Yongbyon Nuclear Scientific Research Center: Snowfall Shows Activity

Commercial satellite imagery of North Korea’s Yongbyon Nuclear Scientific Research Center indicates activity is ongoing throughout the site. Recent snowfall provided a short period to observe activity, based on snow melt.

Intermittent smoke at the thermal plant of the Radiochemical Laboratory (RCL), discharge from the 5 MWe Reactor and Experimental Light Water Reactor (ELWR), and snow melt at the Uranium Enrichment Plant (UEP) and throughout the uranium conversion complex suggest efforts to fulfill Kim Jong Un’s orders to expand fissile material production for the country’s nuclear weapons program are proceeding.

Radiochemical Laboratory

Work has continued to repurpose a small compound located approximately 0.5 km northeast of the RCL and just southwest of the never-completed 50 MWe Reactor that has been associated with military construction brigades; its potential new purpose is yet unclear.

Imagery from early December 2024 revealed more than 40 holes had been dug in the courtyard of the compound, laid out in a grid-like pattern. An additional 100 or so holes were dug in a small field just east of the compound. These holes were squared-off, measuring approximately 1.5 m x 1.5 m.

On imagery from January 31, the roof of the long building separating the two sets of holes had been removed. By February 9, the building was completely razed, along with two others at the compound. By February 22, a rectangular excavation alongside one of the series of holes had appeared. Machinery can be seen operating in between the two sets of holes.

The squared holes may serve as footings for pillars to support two new buildings or one larger building with solid foundations, as observed in similar construction processes.

A new series of smaller holes, measuring approximately 0.5 m in diameter, had been dug around the compound’s perimeter by February 9. By February 22, a solid wall had been built around the complex, resembling that encompassing the RCL and suggesting greater security for the facility.

Possible propaganda placards have been placed along sections of the wall.

The road connecting this facility to Building 500—a suspected radioactive waste storage facility—was laden with tracks in the snow on January 31, indicating some level of activity. Workers were also observed on the access road on that date.

In the same image, two cargo trucks are seen parked along the access road to the RCL’s spent fuel receipt building. One of these trucks has a red cab, such as the type of truck often observed at the 5 MWe Reactor. By February 9, the vehicles had departed, and by February 22, another two appeared.

Thermal (Steam) Plant

On imagery from January 30 and January 31, smoke was observed emanating from the thermal plant located to the south of the RCL. The roof had a patch free of snow, and coal dust residue was observed between the coal crushing building and the thermal plant, indicating traffic and activity in both buildings. By February 9, satellite imagery revealed that the emissions stopped. Smoke was observed again on February 22, along with steam emissions at the RCL.

Past indications of spent fuel reprocessing and plutonium extraction at the RCL have been continuous smoke from the thermal plant and emissions from the RCL for several weeks at a time. Since major renovations to the thermal plant were completed around July 2024, smoke has only been observed intermittently. While a pattern of intermittent smoke emissions does not indicate that a reprocessing cycle has begun, it may mean a lower-level activity is taking place, such as radioactive waste processing or preparation for a reprocessing campaign, which is preceded by the transfer of chemicals to the process area.

Reactor Area

5 MWe Reactor

Imagery from January 31 reveals that the rooftops of the 5 MWe Reactor’s main reactor building and turbine generator are free of snow and steam vapor can be seen emanating from the turbine generator building. The adjacent spent fuel storage building also shows signs of snow melt due to heat from the spent fuel likely discharged during the mid-October 2024 shutdown of the reactor.

Water discharge is observed from the 5 Mwe Reactor discharge point on imagery from January 31 through February 22. All observed signatures indicate that the reactor is operating again after the shutdown.

ELWR

The roofs of the ELWR reactor building and turbine generator building are clear of snow. Heavy warm water discharge is seen emanating from the ELWR discharge point on imagery from both January 31 and February 9. These signatures have been observed with few interruptions since November 2023, and likely indicate preoperational testing and certification, including running and testing the reactor, steam generators, and turbine-generators. Whether or not fuel has already been loaded for testing cannot be concluded from imagery alone.

Snow melt is also observed on the roof of the high bay structure adjacent to the ELWR and the pump house associated with the ELWR.

Winter ice in the Kuryong River seems to be stressing the overflow dam just south of the ELWR pump house. Imagery from late January and early February indicate sections of the dam have been breached, allowing the flow of too much water. As a stopgap measure, an earthen dam has been constructed.

Uranium Enrichment Plant

Previous reporting observed that renovation work at the UEP and uranium conversion facilities appeared complete, given the removal of support materials and equipment located around the complex. However, the purpose of changes made inside these facilities during that construction period is unknown.

Imagery from January 31 shows snow melt at multiple buildings within the complex. Notably, there is only snow melt on Hall 1 of the centrifuge building, suggesting that Hall 2 is either not operating or has better isolation.

Two buildings south of the uranium conversion area constructed in 2023, were secured with fencing in the spring of 2024. The purpose of these buildings is unclear, but their isolation within the Yongbyon complex is unusual. The western building is free of snow, indicating some kind of operations are taking place inside.

Snow melt can also be seen on the roofs of the suspected Isotope Production Plant, indicating some operations are taking place inside as well.