Calculational and experimental analysis on development of some algorithms for the VG-400 reactor power distribution control and monitoring system using the GROG critical assembly

The VG-400 reactor power distribution control and monitoring system uses neutron detector readings in the top axial and radial reflectors for reconstructing spatial energy distribution in the pebble bed core. The detector readings are processed by the methods realized in the MOD and SCURT codes. The spatial distribution of the 235U(n,f) reaction rates over the volume of the GROG critical assembly core, being a scale model of start charging of the VG-400 reactor, is experimentally studied. For two critical assembly states calculations are performed according to the MOD and SCURT codes, permitting to estimate the accuracy of energy release field reconstruction. The conclusion is made that neutron field distributions are more precisely reconstructed in the core centre than at the periphery. The calculation error is 3-9%