Abstract: The method for estimating the air contamination conditions in EPR reactor building during power operation and shutdown is described, and a model for estimation of the H-3 activity concentration is established. Air contamination levels in the equipment room and the work room of reactor building during the power operation and shutdown are evaluated. The results show that H-3 is the main contributor for air contamination in reactor building during the shutdown with a concentration in air of about 0.07 DAC, which could cause a collective dose of about 56 man·mSv in a typical outage

Key words: EPR, air contamination, H-3