Effect of gamma-irradiation on adsorption properties of Slovak bentonites

One of the basic prerequisites for the use of bentonite as engineering barrier in deep geological repositories for radioactive waste and spent nuclear fuel is their stability against ionizing radiation stemming from radionuclides present in radioactive waste and spent nuclear fuel. The aim of this study was to compare the changes in the adsorption properties of selected Slovak bentonites in relation to uranium fission products (Cs-137 and Sr-90), prior to and after irradiation of bentonites with a Co-60 gamma-source and specifying the changes in the structure of Slovak bentonites induced by gamma-radiation. The changes in irradiated natural forms of Slovak bentonites and the changes in their natrified analogues and fractions with different grain sizes were studied from five Slovak deposits: Jels. Jelsovy potok, Kopernica, Lastovce, Lieskovec and Dolna Ves. The EPR spectra of bentonites from deposits Jelsovy potok and Lieskovec with absorbed doses of 10(4) and 10(5) Gy gamma-rays showed no changes in the structure of the studied Slovak bentonites. The changes, which in terms of structure destabilization can be considered insignificant, occurred only in bentonites with absorbed doses of gamma-radiation as much as 1 MGy. The absorbed dose of 1 MGy gamma-radiation did not have an effect on the adsorption of cesium on every studied bentonite. Changes that can also be regarded as insignificant occurred only during strontium adsorption, especially on Fe-bentonite from deposit Lieskovec and Ca-Mg-bentonite from deposit Jelsovy potok, when an increase in the adsorption capacity occurred. Attention should be paid in further research of this topic which would require carrying out experiments on bentonite samples with absorbed doses higher by several orders of magnitude.