Development of load combinations for design of nuclear component - a probabilistic methodology

Procedures are described for the evaluation of reliabilities implied by current component design criteria and for the sytematic derivation of design criteria that achieve specified target component reliabilities. The proposed method of calculating the limit state probability, p/sub F/, of a component considers the uncertainties of load processes and component resistances. The probability distribution of the extreme combined response is developed by convolving probability distributions of static responses with the extreme of the combined time varying dynamic responses. The probability of the component reaching a limit state is the probability that the combined maximum response exceeds the component resistance. A representative sample of components designed in accordance with a set of design criteria will have a frequency distribution of P/sub F/ that represents the limit state probability implied by the criteria set. This technique of reliability evaluation of design criteria can be used to place a new load and/or a new load combination in the proper service level category. The design criteria are derived such that the components of a particular class have approximately the same limit state probabilities. The Load and Resistance Factor design (LRFD) format, which is a generic form of the most current mechanical and structural designmore » criteria, is selected as appropriate for load combination methodology development. The load and resistance factors are selected using an optimization procedure wherein a fuction of the difference between P/sub F/ and the target limit state procedure wherein a function of the difference between P/sub F/ and the target limit state probability, P/sub T/, is minimized over the class of components.« less