This work deals with the validation of a high-fidelity multiphysics system coupling the Serpent 2 MonteCarlo neutron transport code with SUBCHANFLOW, a subchannel thermalhydraulics code, and TRANSURANUS, a fuel-performance analysis code. The results for a full-core pin-by-pin burnup calculation forthe ninth operating cycle of the Temelín II VVER-1000 plant, which starts from a fresh core, are presentedand assessed using experimental data. A good agreement is found comparing the critical boron concentration and a set of pin-level neutron flux profiles against measurements. In addition, the calculatedaxial and radial power distributions match closely the values reported by the core monitoring system. Todemonstrate the modeling capabilities of the three-code coupling, pin-level neutronic, thermalhydraulicand thermomechanic results are shown as well. These studies are encompassed in the final phase of theEU Horizon 2020 McSAFE project, during which the Serpent-SUBCHANFLOW-TRANSURANUS system wasdeveloped