One of the two RBMK-1500 reactor units of the Ignalina nuclear power plant in Lithuania was shut down at the end of 2004 and is currently under decommissioning. The knowledge of radioactive inventory of irradiated materials is very important in the planning of the decommissioning activities and is essential for predicting the radiological impact to personnel during dismantling and management of these materials. The generated radionuclides and their radioactivities in the shield and support plates of the Ignalina Unit 1 RBMK-1500 reactor were modeled in this paper. The reactor shield and support plates, which are made of steel, become radioactive because of intensive neutron irradiation, as they are located close to the bottom and the top of the reactor active core.

The assessment of radioactivity levels in shield and support plates was performed using the computer code ORIGEN-S. The list of radionuclides, their radioactivity levels, and the radioactivity dependence on the initial impurity content and cooling time were assessed in this paper. It was found that 3H, 14C, 36Cl, 55Fe, 60Co, 59Ni, and 63Ni are the main contributors to the radioactivity of the shield and support plates.