212Pb-Bearing Aerosols in Subreactor Rooms of the Chernobyl NPP Shelter

The results of five-year studies in Shelter subreactor rooms are summarized. At height elevations from 0 to 12 m, the mean volume activity (VA) of 212 Pb-bearing aerosols is about 10 Bq m −3 . The main source of 220 Rn and of its daughter 212 Pb is 232 Th contained in the building structures. The maximal 212 Pb VA is observed in the warm period of a year, and the minimal VA, in the cold period. In ventilation releases through the Bypass system, VA of 212 Pb is 4–5 times lower than in subreactor room. The activity median aerodynamic diameter (AMAD) of 212 Pb-bearing aerosols in most cases was within the range 0.06–0.4 µm. During works in subreactor space, the irradiation via 212 Pb inhalation can amount to 3–5% of the annual effective dose limit (20 mSv) adopted in Ukraine.