The present invention provides a two-step probabilistic safety assessment (PSA) method for evaluating a risk of multiple nuclear power plants. To this end, the two-step PSA method for evaluating a risk of multiple nuclear power plants comprises the steps of: (a) extending a core damage accident; (b) assigning a power plant damage group which is grouped in accordance with a power plant damage state based on the core damage accident derived from the (a) step; (c) converting the grouped power plant damage group into a fault tree based on an stored mapping table; and (d) calculating a source term release group fraction, wherein the stored mapping table is a branching probability table in which each of the power plant damage groups is branched to the source term release group.
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