PSI - Issue 50

S.V. Maslov et al. / Procedia Structural Integrity 50 (2023) 178–183 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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formulas (Daychik M.L. et al., 1989) calculated for the elastic behavior of the material and conventionally assumed constancy of the mechanical properties of materials, it is necessary to consider: - functional dependence of the elastic modulus on temperature, - history of metal preloading in the measuring point (considering the peculiarities of the strain diagram, elastic or inelastic behavior of the material), - an increase in Poisson's ratio with the appearance of plastic areas.

Fig. 2 – Stresses and temperatures in the area of the tube board of the intermediate heat exchanger of the BN reactor in the emergency protection operation mode. The layout of the measuring points is at the top right.

In particular, the measured stress change functions σ 1 , σ 2 , σ 5 , σ 6 shown in Fig. 2, constructed by the measuring system using classical algorithms, must be reconstructed considering the plastic behavior of the material. The corresponding functions for the measuring point 5/6 are shown in the figure as red curves with the superscript "*" in the stress designations. 4. Application of the developed control tools in the study of the SSS of BN-type units Unfortunately, the developed means of experimental control cannot provide direct measurements of strain in the dangerous area of the internal surfaces of the equipment for a long time. Therefore, it is reasonable to use mathematical models that use the results of measurements obtained for the controlled points of the outer surface of the structure as input data to build a history of SSS changes in these areas. The efficacy of the created models can be checked in the initial period of operation when direct measurement data on the stresses arising at the dangerous points of the internal surfaces of the elements are available. Numerical methods are used for the calculated determination of the SSS in dangerous points (including the plastic deformation areas), which provide the necessary accuracy of calculations, provided that the temperature fields are set correctly. At the same time, the computational determination of temperature fields at fast thermal processes and the complex nature of the coolant temperature change do not always provide sufficient accuracy of the results due to uncertainties in setting the initial data – in particular, the boundary conditions of the temperature problem. Therefore, the construction of temperature fields requires experimental data, the use of which provides the elimination of these uncertainties. It is necessary to specify the function of change over time of the coolant temperature and the conditions of heat exchange between the walls of the structure and the coolant to determine the calculated SSS in the most loaded IHE elements. We propose to use an algorithm comprising two stages.