INDOOR RADON MEASUREMENT IN FORMER URANIUM MINING REGIONS IN BULGARIA

Abstract

Radon exposure situations have the characteristics of existing exposure situations since the source is unmodified concentrations of ubiquitous natural activity in the earth’s crust. Human activities may create or modify pathways increasing indoor radon concentration compared to outdoor background. The mining and processing of uranium bearing minerals generate a variety of waste materials containing a number of radioactive and non-radioactive hazardous constituents. Conventional underground and open pit mining activities produce overburden, mineralized waste and barren waste rock, which are generally low in their uranium and thorium contents and are left at the mine site. The study focuses on regions of former uranium mining industries, where the radiological risk is higher. Methods: The cumulative (passive) method was used for the study. The measurements are carried out by E PERM® system. Detectors are placed for approximately 6 months in randomly selected houses in former uranium mining sites - Sliven-villages area, Eleshnica and Bachkovo. These sites are situated in mountains in different part of Bulgaria. Results: The results of indoor radon concentration for investigation villages range from 125 Bq/m3 to 4000 Bq/m3. The maximum concentration was measured in Bachkovo village in Rodopi Mountain. This village is the least affected by the former uranium mining industry. Conclusion: The results prove assumption that former uranium mining sites are radon prone areas where radiological risk is higher. The level of indoor radon of residential buildings in areas with higher uranium availability is around or above the recommended reference radon levels. The maximum value of the concentration of radon is measured in areas less affected by uranium mining, proving the necessity to undertake a radon national survey to determine exact radon prone areas. Key words: Radon concentration, long-term measurement, radon prone areas