Government organizations and experts have conflicting views on the power of the nuclear bomb North Korea said it tested on Monday. But they agree that even a small nuclear weapon with low detonating power can be devastating. They also point out that North Korea surprised South Korean and U.S. military authorities by conducting the test in an area not under their close watch, even if it was among nine possible test sites they had pinpointed earlier.

A Failure?

The National Intelligence Service told the Intelligence Committee of the National Assembly the North probably conducted a small-scale nuclear test with a yield of less than 1 kt considering that a 1 kt nuclear test usually produces a reading of 4.0 on the Richter scale. However, it added the situation needs further analysis. The 1 kt yield is tantamount to detonating 1,000 tons of TNT and indicates that detonation of less than that took place on Monday. The 3.58-3.7 register on the Richter scale observed by the Korea Institute of Geoscience and Mineral Resources is lower than the 4-6 register usually associated with nuclear tests. Pakistan, India and China carried out nuclear tests with a yield of dozens of or hundreds of kt, producing readings between 4.5 and 6.

Intelligence agencies initially predicted that if the North conducts a nuclear test, it would generate a yield of around 20 kt after studying the 14 kt nuclear bomb dropped on Hiroshima and the 21 kt one which fell on Nagasaki in Japan during the World War II. “The nuclear test by the North produced tremors weaker than those in usual nuclear tests,” said Lee Choon-geun with the Science ands Technology Policy Institute.

The KIGMR initially estimated that the North’s nuclear test yielded 0.4-0.8 kt after detecting and analyzing tremors but adjusted its estimation upward to “higher than 0.8 kt at least” on Monday afternoon. “It is hard to estimate,” a staffer said. But he added maximum yield “won’t be higher than 5 kt.”

Some experts say the yield might have been far higher than 1 kt as tremors are observed in an abated state as they pass through obstacles such as rock. Prof. Hong Tae-kyung of Yonsei University said the tremors were observed by seismological observatories here after passing through seabeds in the East Sea, which cushion them more than continents. “More accurate analysis and information is needed to determine the exact scale of the nuclear test,” he added.

With the low yield, experts guess that the North either tested a small nuclear weapon or the weapon failed to detonate properly.

How Powerful?

The NIS concluded that North Korea has developed or will have nuclear weapons with yields of 10-20 kt that are more powerful than the one tested Monday. If they were to be used against Seoul or other large cities in the South, the results would be devastating. Simulations secretly conducted by the U.S. Defense Department and the CIA in 1998 show that when a 15 kt nuclear bomb similar to the one dropped on Hiroshima explodes 500 m above the Defense Ministry building in Yongsan, Seoul, it could leave 620,000 dead. All objects within a radius of 150 meters from the explosion would instantly evaporate, and almost all substance within a radius of 1 km would liquefy. A 10 kt nuclear weapon, which is less formidable, would kill at least 180,000 and injure 160,000 if detonated above Seoul, the Defense Threat Reduction Agency (DTRA) under the U.S. Defense Department said.

Location

The NIS told the Intelligence Committee the test site is estimated to be centered at 40.81-N, 129.101-E, some 15 km from Sangpyeong-ri in Kimchaek City, North Hamgyeong Province, but Punggye-ri in Gilju or Hwadae in the province have not been ruled out. The NIS initially guessed the site was a horizontal tunnel in a 360-m high mountain in Musudan-ri in Hawdae, North Hamgyeong Province but corrected its estimate to Sangpyeong-ri in Kimchaek later on Monday.

Kimchaek is not far away from Punggye-ri, which was considered the most suitable place for nuclear testing, and from the missile launch site in Musudan-ri, where the Taepodong-2 missile was fired on July 5 this year.

The North was expected to conduct the test in a shaft, but it seems to have used a horizontal tunnel to hoodwink surveillance by intelligence authorities from South Korea and the U.S.

(englishnews@chosun.com )