North Korea's first nuclear test

compiled by Wm. Robert Johnston
last modified 21 October 2006
Summary

North Korea's first nuclear test was conducted underground on 9 October 2006. The device was plutonium-fueled and the estimated yield was 0.2-1 kiloton. It is likely that this was a test of an improved implosion device small enough for delivery by one of North Korea's ballistic missile systems, although possibilities implying either higher or lower weapon capabilities cannot be excluded. It is also likely that the test failed to achieve the expected yield, which was reportedly 4 kilotons; such a failure could result from several factors and is not necessarily indicative of North Korea's weapon capabilities. If the test was indeed a failure, a second nuclear test is likely.

Background

On 9 October 2006 North Korea conducted its first nuclear test. North Korea had announced on 4 October their intent to conduct a test, and also notified the People's Republic of China 20 minutes before the test. The test was conducted underground (as have all nuclear tests by the other nuclear states since 1980). This is the first known nuclear test by any nation since the underground tests by India and Pakistan in May 1998.

As a demonstration of North Korea's ability and intent to produce nuclear weapons, the test should not be a surprise. Various sources estimate that North Korea first obtained separated plutonium in quantities sufficient for a few nuclear weapons by 1992 to 1994. Separation of plutonium from spent fuel at the Yongbyon site resumed in 2003, following North Korea's withdrawal from the Nuclear Non-Proliferation Treaty. In July 2005 North Korea declared that it had produced nuclear weapons. As of mid-2006 the ISIS estimated that North Korea had produced 43 to 61 kg of plutonium, of which they estimated 20 to 53 kg had been separated. This would be sufficient for 4 to 13 nuclear weapons, by ISIS estimates.

North Korea has already developed and deployed an extensive arsenal of tactical and theater ballistic missiles, most capable of delivering a small nuclear weapon:

North Korea could probably produce nuclear warheads light enough for the Nodong and Taepo Dong 1 and possibly the R-27, but not for the Taepo Dong 2 at full range. North Korea has supplied many of these missiles and components to Iran and Pakistan.

Location

The USGS reported the event took place at 41.294° N, 129.134° E (with a horizontal uncertainty of 9.6 km) at 01:35:27 UTC (10:35:27 AM local time). As of 16 October the USGS earthquake data base lists the location as 41.29° N, 129.09° E and time as 01:35:28.01 UTC.

A possible test site in preparation was previously identified at 41.278° N, 129.089° W, about 1.5 km from the USGS location; ISIS has posted recent satellite imagery of this site. GlobalSecurity.org reports construction of a tunnel at this location, P'unggye-yok, to a depth of 700 meters. Use of horizontal tunnels for nuclear tests facilitates the use of diagnostic tests to help validate a nuclear weapon design. It is not known if the 9 October test was conducted here, or if this site is available for a future test. Reports on 17 October suggest that North Korea is preparing for a second nuclear test, although North Korea recently stated they do not plan to conduct another nuclear test.


(Base image from Jeff Schmaltz, MODIS Rapid Response Team, NASA/GSFC)

The location of the 9 October test is shown as a red dot in the NASA satellite image above (image from 1 May 2003); the larger red circle indicates the uncertainty in the USGS location. The green dot indicates the Yongbyon nuclear facility (at 39.797° N, 125.756° E); the light blue dot indicates the Musudan-ri test site (40.854° N, 129.668° E), used for Taepo Dong theater missile tests.

Yield estimates

Reported magnitude and yield estimates (see CNS for more discussion):

The best current estimate of the yield of the 9 October test is in the 0.2-1 kt range. Further analysis may be able to improve on reported estimates, but lacking open information from North Korea uncertainty in the yield is likely to remain. The figure below plots estimated yield versus seismic magnitude for a variety of historical underground tests for which data is available; the blue box indicates the possible yield (0.2-1 kt) and magnitude (3.9-4.4) of the 9 October test.

Implications

Some sources had expressed doubt that the explosion was nuclear, given the low yield estimates. Such claims were laid to rest on 15 October with reports that the U.S. had successfully detected radioactive effluents from the test. Additional confirmation may be possible from further analysis of the seismic signal; nuclear and conventional explosions can often be distinguished based on seismic signals, although this is sometimes impossible for low yield events.

Regarding the initial disagreement, the Center for Nonproliferation Studies commented "Conclusive results of diagnostic tests should be available within days, but considering the potential risks in bluffing about nuclear capabilities, North Korean claims should be assumed to be true until conclusively proven false." This more cautious position has merits over the position of some analysts who have attempted to extrapolate this to an insubstantial North Korean nuclear capability. The claimed ambiguity regarding whether a nuclear test took place is ironic, given the confidence expressed that international monitoring of the Comprehensive Test Ban Treaty would be able to detect nuclear tests of this size.

The first nuclear test by most nuclear states has been at a yield representative of a full yield test of an implosion nuclear device: 19 kt by the United States (1945), 20 kt by the USSR (1949), 25 kt by the United Kingdom (1952), 65 kt by France (1960), 22 kt by China (1964), 15 kt by India (1974), and 32 kt claimed by Pakistan (1998). The low yield of the North Korean test has been interpreted as a failure, and some sources have suggested that North Korean nuclear capabilities are unsophisticated. This is only one of several possibilities:

In summary, it is unlikely that North Korea was testing a basic implosion nuclear device, as in the first nuclear tests by most nuclear weapons states. More likely, the test was a reduced yield version of an improved implosion design, possibly one suitable for delivery by one or more North Korean missile systems. If so, the test is more comparable to tests first conducted by the United States in 1952 than to the first U.S. test in 1945. The possibility of a test geared towards second-generation principles, e.g. incorporating fusion reactions, cannot be eliminated but is unlikely. Assuming an intended yield of 4 kt and an actual yield of ~0.5 kt, North Korea has likely acquired significant information towards correcting any design problems associated with the reduced yield.

Some media reports (including reports by The New York Times) have ascribed significance to the fact that the test was of a plutonium-fueled device rather than a uranium-fueled device. As background, some critics have doubted claims that North Korea is pursuing uranium enrichment. During the Clinton administration, U.S. intelligence had identified evidence that North Korea was pursuing uranium enrichment. Mounting evidence during the Bush administration prompted the U.S. to confront North Korea on the issue in 2002. In October 2002, the U.S. announced that North Korea acknowledged in one-on-one talks that it was pursuing a uranium enrichment program for nuclear weapons, leading to suspension of fuel oil shipments to North Korea. When confronted by the IAEA on the issue, North Korea declined to address the claims regarding uranium enrichment, which would be a violation of treaty obligations; instead, North Korea announced its withdrawal from the Nuclear Non-Proliferation Treaty in January 2003 and began separation of plutonium from fuel formerly safeguarded by the IAEA. The uranium enrichment program, if efforts have continued, is unlikely to have produced sufficient highly enriched uranium (HEU) for a nuclear device at this time. Most of the North Korean fissile material stockpile is believed to be plutonium processed since 2003.

Analysts both inside and outside the arms control community have expressed widely varying interpretations of the 9 October event and its meaning for North Korean nuclear capabilities. Basic nuclear weapons design is not sufficiently challenging to dismiss the North Korean nuclear threat, however, and the world community must consider seriously this event given North Korea's record on WMD production and on arms exports.


© 2006 by Wm. Robert Johnston.
Last modified 21 October 2006.
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