Digital acoustical models of steam generator in VVER-440 NPP

The method of calculating frequencies of the acoustic standing waves (ASW) in digital acoustic models of steam generator (DAMSG) is similar to that used for the digital acoustical model for nuclear reactors (DAMNR). DAMSG is regarded as an auto oscillatory system that consists of a distinctive group of dissipative non-linear systems that are able to perform oscillations of un-damped nature with parameters independent of primary conditions and determined only by the system characteristics. The verification results of the DAMSG of VVER-440 are showed. An approach has been developed to determine the ASW frequencies generated in the SG. An anomalous boost in the power of pressure fluctuations in the reactor nominal operation mode indicates the presence of acoustical resonances in the bandwidth of the main circulation pump (MCP) rotation frequency which gives rise to the practical significance of the developed new models of the SG. Using DAMSG is able to optimize designs and can help in minimizing unwanted cyclic loads. This is a crucial for maintaining long-term operation in maneuverable modes of all small reactors.