It seems that for whatever reason in the 40s and 50s, flying saucers and other types of UFOs were often sighted over atomic facilities fairly often. This is one of those cases.
Two disks were seen over the uranium mines in the Belgian Congo. The disks flew in formation and zig zags that were intelligent in nature changing altitude and speed and the same times.
Commander Pierre was sent in pursuit from the Elisabethville Airfield. He said that it was saucer-like and about 15 meters in diameter. The color was silvery grey like aluminum and the outer rim was completely covered in fire while the middle stood still.
As the commander chased down the UFOs he estimated their speeds at about 1,500 kilometers per hour. He did mention that because of the speeds and heat that they couldn't be manned, but they acted as if they were.
In the documents below on the last page you will find a sketch of the UFO that he saw during the chase.