He estimated that the site could have produced 40 kilograms of highly enriched uranium.Seoul and Washington concluded in following years that Pyongyang expanded the facility by a factor of two between 2013 and 2014 and that the Yongbyon complex alone produced around 80 kilograms of highly enriched uranium yearly since 2014.Military experts have estimated that North Korea produced some 300 to 400 kilograms of weapons-grade uranium since 2005.