ASSESSMENT OF RESIDENTIAL RADON EXPOSURE IN BULGARIA.

In the light of the new ICRP requirements the first National radon survey has been conducted in Bulgaria in the period 2015-16. Indoor radon concentrations were measured for 1 y in 2778 dwellings of whole Bulgarian territory in order to obtain the systematic data for the distribution of radon. The arithmetic mean is 111 Bq m-3 and the geometric mean is 81 Bq m-3 with geometric standard deviation of 2.15. On the base of the data, an annual effective dose to the Bulgarian population due to indoor radon exposure was estimated at 5.2 mSv and excess lifetime cancer risk at about 2%. The evaluation has been made using the ICRP dose coefficient of 6.7 × 10-6 (mSv h-1)/(Bq m-3), 7000 h occupancy per year and value of 0.4 for the equilibrium factor. This preliminary assessment allows consideration and planning the long-term appropriate radon and exposure reduction measures in the new national action plan.