Radiological characterization of the reactor pressure vessel of Trino NPP for dismantling purposes

The decommissioning of a Nuclear Power Plant (NPP1) is based on the knowledge of radioactivity content and its distribution. The reactor pressure vessel and its internal components have the highest radioactive levels in the plant, considering the contributions of the residual radioactivity due to neutron activation and the surface contamination. This paper presents the steps of the radiological characterization process carried out on the pressure vessel and internals of “Enrico Fermi” NPP. The activation data, computed by analytical procedures in a previous study, are analysed and semi-empirical models have been developed to determine contamination levels where activation is not expected. Non-invasive external dose rate measurements have been performed for a preliminary validation of the activation profiles and to be used in the contamination models. Afterwards, an optimal sampling plan has been adopted to quantitatively validate the current radiological framework 30 years after the end of the lifecycle, in order to get the radiological classification for the optimal choice of the cutting techniques and of the number of radioactive waste containers.