Estimation of radon exhalation rate, natural radioactivity and radiation doses in fly ash samples from Durgapur thermal power plant, West Bengal, India

Coal and its by products often contain significant amounts of radionuclides, including uranium which is the ultimate source of the radioactive gas radon. Burning of coal and the subsequent emission to the atmosphere cause the re-distribution of toxic trace elements in the environment. Due to considerable economic and environmental importance and diverse uses, the collected fly ash has become a subject of worldwide interest in recent years. In the present study, radon exhalation rate and the activity concentration of 238U, 232Th and 40K radionuclides in fly ash samples from Durgapur thermal power plant (WB) have been measured by “Sealed Can technique” using LR-115 type II detectors and a low level NaI (Tl) based gamma ray spectrometer, respectively. Radon exhalation rate varied from 360.0 to 470.0 mBq m−2 h−1 with an average value of 406.8 mBq m−2 h−1. Activity concentrations of 238U ranged from 84.8 to 126.4 Bq kg−1 with an average value of 99.3 Bq kg−1, 232Th ranged from 98.1 to 140.5 Bq kg−1 with an average value of 112.9 Bq kg−1 and 40K ranged from 267.1 to 364.9 Bq kg−1 with an average value of 308.9 Bq kg−1. Radium equivalent activity obtained from activity concentrations is found to vary from 256.5 to 352.8 Bq kg−1 with an average value of 282.5 Bq kg−1. Absorbed gamma dose rates due to the presence of 238U, 232Th and 40K in fly ash samples vary in the range 115.3–158.5 nGy h−1 with an average value of 126.4 nGy h−1. While the external annual effective dose rate varies from 0.14 to 0.19 mSv y−1 with an average value of 0.15 mSv y−1, effective dose equivalent estimated from exhalation rate varies from 42.5 to 55.2 μSv y−1 with an average value of 47.8 μSv y−1. Values of external hazard index Hex for the fly ash samples studied in this work range from 0.69 to 0.96 with a mean value of 0.77.