Radiological impact of surface water and sediment near uranium mining sites

The aim of this study is to assess the radiological impact of surface water and sediment around uranium mining sites 20 years after their closing. The areas under observations are 31 former classical underground uranium mining and exploratory sites in Bulgaria, named as objects. The extraction and processing of uranium ores in the Republic of Bulgaria were ended in 1992. To assess the radiological impact of radionuclides field expeditions were performed to sample water and bottom sediment. The migration of uranium through surface water was examined as one of the major pathways for contamination spread. The range of uranium concentration in water flowing from the mining sites was from 0.012 to 6.8 mgU l −1 with a geometric mean of 0.192 mgU l . The uranium concentrations in water downstream the mining sites were approximately 3 times higher than the background value (upstream). The concentrations of U nat , 226 Ra, 210 Pb, and 232 Th in the sediment of downstream river were higher than those upstream by 3.4, 2.6, 2, and 1.7 times, respectively. The distribution coefficient of uranium reflects its high mobility in most of the sites. In order to evaluate the impact on people as well as site prioritization for more detailed assessment and water management, screening dose assessments were done

Measurements of outdoor radon concentration over 24-hour periods in different settlements in Bulgaria

This work presents the results of continuous radon measurements in open atmosphere, including measurements of air humidity, temperature, pressure and gamma dose rate, in 11 different settlements of Bulgaria. Using AlphaGuard equipment, measurements were made in mountain, spas, plain, sea level and uranium mining environments in the summer period, in series of 10-min intervals over 24 hours., . The analysis of results showed different daily variation among the outdoor radon measurements in different measuring sites. The outdoor radon concentrations ranged from 22 Bq.m−3 (city in lowland) to 180 Bq.m−3 (uranium mining site Eleshnica). Outdoor radon levels were found to be increasing during the night by a factor of 1.5 (in 9 locations), factor 2 (location at sea level) and factor 1 (location in the plain). The relation between outdoor radon concentrations and meteorological factors as well with gamma dose rate was observed

Radiological impact of surface water and sediment near uranium mining sites

The aim of this study is to assess the radiological impact of surface water and sediment around uranium mining sites 20 years after their closing. The areas under observations are 31 former classical underground uranium mining and exploratory sites in Bulgaria, named as objects. The extraction and processing of uranium ores in the Republic of Bulgaria were ended in 1992. To assess the radiological impact of radionuclides field expeditions were performed to sample water and bottom sediment. The migration of uranium through surface water was examined as one of the major pathways for contamination spread. The range of uranium concentration in water flowing from the mining sites was from 0.012 to 6.8 mgU l −1 with a geometric mean of 0.192 mgU l . The uranium concentrations in water downstream the mining sites were approximately 3 times higher than the background value (upstream). The concentrations of U nat , 226 Ra, 210 Pb, and 232 Th in the sediment of downstream river were higher than those upstream by 3.4, 2.6, 2, and 1.7 times, respectively. The distribution coefficient of uranium reflects its high mobility in most of the sites. In order to evaluate the impact on people as well as site prioritization for more detailed assessment and water management, screening dose assessments were done

Radon measurement in schools and kindergartens (Kremikovtsi municipality, Bulgaria

Indoor radon concentration was measured in all schools (n = 9) and kindergartens (n = 7) of Kremikovtsi district, Bulgaria, using passive integrating electret detectors. The study was based on two successive: short and long term set measurements. In first phase, the short term detectors were deployed in all frequently occupied rooms in ground floor. The exposure was during the summer vacation (2011) under close condition with 10 days duration. From the results of short term measurement we have found that the radon concentration in 4 schools and 5 kindergartens were above the recommended National level of 300 Bq m-3 for existing buildings. In order to confirm the initial shortterm measurement long-term measurements for the period from September 2011 to April 2012, in the same buildings of schools and kindergartens were performed under normal functional conditions (second phase). Comparing the results obtained from the short-term measurements under close conditions with the results of long-term measurement, we found that measured values were in correlation (R = 0.817)

Pilot survey of indoor radon in the dwellings of Bulgaria

The first systematic indoor radon survey in four districts of Bulgaria was performed. Three hundred and seventy-three selected ground floor dwellings were measured using the nuclear track detectors during 6 months, from October 2011 to May 2012. It was found that indoor radon concentration varied between 20 and 3560 Bq m−3 with median value of 90 Bq m−3. The fractions of dwellings in four districts: Sofia city, Sofia districts, Plovdiv and Varna above the reference levels of 300 Bq m−3 were 3, 9, 14 and 5 %, respectively. Each data set does not follow a log–normal distribution at a significance level of 95 %. The results of the analysis of the variance showed statistically significant differences among the indoor radon concentrations for the regions between urban and rural municipalities as well for the building with and without basement. These results may be utilised to set up the methodology for a more systematic survey in Bulgaria

Screening for risk assessment around closed uranium mining sites

The aim of this study is to present the environmental impact and health risk 20 years after the closing of the uranium mining industry. The areas under observation are 31 former classical underground uranium mining and exploratory sites in Bulgaria. The geometric mean value of the gamma dose rate (0.33 μSv h-1), measured 1 m above ground in the mining sites, was three times higher than the mean of the gamma dose in the nearby settlements (0.11 μSv h-1). The geometric mean of specific activities for 238U, 226Ra, 232Th, 40K and 210Pb in mining site soil was found to be: 437 Bq kg-1, 291 Bq kg-1, 65 Bq kg-1, 835 Bq kg-1 and 318 Bq kg-1, respectively. Analysis of variance and correlation were applied. The external dose and offsite external hazard index, as health risk indicators, were estimated based on the results. After twenty years there is still environmental contamination in some locations that may cause a health risk, so remediation and monitoring should continue and be maintained

Measurements of indoor radon concentration in kindergartens in Sofia, Bulgaria

As a part of the systematic survey of indoor radon in Bulgaria, indoor radon concentration was measured in 292 kindergartens buildings of Sofia city during 3 month (January – April), 2013 using the CR-39 nuclear tracts detectors. In any building at least two frequently occupied rooms (mainly playrooms) were observed. Altogether 922 measurements were performed. The frequency distribution was well described by the lognormal function. The measured radon concentrations range between 9 and 1415 Bq m-3 with a geometric mean of 101 Bq m-3 (2.08) and arithmetic mean 132 Bq m-3 with a standard deviation of 118 Bq.m-3. The radon concentrations obtained in this survey were compared with radon concentration in Sofia dwellings obtained from previous study. A detailed statistical analysis of the building factors was present

Analysis of the spatial variation of indoor radon concentrations (national survey in Bulgaria)

This paper presents the methodology and results of the national radon survey in Bulgaria and its spatial variability. The measurements were carried out in 2778 dwellings using CR-39 track detectors over two successive 9 and 3-month periods from April 2015 to March 2016. The arithmetic (AM) and geometric (GM) means of annual indoor radon concentration were 111 ± 105 Bq/m3 and 81 Bq/m3 (GSD = 2.15), respectively. The distribution of data has been accepted to be log-normal. Two hypotheses have been investigated in the paper. The first one was a spatial variation of indoor radon concentration and the second was spatiality of the factor that influences radon variation. The indoor radon concentrations in the 28 districts have been significantly different, which prove the first hypothesis. The influence of the factors, geology (geotectonic unit, type of rock, and faults distance of the measuring site), type of the region, and the presence of the basement in the building on radon spatial variation, was examined. The analyses have been shown that they significantly affect radon variations but with a relatively small contribution in comparison to the radon variation between district. Furthermore, the significance and contribution of the investigated factors were different in each district, which confirmed the second hypothesis for their spatiality