Sakhno N. Mathematical models and methods for decision making support to ensure safe operation of NPPs steam generators

Ph.D. thesis is devoted to the development of mathematical methods and models targeted on enhancement of reliability of VVER NPP steam generator heat exchanging tubes nondestructive examination and decision making for their life-time extension. To perform in-depth analysis of steam generator heat exchanging tubes stage and to make the decisions dealing with their further operation, general scheme of system analysis of inspection object nondestructive examination performance was developed. To apply the scheme developed to increase the heat exchanging tubes nondestructive examination reliability, the mathematical model of steam generator heat exchanging tubes eddy current testing was developed and validated based on experimental data. Quantitative estimation of human factor effect on reliability of heat exchanging tubes eddy current results was performed as well. For decision making, dealing with further actions with examination object, the mathematical algorithm for scope determination of heat exchanging tubes eddy current testing performance was developed. This algorithm takes into account current stage of examination object. Existing criterion of scope determination of heat exchanging tubes annual eddy current testing performance was improved based on mathematical algorithm developed. Unified empirical criterion for steam generator tubes plugging was developed as well. To keep system analysis approach the mathematical model of steam generator heat exchanging tubes defect critical dimensions determination was derived. It can be used for performance of additional analysis under implementation of indicated above empirical criterion.