Analysis of Radioactivity Concentration in Naturally Occurring Radioactive Materials Used in Coal-Fired Plants in Korea

국내 석탄연소 발전소에서 취급하는 천연방사성물질의 방사능 농도 분석

Coals and coal ashes, raw materials and by-products, in coal-fired power plants contain naturally occurring radioactive materials (NORM). They may give rise to internal exposure to workers due to inhalation of airborne particulates containing radioactive materials. It is necessary to characterize radioactivity concentrations of the materials for assessment of radiation dose to the workers. The objective of the present study was to analyze radioactivity concentrations of coals and by-products at four coal-fired plants in Korea. High purity germanium detector was employed for analysis of uranium series, thorium series, and potassium 40 in the materials. Radioactivity concentrations of $^{226}Ra$, $^{228}Ra$, and $^{40}K$ were $2{\sim}53Bq\;kg^{-1}$, $3{\sim}64Bq\;kg^{-1}$, and $14{\sim}431Bq\;kg^{-1}$ respectively in coal samples. For coal ashes, the radioactivity concentrations were $77{\sim}133Bq\;kg^{-1}$, $77{\sim}105Bq\;kg^{-1}$, and $252{\sim}372Bq\;kg^{-1}$ in fly ash samples and $54{\sim}91Bq\;kg^{-1}$, $46{\sim}83Bq\;kg^{-1}$, and $205{\sim}462Bq\;kg^{-1}$ in bottom ash samples. For flue gas desulfurization (FGD) gypsum, the radioactivity concentrations were $3{\sim}5Bq\;kg^{-1}$, $2{\sim}3Bq\;kg^{-1}$, and $22{\sim}47Bq\;kg^{-1}$. Radioactivity was enhanced in coal ash compared with coal due to combustion of organic matters in the coal. Radioactivity enhancement factors for $^{226}Ra$, $^{228}Ra$, and $^{40}K$ were 2.1~11.3, 2.0~13.1, and 1.4~7.4 for fly ash and 2.0~9.2, 2.0~10.0, 1.9~7.7 for bottom ash. The database established in this study can be used as basic data for internal dose assessment of workers at coal-fired power plants. In addition, the findings can be used as a basic data for development of safety standard and guide of Natural Radiation Safety Management Act.