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

Resumo

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 ²¹²Pb-bearing aerosols is about 10 Bq m⁻³. The main source of ²²⁰Rn and of its daughter ²¹²Pb is ²³²Th contained in the building structures. The maximal ²¹²Pb 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 ²¹²Pb is 4–5 times lower than in subreactor room. The activity median aerodynamic diameter (AMAD) of ²¹²Pb-bearing aerosols in most cases was within the range 0.06–0.4 µm. During works in subreactor space, the irradiation via ²¹²Pb inhalation can amount to 3–5% of the annual effective dose limit (20 mSv) adopted in Ukraine.