Abstract: An apparatus for monitoring and evaluating the degree of risk associated with continued operation of a nuclear power plant while one or more plant components has failed or is otherwise unavailable. The apparatus has several functional sections, including means for storing a plant-specific data base of component-level core damage logic paths and component level failure probabilities, means for selecting plant condition scenarios by modifying the component failure probabilities to represent plant components actually or potentially unavailable, means for associating a figure of merit with the change in risk of core damage resulting from the unavailable components, and means for displaying the figure of merit relative to a base or reference value. As an interactive tool in the plant, the apparatus PSES displays the probability or risk of core damage almost instantly for any given state of plant readiness.