Alternative method of strength analysis for a heat-power equipment under cyclic loads
DOI:
https://doi.org/10.15276/opu.1.60.2020.10Keywords:
strength, loading cycle, heat power equipmentAbstract
The analysis realized in the work revealed excessive conservatism of the requirements of the Technological Regulations for the WWER Safe Operation regarding the maximum allowable number of loading cycles for thermal power equipment of B and C safety class. The need to revise the requirements for the maximum allowable number of loading cycles is determined mainly by the fact that different equipment can have different structural and strength characteristics, and it can be subjected to different cyclic loads in identical transient and emergency modes. There is presented an alternative conservative method for analyzing the strength conditions under cyclic loads. It takes into account in the general case the difference in the structural and strength characteristics of the heat power equipment of safety related systems, as well as the difference in cyclic loads on different equipment/equipment elements in identical transient and emergency conditions. Based on the presented method, the strength conditions for cyclic loads on welded joints of collectors (critical for strength elements) on the cases of steam generators of South Ukrainian 1 and Rivne 1&2 have been analysed in transient and emergency modes. As a result, it was found that the strength conditions for cyclic loading on the welded joints of the steam generator collectors are fulfilled for all the considered examples. The disagreements in the calculated estimates are determined mainly by the difference in the number of loading cycles in emergency conditions and in modes of violation of normal operating conditions. The developed alternative method for analyzing the strength conditions under cyclic loads is acceptable for other types of heat power equipment – pumps, valves and heat exchangers. The presented method can be used to improve the requirements of regulatory documents governing the permissible number of thermal loading cycles for heat power equipment. The results of the presented work determine the limited approach to the nuclear power plant operation with variable reactor power in operating conditions
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