Nuclear experts cast doubt on Wednesday on North Korea’s claimed first successful test of a miniaturised hydrogen bomb, saying the detected seismic activity suggested a less powerful device.
The announcement followed hints last month by leader Kim Jong-Un that Pyongyang had already developed a hydrogen, or thermonuclear, bomb — a claim greeted with scepticism by experts at the time.
Crispin Rovere, an Australia-based nuclear policy and arms control specialist, said the 5.1 magnitude tremor detected at the North’s Punggye-ri nuclear test site was too small to support Pyongyang’s claim.
“The seismic data that’s been received indicates that the explosion is probably significantly below what one would expect from an H-bomb test,” Rovere said.
“So initially it seems to be that they’ve successfully conducted a nuclear test but unsuccessfully completed the second-stage hydrogen explosion,” Rovere said.
The test came just two days before Kim Jong-Un’s birthday. Analysts said the North’s leader had been looking for a major achievement to highlight at a rare ruling party congress scheduled for May — the first gathering of its kind for 35 years.
“I don’t think it was a hydrogen bomb test. The explosion had to be larger if it was a hydrogen bomb test,” said Choi Kang, vice president of the Seoul-based Asan Institute for Policy Studies.
“I think they are disguising it as a hydrogen test because Kim Jong-un mentioned it before,” Choi said.
A thermonuclear bomb uses fusion in a chain reaction that results in a far more powerful explosion than the fission blast generated by uranium or plutonium alone.
The North has made many unverifiable claims about its nuclear weapons strength, including the ability to strike the US mainland, which most experts dismiss — at least for now.
In September, however, the Washington-based Institute for Science and International Security had raised a red flag over what appeared to be a new “hot cell” facility under construction at the North’s main Yongbyon nuclear complex.
Analysts at the think tank said satellite images suggested it could be an isotope separation facility capable of producing tritium — a key component in the design of thermonuclear weapons.
Bruce Bennett, a senior defence analyst with the Rand Corporation, was also unconvinced by the H-bomb test claim.
“If it were a real H-bomb, the Richter Scale reading should have been about a hundred times more powerful than what we saw, which would have been in the range of seven or so,” he told.
Bennett assessed Wednesday’s explosion as in the 10-15 kiloton range, just less than the Hiroshima blast in 1945.
He said the fusion element of the explosion may have failed entirely, or the fission element did not operate correctly.
But Bennett said the increasing power of the blasts heightened the prospect of triggering an earthquake and the release of radiation from the underground test site, a source of great concern to Chinese people across the border.