Speciation of Cs, Sr, Am, and Pu artificial radionuclides in soils at the Semipalatinsk test site.

This paper reports the speciation of Cs, Am, Sr and Pu in the soil samples of the Experimental Field (EF). The EF is a testing ground of the Semipalatinsk nuclear weapons test site used for surface and atmospheric tests. The study revealed low mobility of artificial radionuclides in the EF site soils. The revealed high radionuclide concentrations in soil mainly exist in tightly bound form. On average, the content of the tightly bound form of Cs was revealed to be below 98%, that of Sr - 94%, Am - 89%, and Pu - 98%. The radionuclides occurrence forms were analyzed in correlation with the physicochemical parameters of soils. Reliable relationships have been established between the content of carbonates and the content of the exchangeable, acid-soluble and strongly bound Sr forms in soils, as well as the content of the water-soluble salts and the content of the strongly bound Pu form in the soil. Similarly, we compared the distributions of the radionuclides speciation and their stable isotopes with their analogous elements in the soil. Unlike Cs and Sr, which are in a tightly bound form in the soils of the Experimental Field site, the main content of soil "competitors" of the Cs radionuclide - K and Cs is observed in an exchange form, less significantly in an acid-soluble form. The alkaline earth metals (analogous elements for Sr) are mainly observed as a composition of the exchangeable and acid-soluble forms. The results allow to conclude that there is no equilibrium distribution of the physicochemical forms of radionuclides introduced into the soil and the natural presence forms of their stable analogs in the soil. Such equilibrium distribution can only be achieved at a complete isotopic exchange in phases and soil components, which under the conditions of the Experimental Field is not possible in the near future. It can be concluded that the behavior of the studied radionuclides in soils is stipulated by the initial form delivered by the fallouts from tests at the EF site.