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Risk Oriented Accident Analysis Methodology (ROAAM+) framework for Nordic BWR is a further development of ROAAM ideas, where development and application of the framework are based on iterative processes of refinement of knowledge, and where risk analysis is used as a guiding tool in the identification of the major sources of uncertainty. ROAAM+ framework employs extended treatment of safety goals, where both “possibility” and “necessity” of containment failure are considered in the analysis. One of the most important features of the ROAAM+ treatment is risk quantification in different “state-of-knowledge” situations, e.g. where complete, partial or no probabilistic knowledge available. To assess the importance of the missing information, i.e. when no probabilistic knowledge is available, distributions of epistemic modelling parameters are considered as uncertain and sampling in the space of possible probability distributions of these parameters is performed. The main goal of this work is to demonstrate an approach for risk quantification in different state-of-knowledge situations and evaluate the effect of the selection of the distribution families and parameters characterizing distributions on risk analysis results., QC 20200914