The content of natural radionuclides in lignite samples from open pit mines “Kolubara”, Serbia

Abstract

Coal as the most widely used fossil fuel contains traces of naturally occurring radioactivity from uranium and thorium series and 40K. The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) estimated that average concentrations in coal worldwide are 50 Bq/kg for 40K and 20 Bq/kg for both 238U and 232Th (range 5 Bq/kg – 300 Bq/kg). [1] Activity concentrations of naturally occurring radionuclide 40K, 238U and 232Th for tree groups of samples of coal and mineral matter mixed with coal (I (2008 year – 30 samples), II (2009 year – 26 samples) and III (2010 year – 26 samples)) are presented in this paper. Representative samples of different coal quality were especially collected at different locations at open pit mines in RB “Kolubara” which has annual production of 29 millions tones of lignite for the power generation at TPP “Nicola Tesla”, Obrenovac. The samples were pulverized, dried and sealed in Marinelli plastic boxes 0.5 l, and stored for forty days until radioactive equilibrium between 226Ra and its decay products were achieved. All samples were measured by means of coaxial germanium HPGe detector (ORTEC GEM-30, 30 % relative efficiency and 1.8 keV resolution for 60Co at 1332 keV line). The detector was calibrated using standard solutions with radionuclide activities certified by CMI [2]. The experimentally obtained spectra were processed using Canberra’s Genie2000 software. The activity concentrations of 238U and 232Th were determined indirectly from the gamma-rays emitted by their progenies while 40K was determined directly by its gamma-line of 1460.8 keV. It can be seen from this table that the measured coal samples have low activity concentrations and the artificial radionuclides were not detected. The obtained activity concentrations of naturally occurring radionuclides in analyzed coal samples are comparable with those in coals from other countries [3, 4]