Nuclear Infrastructure: Yongdeok High Explosives Test Site

Deep in the western hills and mountains of North Korea lies a large fenced-off complex that occupies an entire valley. Just 7.4 km from the ancient city gate of Kusong is the Yongdeok High Explosives Test Site. (Note: it is alternatively spelled Yongdoktong.)

This facility was constructed in the 1980s and conducted numerous conventional explosive tests as part of North Korea's nuclear weapons program in the 1990s. The testing of these high explosives relates to the conventional explosive materials that make up the "lenses" within nuclear devices that compresses the fissionable core, initiating criticality and the nuclear explosion.

Kim Jong Un standing beside what has been humorously called the "disco ball", the primary stage of a nuclear device. The small circles are the locations of each polygonal, high explosive lens.

Explosive lens design and testing used to occur at the Yongbyon Nuclear Scientific Research Center but was later moved to Yongdeok once the complex became operational. As a dedicated testing and production center, Yongdeok is spread out over an area of approx. 6.3 square kilometers, with discreet facilities for the various research, design, testing, and production centers. 

It is suspected by senior US intelligence officials that Yongdeok's purpose has expanded over time, particularly since North Korea's early nuclear tests, to also become the country's primary nuclear warhead storage facility as well as its nuclear warhead assembly center.

Overview of Kusong and Yongdeok. 

There are different kinds of high explosive lens testing that can be done. These tests consist of more than just setting off a shell of explosives but involve creating an analogue core (to replicate the effects of the explosion on a real nuclear core) and recording the results in minute detail to ensure proper design and physical affects.

The simulated cores can be made up of inert, depleted uranium or even titanium. The cores are then surrounded by an explosive shell (made up of between 2 and 96 individual lenses) and the shell detonated. This compresses the metal core at temperatures so high that the core melts and reacts similarly like the real thing - just without the ensuing blast and destruction.

This kind of testing is called hydrodynamic because the core liquifies, and it has been the most common way to test this part of a nuclear device without needing to set off an actual bomb. Monitoring the implosion millisecond-by-millisecond is also energy intensive, and the entire process requires advanced technical skills.

With that said, the production sector does have a large electrical substation in the area to provide electricity and that could support modern testing (which can't be detected by outside parties). But the exact building this might occur in hasn't been publicly identified. It's also possible the tests happen in an underground test chamber.

The Yongdeok High Explosives Test Site with its main sectors highlighted.

Yongdeok can be generally divided into two main sectors, an administrative sector and a production sector which also has a residential district and is likely where testing takes place.

Yongdeok's administrative sector (2003).

Within the administrative sector are two main compounds, the administrative compound and the main security compound for Yongdeok. The administrative center will, undoubtedly, not only have offices dedicated to overseeing operations at Yongdeok but also to liaise with the multiple other nuclear research facilities throughout the country, and to develop new lenses (components, geometry, etc. to fit newer warhead designs). 

Yongdeok's production and testing area (2003).

In the production sector are the main industrial and testing areas as well as the largest housing district within Yongdeok.

There are multiple storage and handling facilities for explosive materials, assembly buildings, a large electrical substation, and other support buildings.

Yongdeok housing district (2003).

In 2003, this housing district included twelve single-story houses, eleven three-story apartment blocks, and a single-story multifamily home. These would provide space for approximately 148 families of scientists, engineers, technicians and other personnel.

Yongdeok housing district (2012).

By 2012, four additional houses were built next to the original cluster of eight homes, and a further 26 single-family houses were constructed across from the main district, bringing the total to 178 housing units in this area.

Explosives handling area (2003).

In this part of the production sector, eleven structures were protected by berms in 2003. Some are simply storage for raw materials, others for mixing and creating the final explosive mix, and still others for additional purposes.

However, the buildings within the "area of interest" box will undergo a change in the years ahead.

Explosives handling area (2012).

By 2012, the two long buildings within the area of interest had been replaced by five smaller storage structures protected by a berm. However, the activities within the long buildings may have simply been transferred to a new, single long building that was built a few meters away from the originals.

The reasons for this development likely had to do with safety or a change in the materials being handled at this site. 

Area that will eventually host an underground facility. (2003)

Yongdeok has multiple underground and hardened structures, but the most interesting and possibly largest is located at 40.030719° 125.307414°.

Two entrances are clearly visible in this 2017 image.

Sometime between 2003 and 2012, North Korea constructed this underground facility across from an unidentified set of industrial buildings. 

Normally, reviewing low-resolution LANDSAT imagery can help pinpoint a construction year as tunneling work results in large amounts of spoil (debris), which is typically dumped nearby. However, I can't find any clear signs of construction work, which means North Korea took specific care to limit what could be seen via remote observation. This probably included the use of netting to obscure the area and the removal of debris by trucks - leaving directly from the excavation site and not allowing any of it to pile up.

Underground entrance in 2021. Note, a building now covers the entrances.

The entrances are spaced ~13 meters apart and are large enough to accommodate motor vehicles. But, in 2020, the entrance was obscured by a new building. Reported on by CNN and Arms Control Wonk, the 35-meter-wide building covers the entrances but doesn't block them, and the building actually extends back into the hillside with the two entrances still very much visible. 

The purpose of the underground facility isn't publicly known. Whether it's testing, assembly, storage, or something else, the UGF continues to play an apparent central role in activities at Yongdeok.

Agricultural area (2017).

Large parts of Yongdeok are actually cultivated fields and small greenhouses, as very little cleared land in North Korea is allowed to lay fallow. The grounds next to the administrative compound are no exception. In 2017, the area held a small park but most of the land were fields. 

Agricultural area in 2023.

By 2023, a segmented garden area covering 1.2 hectares was established and three larger greenhouses were built along with two additional buildings. At the park, swimming pools were installed.

Gardens similar to this have been popping up around North Korea for the last decade or so. The food can either be grown to supplement the diets of those living in the area or grown as crops for sale (domestically or even for export), but it's most likely in this case that they're being grown to supply Yongdeok.

Probable COVID quarantine facilities (2021).

As I first hypothesized on AccessDPRK and then confirmed with NK News, North Korea built scores of COVID quarantine centers around the country. They all share the same visual signatures: external guard posts, an outer fence, and an inner wall. Sometimes they converted existing structures and other times purpose-built facilities were constructed. 

Most of these isolation centers are civilian, but some can be found at military bases. And for Yongdeok, a total of three exist, with two being built next to each other in 2021.

Detail of Site 2. 

Usually, a whole town might only have one of these secured quarantine facilities, but Yongdeok has three (the third is located at 39.993325° 125.341502°). This could be because of the national security risk posed by having a pandemic decimate the skilled population that lives and works at the site that they wanted to ensure enough treatment space was available. 

It could suggest that COVID not only hit Yongdeok but did so particularly badly, necessitating additional sites. Or maybe there's three because each one provides a larger space to patient ratio (individual rooms perhaps instead of the rows of beds at civilian facilities), so they simply needed to build more to have the required space. 

In any case, the placement of quarantine facilities at Yongdeok underscores the importance the regime places on it. Such facilities haven't been located at ballistic missile bases or even at most other military sites (including Punggye-ri). But Yongdeok has three.

In all, Yongdeok is comprised of hundreds of buildings, its own security infrastructure, and has facilities for storing and manufacturing explosive material, testing the lenses, research and development, and assembly and storage of nuclear devices. There are also enough residential units to house approximately 1,100 individuals on-site (including family members).

Yongdeok plays a critical role in North Korea's nuclear program and will for the foreseeable future. Although details of the activities at the site are unknown, satellite imagery offers us a window into one of the most secret locations in the country.

And, who knows, after Kim showed off the Kangson Uranium Enrichment Plant for the first time, maybe we'll get an official look at Yongdeok one day. 

I would like to thank my current Patreon supporters who help make all of this possible: Donald Pearce, David M., Dylan D, Joe Bishop-Henchman, Joel Parish, John Pike, Jonathan J., Kbechs87, Raymond Ha, Russ Johnson, Squadfan, and Yong H. 

--Jacob Bogle, October 26, 2024

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Kim's 116-km-Long Palace Highway

Access to the various palaces and villas around the country is provided by relatively short runs of roadway - a few kilometers or so - coming off of the local road network. But there is also a highway that runs nearly the entire length of a province that is dedicated to providing transportation between two palaces: Changsong and Hyangsan. 

Map of the overall system, with the palace highway in white and National Highway 65 in black.

Starting in the early 1990s, a 116 km-long and tree-lined highway was constructed over the course of about three years. 

The highway begins at National Highway 65, just south of the town of Hyangsan. From there, it goes west, winding its way through forested hills and low mountains, until it reaches the Changsong Palace complex on the Chinese border. The villas at Hyangsan are accessible from NH65 and are approximately 20 km from the on-ramp to the palace highway.

Unlike civilian roads, the highway is only sparsely connected to local road networks with intersections. I was able to locate a total of 14 intersections, but several of them are actually part of the palace highway to enable Kim's motorcade to bypass tunnels in the event one collapses or is otherwise blocked. And at least one intersection is simply for a small access road to a military base. 

The palace highway cut through an original local road in multiple spots (such as imaged here), rendering it useless for long distance travel.

What also became apparent while looking for intersections, is that the highway was built over the path an older road which connected the northern parts of North Pyongan Province. Now, that older road is highly fragmented, with parts being completely disused. And the locals are largely left with winding dirt paths instead of a paved highway. 

Obong-ri Leadership Train Station.

The palace highway is also connected to the Kim's leadership rail network through another road that leads from the Obong-ri Leadership Train Station (40.305346° 125.205669°), north of the town of Taegwan. The station itself was constructed ca. 1990-91 and a road leads from the station and connects to the main highway 12 km away.

The Obong-ri Leadership Station is unique among the two dozen or so other leadership train stations because it also contains an underground support facility.

It's impossible to go anywhere in North Korea and not be near some kind of military installation, but as an aside, I do think it's worth noting that the highway runs within 5 km of the Unsal MOUT (military operations on urbanized terrain) training complex which is the largest in the country, two other large bases, and the Taegwan Ballistic Missile Base.

Changsong Runway (built ca. 2017).

In light of Kim Jong Un's penchant for flying and building runways at his favored palaces, one might ask why the highway was built at all when Kim Jong Il could have simply opted to fly, like Kim Jong Un has. Well, Kim Jong Il was terrified of flying. So, he only ever took trains and motorcades; flying only when absolutely necessary (the last time I'm aware of a flight was back in 1965).

And so, it makes a lot of sense that he would have invested in having a dedicated road built to connect two of the Kim's most enjoyed getaways. 

Since Kim Jong Un does seem to prefer to fly, with a runway at Changsong and helipads at both Changsong and Hyangsan, it is unclear whether or not the highway plays the same role as it did during his father's life. Occasionally, some of the intersections appear to be blocked off, and there aren't examples of normal traffic flow. So the highway is still restricted, but it may be getting a lot less use than in the past.

The highway is yet another example of the Kim family treating the resources of North Korea as their own personal property by destroying civilian infrastructure in order to build a private road that will have used a tremendous amount of resources that could have otherwise been used to help the people.

I would like to thank my current Patreon supporters who help make all of this possible: Alex Kleinman, David M., Amanda Oh, Donald Pierce, Dylan D, Joe Bishop-Henchman, Jonathan J, Joel Parish, John Pike, Kbechs87, Russ Johnson, Yong H.

--Jacob Bogle, 6/9/2024

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DPRK's Fuel Transport and Storage Network: an Introduction

North Korea doesn't have its own domestic supply of oil and relies on legal and illicit transfers of petroleum products for its economy to function. While AccessDPRK has documented the proliferation of gas stations around the country, those exist parallel to North Korea's traditional oil storage and delivery network, which it has maintained for decades. 

Pyongyang-Kaesong Highway gas station at 38.973769° 125.719252°. Image: Wikimapia/Mar12.

In much of the world, going to your local gas station is how most individuals get fuel. There are stations for cars, trucks, and there are dedicated fueling depots used for institutions that have large fleets of vehicles like municipalities. But until recently, getting fuel in North Korea wasn't so simple.

Sixty-nine percent of the 190 gas stations identified by AccessDPRK have been built under Kim Jong Un, and even those aren't enough to cover every town and village - let alone the needs of factories, universities, collective farms, and other organizations that operate multiple vehicles and pieces of equipment.

So, most organizations still rely on an older system of refueling. 

While the specifics of how this system works remains little understood, I feel that I have been able to locate enough of the infrastructure (which is often buried underground or in hardened structures) to write an introduction to this system that serves as the backbone of fuel delivery and storage in North Korea.

To place this system in context, I'll quickly review North Korea's petroleum infrastructure.

North Korea is only allowed to legally import 4 million barrels of unrefined petroleum products and 500,000 barrels of refined petroleum products (like gasoline and kerosene) each year under United Nations' restrictions.  

North Korea imports petroleum products via ship and rail transfers as well as from a single pipeline coming from China into Sinuiju, the PRC-DPRK Friendship Oil Pipeline. North Korea has two refineries but largely relies on the Ponghwa Chemical Factory which is nearest Sinuiju. 

This map shows where North Korea's refineries and main oil terminals are located.

From its refineries and system of storage depots at key coastal terminals, legal (and an ever increasing amount of illegal) petroleum products are then transported to intermediate depots around the country. 

As mentioned, part of the fuel is sent from those terminals via rail and then truck to the country's gas stations.

But as you can see, they are not evenly distributed around the country and also only provide a limited storage capacity.

The bulk of the nation's fuel gets stored elsewhere, at facilities large and small, and can then be transported to factories, farms, and other organizations that need to fuel their own vehicles and equipment.

Map of just some of North Korea's internal petroleum storage facilities.

I currently have nearly ninety of these internal storage sites located. As mentioned earlier, most of the facilities are either underground or located within covered/hardened bunkers, making their identification difficult. Most, however, are near railways and so I believe I will be able to locate a considerably greater number of them in the future.

But with the sites that have been located, I can show each of the steps from the main terminals down to the local level.

Nampo's key petroleum depot is located at 38.720407° 125.366678°. It is one of North Korea's most important petroleum storage facilities, and also receives shipments from vessels engaged in illegal transshipment operations. 

Currently it has fifteen storage tanks for different types of refined petroleum products. The depot has grown in recent years with two new tanks added since 2019, and there is prepared space for a further twelve tanks. Two additional facilities also lie within a few hundred meters from this site.

Taedong Storage Site 39.094303° 125.615255°

From the main receiving depots like Nampo, petroleum can be shipped by rail to intermediate storage facilities. This one is near the town of Taedong, west of Pyongyang.

The Taedong Petroleum Storage Facility.

At Taedong, four large storage tanks - each approx. 20 to 25 meters in diameter - are partially set underground and are covered with large mounds of dirt.

Oil is brought to them via a pipeline from a rail terminal 750 meters away. Once inside the complex, the main line splits into smaller feeder pipelines that can fill or drain each tank independently. Taedong is one of the largest of these internal facilities and is just 1.3 km away from five anti-aircraft artillery batteries, and it is covered by several surface-to-air missile sites as well owing to its proximity to Pyongyang. 

Within Pyongyang is a large, central storage facility at 39.082890° 125.707182°.

The complex covers 12.4 hectares and contains large storage tanks like at Nampo, and smaller tanks that can be seen in towns outside of the capital and even at gas stations.

From these larger storage facilities, the fuel is then distributed via tanker trucks to their destined town or village.

One such site is in Kuum-ni at 38.898954° 127.908719°.

In this 2004 image, the individual storage tanks are visible.

Kuum-ni lies on the rail line in between Changjon and Tongchon in Kangwon Province. Its storage site comprises fifteen tanks, each 10-11 meters long.

By 2013, the tanks have been covered up.

Over time, most of the open tank facilities like Kuum-ni have had their storage tanks placed in bunkers or covered over with soil. In this 2013 image, new vent pipes are visible as small white dots.

Civilian organizations (factories, farms, etc.) have their own on-site fuel storage, and can draw from these "community" facilities. Sometimes it's a considerable amount (thousands of liters) or just a few small storage barrels, depending on their individual needs. 

The military has its own fuel supply system, and their needs are prioritized over civilian organizations. 

This system, while theoretically efficient in a country lacking internal pipelines, is also prone to abuse as local party bosses have considerable influence over the local fuel supply. And, there many opportunities for fuel to be stolen or diverted elsewhere; from black market activity to diversion for personal use, and the occasional need to 'donate' fuel back to the government, an unknown but likely large percentage of the country's fuel supplies end up being taken out of normal availability.

Regardless of the inefficiencies in North Korea's supply structure and economic policies, the country has managed to continue to import far more fuel than UN limits allow, even through the border closures brought on by the pandemic. 

Given a lack of comprehensive data about North Korea's imports, monitoring other parts of the country's petroleum infrastructure, like the growth, renovation, or demolition of storage facilities, can provide additional insight into how much the country is capable of bringing in and storing long-term. 

Petroleum storage, while not always the most interesting subject, plays a role in North Korea's ability to withstand sanctions, border closures, and any future blockade during a war. Improving our understanding of this topic can also help us to gauge the strength of its economy and its ability to manufacture a range of goods. 

I would like to thank my current Patreon supporters who help make all of this possible: Alex Kleinman, Amanda Oh, Donald Pierce, Dylan D, Joe Bishop-Henchman, Jonathan J, Joel Parish, John Pike, Kbechs87, Russ Johnson, and Squadfan.

--Jacob Bogle, 1/21/2024

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Building North Korea's Bomb

If you've ever looked at a diagram of a nuclear bomb (whether of Little Boy or of a modern miniaturized warhead like the W-87), you might be forgiven for thinking constructing such devices looks fairly straightforward.

For a gun-type fission weapon (like Little Boy), you simply fire a hollow chunk of uranium at a solid cylinder slug of uranium, setting off a chain reaction. For a simple implosion-type weapon, you just wrap a core of plutonium in a shell of conventional explosives and detonate it. That will create an implosion shockwave, compacting the plutonium until it reaches criticality and explodes with the force of thousands of tons of TNT. 

Even today's advanced two-stage thermonuclear weapons can be rendered in handy graphics. But the simplicity of popular descriptions of how nuclear bombs work belies their devilish complexity.

Diagram of the W-87 two-stage thermonuclear warhead used by the United States. Image: US News & World Report.

All of these descriptions and diagrams are simply distillations of feats of physics and engineering that took thousands of people and billions of dollars to produce in each of the countries that have developed their own weapons.

The world's nuclear weapons programs rely on physicists, engineers, often some of the most powerful supercomputers in history, and networks of manufacturing centers that are responsible for safely producing the uranium and plutonium needed as well as the scores of individual components that make up a working nuclear device.

In the United States, the primary assembly of nuclear warheads takes place at a single location in Texas. But that's just the final step in a long chain of research and production that involves facilities across the country, from the mountains of Tennessee to the deserts of New Mexico.

Likewise, North Korea's nuclear weapons program is a decentralized affair that includes mining sites surprisingly close to the DMZ to top secret underground storage facilities just a couple hours away from the border with China. 

In this article, I will attempt (with a caveat) to layout North Korea's nuclear weapons infrastructure. 

That caveat is: no country makes its nuclear secrets easy to uncover. Building a nuclear weapon takes the combined efforts of thousands of people, and uncovering the exact design components and in which factory which part is made is typically highly classified information. Because of that, this can't be a comprehensive exposé. There is still plenty about Pyongyang's nuclear program that isn't publicly known, and plenty that isn't even known to government intelligence agencies.

However, there is enough known information to provide a solid outline of many of the facilities North Korea uses to produce their nuclear arsenal.

With that in mind, let's get to it.

Kim Jong-un National Defense University.

The first steps to building a bomb are in research and development. For North Korea, this takes place at several institutions including the Atomic Energy Department of Kim Il-sung University (39.059259° 125.767729°), the Physics Department of Kim Jong-un National Defense University (39.169623° 125.776838°), as well as three departments within the Pyongsong College of Science (the Chemical Department, Physics Research Institute, and Atomic Energy Research Center). Additional research also takes place at some of the locations I'll discuss in greater detail below.

Once you have the theories and designs worked out, you need some raw materials.

North Korea has modest uranium deposits and has mined it from locations across the country including at the Wolbisan Mine and at mines near Sonbong. However, North Korea's primary uranium mine is located in Pyongsan (38.323984° 126.436512°).

Pyongsan uranium mine and concentration plant. 

The Pyongsan uranium mine (also called the January Industrial Mine) is an anthracite coal mine that contains usable concentrations of uranium as an impurity. The mine has five mining shafts with one, possibly two, currently active. 

From the mine, the ore is taken via a conveyor system about 500-meters-long to the uranium concentration plant and mill.

The people over at Arms Control Wonk and the Center for Strategic and International Studies have written in-depth reports on the history and workings of the Pyongsan Uranium Concentration Plant. But here's a brief rundown.

Pyongsan Uranium Concentration Plant.

Construction on the plant began in 1985 and it was operational by 1990, albeit on a limited scale. Full-scale production wasn't reached until ca. 1995.

The ore is brought to Pyongsan where it is processed to separate out the uranium from the rest of the minerals found in the coal source material.

The uranium is found in reported concentrations of between 0.26% and 0.8%, and at least 10,000 tonnes of ore are mined each year; although, this estimate varies widely and annual production levels also vary year-to-year. This is then processed and concentrated into what's commonly known as yellowcake, which is 80% pure uranium. 

The uranium extraction process involves (simplistically): crushing the coal, sampling, grinding it down into a powder, adding sulfuric acid and sodium chlorate to leech out the uranium, washing it, running it through an extraction circuit and salt solution, and passing it through precipitation tanks where the concentrated uranium can be gathered, and dried. The yellowcake is then packed and shipped off for enrichment.

After processing, as much as 272 tonnes of yellowcake uranium leaves the plant annually in the form of triuranium octoxide (U₃O₈) and uranium dioxide (UO₂). 

North Korea does have a second uranium concentration plant at Pakchon (39.710533° 125.568319°). It began operations in 1979 as a pilot plant, but has been in caretaker status since at least 2002, with only low-level activities noted from time to time, leaving Pyongsan as the only active uranium mill.  

From Pyongsan, the uranium needs to be enriched. There is only one verified enrichment facility, at Yongbyon. There is a suspected site near Pyongyang at Kangson (38.957195° 125.612159°), but there is considerable debate within published sources about Kangson's purpose.

Other raw materials besides uranium are needed to support the country's nuclear program (from graphite to tungsten), but which mines exactly are used isn't known. However, there are several identified mines that could provide North Korea with some of the needed materials. 

There are several specialty materials and components associated with uranium enrichment and modern warhead manufacturing that North Korea is not known to have the capabilities to produce domestically, but the country clearly has enough legacy technology and skill to overcome those shortcomings and to produce these deadly weapons. 

The Yongbyon Nuclear Scientific Research Center (39.796977° 125.755110°) is North Korea's key nuclear facility. With a history dating back to 1963-64, Yongbyon plays a central role the country's development of nuclear weapons.

Yongbyon Nuclear Scientific Research Center.

Located some 85 km north of Pyongyang, the complex covers a 24.8 sq. km. area that's surrounded by fences and guard posts. Within Yongbyon lies the town of Dong-an (formerly Sang-dong) which serves as the civilian quarter and houses all the scientists, researchers, technicians, their families, and everyone else needed to run the town and research centers. 

Southeast of the town is a walled compound containing the research center's administration, laboratories, and various other facilities. South of that, is an adjacent walled compound that houses the 5MWe nuclear reactor and the Experimental Light Water Reactor, as well as the spent fuel storage building. 

Elsewhere in Yongbyon is the Radiochemistry Laboratory (39.781174° 125.753286°) where plutonium is produced as well as radionuclides used in nuclear medicine. And then there is the uranium fuel fabrication facility (39.770255° 125.749224°) where the uranium brought in from Pyongsan is further processed and enriched into weapons-grade material. The fuel fabrication facility is also used to manufacture the fuel rods needed for the nuclear reactors.

The uranium complex at Yongbyon, including the enrichment halls.

Estimates place Yongbyon's annual capacity to be 100 kg of highly enriched uranium and 6 kg of plutonium. The enrichment hall at the uranium fuel facility was enlarged in 2013 and again in 2021, indicating an increase in North Korea's enrichment activities.

According to the Center for Arms Control and Non-Proliferation, North Korea has enough fissile material to build a further 45-55 nuclear warheads. 

Another change of note within Yongbyon has been the construction over the last decade of enough housing for ~3,200 new residents. The increase in Yongbyon personnel, the enlargement of the uranium fuel fabrication facility, and other changes in recent years (at Yongbyon and elsewhere) have enabled Kim Jong-un to ramp up the production of nuclear warheads.

This increase in capacity was reflected in a 2022 speech by Kim Jong-un in which he vowed to "exponentially increase" the size of the country's nuclear arsenal. 

However, simply having a pile of enriched uranium and plutonium doesn't a nuclear bomb make.

Yongdoktong nuclear complex.

Nuclear weapons use shaped charges made of conventional explosives as an "explosive lens" to collapse the inner shells within the device and lastly to compress the core of fissile material, initiating the chain reaction.

Yongdoktong (40.004320° 125.339377°), just east of Kusong, is where these lenses are developed, tested, and manufactured. 

A review of Landsat images reveals that construction of the complex began ca. 1987 with most of the work completed by 1992. In more recent years, several changes have been noted including at least 18 new buildings or building renovations since 2016, the addition of greenhouse and garden facilities in 2019, and ~47 new housing units, most of which were built since 2020. On top of that, in late 2020, a new building was constructed to cover the entrance to an underground facility near the main production center.

Explosive lenses are often produced at or near the same facility that conducts the final assembly of warheads. The size of Yongdoktong, its several distinct sections and underground sites - to me - makes it a candidate location for where North Korea builds their completed nuclear warheads.

Additionally, it is where intelligence sources suggest that North Korea stores its warheads in underground facilities within the complex. 

Regardless, warheads may then be taken from Yongdoktong to Punggye-ri for underground nuclear testing or they could be sent to one of a dozen or so ballistic missile bases.

Punggye-ri nuclear testing complex.

Punggye-ri (41.279084° 129.087133°) is North Korea's only nuclear test site. The facility runs south from Mount Mantap and down a valley for ~17 km. At the foot of Mount Mantap, four tunnels for underground nuclear testing were dug. From there, a series of administrative, support, and guard buildings are situated along the valley.

The exact year that Punggye-ri was established is difficult to ascertain but excavation work on the testing tunnels began in the early 2000s, and the site was being monitored by South Korean intelligence agencies as early as the 1990s.

To-date, six underground nuclear tests have been conducted, but only three of the four tunnels have ever been used. The first test took place in 2006 and the most recent (and most powerful) nuclear test occurred on Sept. 3, 2017. After that, North Korea announced that they had successfully completed the tests required to prove the validity of their nuclear weapons designs, and that Punggye-ri would be shuttered. 

On May 24, 2018, in front of foreign media who were especially invited to attend, the tunnel entrances were ceremonially blown up. However, doubts of Punggye-ri's closure were raised almost immediately. In the coming months and years, satellite evidence revealed that the facility had only been placed in caretaker status and remained suitable for future tests.

In 2022, new construction activity at the site was identified and U.S. officials later announced that the facility had been repaired and that further nuclear tests could take place at any time.

Validating the design of new warheads through testing is an important step in developing a credible nuclear force, particularly as North Korea advanced from testing crude nuclear devices (as in 2006) to developing miniaturized thermonuclear devices that could be mounted onto missiles. 

It is likely that further testing will be required as North Korea refines its designs and develops new variants. Currently, it is generally accepted that North Korea now possess ~30 operational nuclear warheads and is actively building more.

Map of known operational ballistic missile bases.

Ballistic missiles require adequate device miniaturization and heat shielding to deliver a functional warhead to the target. U.S. intelligence assessments concluded that North Korea had developed the capability to miniaturize a nuclear device and mount it onto a ballistic missile by 2017.

However, there is still debate whether or not Pyongyang has yet developed the capability to manufacture the necessary heat shielding for the reentry vehicles that are used in hypersonic missiles and MIRVs (multiple independently targetable reentry vehicles) that North Korea's seeking to acquire.

The country has around a dozen operational ballistic missile bases and a further dozen or so support facilities (for equipment storage, training, etc.). These bases are roughly divided into three "belts" around the country, with medium-to-intermediate range ballistic missiles and intercontinental ballistic missiles being deployed at bases in the "operational" and "strategic" belts (in the center and northern parts of the country respectively), and short-range missiles deployed in the "tactical" belt close to the DMZ. 

There are questions whether or not any warheads are actually stored at these missile bases, ready to be launched, or if they are all held at Yongdoktong and would only be moved to missile bases following a direct order from Kim Jong-un. 

Keeping them at Yongdoktong would introduce a serious delay in North Korea's ability to rapidly launch a nuclear-armed missile as the warheads would have to be transported from there to the bases. (The nearest operational base to Yongdoktong is over 50 km away by road.)

But for now, any discussions about deployed warheads or North Korea's nuclear command and control remains largely speculative.

What isn't speculative is that North Korea has worked for decades to develop the technology and infrastructure needed to build a nuclear arsenal, despite international condemnation and despite the tremendous hardships the nuclear program has caused the people of North Korea. 

And although I was able to highlight several publicly known nuclear facilities in this article, North Korea is known to have other undeclared research and industrial centers that play a role in the country's nuclear weapons program. Having a detailed accounting of these sites will be imperative to any successful denuclearization or arms limitations agreement in the future.

I would like to thank my current Patreon supporters who help make all of this possible: Alex Kleinman, Amanda Oh, Donald Pierce, Dylan D, Joe Bishop-Henchman, Jonathan J, Joel Parish, John Pike, JuneBug, Kbechs87, Nate Odenkirk, Russ Johnson, and Squadfan.

--Jacob Bogle, 8/26/2023

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Kim Jong Un's Underground Pyongyang

Verifying the existence of underground facilities can be a difficult task, especially when their existence is a state secret. But rumors eventually come out and tantalizing hints of their presence can sometimes be found.

For North Korea, these rumors tell of secret subway lines beneath Pyongyang and underground highways connecting major palaces, maybe even reaching as far north as the border with China. I have written quite a lot about North Korea's underground infrastructure, but direct evidence and declassified sources still remain scarce. 

Overview of the Pyongyang Government District.

However, within the secured government district of Pyongyang are signs of multiple tunnels and underground structures. While it's impossible to know how they all connect to one another or even if they do, their locations and prevalence do hint at a fairly robust underground network that supports the infrastructure, transportation, and security needs of Pyongyang's most important district.

The easiest way to identify underground facilities is to either spot their entrances or actually catch them being constructed. For the secured government district, most of the buildings were constructed decades ago, placing their secrets out of reach for those without security clearances. But under Kim Jong Un, there have been some substantial changes to the district and that has given North Korea watchers an opportunity to see observe some of them.

There are two main sets of tunnels within the 138-hectare district that are visible to satellite. The first is a set of four tunnels near the Central Committee Office building (also known as Kim Jong Un's office) and the adjacent villa (Residence No. 15). The second is a set of four tunnels leading to underground parking garages beneath three buildings that were constructed in 2018-2019.  

There is also a possible tunnel, marked in light blue, but I can't fully verify that it is a tunnel. In some images, however, it appears that there may be a road tunnel that dives under a gate near Kim Kyong-hui Hall, just south of Changgwangsan House.

But the tunnels around Kim Jong Un's office and Residence No. 15 are quite clear.

April 10, 2020 image of the four tunnels around the Central Committee Building (Kim's office) and his district villa, Residence No. 15.

Apart from the tunnels by the villa and office, which I'll detail next, there is also a smaller tunnel in the maintenance complex. This complex handles building heating and cooling equipment, provides maintenance services, and may also play a role in electricity and water supply to the adjacent buildings. The tunnel (39.016557° 125.743544°) is 5-6 meters wide and runs toward the southwest. It's visible on all satellite imagery going back to 2000.

The tunnel may simply lead to a hardened bunker housing additional equipment or it could actually connect into the Office 39 complex (which includes the Kim Il Sung Revolutionary History Institute [39.016134° 125.741890°] and other Party buildings). Given its size and location, I do not think this tunnel plays any special security role. Rather, it's most likely just an access tunnel for providing building services.

April 1, 2023 image showing changes since 2020.

In 2022 a villa was rebuilt and enlarged, and in late 2022 a new hardened structure was built over the site of the tunnel nearest Kim's office building. 

The 'office tunnel' is large enough for vehicles and may lead to an underground garage or a larger underground complex. The hardened structure above it is approximately 60 by 30 meters in size and rises approximately 3 meters above the surrounding gardens.

Conjectured tunnel layout.

Due to the number of visible entrances, a concept of the tunnel layout can be formed with some confidence despite not having all the information. 

The covered walkway from Residence No. 15 was constructed in 2010. It resembles another such walkway that was built in 2017 in the armed forces district 5 km north at 39.062677° 125.740196°. 

The southern tunnel entrance was also constructed ca. 2010-11. Following the path drawn in the above image, the southern tunnel is about ~150 meters from the northern tunnel at the Central Committee Office Building (CCOB). 

The northern tunnel, however, was only constructed in 2018. This means that the southern tunnel likely went directly to the CCOB, where an alleged 60-car garage also exists beneath the assembly hall. 

This connection allows people from Residence No. 15 to travel on foot or by car directly and safely to the CCOB. Then, in 2018, a new tunnel was built from the CCOB that would link up with the southern tunnel.

This construction also included the building of an underground structure which was later (2022) replaced by the 60 x 30-meter hardened structure now seen in satellite images. Allegedly, a small, electrified rail car is also employed within the tunnels, but I haven't seen any supporting evidence of that.

To the north of the Central Committee Office Building, between 2018 and 2020 four currently unidentified buildings were constructed. These buildings include glass-covered entrances to underground parking garages that, most likely, would also double as bomb shelters in the event of an air attack.

Underground garage entrances under construction in June 2020.

The underground garage entrances after completion are covered by glass canopies.

There are also reports (including from Hwang Jang-yop) that the Pyongyang Metro has a secret line for government use that connects important government and military installations around the capital, and that it even reaches as far as Nampo and Sunchon (50 km away). While this has never been independently verified, the government district does lie within 2 km of four subway stations, with the closest being Pongwa Station at only 600 meters away from Kim's office.

As most of the district was constructed in the 1960s and 1970s (as was the metro), underground entrances to the metro system could be hidden beneath key administrative buildings, beyond the prying eye of today's satellite fleet. I have doubts about a sprawling network of transportation tunnels connecting far flung facilities, but a local network connecting underground command centers and emergency escape routes is quite plausible. 

Location of other known tunnels and underground facilities (UGF).

Whether underground sites exist in isolation or connect to larger tunnel networks beneath the government district and beyond, the sheer number of bomb shelters and other underground facilities alleged to exist makes the possibility of a successful "decapitation strike" by South Korea or the United States far more difficult and less likely to be effective, as such an attack relies on knowing where the target individuals are and killing them before they have time to escape to another location.

While I can't comment as to the quality of their construction, as a regime hyper-focused on survivability, North Korea probably has the greatest density of underground facilities and secret tunnels of any country on earth. 

I would like to thank my current Patreon supporters who help make all of this possible: Alex Kleinman, Amanda Oh, Donald Pierce, Dylan D, Joe Bishop-Henchman, Jonathan J, Joel Parish, John Pike, JuneBug, Kbechs87, Nate Odenkirk, Russ Johnson, and Squadfan.

--Jacob Bogle, July 24, 2023

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Construction at Huichon

Huichon is an industrial city in Chagang Province, North Korea that has been experiencing a construction boom over the last few years.

This latest round of work would likely not have occurred if it weren't for the completion of Huichon Hydroelectric Dam No. 2 - a project that was mired in complications and may have played a role in Kim Jong Il's death. The dam along with ten other hydroelectric generating stations built along the Chongchon River from ca. 2010-2019, have a combined generating capacity of 420,000 kW.

At the start of Dam No. 2's construction, approximately ninety multi-family housing buildings were also constructed in downtown Huichon that provided space for around 500 families. 

This current ongoing construction boom began in 2020. Some of the projects have been reported on by DPRK media such as in the Rodong Sinmun and in a television program titled "The Look of a New Town" which aired in July 2020. But others haven't been officially acknowledged yet. With that in mind, I'd like to highlight some examples that can be seen via satellite imagery. 

To start, there is a kilometer-long road tunnel (40.198067° 126.278119°) that connects two other projects I'll be discussing with the rest of Huichon and the Huichon Industrial Cooperative, which is a collection of factories near the center of the city. 

Satellite imagery reveals new spoils piles, suggesting that the interior of this tunnel is either being renovated or that the tunnel is being enlarged in some way.

The tunnel area as seen on October 2, 2020.

New work at the tunnel site as seen on Sept. 1, 2022.

Although the tunnel looks like a typical road and can be accessed from one of the city's main arteries, the road only leads to and from the Chilsong Electrical Appliance Factory. This feature becomes more interesting when you consider that the hill it runs through contains a warren of other tunnels, suggestive of a large underground facility (discussed further below).

Chilsong Electrical Appliances Factory as seen in 2018.

This tunnel leads directly to the Chilsong Electrical Appliance Factory (40.202665° 126.278621°) which is in the process of being completely rebuilt.

Little is publicly available about the specifics of the factory, but Kim Jong Il visited it in March 2010 and said that the factory was an important part of the country's economic future. However, that's the only leadership visit to the factory I can find in online sources. Regardless of the exact role of the factory, the fact it is being doubled in size attests to its continued importance. 

The factory is undergoing expansion. As seen in November 2022.

In 2018, the overall factory area covered approximately 12.5 hectares. In 2019/2020 the old factory was demolished and construction of a new factory campus began. This new area covers approximately 30 hectares and includes not only typical industrial buildings but will also have a stadium (somewhat common at large industrial sites), factory museum, revolutionary history/Juche museum, a health clinic for workers, and other amenities. 

The early stages of construction seem to have been carried out quickly, but it has since stalled. Little new activity is visible between October 2020 and December 2022. This may be a reflection of the COVID-19 pandemic's economic toll on the country.

Foundations for new apartment blocks across from the Chilsong Factory.

Across from Chilsong (at 40.208419° 126.281558°) the foundations for 21 apartment buildings have also been constructed, perhaps as new worker housing for the expanded factory. Previously, only farmland and a few small houses existed on the site, but they were cleared away for the new apartments sometime between 2019 and 2020. However, like the stalled progress on the factory, only the foundations of the apartment buildings have been constructed, and the work appears relatively inactive as of Dec. 2022.

As mentioned earlier, the Chilsong factory is connected to the rest of Huichon via a tunnel. The hill the tunnel runs through has several other smaller tunnels that indicate the presence of a large underground facility (UGF) at 40.188214° 126.275511°.

The hillside is encircled by a newly built 3.5-km-long perimeter road (yellow) that can also be used to reach Chilsong and that connects to the six other tunnels (white) clustered at the southwest of the hill. There is no way to know how the tunnels are actually arranged or if there are large rooms within the hill, but I've created a speculative map of the interior tunnel arrangements based upon the location of each entrance and service adit.

There are three main entrance points to the hill. These are located together, and each entrance is protected by a small, covered structure. Previously, a series of greenhouses existed on the site as well but those have been demolished. 

Excluding the main road tunnel, if my estimated tunnel layout is considered, there are at least 3 kilometers of tunnels inside the hill.

After reviewing the available imagery, there isn't enough visual evidence to say if a factory complex exists underground or if the site is being used as a hardened storage facility. However, other "electrical appliance" factories are known to be involved in North Korea's armaments industry, and the closed-off nature of the underground facility and Chilsong factory raises further questions.

The Huichon COVID-19 isolation ward.

Within the new complex of the Chilsong Factory is one of over 80 (and counting) suspected COVID-19 isolation wards. Located in an out-of-the-way building (40.201310° 126.281072°) at the inactive construction site, the COVID ward was established in 2021. The 180-square-meter building is surrounded by a wall, has two guard posts, and all of that is surrounded by a perimeter fence. 

Public information is sparse about these facilities, but because of their high security and relatively small size, I surmise that they are used to isolate those who test positive for COVID-19 or have an otherwise unidentified fever until they either recover or need to be transported to a hospital that can provide intensive care (at least, North Korea's version of intensive care). 

As part of the overall construction in the Huichon area, this school (40.205530° 126.244176°) and nearby housing have been reconstructed. The school will be 2-3 stories in height and there have been 14 new housing buildings constructed. Each building contains 2-4 individual housing units.

Across the river from the school a further 78 houses were built totaling 156 family units. The houses are in the new "countryside" architectural style promoted by Kim Jong Un in recent years.

The last construction project I want to discuss is the ongoing work at the Hagap Underground Facility (40.081244° 126.188535°).

Hagap is an underground complex 13-km south of Huichon that has an uncertain purpose. Construction began in 1991 but after several years of work it was apparently never completed. Following a prolonged period of inactivity, activity resumed in 2016. I have written about the progress at Hagap a couple of times (in 2017 and in 2019), and work is still ongoing.

Construction activity in 2016-2019 had been focused on improving access roads and building new tunnels, but since 2019 temporary worker's housing and workshops were constructed at the front of the complex, suggesting work is now being carried out in the interior of the main underground area.

As seen in the above image, construction work and landscaping have been completed at this auxiliary entrance site.

Secret nuclear facility, underground state archive, or something else, after 32 years of construction Hagap's purpose still isn't known. However, unlike the neglected underground facility at Kumchang-ni, North Korea seems intent on giving Hagap life and warrants continual monitoring.

I would like to thank my current Patreon supporters who help make all of this possible: Alex Kleinman, Amanda Oh, Donald Pierce, Dylan D, GreatPoppo, Jonathan J, Joel Parish, John Pike, JuneBug, Kbechs87, Russ Johnson, and Squadfan.

--Jacob Bogle, 4/23/2023

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