[en] We developed a full-scale 3D model of the initially fueled core of the VVER-1000 water-moderated power reactor for criticality calculations by the code PRIZMA. The core contains 163 hexagonal fuel assemblies of different types. The model includes blocks of in-core detectors which are arranged in the central pipes of 64 fuel assemblies in the entire core. Each block unites seven detectors equally spaced in the fuel assembly length. The sensing element of the detectors is rhodium emitter shaped as a slim cylinder. Conversion functions which relate the number of fission reactions in fuel elements closest to the central pipe and the number of neutron absorption reactions in the rhodium emitter were obtained through PRIZMA calculations where we estimated the rate of neutron adsorption reactions in the rhodium emitter and the rate of fission reactions in six fuel elements closest to the detector. The emitter's volume is negligible compared to the core volume and neutron flux in the detectors can hardly be estimated through analog Monte Carlo tracking. We used splitting and Russian roulette to make calculations more efficient. With these methods statistical uncertainties in the calculated rates of neutron absorption in rhodium were acceptable. In each of the 64 fuel assemblies with in-core detectors, we defined a set of cylindrical surfaces for splitting. Their axis coincided with that of the central pipe. When a particle crossed any of the surfaces to the cylinder axis, it was split into a number of identical particles. The Russian roulette was applied to particles which crossed the surfaces back. At collision points, particle weights were corrected in accord with a one-dimensional weight function defined in the entire volume of the fuel assemblies