[en] The IR-8 pool type research reactor of RRC KI was commissioned in 1981 for carrying out fundamental and applied researches in various areas of science and technique. MCU-PTR code with the MCUDB50 constants library was created to ensure the safe operation of the reactor and for the calculation support of experimental research. The MCU-PTR code is intended for simulation of neutron transport by means of the Monte Carlo method on the basis of evaluated nuclear data taking into account of changes in the nuclide composition of materials in interaction with neutrons. Full-detailed 3D mathematical models of different states of the IR-8 reactor were created for precision neutronics calculations with use of MCU-PTR code. The code verification for pool and tank type research reactors performed based on IHECSBEP Criticality Benchmark Experiments and experiments carried out at the IR-8 reactor. The MCU-PTR code is currently used for calculations of the IR-8 reactor taking into account of fuel burn-up with HEU or LEU, poisoning of the beryllium reflector and burn-up absorber in CPS rods. (author)