The final shutdown of an NPP is followed by a post-operational phase, during which measures are taken to prepare the plant for decommissioning. One of the essential tasks in preparing the NPP for decommissioning is to obtain precise knowledge of the radioactivity content within the plant's components, particularly in the RPV and its internal structures, which typically exhibit the highest levels of radioactivity. To address this challenge, a novel method combining two Monte Carlo codes, MCNP and FLUKA, was developed to evaluate the activation distribution within the components of an NPP. This paper provides an overview of the methodology and demonstrates its application through the activation calculations of selected RPV internal components of a 1300 MWe Siemens/KWU PWR. The calculations yielded results with high accuracy, demonstrating that the method can serve as a non-destructive tool for radiological characterization of the plant's components.