Using the example of the Chernobyl nuclear catastrophe, this article analyses a unique mechanism regarding the transformation of ontological security into ontological insecurity and then cultural trauma. It demonstrates how, from ontological security constructed by the Soviet ideology, Chernobyl moved to ontological insecurity understood as a breakdown in the established beliefs. By blaming the Soviet system in a public sphere, ontological insecurity was transformed into a cultural trauma. The article then presents a comparative analysis of Belarus and Ukraine in their construction of two types of cultural traumas: continuous; and retrospective. In the years 1986–1991, a continuous trauma took place in the form of protests against the established political system. After the directly affected countries received their independence in 1991, a retrospective trauma occurred in the form of recollection of what happened in Chernobyl. The official Belarus media understood the Soviet Union as its golden age and controlled most of the media space; fewer attempts were made to construct the Soviet state as a Chernobyl perpetrator. The official Ukraine media did not consider the Soviet past as its golden age and had a more pluralistic media; there were more instances in which it criticised the Soviet state for irresponsibility.