Yongdok-tong Nuclear High Explosive Test Facility: Part 1

Key Findings

• The Yongdok-tong Nuclear High Explosive Test Facility is the only known operating facility in the country for testing designs and components for high-explosive detonation of nuclear weapons. This is the most comprehensive report of this secret facility currently available at the unclassified level.
• Located 46 km northwest of the main nuclear complex at Yongbyon and 115 km from Pyongyang, Yongdok-tong development began after North Korea signed the Non-Proliferation Treaty in 1985 as the successor to the Yongbyon Nuclear Research Center, serving as the primary location for high-explosive testing of implosion-type plutonium-core nuclear weapons designs and potentially for gun-type, highly enriched uranium nuclear weapons designs.
• Based on South Korean Defense Ministry estimates in 2015 that North Korea had conducted "more than 100" high-explosive detonator device tests, this number could potentially be as high as 150 today.
• The publication of this report may result in a North Korean response that could complicate the future identification of specific elements and activities at the Yongdok-tong facility. Such responses could include suspension or termination of open-air, high-explosive nuclear detonator testing, or the emergence of such testing at other locations within the nation to conceal or deceive observers about North Korea's nuclear weapons development status and infrastructure.
• As a critical component of North Korea's nuclear weapons development program, the Yongdok-tong Nuclear High Explosive Test Facility should be subject to declaration, verification, and dismantlement in any future denuclearization agreement with North Korea.

This report is the first of a three-part series on the Yongdok-tong Nuclear High Explosive Test Facility, a critical component in the research, development, test, and evaluation (RDT&E) of North Korea's nuclear warheads. It also serves as the most comprehensive report of the facility currently available at the unclassified level.¹ Part 1 provides an overview of the facility and its development history from the 1980s to the 2000s. Part 2 discusses the development history from the 2010s to the present, and Part 3 covers the underground facilities at Yongdok-tong and reports of other nuclear high-explosive testing and weapons storage locations elsewhere in North Korea.

Research Note

The organization and description of the Yongdok-tong Nuclear High Explosive Test Facility and its development over the last 30 years detailed in this report were made possible through the analysis of 56 medium- and high-resolution commercial and declassified satellite images, interview data, and extensive open-source and declassified document research.² This research has also provided a basic understanding of its development as the successor to the Yongbyon Nuclear Research Center, serving as the primary location for high-explosive testing of implosion-type, plutonium-core nuclear weapons designs and, according to defectors, potentially for gun-type, highly enriched uranium nuclear weapons designs.³

This analysis, while extensive, is not exhaustive. An even more comprehensive examination of the Yongdok-tong facility and the broader North Korean nuclear infrastructure will yield greater insight and potentially reveal new components of the nation's nuclear infrastructure.

As with other reports produced by the CSIS Korea Chair concerning North Korea's nuclear infrastructure, the publication of this report may result in a North Korean response that could complicate the future identification of specific elements and activities at the Yongdok-tong facility. Such responses could take the form of significant reduction in the facility's pattern-of-life activities, the suspension or termination of open-air, high-explosive nuclear detonator testing, or the emergence of such testing at other locations within the nation to conceal or deceive observers about North Korea's nuclear weapons development status and infrastructure.⁴

Although 56 high- and medium-resolution satellite images were analyzed during the preparation of this report, the images ultimately presented in this report were purposely selected for their sensor resolutions, off-nadir angle, unique view, or absence of foliage. This provides a more unobstructed and detailed view of the structures and activities within and around the Yongdok-tong facility.

Finally, it is crucial to acknowledge that the accuracy of any unclassified discussion regarding North Korea's nuclear, biological, chemical, or ballistic missile programs remains a persistent challenge. Some aspects of the information and research utilized in preparing this report will likely ultimately prove to be incomplete or inaccurate. Nevertheless, the report aims to present a novel and distinctive perspective on the subject and to foster future discussion.

Overview

The Yongdok-tong facility (40.039607, 125.306653), located in North Pyongan Province, is approximately 46 kilometers northwest of the Yongbyon Nuclear Research Center. Established in the mid- to late 1980s to test high-explosive detonator devices for nuclear weapons, the Yongdok-tong facility was an important part of North Korea's accelerated indigenous development of its nuclear infrastructure during the 1980s and 1990s. Given the timing of the facility's establishment and statements from the U.S. and South Korea, the Yongdok-tong facility subsequently assumed the primary responsibility for high-explosive detonator testing formerly conducted at the Yongbyon Nuclear Research Center. Although the high-explosive testing at Yongdok-tong likely primarily focused on developing and testing implosion devices designed to compress a plutonium core to set off a nuclear explosion, defector statements suggest that it may have also included testing of "gun-type" highly enriched uranium weapons designs.⁵

One of the earliest known public disclosures of the existence of what would become known as the Yongdok-tong Nuclear High Explosive Test Facility dates to November 1998 when a South Korean newspaper, Chosun Ilbo, reported based on "relevant authorities" that "North Korea has built a high explosive test site, essential for nuclear development in utmost secrecy near Kusong-si, North Pyongan Province." This information was reportedly leaked from a U.S. intelligence assessment based upon KH-11 satellite imagery collected during early 1997.⁶ The same source recounts that the facility had "conducted at least several high explosive tests so far.⁷ "The Korean newspaper also reported that this "…high explosive test site consists of an experimental explosive manufacturing plant, a warehouse, and an outdoor test site located in a deep valley and is said to maintain extreme security by painting the access road with camouflage paint."⁸

The facility has remained active in all satellite imagery from 2002 to 2025 reviewed for this report. It has witnessed numerous pattern-of-life and infrastructure changes, such as the construction of miscellaneous buildings, greenhouses, housing, and excavation activities. These latter developments likely reflect changing program, research, and development priorities over the years. The changes have likely been accompanied by an increase in the number of personnel assigned.

It is believed that the facility has not been discussed during U.S.-North Korea nuclear talks. However, as a critical component of North Korea's nuclear weapons development program, the Yongdok-tong facility should presumably be subject to declaration, verification, and dismantlement in any future comprehensive and verifiable denuclearization agreement with North Korea.

Of the locations over the years where high-explosive nuclear detonator tests are reported to have been conducted, only the Yongdok-tong facility appears to be currently operational and dedicated to this mission.

Organization and Development

The Yongdok-tong Nuclear High Explosive Test Facility is located at Yongdok-tong (용덕동), Taegwan-gun (대관군), North Pyongan Province (평안북도), North Korea. It sits approximately 115 kilometers northwest of Pyongyang, 312 kilometers northwest of Seoul, 25 kilometers northwest of the now-abandoned Taechon Atomic Energy Research Center, and 46 kilometers northwest of the Yongbyon Nuclear Research Center. The facility is currently assessed to encompass approximately 19 square kilometers, centered along a deep 6-kilometer-long valley. This valley includes the agricultural villages of Tokpung-ni, Yongdok-tong, and Yongdong-ni. There is a reasonable chance that additional small activities subordinate to the facility are located outside of the single valley identified in this report. However, such activities have yet to be identified in public reporting or satellite imagery.

Its location within a broader restricted area enhances the facility's overall security. Additionally, there are at least six isolated compounds with small, cultivated fields located in the hills above and around the Yongdok-tong facility. The positioning of these compounds suggests that they likely serve some security role.

There are conflicting opinions on what component(s) of the Korean People's Army (KPA) or the then Ministry of Public Security were responsible for the construction of the Yongdok-tong facility. At present, the prevailing thought is that an engineering brigade subordinate to one of the Engineer Bureaus of the Ministry of Public Security had overall responsibility for construction while elements of various KPA engineering units provided assistance as required.⁹

Satellite images show that the development of the Yongdok-tong facility began sometime in the late 1980s. A declassified KH-9 image collected on September 26, 1984, shows that the narrow main valley in which the Yongdok-tong facility would soon be built initially contained only the small agricultural villages of Tokpung-ni, Yongdok-tong, and Yongdong-ni along with their cultivated fields and support structures. Medium-resolution Landsat satellite imagery suggests that construction of the Yongdok-tong Nuclear High Explosives Test Facility was undertaken sometime between 1987 and 1989.

The construction of the Yongdok-tong Nuclear High Explosive Test Facility was undoubtedly a component of the dramatic expansion of North Korea's nuclear infrastructure during this time. In the early 1970s, North Korea used indigenous technology to expand the IRT-200 research reactor. This was followed in the early 1980s by the development of the 5MWe reactor, 50MWe reactor, Fuel Fabrication Facility, Pyongsan Uranium Concentrate Plant, and open-air, high-explosive core-compression testing at Yongbyon.

Despite joining the Non-Proliferation Treaty (NPT) in December 1985, North Korea continued its nuclear ambitions on the ground, as evidenced by the initiation of development at Yongdok-tong in the late 1980s and the first indications of the reprocessing plant construction at Yongbyon in 1987. It was also during this time, between 1985 and 1990, when the Radiochemistry Laboratory and the second waste storage facility (Building 500) were developed at Yongbyon, as well as the construction of a 200 MWe (800 MWt) reactor at Taechon. North Korea also held discussions with the Soviet Union for the installation of four VVER-440 reactors near Sinpo and reportedly conducted ongoing open-air, high-explosive core-compression testing at Yongbyon.¹⁰

There are few available and reliable open-source references to high-explosive testing or nuclear facility in the Kusong (sometimes transliterated as Guseong) area or at Yongdok-tong through the late 1980s and 1990s. However, on November 22, 1998, a report appeared describing what would subsequently be identified as the Yongdok-tong Nuclear High Explosive Test Facility. Choson Ilbo, citing an "official with ties to the intelligence field and who is well versed in North Korean affairs, states that:

North Korea has built a high explosive test site, essential for nuclear development in utmost secrecy near Guseong-si, North Pyongan Province, and has conducted at least several high explosive tests so far.

…This high explosive test site consists of an experimental explosive manufacturing plant, a warehouse, and an outdoor test site located in a deep valley and is said to maintain extreme security by painting the access road with camouflage paint. U.S. intelligence authorities have been tracking the location of this test site for over three years based on the testimony of North Korean defectors and confirmed the location using the KH-12 spy satellite early last year.

…The high explosive test site is intended to develop a detonator for nuclear weapons.

…A source familiar with North Korean intelligence said, "North Korea's Yongbyon high explosive test site is far away from the explosives manufacturing plant and test site, but the new site has these two facilities close to each other, allowing for more efficient testing." ¹¹

In 1999, further coverage based upon information reportedly from the U.S. and passed to South Korea revealed "at least two detonating tests were conducted in 1998" in the Kusong area.¹² These are presumed to have been conducted at the Yongdok-tong facility.

One of the earliest attempts to identify the precise location of the Yongdok-tong facility was made by Osamu Eya in his 2000 book Great Illustrated Kim Chong Il. Regrettably, the facility he identified was not the Yongdok-tong facility but the No. 112 Factory in Kusong.¹³

2002: First Detailed Look at the Facility

The first readily available, high-resolution commercial satellite image of the area was acquired on March 7, 2002, providing a more precise location. This image shows that the facility is in a deep valley that extends off the upper end of a larger valley east of Kusong, located between Sonmu-san (선무산, Sonmu Mountain) on the east and Ponghwangdae-san (봉황대산, Ponghwangdae Mountain) on the west. The valley in which the facility is located is bisected by a stream with the facility's activities dispersed along both sides and extending approximately 6 kilometers up the valley. Functionally, the facility can be broadly divided into ninegeneral types of activities:

• Headquarters and administration area
• Main support area
• High-explosives storage and fabrication area
• Open air, high-explosive test area
• KPA barracks
• Secure compounds
• Warehouse and storage areas
• Agricultural support areas, including greenhouses
• Underground facility entrances

The facility starts at the base of the valley, where there is a housing area on the west bank of the stream at the location of the former agricultural area known as Tokpung-ni. This housing area consists of 24 structures, with some still under construction. Approximately 600 meters to the west of this housing area is a barracks compound along the southern slope of Wondu-kogae (원두고개, Wondu Hill) that likely houses an active Korean People's Army. Immediately to the east of the housing area and across the stream are several buildings. The largest appears to be a three-story structure likely used for laboratories or offices.

Approximately 280 meters north of the housing area, on the same bank but separated by cultivated fields, is the headquarters and administration area consisting of approximately eight buildings. Immediately north and on the east side of the stream is the main support area. Divided into three sections-workshops, motor vehicle maintenance and storage, and warehouse-it consists of nine buildings. From this time forward, satellite imagery frequently shows varying numbers of trucks, buses, small vehicles, and shipping containers present in the motor vehicle maintenance and storage area. Likewise, piles of sawdust are often observed outside of one of the buildings in the workshop area, indicating a woodshop. Approximately 170 meters east of the motor vehicle maintenance and storage area is a small, secured compound consisting of two buildings and what appears to be a guard post secured within a fence. Approximately 20 meters further east is the facility's electricity substation, which draws power from the Supung Dam and hydroelectric plant located approximately 52 kilometers to the north on the Amnok-gang (Yalu River).

Moving 350 meters further up the valley across from the main support area, and on the west bank, is an area with one building likely used for laboratories or offices partially surrounded by a revetment. Several empty revetted positions suggest the presence of previous structures and activities and several small, cultivated fields.

Approximately 650 meters further up the valley and at the site of the former agricultural village of Yongdok-tong, from which the facility gets its name, is a large flat stretching approximately 700 meters along the east bank of the stream. This area consists of 19 dispersed buildings of various sizes; some are partially revetted, and others appear to be warehouses. More significantly, there are also three fully enclosed revetted explosive storage magazines within the southern half of the facility. At the north end, there is another explosives storage area with five semi-enclosed revetted explosive storage magazines enclosed on only three sides. Taken together, this suggests that the area serves as the facility's primary explosives storage and fabrication area and that buildings in this area are, at a minimum, responsible for preparing the explosives for detonator tests.

Moving 670 meters up the valley on the east side of the stream is an entrance to a short, narrow branch valley that extends approximately 700 meters to the northeast. Within this valley is a small, remote support facility with three buildings (one of which appears to be a warehouse), a probable water storage tank, and a pumphouse. The upper end of this valley will undergo minor excavation sometime between 2002 and 2003, leading some to speculate that an entrance to an underground facility (UGF) entrance is located here.

Further up the valley where the former agricultural village of Yongdong-ni was located is an area that extends approximately 800 meters on both sides of the stream that contains four activities-cultivated fields, KPA barracks compound, support area, and the second explosive storage area with four revetted magazines. These characteristics suggest that this location is the primary open-air, high-explosive test area. The cultivated fields with two associated buildings are located on the west bank of the stream. While cultivated fields and agricultural activity are common throughout the Yongdok-tong facility, the March 7, 2002, image is of interest as it has what appears to be 11 small craters that are all approximately 3 meters in diameter.

Given that the off-nadir angle at which the image was collected yielded a ground sample distance (resolution) of only 70 centimeters, this makes positive identification challenging.¹⁴ The pattern and size of these craters generally match what has been reported over the years as being evidence of open-air, high-explosive core-compression detonator tests. It is not unusual for such tests to use two craters for each test, with one crater used for testing the device while the second nearby crater is used for testing instrumentation.¹⁵ If correct, this suggests both a relatively intensive testing campaign and a significant increase in testing levels compared to previously reported levels.

A report dated December 17, 2002-nine months after the March 7, 2002, satellite image-states that the U.S. Defense Intelligence Agency had informed South Korean Joint Chiefs of Staff chairman Yi Nam-sin that "…North Korea conducted about 70 high explosive detonation tests in the Yongbyon nuclear facility between 1983 and 1993 and three to four tests in an area around Kusong, North Pyongan Province between 1998 and 1999."¹⁶ A year later, similar reports allegedly based upon satellite imagery appeared with similar information but specifically identified the Yongdok-tong location.¹⁷ By comparison, a subsequent image collected on June 11, 2024, with a ground sample distance of 1.04 meters, showed no evidence of any craters.

The KPA barracks compound consists of four buildings and a greenhouse. From here, a dirt road extends east for 220 to 250 meters up a branch valley to the northeast, leading to a small remote support facility. Visible at the end of this road is what is likely a waste pile of rock from a recent excavation. Due to the image quality, the precise excavation site is not clearly visible. The third revetted explosive-storage position is located on the north side of the open-air high explosives test area, consisting of four fully enclosed revetted explosive storage magazines.

At present, both the open-air, high-explosives test area and the explosive testing conducted here at the Yongdok-tong facility can't be ruled out that earlier testing during the 1990s was conducted elsewhere within the facility.

Aside from the agricultural activities observed higher up the facility's primary valley, several remote small compounds are scattered in the hills around and above the Yongdok-tong facility. While all of these have small gardens or cultivated fields, their number and positioning suggest that they have at least a security mission for the facility.

That North Korea would continue to conduct high-explosive testing at the Yongdok-tong facility during the 2000s is indicated by a 2009 International Crisis Group report on North Korea's Nuclear and Missile Programs that states:

… DPRK engineers may still be working to improve or verify bomb designs. They continued high explosive implosion testing at the Yongdok-dong test site in the city of, Kusong, North P'yong'an Province, through late 2008, but these could also be for political purposes since the North knows the tests are visible to U.S. intelligence.¹⁸

This report is the first of a three-part series on the Yongdok-tong Nuclear High Explosive Test Facility, a critical component in the research, development, test, and evaluation (RDT&E) of North Korea's nuclear warheads. Part 1 provides an overview of the facility and its development history from the 1980s to the 2000s. Part 2 will discuss the development history from the 2010s to the present, and Part 3 will cover the underground facilities at Yongdok-tong and reports of other nuclear high-explosive testing and weapons storage locations elsewhere in North Korea.

Related