comparison, the atomic bomb dropped on Hiroshima in 1945 exploded with 15 kilotons of energy.)
A hydrogen bomb would have yielded “hundred of kilotons or, even if it is a failed test, tens of kilotons,” Lee told reporters. The North’s last nuclear test, in February 2013, set off a magnitude 4.9 tremor.
The South estimated that the bomb detonated Wednesday had resulted in a magnitude 4.8 seismic event, smaller than the 4.9 to 5.2 range that American, European and Chinese authorities had reported.
Hwang In-mu, a vice defense minister of South Korea, told reporters that the North’s claim was “a bit of a stretch.”
Park Ji-young, a senior analyst at the Asan Institute for Policy Studies in Seoul, said, “I suspect the bomb they tested was a boosted-fission weapon.”
He added that the nuclear test site was not suitable for such a gigantic explosion as that of a hydrogen bomb. “Countries like the United States and Russia did their H-bomb tests in very remote places,” he said.
Karl Dewey, an analyst for IHS Jane’s, was similarly skeptical. “It is highly likely that rather than a thermonuclear explosion, the claim of a hydrogen bomb is disinformation by the North Korean regime,” he said in an interview. A hydrogen bomb would most likely involve a fuel called lithium deuteride, he said, “and it is not known if North Korea has the infrastructure to produce such material.”
But Victor Cha, a Georgetown University scholar of North Korea and a former adviser to the National Security Council, said the North’s test needed to be taken very seriously, even in the absence of proof that it was a hydrogen bomb. “We won’t know for a while, if ever,” he said. “From a national security perspective, I don’t have the luxury of downplaying the North Koreans’ claims, and would doubt the doubters.”
In Seoul, President Park Geun-hye convened an urgent meeting of her top national security
aides. As South Korea’s military increased its vigilance along the heavily militarized border with the North, its diplomats rushed to discuss with allies what Park called “strong sanctions” against Pyongyang. She said that a boosted-fission bomb would also mean that North Korea was pursuing technologies for a hydrogen bomb.
“Now, the government should closely cooperate with the international community to make sure that North Korea pays a corresponding price for the nuclear test,” Park was quoted as telling her aides.
Park said that more analysis was needed to verify Pyongyang’s claim, but that if true, it “could potentially shake up the security landscape of Northeast Asia and fundamentally change the nature of the North Korean nuclear threat.”
Prime Minister Shinzo Abe of Japan called the test “totally unacceptable” and “a grave threat to Japan’s security,” adding that the country would work with other nations and at the United Nations Security Council to take “firm measures” against Pyongyang.
North Korea is banned from conducting nuclear tests under a series of resolutions the Security Council has adopted in recent years. “The DPRK’s nuclear test, if confirmed, is in clear violation of U.N. Security Council resolutions and is deeply regrettable,” Yukiya Amano, director general of the International Atomic Energy Agency, said in a statement, using the initials for the North’s formal name, the Democratic People’s Republic of Korea.
Pyongyang’s sole major ally, China, has been increasingly impatient with the North’s behavior and did not hide its displeasure Wednesday. “Today, despite the opposition of the international community, North Korea carried out a nuclear test,” Hua Chunying, a spokeswoman for the Chinese Ministry of Foreign Affairs, said at a news conference in Beijing. “China is strongly against this act.”
Russia, which, like China, shares a border with the North, joined the condemnation. “Such actions are fraught with further aggravation of the situation on the Korean Peninsula,” Reuters quoted Maria Zakharova, a spokeswoman for Russia’s Foreign Ministry, as saying.
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