Yongbyon Nuclear Scientific Research Center: Construction Nearing Completion at Radiochemical Laboratory

Recent commercial satellite imagery of the Yongbyon Nuclear Scientific Research Center indicates roof repairs at the Radiochemical Laboratory’s (RCL) Thermal (Steam) Plant appears complete, covering recently-installed new or refurbished steam boilers. While occasional smoke emissions have been observed coming from the plant—a usual indicator of reprocessing activity—the inconsistent frequency suggests a reprocessing campaign is not underway. Excavation of a grid-like series of holes is underway at a nearby facility, the purpose of which is unclear.  

Full water discharge from the 5 MWe Reactor indicates it is operating again after a three-month-long hiatus, and start-up testing appears to be ongoing at the Experimental Light Water Reactor (ELWR).  

These activities appear consistent with Kim Jong Un’s orders to expand the country’s nuclear weapons arsenal, laying the groundwork for continued stockpiling of fissile material.   

Radiochemical Laboratory

In the past, an indicator for reprocessing at the RCL has been smoke emanating from the thermal plant located to the south. Major renovations began on the thermal plant in March 2024 and appeared to be completed by July. While emissions were seen coming from the thermal plant on imagery from December 3, the plant has not gone into extended operation, so there is no indication that another reprocessing cycle has begun.

Imagery from December 9 showed approximately 40 holes had been dug in the courtyard of a small compound located 0.5 km northeast of the RCL, previously associated with military construction brigades. A similar series of around 20 holes had also been dug in a small field just outside of the compound to its east. These series of holes were laid out in grid-like pattern and measured approximately one meter in diameter.

As of imagery from December 24, the total number of holes had more than doubled. On the west side of the compound, holes have been squared-up and covered, measuring approximately 1.5 by 1.5 meters. Large numbers of workers are observed at the site.

These holes do not appear to be associated with construction activity, leaving questions as to their purpose. Given the location of this facility and its proximity to other radioactive waste burial sites—the Old Waste Site and Building 500—it remains to be seen whether this construction is also related to radioactive waste management. 

The digging does not yet appear complete given the number of personnel still present at each site. Of note, on imagery from December 9, a cargo truck was seen on the road adjacent to Building 500. On December 24, a cargo truck was seen on the access road to the RCL’s spent fuel receipt building.

Reactor Area 

5MWe Reactor 

The 5 MWe Reactor is critical for the country’s production of weapons-grade plutonium. In the past, key signatures of activity in the reactor area have included the presence of vehicles near the building and the existence (or lack of) of cooling water flow from the discharge point. 

In a previous report from May 2024, water discharge had stopped, likely indicating a refueling operation. Currently, there is a full water discharge, indicating it is operating again. Imagery from December 24 revealed significant ice melt from the 5 MWe outflow.

In late September 2024, imagery revealed land near the spent fuel storage building had been excavated, three square possible vault covers were opened in the courtyard. By mid-November, the three openings were covered over. On imagery since December 9, the area appeared to be walled-in, with a small building within the enclosure. The purpose of these activities is unclear.

ELWR 

Intermittent water discharge at the ELWR continues, indicative of ongoing testing and certification. As the first light water reactor in North Korea, a thorough testing cycle is to be expected.  

Reactors take time to bring into operation and undergo a period of continuous testing. A probable testing phase began in October 2023. Six months later, water discharge stopped for the month of April 2024. Water discharge was restored through August, when it again was shut off. Outflow resumed once again in mid-November. On imagery from December 24, small and large ELWR outflows were running. Warm water outflow was observed just north of the ELWR pump house.

Uranium Enrichment Plant (UEP) and Conversion Facilities 

The UEP and uranium conversion facilities have also been undergoing renovations for the past three years. Imagery from December 9 reveals work on the conversion buildings—seemingly the last in the area to be refurbished—appears to be complete, and the surrounding grounds have been tidied of construction materials and other objects. It is unclear what has changed inside these facilities, but there have not yet been signatures indicating operations have resumed.

Levee Construction  

Located on either side of a large bend in the Kuryong River, the Yongbyon complex is prone to flooding due to elevation variations in the river. Work has been done over time to manage the flow of the river during both the wet and dry seasons, largely by the construction of causeways and dam reconstruction. The river at this location is relatively shallow and meanders through the landscape. 

In the past, these efforts have largely failed to protect the growing fields in the face of heavy annual rains. However, imagery from December 9 reveals work to reinforce flood protection measures. In two locations along the river, work is being conducted to harden the levees along the west bank of the river—at and above the reactor area and main research and administration area—and on the east side of the riverbank at the bridge and causeway crossing near the RCL and UEP facilities. This differs from previous water management efforts as the height of the levee is being raised and the riverside facing is being hardened. It is unclear how extensive these embankments will be.