Relevance. The nuclear power plant contains a large number of equipment and pipelines subject to flow acceleration corrosion. As a result of a combination of various parameters - sizes (diameters, wall thickness), operational parameters (internal pressure, temperature), steels and elements types - the number of design cases is tens of thousands, without counting the possible forms of thinning. The process of maintenance and repair at the stations are doing an assessment of the accordance of actual and allowable values of wall thicknesses. The ensuring safe operations of equipment and pipelines have been introduced correction functions for regulatory functions, taking into account the forms of thinning, to determine the permissible thinning. The aim of the work. The task is to determine the influence of the forms and types of thinning on the stress-strain state and to determine the most critical thinning for straight sections of pipelines subject to flow acceleration corrosion taking into account emergency conditions. Methods. The allowable values of stress concentration factors (deformations) of pipelines subject without flow acceleration corrosion was determined taking into account allowable values, the requirements of the federal norms and rules for emergency operating conditions. For researches of the stress concentration coefficients were used the finite element method and analytical methods for various shapes, sizes and depths of thinning. Results. A method has been developed, that allows getting the maximum allowable values of stress concentration factors (deformations) for emergency operation, which afford to determine the maximum allowable depth of thinning in emergency conditions - an above criterion. The researches have been carried out definition of the stress concentration factors for local thinning with various types of these thinning. The functions of concentration coefficients depending on the geometric parameters of local thinning wall thickness were determined for a straight section of the pipeline. As a result of the research, the dependences of the sizes of thinning on the concentration coefficients for straight pipelines were created and a master-curve was obtained. The researches were carried out take into account the load from internal pressure and bending moment.

Relevance. Non-destructive testing of metal determines the actual state of the metal, the presence of discontinuities and their sizes, and also allows to determine what mechanisms of metal degradation were subjected to. One of the main characteristics of the quality of non-destructive testing is the detectability of discontinuities and defects. If no defects were missed, then its possible to guarantee the reliable operation of the facility until the next scheduled inspection. The article is devoted to the study of the probability function of detecting defects and determining the probability of the existence of a residual defect with a size exceeding the permissible value. The aim of the work - to develop a method to determine the probability of the existence of a residual defect with a size exceeding the permissible value after non-destructive testing and repairs of equipment and pipelines of a nuclear power plant. Methods. During the work formulas for the probability of detecting a defect and initial defectiveness, regulatory requirements in the field of certification of flaw detectors, and the results of research on non-destructive testing were used. Results. A method for determining the probability of defects with a size exceeding the allowed value, using the example of a reactor vessel, is presented. The method is based on residual defects, which takes into account the detectability of defects. The value of the coefficient that takes into account the influence of the human factor, instrument and methodological shortcomings or complexity of access to the control point is determined, which reduces the degree of uncertainty in determining the residual defect. The results of this work permit to evaluate the probability of the existence of a defect with a size exceeding the allowed value. The development of a residual defect to critical values characterizes the initial event for the destruction of the integrity of the structure. Thus, the probability of a residual defect can be used when performing a safety analysis of the water-water energetic reactor vessel.

Relevance. To ensure the safety of a nuclear power plant on the basis of the requirements of norms and rules in the field of the use of atomic energy for pipelines of the primary circuit of a nuclear reactor, the design should apply the leak before break concept. The main idea of the concept is to prevent a sudden rupture of the pipelines of the reactor coolant loop, and consists in substantiating the fact that the rupture is preceded by the formation of a stable through crack, which is detected by the provided leak control means. When substantiating the concept, it is assumed that break without leak is an impossible event. This article provides a method for determining the probability of a failure event without a leak. Purpose - estimate the probability of the existence of a defect that can lead to the destruction of the vessel or pressure pipeline without leakage, as well as the probability of failure without leakage for a known number of loading cycles. Methods. To systematize the data obtained by different methods of non-destructive testing, conservative assumptions were used to determine the area of detected defects. On the basis of the obtained defect sizes, the defect size regions were determined, which can determine the scenarios of crack growth. Using the methods of mathematical statistics, the probability of the existence of a defect, which can lead to failure without leakage, was determined. Based on the methods of the theory of reliability, a comparison of the obtained probability of destruction with the admissible value is carried out. Results. A method for processing non-destructive testing data based on an assessment of the area of detected defects has been developed to systematize the data obtained by different non-destructive testing methods. The criterion for the development of cracks according to the scheme leak before destruction is determined. A method has been developed for determining the probability of a defect that can lead to failure without leakage. An example of calculation based on feed water pipelines is considered.