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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made according to the optimal technology were used in the experimental studies of the heat exchanger of the BN reactor. a b

Fig. 1. Protective foil surface: (a) – before tests; (b) – after tests

3. Application of the developed experimental control tools in the study of the SSS of facilities with BN reactors Power plants with BN reactors have an integral equipment layout, in which the core and primary circuit equipment (main circulating pumps and intermediate heat exchangers (IHEs)) are located in the reactor vessel. Using liquid metal coolant does not require the creation of high pressure in the primary circuit, so the body and the internal elements placed in it have a relatively small thickness. This avoids dangerous temperature gradients in the structure walls, even with rapid changes in the coolant temperature. At the same time, there may be temperature stresses in the interface areas of the housing elements of different heat capacities in the elements of the 2nd circuit – IHEs and steam generators with rapid temperature changes. The study of the change in SSS in such zones is an important task since, at high temperatures, the arising stresses can cause the accumulation of residual deformations and lead to changes in the geometry and loss of the structure serviceability. Therefore, the elements of the IHE – the transition zones of the upper plate of the tube board and the upper plate of the protection unit into the cylindrical shells of the IHE body – were selected for the research of the SSS using experimental measuring instruments and the developed methodology. Due to the limited resistance of low-inertia measuring instruments to the corrosive environment, the research was conducted during commissioning tests of the power plant. For this purpose, a pilot batch of sealed strain gauges similar to those used in bench tests was used. The peculiarity of the measurement technique is the use of a special sample of strain gauges installed in the area of maximum temperatures on the unloaded material samples of the natural structure. Processing the readings of these strain gauges allows for determining the random error of measurements related to the strain gauge drift. Such a technique is a feature characteristic of long-term strain measurements at variable temperatures above 350 ° C. Fig. 2 shows some results of determining the stresses in the IHE elements. As seen from the above graphs, the greatest stresses occur in the interface areas of elements with different heat capacities and having different change rates in the metal temperature. The functions of stress changes in time have a non-monotonic character due to the complex nature of heat exchange in the circulation circuit, which is difficult to consider in the calculated analysis of temperature fields. The developed algorithm for processing the results of strain measurements, implemented in the measuring system of BN-type reactors, has features associated with changes in the mechanical properties of structural materials at operating temperatures. It is also necessary to consider the possible occurrence of plastic areas in the places where strain gauges are installed. Therefore, to determine the stresses from the values of measured strains instead of the