Assessing Structural Integrity of NPP Equipment and Pipelines by Coupled Calculations in ANSYS and RELAP Codes

One of the milestones leading to the unit transition to long-term operation is the assessment of the current technical state of equipment and pipelines during the periodic safety review. An integral part of this assessment are the strength calculations within the necessity to take into account rapid thermohydraulic parameters changing during non-stationary transients. Such calculations are characterized by the need for taking into account the relationship between equipment units and pipelines of the reactor coolant system. This task requires additional development of a complex three-dimensional FE model of reactor coolant system. The submodeling approach was used to perform the strength calculation of primary equipment. This approach involves the step-by-step process of strength calculations including the development of a thermohydraulic model with thermohydraulic analysis, the creation of a simplified complex finite element model of the reactor unit containing basic equipment and pipelines, validation, detailed transfer of boundary condition datasets for finite element model and determination of stress strain state for all calculation modes, and performance of the specified calculations of the equipment by a method of submodeling at the end. In general, the implementation of the whole complex of thermohydraulic and strength calculations within one program code is a quite complicated task and requires creating a separate approach. This paper presents the results of developing a comprehensive approach using the coupled calculations in the thermohydraulic and strength codes.