ESTIMATE OF THE DOSE-INCREMENT DUE TO OUTDOOR EXPOSURE TO GAMMA RAYS FROM URANIUM PROGENY DEPOSITED ON THE SOIL AROUND A COAL-FIRED POWER PLANT IN AJKA TOWN, HUNGARY

Abstract— Brown coal unusually rich in uranium is burnt in a coal-fired power plant that lies inside the confines of a small industrial town named Ajka, Hungary, and has been operational since 1943. The 238U (226Ra) activity discharged to the atmosphere per unit electrical energy produced was about 330–400 GBq (GW y)−1, which is 66–80 times more than that was estimated by UNSCEAR (1988) as a characteristic value for old type coal-fired power plants [5 GBq (GW y)−1]. The objective of this study was the experimentally established assessment of the artificial increment in the dose from external exposure to gamma rays of terrestrial radionuclides outdoors. Soil samples were collected in and near Ajka from 81 locations. The samples were investigated by Ge(Li) gamma spectrometry. Considerably elevated concentrations of uranium and its progeny have been measured in most of the samples that were collected near to the plant. Concentrations of 238U and 226Ra in the top (0–5 cm depth) layer of undisturbed soil at public areas inside town were 4.7 times higher, on average, than those in the uncontaminated deeper layers. Dose rate in air (air kerma) from external exposure to terrestrial gamma rays outdoors at a height of 1 m and effective doses were estimated from the measured activity concentrations using some relevant literature data. The estimated artificial increment in the dose rate in air was, on average, 32.8, 10.3, and 102.1 nGy h−1 at public areas, vegetable gardens, and backyards, respectively. The mean artificial increment in the annual per caput effective dose from external exposure to terrestrial radionuclides outdoors is 21.8 &mgr;Sv y−1. The collective dose commitment per unit energy generated from outdoor exposure to the deposited uranium progeny is about 8.0–9.1 person Sv (GW y)−1, which is 67–76 times more than that evaluated by UNSCEAR (1988) for a typical “old” coal-fired power plant [0.12 person Sv (GW y)−1]. Ajka is a suitable place for studying the dosimetric consequences of the utilization of coal for energy production experimentally.