This report fulfills a commitment made on June 9 in a post on X that identified the new site at Yongbyon, mentioned in a June 9 statement to the International Atomic Energy Agency (IAEA) Board by Director-General Rafael Grossi.[1] According to Grossi, the IAEA is "monitoring the construction of a new building at Yongbyon which has dimensions and features similar to the Kangson [aka Kangsong] enrichment plant." [2] But Grossi did not state its purpose, or that it is an enrichment plant.
The Institute identified in the post a new building rapidly constructed in a small complex between the Radiochemical Laboratory and the abandoned 50 MWe reactor at Yongbyon, located at 39°47'6.14"N, 125°45'31.61"E. Figure 1 shows the new building as of June 5, 2025. Figure 2 shows its location at Yongbyon.
North Korea has portrayed more confidence in its ability to construct nuclear facilities, as evidenced from its publicized display of its cascade halls at Yongbyon and likely Kangsong in September 2024 and January 2025. [3] The rapid construction of this building reflects that growing confidence given its possible nuclear related function and close proximity to other key North Korean nuclear facilities.
The layout of the building, as far as can be seen during the short construction period, would be suitable for an enrichment hall. However, more information will be needed to make a determination on the function this building will perform.
Analysis of the New Building
The new building was built on the levelled ground of a pre-existing cluster of buildings, connected by road to the Radiochemical Laboratory in the South and the 50 MWe reactor in the North. One of three main buildings and a few sheds that were previously at the location were razed to make room for the new construction; the other two pre-existing main buildings remain at the site. While the site is near a declared nuclear waste site, the previously existing cluster does not appear to have performed a nuclear-related function, instead, it may have been a farm or similar support site (see Figure 3).
Preparations for the construction of the building first appeared in December 2024. The leveling of a pre-existing building to make room for the full extent of the main hall's foundation occurred by February 10, 2025. By March 5, a new security perimeter wall had been erected around the site and construction for the main hall's foundation had progressed (see Figure 4). Based on a March 30 image, where construction is further along and initial wall structures as well as a roof truss are visible, it appears that a long, high-bay hall, measuring about 110 by 20 meters, is built on top of the main building's foundation, and two parallel side sections for operational support run alongside the hall and add to the overall width of the building. Of note, the long hall features a reinforced structure crossing it in the middle (see Figure 5).
By April 30, walls for the new building were erected and a blue, slightly slanted roof was being added in panels. On that date, the roof was only partially completed, and the gaps in the roofing appeared to show that at least the northern operational support section has mixed heights and at least a partial second floor (see Figure 6).
The most recent image, taken on June 5, shows the building externally complete. The entire building, as measured by the roof, has dimensions of roughly 117 meters by 45 meters. The outer walls on at least two sides, the long north side and the short east side, show two levels of windows, but given the rapid speed of construction, and what is visible throughout the construction process, it appears to be a single central longitudinal high-bay hall with the two parallel side sections for operational support, where all side sections may have two or multiple floors for different equipment.
Figure 1. A new building at Yongbyon with similar dimensions to the main building of the suspected Kangsong enrichment plant.
Figure 2. The new building's location is at a pre-existing cluster of small buildings between the reprocessing plant and the abandoned 50 MWe reactor at Yongbyon.
Figure 3. Construction related to the new building is first visible in satellite imagery dated to December 2024.
Figure 4. At the beginning of March, the foundation for the main hall of the new building, as well as a new separate enclosing perimeter security wall, are clearly visible.
Figure 5. Within a month, support beams and a roof truss for a center, high-bay hall were erected, as well as partial walls for operational support sections running north and south alongside it.
Figure 6. Another month later, the walls are erected and the roofing for the high-bay hall is complete. The roofing for the support sections is partially complete.
Comparison to Kangsong
The new building at Yongbyon shares similar structural and design characteristics to Kangsong (see Figure 7). The overall new building's dimensions are 117 meters by 45 meters wide, which is similar to the main building at Kangsong, which measures 115 meters by 48 meters.
A comparison of satellite imagery of the new building taken during its rapid construction and what is known about the structure of Kangsong reveals similarities in overall design, but key differences in size of the internal halls. Each building is assessed to consist of a main internal long high-bay hall surrounded by support sections. The internal high-bay hall of the new building at Yongbyon is roughly 20 meters wide, while the main hall at Kangsong is assessed to be 40 meters wide. As such, the width of the new hall is closer in size, but slightly wider than the known enrichment halls at Yongbyon, each of which is estimated to be 15 meters wide.
Further, both Kangsong and the new building have two rows of external windows, suggesting the possibility of two floors in some sections. Kangsong is also assessed to have at least a partial second floor for a control room area. Both buildings have roofs that are slightly slanted, but unlike Kangsong, the new building's roof does not have skylights and the building does not extend past the slanted roof on the short ends of the building, as is the case for Kangsong (see the rectangular flat roofs on either end of the building after the slanted roof ends in Figure 7).
As noted above, the March 30 image shows that a reinforced structure crossing the middle of the hall was installed. This structure could hold a support bridge used for observation of an enrichment cascade hall and the installation equipment similar to the ones observed in images released by North Korea and assessed to be taken at Yongbyon and Kangsong.
Ultimately, more information will be needed to determine the purpose of this new building. Given its similar design characteristics to Kangsong, an enrichment hall is plausible, but the location of the new building, near the abandoned 50 MWe reactor and the reprocessing plant, could also suggest a different type of processing facility. The Institute will continue to monitor the site for any new developments and information that can be used to determine a function.
Figure 7. A side-by-side comparison of the new building constructed near Yongbyon and the Kangsong facility. The buildings are externally similar in size and shape (ignoring the blue-roofed annex at Kangsong, which was only added recently).
1. Post by the Institute on X on June 9, 2025, https://x.com/TheGoodISIS/status/1932078893550236050. [↩]
2. IAEA Director General's Introductory Statement to the Board of Governors, June 9, 2025, https://www.iaea.org/newscenter/statements/iaea-director-generals-introductory-statement-to-the-board-of-governors-9-june-2025. [↩]
3. David Albright and Spencer Faragasso with Sarah Burkhard, "North Korea's Uranium Enrichment Facilities: What We Learned from KCNA's Images," Institute for Science and International Security, April 24, 2025, https://isis-online.org/isis-reports/detail/north-koreas-uranium-enrichment-facilities-what-we-learned-from-kcnas-image/. [↩]
