Validation of Monte Carlo activation calculation for V1 NPP reactor concrete shaft

•History of the V1 reactor showed that shielding assemblies were placed into the core.•The calculation of concrete shaft activation was performed using MCNP5 v. 1.6. code.•The activities of radionuclides were determined and compared with measured data.•The need for accurate material composition was demonstrated by sensitivity analyses. This work is aimed at developing an advanced model of the Slovak VVER-440/V-230, reactor in the MCNP code, to calculate induced activity in ex-vessel structural components and to validate obtained results to achieve an effective calculation tool for decommissioning purposes. A survey of the V1 NPP operating history revealed that after 12 fuel cycles the shielding assemblies were placed at the core boundary positions thereby reducing the core and decreasing the neutron flux on reactor pressure vessel as well as in adjacent ex-vessel components. Representative fuel cycles were selected for given periods. Model of the V1 reactor at the core level was developed, covering in-vessel and ex-vessel components. The activation calculation of the reactor concrete shaft at the sample volume location was performed using the MCNP5 code with the ENDF/B-VII cross-section library. Activities of selected radionuclides were determined and verified by measurements of samples at the Slovak University of Technology.