220Rn as an additional factor of radiation hazard in the Shelter

In 2003–2007, the content of 212 Pb ( 220 Rn daughter product) inside the Shelter was, as a rule, in the range 0.5–5 Bq m −3 . No seasonal and time dynamics of the 212 Pb concentration and no relationship with the technical activity were revealed. At simultaneous sampling of aerosols, the volume activities of 212 Pb in the bypass were higher by 1–2 orders of magnitude than in the surrounding medium (local zone). Hence, the sources of 220 Rn emanation, in particular, 232 U are inside the Shelter. Among 220 samples taken in the bypass, 94% had the activity median aerodynamic diameter of aerosol particles bearing 222 Rn and 220 Rn daughter products in the range from 0.05 to 0.4 μm. For the Shelter staff members, 222 Rn and 220 Rn daughter products, and also submicron size of their carriers are negative factors which were not taken into account previously when determining ionizing irradiation doses. The additional inhalation doses can reach tens of percents of the permissible annual dose.