Introduction. In the nuclear power industry, ensuring nuclear and radiation safety is of paramount importance, therefore all aspects that may affect safety are considered in a deterministic and probabilistic approaches.

As part of the safety justification, consideration of earthquakes of various intensity levels is regulated by safety standards. At the same time, the deterministic analysis of the earthquake and the models and calculation methods used are quite well-established, and in the probabilistic way, a relatively large number of different approaches have been developed and used as part of PSA level 1. The results of the evaluation of the conditional probability of failure of system elements, buildings and structures depending on the intensity of seismic impact on the free ground surface of the site depends on the approach used for the calculations.

Aims. To perform a comparative analysis of various methods for constructing a failure probability curve under seismic impact.

Materials and methods. A comparative analysis of the use of various approaches to the construction of a failure curve under seismic impact for a relatively simple case is performed. The results of the calculations showed that the scaling method leads to the most conservative results. The use of linearization methods and the method of moments give more realistic estimates, which can have a positive impact on the results of PSA level 1.

Conclusions. A comparative analysis of some approaches has practical interest and is relevant, since various methods can contribute more than 50% to the core damage frequency, which creates a significant imbalance in the safety of nuclear power plants.

 

In accordance with the Federal rules and regulations of the Russian Federation (paragraphs 2.8, 2.9 of RR-064-17) and international standards (IAEA SSG-3), the OUAE (the object of the use of atomic energy) project should provide information on interrelated processes, phenomena and factors of natural origin identified during engineering surveys and studies, and the parameters of relevant combinations of external hazards are determined, for which an analysis of their impact on the safety of the NPP as part of the NPP design and beyond-design accidents should be performed. Combinations of hazards can have a stronger impact on the safety of the station than each impact considered separately, and the frequency of occurrence of the combination can be comparable to the frequency of occurrence of individual impacts. Currently, probabilistic approaches are not presented in the regulatory documents of the Russian Federation and international norms. The paper [1] presents a methodology based on the theory of copula functions, the practice of which has shown that the determination of the frequency and intensity of combinations is influenced by taking into account the empirical parameters of the distribution function: correlation coefficients, tail dependencies. The analysis of the effect of taking into account the value of tail dependencies on the result of choosing a model copula function within the selection of combinations of external natural factors that should be taken into account in the project of the OUAE is carried out. It is shown that the approach presented in [1] needs to be supplemented with an estimate of the value of the upper tail dependence based on statistical data, since due to a more complete application of the properties of copula functions, the depth of justification of the results increases.