On May 25, two years and seven months after its first nuclear test, North Korea conducted its second nuclear test at Phunggye-ri, in the northeastern part of the country, which is close to the East Sea and about 375 kilometers northeast of Pyongyang. According to the U.S. Geological Survey, the second test took place about 6 kilometers west of the 2006 test.
Martin Kalinowski at the University of Hamburg in Germany estimated the test's yield at about 1.5 to 4.5 kilotons TNT equivalent, with a most likely yield of 2.5 kilotons TNT based on the seismic magnitude of 4.52 measured by the International Data Centre. Won-Young Kim and Paul Richards at Columbia University estimated a yield of about 2.2 kilotons TNT for hard rock, using the seismic magnitude of 4.7 measured by the Geologic Survey. Those estimations are consistent with my estimate of 2.2-2.8 kilotons TNT for an underground nuclear test in hard rock, using Geologic Survey data. (My estimations are based on the following two equations: (1) [Richter scale] = 4.262 + 0.973 log [explosive yield] for hard rock underground nuclear test; and (2) [Richter scale] = 4.45 + 0.75 log [explosive yield] for a stable tectonic underground nuclear test.)1
The explosive yield was several times greater than that of the 2006 North Korean test, which was estimated at less than 1 kiloton TNT. Although the test had a lower yield than that of the Nagasaki bomb, which had a yield of about 20 kilotons TNT, if it had been detonated in a densely populated urban area, the device would have been powerful enough to kill tens of thousands of people.
The second test also had a greater impact on South Korea. When North Korea conducted its first nuclear test, the former South Korean government, headed by President Roh Moo-hyun, was shocked because it had insisted on a denuclearized North Korea. Nonetheless, the Roh administration continued its policy of engagement with the North without interruption. President Roh even said that North Korea's development of nuclear weapons was for defensive, not offensive, purposes.
Because of the post-1998 "Sunshine policy" of the previous South Korean government, many South Korean nongovernmental organizations and the public weren't concerned about North Korea's threats, believing that Pyongyang would never use nuclear weapons against them. Few proposed that Seoul should acquire nuclear arms in response. So as not to provoke North Korea, the Roh administration disregarded the assertion by the opposition party--now the Hannara ruling party, or Grand National Party--that South Korea should fully participate in the Bush administration's Proliferation Security Initiative (PSI) to interdict possible shipments of weapons of mass destruction by North Korea.
But just a day after Pyongyang's second nuclear test, current South Korean President Lee Myung-bak announced that Seoul would fully participate in the PSI. (South Korea had been participating in the PSI only as an observer since 2005.) In response, North Korea warned that any stoppage and/or search of a North Korean ship would be a declaration of war. Further, South Korean Foreign Minister Yu Myung-hwan and Secretary of State Hillary Clinton agreed to U.S. "extended nuclear deterrence" against a North Korean nuclear attack on South Korea, according to recent South Korean news accounts.
One reason for Washington extending its nuclear deterrent to South Korea is to reduce Seoul's motivation to pursue a nuclear capability of its own. However, it also will justify North Korea's rationale for strengthening its nuclear capabilities.
And regardless of U.S. assurances, it seems some South Korean politicians are so fed up with North Korea's never-ending threats toward the South that they are having serious discussions about Seoul's "nuclear sovereignty."
Nuclear sovereignty is interpreted in two ways in South Korea. Conservative politicians, nongovernmental organizations, and some of the public think it means that South Korea should develop its own nuclear weapons to defend against the North. (The domestic criticism of this stance: That such an action could result in international sanctions against South Korea and a nuclear arms race in the region.) The other interpretation is that Seoul should develop capabilities to produce nuclear weapon materials by building nuclear fuel cycle facilities, including uranium enrichment and reprocessing.
After the test, politicians and the media (conservative and liberal alike) have begun actively insisting that South Korea should, like Japan, pursue a reprocessing capability to reduce the burden of the country's spent fuel and a uranium enrichment capability to reduce its dependence on foreign enrichment services. Japan already has such facilities, which are widely viewed as providing it with a virtual nuclear deterrent.
As such, legislators are starting to complain that the current U.S.-South Korean agreement on the civilian use of nuclear energy, which prevents Seoul from reprocessing and will expire in 2014, should be renewed to allow South Korea the same rights as Japan. They also argue that since North Korea has violated the 1992 Joint Declaration on the Denuclearization of the Korean Peninsula, in which both countries agreed not to possess reprocessing and uranium enrichment facilities, South Korea need not comply either. Further, Seoul has scheduled its first ever space rocket launch for late July, perhaps to offset Pyongyang's missile threat. What the South Korean government needs to realize, though, is that such actions only further destabilize the region.
1Lynn R. Sykes and Goran Ekstrom, "Comparison of Seismic and Hydrodynamic Yield Determinations for the Soviet Joint Verification Experiment of 1988," Proceedings of the National Academy of Sciences, May 1989, Vol. 86, pp. 3,456-3,460; Richard L. Garwin and Frank N. von Hippel, "A Technical Analysis: Deconstructing North Korea's October 9 Nuclear Test," Arms Control Today, November 2006.