Mazurok O. The thermal-hydraulic analysis methodology improvement in framework of vessel reactors lifetime extension.

At the moment, Ukraine and other countries are implementing a program of NPPs lifetime extension. At the same time, special attention is paid to the assessment of the technical condition and lifetime extension of the reactor pressure vessel. An aging management program after the lifetime extension is also being implemented and upgrades to increase the reactor thermal power can be implemented. In this case, it is mandatory to assess the technical conditions, including the reactor pressure vessel. For this purpose, in particular, special methodologies are used for thermal-hydraulic analysis are used worldwide. This paper analyzes the main existing methodologies of thermal-hydraulic analysis used in Ukraine and worldwide, in order to determine their relevance in relation to the specifics and current state of Ukrainian NPPs power units, taking into account practical domestic experience. According to the results of the methodologies analysis, including approbation of domestic methodologies, the inconsistencies of existing methodologies with sustainable domestic practice were identified and ways to optimize the requirements for thermal-hydraulic analysis were proposed, in particular, by reasonable reduction of the calculation analysis scope (number of scenarios). Based on this and the author’s experience, an improved (optimized) resistance to brittle fracture substantiation methodology of the reactor vessel in part of thermal-hydraulic analysis was developed.