Probability of restoring power to the transmission power system and the time to restore power

Probabilistic safety assessment requires inputs related to the probability of restoring certain equipment versus the available time interval available. The data about the history of events include descriptions of events and the time for restoring the failed equipment. The objective is to determine the approximation function, which can be understood also as a cumulative distribution function for the probability of restoring equipment and to apply it considering the database of previous events. The method includes selection of the function and its fit in order to find the coefficients that match the function to the data. The root mean square method is used for getting the best fit regarding the parameters of the function. The resulted function gives the probability of restoring power before the determined time, e.g. the coping time. The resulted probability can be used in the event trees within the probabilistic safety assessment models. The application of the method was placed to three regions and the resulted functions for probability of restoring power before the determined time were compared to the probabilistic safety assessment of actual nuclear power plant. The results show the differences in core damage frequency and thus in nuclear safety for selected three regions.