Transfer of natural radionuclides from soil to the grass around uranium mine area Žirovski vrh, Slovenia

Abstract

Uranium mine Žirovski vrh in Slovenia was closed in the year 1993. In the past years a lot of work was done for restoration of the area around the mine. There are two tailing sites, Jazbec and Borst, filled with material with high specific activity of 226 Ra. Tailings are covered by different layers of clay and soil in depth of 2 m for reducing radon exhalation rate. Gras, growing on the surface of tailing sites has been used as fodder for domestic animals. We were interesting about the amount of the specific activity of natural radionuclides 238 U, 226 Ra or 210 Pb, transferred from the covering soil on the tailing to the grass on the surface area. The transfer factors of naturally occurring radionuclides have not been studied to the same extent as their artificial counterparts, but some comprehensive investigations have been done by various institutions around the world. In case of 226 Ra calculated values are two times or four times bigger than measured. For 210 Pb measured values are up to hundred times bigger than calculated. The reason for that is radon in the air, decays to the 210 Pb, deposited on the grass and not 210 Pb coming from the soil.