Methodology and conclusions of activation calculations of WWER-440 type nuclear power plants

• Activation calculation of two WWER-440 type nuclear power plants.
• Detailed description of the applied activation calculation methodology.
• Graphical results for total activity and waste index categorization.
• General conclusions for activation applicable in the case of PWR reactors.

Activation calculations for two nuclear power plants of WWER-440 type have been performed by the authors in order to assist the decommissioning planning by assessing the radioactive inventory present at the time of and at different times after the final shutdown. According to related international literature and studies performed earlier by the authors, considering the activity more than 99% of this inventory is concentrated in the materials directly surrounding the reactor core, where the predominant evolution of radionuclides is generated by neutron induced nuclear reactions. In order to obtain the highest possible accuracy in modelling, three-dimensional Monte Carlo neutron transport calculations were performed. Besides the methods and models applied to these analyses, the paper also summarizes the results that can be generally applied to such nuclear power plant types. At the time of shutdown, the total activity of the stainless steel components is about 6 × 1016 Bq and 1.3 × 1017 Bq for the two NPPs considered. The biological shielding concrete constitutes approximately 7 × 1013 Bq and 1.1 × 1014 Bq.