Environmental impact assessment of radioactive gaseous releases from modern accelerators: case studies of low- and medium-energy regime

The operation of particle and ion accelerators involves the activation of the air in the bunker where the equipment is located and then the planned release into the atmosphere of radioactive effluents in gaseous form. The evaluation of the impact on the population of these effluents requires the knowledge of several parameters, first of all the source term. To this aim, analytical algorithms are presented for evaluating the air activation in rooms hosting different types of modern accelerators, in particular an ion accelerator for radiotherapy, accelerators for fusion neutron sources and linear accelerators for radiotherapy (above 10 MV). A simplified model is used to assess the thermal neutron flux (mainly when a refined Monte Carlo model for calculations is not available), which is responsible for the production of airborne 41Ar, the major concern for environmental contamination. The concentration of this contaminant in the bunker and the related release in the environment are evaluated considering a ventilation system that ensures a proper number of air changes. To verify compliance with the environmental standards, screening dose calculation factors from international reports are employed.