After I stated that “I can’t speak to whether it’s necessary to reprocess” the “type of spent fuel” produced by the original Yongbyon reactor, someone more knowledgeable than I wrote “It is necessary.”

That was my impression. I would add that the UK in 2014 was looking for a way to dispose of Magnox spent fuel, according to this report from the British Nuclear Decommissioning Authority. If the British were looking into that topic in 2014, it’s probably safe to say that the North Koreans during the 1980s probably had to reprocess the spent fuel .