Given the lack of access to North Korea’s nuclear facilities at Yongbyon, outside observers rely on a variety of tools to monitor what is happening throughout the complex. High resolution commercial satellite imagery is useful for detecting movement as well as external signs and developments. Thermal imagery indicates variances in the heat signatures of buildings versus their surroundings, helping to identify when specific facilities are operational. When combined, the information gleaned from these tools should be reinforcing and can help prevent the type of deception that can occur when relying on satellite imagery alone.
Thermal imagery of the Yongbyon Nuclear Scientific Research Center from January 2015 to August 2016 supports the numerous reports of activities observed in commercial satellite imagery over the same period. In spring 2016, thermal imagery showed concentrated heat patterns at the Radiochemical Laboratory, a significant deviation from the same period in 2015, as well as strong temperature differences from the surrounding area. These patterns reinforce reports based on satellite imagery that North Korea conducted a spent fuel reprocessing campaign earlier this year.
Thermal patterns at the 5 MWe Reactor over this same period showed no significant deviations. Satellite imagery analysis indicated that the reactor has either not been running or has been operating at very low power levels. Additionally, there were no thermal patterns at the Experimental Light Water Reactor (ELWR), supporting the conclusion that the reactor is not yet operational.
Thermal imagery from early 2015 indicated no unusual heat signature around the Radiochemical Laboratory where North Korea reprocesses spent nuclear fuel. By late spring and early summer 2015, diurnal heating of dark-colored roofs began to show increased thermal patterns. However, these “warm season” images were likely indicative of daytime solar heating patterns where buildings generally are warmer than the surrounding terrain. Later in 2015, as the daily temperatures began to drop, the thermal patterns also dropped, inconsistent with sustained operations. This continued into winter.
Beginning in February 2016, however, a more significant thermal pattern began to develop in and around the Radiochemical Laboratory. Comparisons between March 2015 and 2016 indicate that heat concentration increased significantly, as illustrated in Figures 2 and 3. The temperature of the Radiochemical Laboratory is, on average, 30 percent warmer than its surrounding area in 2015. However, in 2016, the heat signature is much more pronounced, indicative of increased activity and very likely associated with a reprocessing campaign at this facility. These thermal patterns support analyses by 38 North from April 15 and May 31 and the Institute for Science and International Security, from April 15, April 29, and May 27, derived from high resolution satellite imagery that a reprocessing campaign was underway.
Throughout spring 2016, increased activity was observed in satellite imagery at the Radiochemical Laboratory and thermal signatures remained high as of May (Figures 4-6). By August, those signatures (Figures 7 and 8) were still high, although satellite imagery analysis had shown that the reprocessing campaign had already probably finished. Some explanations for continued high thermal patterns could include: 1) in fact the reprocessing campaign had not yet been completed; 2) the reprocessing campaign was essentially done but ancillary operations were still underway; and 3) the building likely needed time to cool down after a reprocessing campaign, especially during a hot weather month.
5 MWe Reactor and ELWR
Thermal imagery showed no unusual signatures around the 5 MWe Reactor in early 2015. Some daytime heating occurred during the warm season but fell again in the fall. These thermal patterns support satellite imagery analyses that throughout 2015, the 5 MWe Reactor was either operating intermittently at low power levels or not operating at all. The reports were published on January 28, July 24, and September 15, 2015.
Thermal imagery from January to August 2016 showed no significant changes for the 5 MWe Reactor, suggesting that it had either not been restarted since refueling, or was operating at a limited capacity.
During this same time period, there were no thermal signatures at the Experimental Light Water Reactor, confirming other reports that the reactor was not yet operational.
Figure 1. Overview of Yongbyon Nuclear Scientific Research Center Area from July 14, 2016.
Figure 2. A thermal signature comparison of Yongbyon between March 2015 and March 2016.
Figure 3. Semi-transparent thermal imagery overlay (Landsat 7, US Geological Survey) on natural-color high resolution imagery (Pleiades, Airbus Defense & Space) in March 2015 and March 2016.
Figure 4. Thermal signatures of Yongbyon from May 18, 2016 (Landsat 7, US Geological Survey).
Figure 5. Semi-transparent overlay of May 18, 2016 thermal imagery (Landsat 7, US Geological Survey) on top of May 22, 2016 natural-color high resolution imagery (GeoEye-1, DigitalGlobe).
Figure 6. Close-up view of Radiochemical Laboratory with semi-transparent overlay of May 18, 2016 thermal imagery (Landsat 7, US Geological Survey) on top of May 22, 2016 natural-color high resolution imagery (GeoEye-1, DigitalGlobe).
Figure 7. Sustained thermal signatures over the primary Radiochemical Laboratory buildings from August 23, 2016 (Landsat 7, US Geological Survey).
Figure 8. Semi-transparent overlay of August 23, 2016 thermal imagery (Landsat 7, US Geological Survey) on top of August 22, 2016 natural-color high resolution imagery (Pleiades, Airbus Defense & Space).
 Moderate resolution (~100 m) thermal imagery is available from three US satellites (i.e., LANDSAT 7, LANDSAT 8 and Aster) and collected roughly every two weeks. Barring cloudy images, this provides a relatively frequent collection interval to observe thermal patterns associated with buildings and systems that have longer thermal cycles, such as a nuclear reactor or power generators as well as buildings with sustained operations.
38 North, “North Korea’s Yongbyon Nuclear Facility: Sporadic Operations at the 5 MWe Reactor But Construction Elsewhere Moves Forward,” 38 North, July 24, 2015, https://www.38north.org/2015/07/yongbyon072415.
38 North, “North Korea’s Yongbyon Nuclear Facility: Restart of the 5 MWe Reactor?” 38 North, January 28, 2015, https://www.38north.org/2015/01/yongbyon012815.
38 North, “More Evidence of Possible Reprocessing Campaign at Yongbyon; Progress at Experimental Light Water Reactor,” 38 North, April 15, 2016, https://www.38north.org/2016/04/yongbyon041516.
38 North, “New Evidence of Probable Plutonium Production at the Yongbyon Nuclear Facility,” 38 North, May 31, 2016, https://www.38north.org/2016/05/yongbyon053116.
Albright, David, and Serena Kelleher-Vergantini, “April 2016: Monitoring Activities at Yongbyon Nuclear Site,” Institute For Science and International Security, April 29, 2016, http://isis-online.org/isis-reports/detail/april-2016-monitoring-activities-at-yongbyon-nuclear-site.
Albright, David, and Serena Kelleher-Vergantini. “Update on North Korea’s Yongbyon Nuclear Site.” Institute For Science and International Security, September 15, 2015, http://isis-online.org/uploads/isis-reports/documents/Update_on_North_Koreas_Yongbyon_Nuclear_Site_September15_2015_Final.pdf.
Albright, David, and Serena Kelleher-Vergantini. “May 2016: Monitoring Activities at the Yongbyon Nuclear Site,” Institute For Science and International Security, May 27, 2016.
Albright, David, Olli Heinonen, and Serena Kelleher-Vergantini. “Correlating the Operation of the Coal Plant to Reprocessing Activities at Yongbyon.” Institute For Science and International Security, April 15, 2016, http://isis-online.org/isis-reports/detail/may-2016-monitoring-activities-at-the-yongbyon-nuclear-site/10.