In recent years, North Korea reportedly has operated two outdoor high explosive (HE) test sites for the development of nuclear weapons.  These two sites are called in Western media or sourcing Yongdok-dong, aka Yongdok or Yongdok-tong, and Kumchang-ni, aka Kumchangni or Kumchang-ri.  They were built after the closure in the early 1990s of North Korea’s first high explosive test site at the Yongbyon nuclear center.  Figure 1 shows their identified locations.  Figure 2 shows a side-by-side comparison of the high explosive test areas. While Yongdok-dong appears to be operating as of late 2025, Kumchang-ni appears to have stopped operation recently.

This type of site is necessary in nuclear weapons programs developing fission implosion weapons.  They allow for the multiple testing of subcomponents of a fission design containing high explosives and of a complete nuclear device with a surrogate non-fissile nuclear core, often natural or depleted uranium, instead of plutonium or weapon-grade uranium.  In early programs, the successful completion of this latter test, called a “cold test,” when appropriately instrumented, served to certify the design and firing mechanisms.  In more advanced programs, like North Korea’s, such sites allow for the initial development of more advanced designs, especially miniaturized or more tailored designs, potentially reducing the number of full-scale underground tests or in certain cases eliminating the need for them.

The reason for North Korea’s operating two sites is not known.  The test sites may be used by competing North Korean weaponization groups, possibly working on different multi-point initiation designs, main charge designs, types of neutron initiators, or fissile materials.  They also may have different allowances for the amount of high explosives allowed per test at each site. 

In terms of miniaturization, North Korea may have looked at ways to reduce the diameter of an implosion device via, for example, increasing compression or developing ovoid shaped fission devices, intended for delivery on thinner missiles.  These types of designs can be developed without needing full-scale nuclear testing.^[1]  Given the lack of any underground testing since 2017, these tests were likely intended to lead to fieldable fission-based nuclear weapons.

Figure 1.  The locations of two of North Korea’s current suspected high explosive test sites.  The original high-explosive test site at Yongbyon was shut down in the early 1990s. 
 

Figure 2.  A comparison of the two probable high explosive test sites at Yongdok-dong and Kumchang-ni. 

Initial High Explosive Site at Yongbyon

North Korea has a long history of operating high explosive test sites for nuclear weapons development.  In the 1980s and early 1990s, North Korea operated an outdoor high explosive test site adjacent to the north side of the Yongbyon nuclear center (Figure 3), conducting reportedly at least 70 high explosive tests before the site was shut down.^[2]  North Korea had shut down the site when it decided to hide its nuclear weapons program from the International Atomic Energy Agency (IAEA) after signing a comprehensive safeguards agreement in 1992 under the Nuclear Non-Proliferation Treaty. Nonetheless, this ruse did not work, as is well known.^[3]  The IAEA asked to go to the high explosive test site.  North Korea allowed a visit in September 1992 but refused to let the IAEA take environmental samples.  North Korea denied the site was nuclear weapons-related but instead claimed that it was only for “explosives metal forming”.^[4]  The IAEA was unsuccessful in proving otherwise, and the site remained a point of contention.

Figure 3. February 2000 commercial Ikonos satellite image showing the closed high explosive test on the north edge of the Yongbyon nuclear center.  Several buildings and a few possible craters are visible in the image, although the site had been inactive since about 1991-1992.  Source: David Albright and Kevin O’Neill (eds), Solving the North Korean Nuclear Puzzle, (Washington, DC: Institute for Science and International Security Press, 2000). 

Yongdok-dong High-Explosive Test Site

The Yongdok-dong (40° 2'59.43"N, 125°18'45.38"E) high-explosive test site has reportedly existed since the 1990s.  It is in the Pyongan Province, about 115 kilometers northwest of Pyongyang and about 50 kilometers northwest of the Yongbyon nuclear center (see Figure 1). There is considerable satellite imagery coverage available of the site, as well as open source reporting.^[5]

Two parts of the site are focused on here.  They are a high-explosive storage area and what appears to be an isolated outdoor high explosive test site nearly one kilometer away. 

High Explosive Storage and Handling Buildings

Figure 4 shows an area that comprises what look to be high explosive storage and handling buildings.  These buildings consist of three small square buildings and one large rectangular building, situated inside four-sided earthen berm containment areas.  In late October 2025, several of these buildings underwent renovations, with the structures being rebuilt (see Figure 4).  These buildings are situated on the hillside and are surrounded by earthen berms to provide extra blast protection. By mid-November, the renovations were complete (see Figure 5). 

Outdoor Test Location

In the Northern section of the complex, at an isolated building located in a remote valley, activity has been seen that indicates possible outdoor high explosives testing (see Figure 6). This small concrete building/structure is situated in a cleared section of the woods.  On its northern side, the vegetation has been removed, exposing the barren earth, and a rectangular flat earthen pad, likely a firing pad, can be seen immediately adjacent to the building.  On the pad, small craters can be periodically seen, most likely from high explosive tests.  Google Earth imagery from June 30, 2023, and Vantor imagery from November 17, 2025, show clearly these possible test craters (see Figures 7 and 8).  This indicates that the building is likely a measurements and instrumentation facility.  The craters typically range from 1.7 to 3 meters wide.

This facility differs significantly from known Chinese high explosive test facilities, such as the high explosive test facility at Haiyan that is a well-known location and currently a popular museum and tourist destination.  Many ground photos are publicly available of its facilities.  At Haiyan, the high explosive test bunker is earthed over and has wavy steel plate-faced walls that face the firing pad (see Figure 9). Comparatively, at Yongdok-dong, this probable high explosive test area consists of only a flat walled probable measurements and instruments building and what appears to be an outdoor firing pad. Further, the measurements and instruments building is not earthed over. 

 

Figure 4.  A view of the likely high explosive storage and handling buildings under renovation at Yongdok-dong. 

Figure 5.  A view of the high explosive storage and handling buildings after the renovations have been completed. 

Figure 6. An overview of the probable outdoor high explosive test site at Yongdok-dong.

Figure 7.  A view of the probable Yongdok-dong outdoor high explosives test site from June 2025. 

Figure 8.  A view of the probable Yongdok-dong outdoor high explosives test site from November 2025. 

Figure 9.  Closeup of “Test Area One” at the Chinese Plant 221, with an inset ground photo showing that it is now part of a national museum.  A model of a nuclear weapon test device with an ovoid shape is located on the firing pad. 

 

Kumchang-ni Probable High Explosive Test Site

To date, little is known publicly about the second high explosive site, including its exact location.  It is not to be confused with the Kumchang-ni underground facility, which is a large, excavated underground complex located in North Pyongan Province of North Korea, north of the city of Kusong, consisting of tunnels and underground chambers.  This suspected nuclear site was inspected by the United States in the late 1990s and found to be empty at that time.

The existence, but not the location, of this high explosive test site at Kumchang-ni was relayed to the Institute by multiple North Asian officials.  The Institute used Google Earth to conduct a wide area search in the area of the Kumchang-ni underground facility.  The search revealed a candidate for a suspected high explosive test site near the underground site.  The suspect site is situated in a hilly area roughly 15 kilometers from the Yongdok-dong high explosive test site, and only one kilometer from the Kumchang-ni underground complex, having these coordinates: 40° 6'30.34"N, 125° 8'55.35"E. 

Once located, a media report was discovered offering an alternative explanation of the site.  A group called Strategic Sentinel assessed and labelled the site as a missile launch site.^[6]  Rather, based on satellite imagery, the available evidence and the design of the facility are more consistent with nuclear weapons development, suggesting that the site is likely the high explosive test site described by knowledgeable officials to the Institute. 

The complex consists of a bunkered facility with two nearby above ground support buildings located in an isolated valley similar to Yongdok-dong (see Figure 10).  Google Earth satellite imagery from as early as 2010 shows the facility being present at that time, and that little has changed since then (see Figure 11), apart from possible disablement in early 2025.  This site has somewhat similar design characteristics to the one seen at Yongdok-dong.  The site consists of a small support complex with a few buildings, roughly 250 meters by the road from an isolated probable instrumentation and measurements bunker. The instrumentation and measurements bunker has earthen sloped berms on three sides facing the assessed firing pad for additional blast protection.  Directly adjacent to the instruments and measurements bunker is what we assess to be an open air test pad in a surrounding vegetation cleared area. Satellite imagery shows that the roof of what appears to be a fire control section of the bunker was removed in early 2025 and has not yet been replaced; therefore, we believe that this site may no longer be operable. 

What are likely blast craters from previous high explosive tests are visible on the outdoor pad (see Figure 12).  The observed probable blast craters are between 5 and 7.8 meters wide, which are considerably larger than those seen at the probable outdoor high explosive test facility at Yongdok-dong, which typically range from 1.7 to 3 meters in diameter. 

Differences in Crater Sizes at Two Sites

There are several possible explanations for this difference in crater size at the two high explosive test sites.  One possible explanation is that the facility at Kumchang-ni allows for larger explosive charges because it is a more blast resistant structure than the one at Yongdok-dong.  For example, Yongdok-dong may only be able to handle a “hemisphere” sized charge with surrogate materials, rather than a “full sphere” with surrogate materials at Kumchang-ni.  Using only a hemisphere would reduce the size of the test charge used.  Another possible explanation is that each facility is testing completely different nuclear weapons designs, inevitably involving different amounts of high explosives and surrogate cores, such as tests representing different fissile materials (e.g. uranium versus plutonium) or advanced weapon designs.  In addition, North Korea may have detonated many near- or full-size surrogate fission devices featuring new types of neutron initiators for use in designs with weapon-grade uranium cores instead of plutonium cores or able to withstand space flight.  In sum, depending on the design of the final assembled weapon system, the amount of high explosives can significantly differ, and this could account for the varying sizes in the test craters seen at either site. 

Figure 10.  An overview of the probable outdoor high explosive test site at Kumchang-ni. 

Figure 11. Kumchang-ni outdoor probable high explosives test facility as seen in a Google Earth image from 2010. 

Figure 12.  Two views of the probable Kumchang-ni outdoor high explosive test site from September and December 2025. 

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