North Korea Increases Nuclear Weapons Grade Plutonium Production

• The Radiochemical Laboratory operated intermittently and there have apparently been at least two unreported reprocessing campaigns to produce an undetermined amount of plutonium that can further increase North Korea’s nuclear weapons stockpile. This suggests batch rather than continuous processing of spent fuel rods from the 5 MWe Reactor during the period of analysis.
• Increased thermal activity was noted at the Uranium Enrichment Facility. It is unclear if this was the result of centrifuge operations or maintenance operations. Centrifuge operations would increase the North’s enriched uranium inventory; however, based on imagery alone, it is not possible to conclude whether the plant is producing low or highly enriched uranium.
• The thermal patterns at the probable Isotope/Tritium Production Facility have remained consistent, suggesting that the facility is not operational, or is operating at a very low level. This means, the facility is likely not producing tritium, which is an essential isotope used in the production of boosted yield nuclear weapons and hydrogen bombs.
• From December 2016 through January 2017, the thermal pattern over the Experimental Light Water Reactor (ELWR) was elevated. While that might indicate that the reactor was operational, the likelihood is low since the pattern does not appear in subsequent imagery over the last six months. It is possible that there are alternative explanations for the elevated pattern, for example, short-term activity at the ELWR such as the heating of pipes to prevent freezing. Regardless, any activity at the ELWR is cause for concern and bears continued monitoring.
• The 5 MWe Reactor has either been intermittently operating at a low-level or not operating. The notable exception to this was during December 2016 and January 2017 when thermal patterns suggests a higher level of operations.

Analysis

Radiochemical Laboratory: Examination of the thermal patterns associated with the Radiochemical Laboratory (reprocessing facility) show significant deviations from month to month. Concentrated heat patterns were observed with stronger temperature differences from the surrounding area between September to October of last year. The thermal patterns then returned to lower levels until March 2017, when a distinct increase in thermal activity is observed that has continued through last month. These intermittent surges in thermal activity suggest North Korea has conducted batch rather than continuous processing of spent fuel rods from the 5 MWe Reactor. It is typical to allow the spent fuel rods to rest for a while in cooling ponds to both cool and allow less stable plutonium isotopes (PU-238, etc.) to bleed off. These reprocessing campaigns do not necessarily occur immediately after spent fuel rods are removed from the 5 MWe reactor. The June 2017 thermal activity coincides with an increase in activity noted in a March 2017 analysis based upon natural color imagery.

1. [1]
   Landsat 7 imagery was used exclusively due to an ongoing issue causing reduced accuracy of Landsat 8 thermal sensors.
2. [2]
   It is important to understand several limitations when using Landsat 7 thermal imagery for this type of analysis. Among these is that the data is collected at 60 meters ground sampling distance (GSD). That is, each pixel represents 60 meters. It is then resampled down to 30 meters GSD. Additionally, the Landsat 7 thermal sensor is measuring both the thermal response of the ground plus the air column above it. It is not unusual for a prevailing wind, which over Yongbyon at this time of year, generally originates out of the northwest or north, to carry the heated air column from one point to another (e.g., the 120-150 meters from the 5 MWe Reactor over the ELWR). In the current and previous 38 North thermal studies, we are pushing Landsat data to its limits.
3. [3]
   Typically, a reactor would be loaded and started up at low power to heat and pressurize the coolant and adjustments would be undertaken to balance the pressure and flow through the system. Once operators are assured that the settings are correct the system can then be operated at full power. Once reactor operations commence, there is a requirement to continuously cool it to remove heat, even if it is only from radioactive decay. If a reactor has started up and subsequently shut down after a short period of low-level operation, the residual heat removal system would not need to remove significant heat because the core would be new. That heat is carried away by cooling water and never gets into the air.