Factors Related to Past DPRK Nuclear Tests

Executive Summary

In light of recent analyses about a possible next nuclear weapon test by the DPRK [i], ONN has compiled data related to each of the six previous nuclear weapon tests of the DPRK, specifically the timing of the previous tests, nuclear test site preparations, launch vehicle development, environmental factors and the political context. These factors may assist in assessing when a next test might take place. It should be noted, however, that there may be other relevant factors that cannot be fully understood from open sources (e.g. the intentions of Kim Jong Un).

Past Nuclear Tests

Timing - Times, Days, Dates

All six previous nuclear tests took place between 9:30 and 12:30 (KST). On the other hand, there appears to be no strong correlation between the timing of the tests and the day of the week. Five out of the six nuclear tests were conducted on or in the lead-up to major anniversaries in the DPRK. Two tests took place on or very near a significant date on the US calendar: the second test (2009), which took place on US Memorial Day; and the sixth test (2017), which took place one day before US Labor Day. Three nuclear tests took place during US or ROK presidential election campaigns or inaugurations: the third test (2013) took place on the day of the 2013 US State of the Union Address and nearly two weeks before the inauguration of former-ROK President Park Geun-hye; the fifth test (2016) took place in the month before the 2016 US presidential election; the sixth test (2017) took place just less than four months after former-ROK President Moon Jae-in's inauguration.

Nuclear Test Site

No clear signatures of test preparations at the Punggye-ri nuclear test site were identified using commercially available satellite imagery. For the first (2006) and second (2009) nuclear tests, no sufficiently high-resolution satellite imagery has been identified that could be utilized to make such assessments. Several signs of activity starting at approximately three months before the third (2013) nuclear test were identified, including an increase in the number of personnel and vehicles near the test tunnel, concealment of the tunnel entrance, a probable cable line stretching from the tunnel entrance and a probable satellite dish near the tunnel entrance. [ii] In the run up to the fourth (2016), fifth (2016) and sixth (2017) nuclear tests, no clear signs were visible in available satellite images. [iii] 

Launch Vehicle Development

The DPRK's timing of nuclear tests seems to be correlated with its launch vehicle development programme schedule - five of the previous six nuclear tests were undertaken within three months of a long-range rocket or satellite launch. Conversely, the longest span of time separating a launch from a nuclear test was a failed test in April 2012, which was just over ten months before the third nuclear test (2013).

DPRK Statements

In two of the six previous nuclear tests, the first test (2006) and the third test (2013), explicit comments were made by the DPRK leadership in the weeks prior to the tests clearly indicating its intention to perform a nuclear test. No similarly explicit statements were identified as having been made in the leadup to the other nuclear tests.

Environmental Factors

None of the DPRK's previous nuclear tests, or intercontinental ballistic missile (ICBM) or satellite launches, were conducted in June or August. [iv] The inactivity in June is assessed as likely related to state-wide manpower-intensive agricultural projects, which may require the mobilization of the military during the rice transplantation season between mid-May and mid-June. [v] With respect to August, heavy rainfall could potentially damage the nuclear test site and impact test operations.

Political Context

The second nuclear test (2009) took place while then-DPRK leader Kim Jong Il's health was deteriorating and the DPRK was in a transition period.