Even if Beijing signs on to U.N. punishment if the North conducts a test, there may be less hurt for Pyongyang than Washington wants.
The impact of tougher sanctions would be ‘‘a drop in the bucket compared with the tidal wave of China-North Korean trade’’ that has risen sharply since 2008, even as inter-Korean trade has remained flat, said John Park, a Korea expert at the Massachusetts Institute of Technology.
Trade figures show North Korea’s deepening dependence on China. Pyongyang’s trade with Beijing surged more than 60 percent last year, reaching $5.63 billion, according to South Korea’s Statistics Korea. China accounted for 70 percent of North Korea’s annual trade in 2011, up from 57 percent in 2010.
North Korea’s 2006 nuclear test had an estimated explosive yield of 1 kiloton. The Los Alamos National Laboratory estimated in 2011 that the North’s test on May 25, 2009, which followed U.N. condemnation of an April long-range rocket launch, had a minimum yield of 5.7 kilotons. The atomic bomb that hit Nagasaki at the end of World War II was about 21 kilotons.
Both North Korean tests used plutonium for fissile material. Without at least one more successful plutonium test, it’s unlikely that Pyongyang could have confidence in a miniaturized plutonium design, according to an August paper by Frank Pabian of Los Alamos and Siegfried Hecker of Stanford University.
North Korea’s small plutonium stockpile is sufficient for four to eight bombs, they wrote, but it may be willing to sacrifice some if it can augment information from the previous tests. Pabian and Hecker predicted that Pyongyang may simultaneously test both plutonium and highly enriched uranium devices.
A uranium test would worry the international community even more, as it would confirm that North Korea, which would need months to restart its shuttered plutonium reactor, has an alternative source of fissile material based on uranium enrichment. North Korea unveiled a previously secret uranium enrichment plant in November 2010.
‘‘Whether and when North Korea conducts another nuclear test will depend on how high a political cost Pyongyang is willing to bear,’’ Pabian and Hecker wrote.
Another test would also undermine Pyongyang’s assertion that its long-range rocket launches are for a peaceful space program and not what outsiders see as the development of ballistic missiles that could eventually deliver nuclear weapons.
On the same day as this month’s rocket launch, an unidentified North Korean Foreign Ministry spokesman told state media that a hostile U.S. response to a failed launch in April of this year had forced Pyongyang ‘‘to re-examine the nuclear issue as a whole.’’
The statement was a clear threat to detonate a nuclear device ahead of any U.N. Security Council action, said Baek Seung-joo, an analyst at the state-run Korea Institute for Defense Analyses in Seoul.
Pennington reported from Washington. Associated Press writers Hyung-jin Kim and Sam Kim contributed from Seoul.