Analysis of a high-frequency component of neutron noise in VVER-1200 dynamic modes

For the first time, the article raises the problem of the possibility of using the high-frequency component of neutron noise to monitor the state of fuel assemblies and fuel rods during operation, since for long-time neutron noise research was limited to a frequency of 50 Hz. A brief historical summary presents the main points and stages of the development of neutron noise control, as well as the personalities of individual scientists who have made fundamental contributions to the development of neutron noise diagnostics. Using the example of data from the Novovoronezh NPP obtained during dynamic tests in 2022, the authors show the possibility of estimating the natural fluctuations of the control bodies of the control system as a function of frequency-depth of immersion in the core. This dependence makes it possible to build an alternative channel for monitoring the position of the regulatory authorities. Based on spectral estimates of high-frequency neutron noise, the possibility of detecting the boiling mode of the coolant with localization of the location by the height of the fuel assembly is substantiated. For the first time, data (frequency composition) on possible natural fluctuations of fuel rods (parts of fuel rods) measured directly during operation is presented. These values are given in the form of specific values, and not in the form of a frequency range calculated based on the results of bench tests. A critical approach to the problem of preliminary tests of fuel assembly layouts at various stands in terms of the sufficiency of information and its validity is presented. For the convenience of visualization and compression of information, a new representation of the cascade of spectra is introduced in the form of contour graphs, which makes it possible to identify common patterns on a large amount of data as efficiently as possible. The necessity of further research on neutron noise issues at existing nuclear power plants is argued in connection with the introduction of a new fuel assembly design (TVS-5), which has significant differences.