In his November 2025 statement to the Board of Governors, the International Atomic Energy Agency’s (IAEA) Director General’s statement included new information about nuclear activities at the Yongbyon nuclear center.  While the IAEA did not issue a formal report, his statement is worth incorporating into recent satellite imagery analysis.

Experimental Light Water Reactor (ELWR)

According to Grossi’s statement, the Experimental Light Water Reactor, with a nominal power of 100 Megawatt-thermal, “continued in stable operation until early-August 2025 but has likely been shut down since then.”  This is consistent with the lack of water discharge from the secondary cooling system observed in available satellite imagery. The last day where water outflow is visible is August 8.  Water outflow is visible again in imagery dated to November 13 but stops again for several days.  Starting on November 24, water outflow is consistently visible again.  Figure 1 shows water discharge from the reactor’s secondary cooling system on December 5.  Importantly, this image also shows snowmelt around the discharge point and light snowmelt on the roof of the reactor’s turbine building, indicating the reactor is producing heat, consistent with operation.   

When the ELWR was shut down in August, the reactor was about two months short of two years of operation.^[1]  During this time of operation, there were other periods where the reactor was shut down for brief periods, leading the IAEA to assess that the reactor was operating “for approximately 70%” of the time between August 2024 and August 2025.^[2]   The power of the reactor during this period is unavailable and is unlikely to have reached full power.  Nonetheless, the ELWR has likely been generating plutonium in its fuel.  The amount cannot be determined, without knowing more about its power during this year, but the reactor may have produced several kilograms of plutonium in its fuel.  As North Korea learns to operate this reactor and avoids accidents, this reactor could produce as much as approximately 20 kilograms of weapon-grade plutonium per year. 

The length of this most recent reactor shut down raises the issue that North Korea has or will at some point discharge irradiated fuel and refuel the core of the reactor.   If so, the discharged, irradiated fuel is expected to sit in a spent fuel pond for several months.  Whether North Korea has put in place the capabilities to separate plutonium from the irradiated fuel, which is likely a low enriched uranium oxide fuel, is unknown.  There are alternative ways for North Korea to use the reactor for its military nuclear program, including the production of weapon-grade plutonium in targets, where both removal and replacement of targets is independent of core refueling and do not require an extended shut down of the reactor.  Further, the targets can be designed to facilitate the chemical process of separating the plutonium.^[3]

5 MWe Reactor

According to the IAEA, the 5 MWe reactor was likely shut down in August 2024 for refueling, began a new cycle of operation in mid-October 2024, and as of November 2025 “continues to operate in its seventh cycle.” Satellite imagery with snow cover from December 5 shows hot water being discharged from the 5MWe reactor's secondary cooling system and steam rising from the nearby turbine building, indicating the reactor is operating.  See Figure 1. 

Figure 1.  A recent winter scene of the two nuclear reactors at Yongbyon, the 5MWe reactor and the ELWR, shows signs of operation for both reactors.  

Plutonium Separation Plant aka Radiochemical Laboratory

The IAEA assesses that North Korea conducted a reprocessing campaign from fuel irradiated in the 5MWe reactor at the plutonium separation plant, aka Radiochemical Laboratory, this year, starting in late January,^[4] with signs of ongoing reprocessing activities until September 2025.    The IAEA cites a key sign that a reprocessing campaign has begun, namely signs of steam generation, but also “occasional deliveries of chemicals to the Radiochemical Laboratory.”  Visible signs of steam generation, such as smoke emanating from the stack of the coal-burning steam production plant, reportedly seized sometime after June 2025.^[5]  Steam generation is associated with both early stages of the reprocessing campaign –used in steam stripping of volatile undesired fission products – as well as post-separation activities, producing heat for nuclear waste minimization and solidification. 

The amount of plutonium separated in this campaign is uncertain, but values of four to six kilograms of weapon-grade plutonium are reasonable estimates for this aged reactor.

Interestingly, recent imagery continues to show activity at the spent fuel reception building.  As of November 24, a truck or container appears outside the spent fuel receipt building (see Figure 2).  Imagery dated to December 8 also shows the door to the spent fuel reception building’s door open with a truck entering or exiting. 

Figure 2.  The Radiochemical Laboratory at Yongbyon where North Korea separates plutonium from fuel irradiated in the 5MWe and which showed signs of a reprocessing campaign earlier this year.  

Kangsong-Like Building at Yongbyon: Suspected Enrichment Plant

North Korea began constructing a building similar in dimension to the suspected Kangsong enrichment plant at the end of 2024. The IAEA first raised concern about this building in June 2025, and the Institute subsequently identified the location just north of the Radiochemical Laboratory at the Yongbyon nuclear complex. The new building’s overall dimensions are 117 meters by 45 meters wide, which is similar to the main building at Kangsong, which measures 115 meters by 48 meters.  The layout as far as can be discerned from available imagery before the roof went on features a high bay center hall with two parallel side sections for operational support running alongside the hall.  Images taken with a larger incident angle show two rows of windows, consistent with the outer walls of the Kangsong facility.^[6] 

While the main building appeared externally complete as of early June, support buildings and physical security measures around the main building were still being constructed.  As of mid-November, construction around the main building also appears externally complete and North Korea has likely begun constructing the interior of the building.  As of November 18, a truck can be seen docked outside the main building.  Figure 3 shows the additions that were made over the last five months, including cooling units, increased physical security of the plant, and likely incoming power supply infrastructure. [7]  

The physical security measures include wall panels that serve as a visible shield, with wired fencing on top of the wall panels to extend height, as well as a security gate with a security checkpoint.  North Korea also added a covered bridge to connect a support building within the security perimeter to the main building.  The incoming power supply appears connected to an electrical substation near the abandoned 50 MWe reactor.  A second source of power would be expected, perhaps coming from the road leading north from the plutonium separation plant, but has not yet been identified. 

The six cooling units can be compared to cooling units previously visible at the existing Yongbyon enrichment plant within the Fuel Fabrication Complex.  Here, satellite imagery showed first three, then six units, after the doubling of the floor space in 2013 (see Figure 4).  North Korea subsequently moved all six cooling units into a single row.  The original three units were upgraded but otherwise the six units remained in this arrangement until one single cooling unit was removed in 2020, followed by the removal of all remaining five cooling units in 2021.[8]  Since then, it is unclear how North Korea is maintaining a constant temperature at the enrichment plant.  Cooling units present at the Kangsong enrichment plant resembling those at the Yongbyon enrichment plant were also a key consideration in governments’ assessment of the facility.  Further, the IAEA reports the delivery of additional cooling units to the suspected Kangsong enrichment plant in August 2025, in line with a suspected expansion of enrichment activities at Kangsong.  However, the cooling units at Kangsong are also not readily visible in satellite imagery. 

Overall, the secure power supply, high physical security, and addition of cooling units are increasing the likelihood that this new construction is indeed an enrichment plant.  It is not clear why the level of visible security measures are higher than those for the existing enrichment plant at Yongbyon, but it could be an indication that this facility is primarily built to produce weapon-grade uranium.  The existing enrichment plant at Yongbyon may also be used to produce WGU, but perhaps only in certain parts of the plant, with other parts of the plant likely producing low enriched uranium for the ELWR.   Figure 5 shows a recent image of the existing enrichment plant. 

The output of the suspected new facility is not yet estimated, since the capacity of the planned centrifuges is unknown. North Korea has stated it has improved its centrifuges and installation of such centrifuges in this plant would make sense.  An earlier Institute study discusses these new centrifuges and provides more details about the Yongbyon and Kangsong centrifuge plants.^[9]

Figure 3.  The suspect enrichment plant under construction at Yongbyon. 

Figure 4.  The cooling units at the existing enrichment plant at the fuel fabrication complex as visible in 2014. 

Figure 5.  The enrichment plant at the Fuel Fabrication Complex underwent expansion in 2022.