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

Institute of Occupational Safety, Chengdujska street 25, 1260 Ljubljana-Polje, Slovenia e-mail: peter.jovanovic@zvd.si

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 Boršt, filled with material with high specific activity of ²²⁶Ra. 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 ²³⁸U, ²²⁶Ra or ²¹⁰Pb, 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 ²²⁶Ra calculated values are two times or four times bigger than measured. For ²¹⁰Pb measured values are up to hundred times bigger than calculated. The reason for that is radon in the air, decays to the ²¹⁰Pb, deposited on the grass and not ²¹⁰Pb coming from the soil.