Neutron noise control methods for channel-by-channel coolant flow rate in the core

Abstract

In the presented article, the authors discuss the issues of measuring the coolant flow rate using neutron noise technology. The noise method for estimating the channel-by-channel coolant flow rate based on fluctuations in the intraband neutron flux has been widely used for VVER-440 cover fuel assemblies. To calculate the coolant flow rate, it is necessary to estimate the delay time of the signals of two direct charge sensors using the frequency method based on the local extremes of their coherence function. The equation of pure transport of temperature fluctuations is derived. Other cases are the presence of global neutron noise, uncorrelated noise on each measuring channel is not considered. The authors took into account horizontal coolant overflows between neighboring fuel assemblies for shell-less fuel assemblies of VVER-1200 reactor installations. The error in determining the coolant flow rate has been estimated. The concepts of sink structures and sink frequencies are introduced, which are an infinite sequence of periodic extrema – maxima and minima – spectral functions arising from trigonometric multipliers or terms of the type ,   ,  cos . The differences between the fuel assemblies -5 and the standard fuel assemblies for the VVER-1200 are briefly described. For the first time, the coolant flow rate in fuel assemblies-5 was estimated and compared with the speed in standard fuel assemblies for four time points. The necessity of monitoring channel-by-channel coolant flow rates is substantiated in order to identify fuel assemblies with consistently low and consistently high coolant flow rates. These conditions may be due to the specific loading of the core, the invariable design features of VVER-1200, namely, the diameters of the pipes in the blast furnace above this fuel assembly, the proximity of the core enclosure, the presence of an air defense system and thermal control channels in this fuel assembly.