Roof repair work spotted at the Pyongsan uranium mill

In exciting news,  Planet Labs snapped its first Skysat (0.8m resolution) image of North Korea’s uranium mill at Pyongsan on April 14, 2020. The image shows North Korea completed roof repair work on the largest building at the complex. This is a part of a long running cycle of rust and repair conducted at the building.

  The current repair work might help open source analysts understand the function of that building, as well as to observe that it continues to operate – as a part of the complex’s effort to produce uranium yellowcake for North Korea’s nuclear programs.

North Korea declared the Pyongsan uranium concentration plant to the IAEA in 1992, and was one of two locations where they milled uranium. One location, the pilot mill at Pakchon, was scheduled to be decommissioned sometime after Hans Blix’s visit in 1992, leaving the much larger mill at Pyongsan as the primary location for observation in the open-source to better understand the front end of North Korea’s nuclear fuel cycle.

Over the past year I have been working on a project that is attempting to review and better understand this cycle.  CNS will publish a more detailed report on those findings in the next couple of months, but for now I want to talk about an interesting signature detected at the Pyongsan uranium mill, and what it means for better understanding this unique site.

Little information exists about the Pyongsan mill in the open source literature.  There is a short clip of Blix visiting the site in 1992, and a North Korean defector, Kim Tae-ho, who described the site in a book.  (He called it the Namchon Chemical Complex.)

But we can begin to speculate on the purposes of different buildings based on the type of wear that occurs from normal operations.  A case in point is the building seen above which has a roof that is designed for a specific type of ventilation and is consistently rusting in a very specific location – I believe this is the building where North Korea conducts acid leaching to separate uranium from the ore.

There are different processes to leach uranium, but Kim Tae Ho claims North Korea used acid leaching, as do other sources. Any building with acid-filled tanks that are used to dissolve uranium-bearing ore require a lot of ventilation. More importantly, though, the acid fumes can also corrode the building being used for leaching, in the case of a metal roof, we see as rust.  Below we can see a natural draft ventilation building being used for electrowinning (which involves a similar acid) at the Gunnison Project copper extraction plant, in Arizona. Notice how the area around the ventilation opening is severely rusted.

Gunnison Copper Extraction Plant. Source: Google Earth/Maxar
Source: J.A. Murray, M.R. Nees and P.W. Krag, “Acid mist containment in electrowinning using Bechtel’s electrode cap,” (1996). Available here.

We see the same cycle of rusting and repair at one building in particular at Pyongsan in Google Earth – which I believe is probably the uranium leaching tankhouse.  This strongly suggests the use of acids or other corrosive chemicals used in the milling process. North Korea put a new roof on the building in 2014, roof corrosion was evident as early as 2016, and the damage was particularly severe by the end of 2019.  Note that in the 2019 image, one corner of the roof has begun to rust through. Interestingly enough, that corner seems to have been a point for damage before the 2014 re-roofing. The image on April 14, 2020 shows that North Korea has now repaired the roof, particularly the corner where the most severe damage has been repaired.

(The wavy images from Google Earth are an artifact of processing. I downloaded the image taken by Planet’s and processed it with ENVI, so the image is ortho-rectified correctly and looks better.)

So what does all of this mean? It was an important step toward understanding the process flow at the Pyongsan uranium mill and how it relates to other observable structures. My job over the past year has involved matching other steps in the process to other structures at Pyongsan, using similar sorts of signatures, other clues and the process of elimination. For example, the building just south of the suspected uranium leaching tankhouse has the same natural draft ventilation design but does not show the same corrosion. That’s a hint — but you’ll have to wait for the report.

The ongoing rust and repair work also demonstrate that operations are continuing at Pyongysan where North Korea produces uranium yellowcake for use its nuclear programs.

Huge thanks to Jeffrey Lewis, Catherine Dill, and Zak Kallenborn for the editorial help

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