Speciation of 137Cs, 90Sr, 241Am, and 239+240Pu artificial radionuclides in soils at the Semipalatinsk test site.

This paper reports the speciation of 137Cs, 241Am, 90Sr and 239+240Pu 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 137Cs was revealed to be below 98%, that of 90Sr - 94%, 241Am - 89%, and 239+240Pu - 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 90Sr forms in soils, as well as the content of the water-soluble salts and the content of the strongly bound 239+240Pu 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 137Cs and 90Sr, which are in a tightly bound form in the soils of the Experimental Field site, the main content of soil "competitors" of the 137Cs radionuclide - K and Cs is observed in an exchange form, less significantly in an acid-soluble form. The alkaline earth metals (analogous elements for 90Sr) 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.

Transfer parameters of radionuclides from soil to plants at the area of craters produced by underground nuclear explosions at the Semipalatinsk test site.

A study to determine 137Cs, 90Sr, 241Am, 239+240Pu radionuclides in vegetation cover of the area of craters produced by underground nuclear explosions at the Semipalatinsk test site (STS) is summarised in this paper. Transfer factors (Tf) required for the quantitative description of the radionuclides transition from the soil to aboveground plant parts were found to be highest for sagebrush (Artemisia sublessingiana), Tf values for 90Sr were gradually decreasing with increasing distance from the dump zone. When arranging the radionuclide transferring factors in descending order, the following sequence was obtained: 90Sr Tf > 137Cs Tf > 241Am Tf > 239+240Pu Tf, which is consistent with International data. All Tf derived are much higher than those ones derived earlier for epicenters of aboveground nuclear tests and are closest to values for conventionally "background" areas at the Semipalatinsk test site.

Radioactive particles released from different sources in the Semipalatinsk Test Site.

A total of 456 nuclear tests were performed from 1949 to 1989 at the Semipalatinsk Test Site (STS) in Kazakhstan, as part of the nuclear weapon test program of the USSR. To identify if radionuclides such as 137Cs, 90Sr, 241Am, 239+240Pu were associated with radioactive particles, soil samples were collected at selected contaminated sites (i.e. Experimental field, Excavation sites, Fallout plume sections, Background global fallout area, and Degelen Mountain) within the STS. A series of techniques have been applied to identify the size distributions of radionuclides, the prevalence of radioactive particles in soils, and the degree of leachability of particle associated radionuclides by different agents. In addition, selected particles were characterized non-destructively using digital autoradiography, environmental scanning electron microscopy (ESEM) and synchrotron radiation microscopic X-ray techniques. Radioactive particles were identified at all sites; large vitrified particles were identified at epicenters, and the size of particles decreased along the plume with distance from the epicenters. The radioactive particles identified varied in composition, size and leachability. In general, 137Cs, 241Am, 239+240Pu were strongly associated with solid phases (90-99%) in soils, while 90Sr exhibited much greater variability. The fraction of 90Sr present in exchangeable forms was low close to epicenters, while the extractability increased along the plume as the particle size distribution decreased. The results suggest that at least four different types of radioactive particles are present at STS: 1) Relatively large spherical particles with a shiny glazed, melted surface with internal porous structure, and surface layers enriched in transuranic elements, identified at epicenters of detonations, 2) Vitrified irregular particles probably originating from debris of nuclear device with interactions from soil components, also identified at epicenters of detonations, 3) Particles with visually unchanged structure, containing micro-inclusions of fissile materials associated with soil components, also identified at epicenters; 4) Particles with amorphous structures associated with underground detonations, identified in soil in the vicinity of the entrance of the detonation tunnels at the Degelen Mountain. These were probably formed by secondary mechanisms due to sorption and fixation of radionuclides. Thus, the present work shows that the STS should be considered an important observatory site to link particle characteristics to specific sources and to release conditions as well as to ecosystem transfer of particle associated radionuclides.

Transfer of radionuclides to plants of natural ecosystems at the Semipalatinsk Test Site.

A systematic study devoted to 137Cs, 90Sr, 241Am, 239+240Pu radionuclides in vegetation cover from several spots of the Semipalatinsk test site (STS) is summarised in this paper, highlighting the main findings obtained. The analysed spots are characterized by various types of radioactive contamination. Transfer factors (Tf) required for the quantitative description of the radionuclides transition from the soil to aboveground plant parts were determined, being found that, on average, the minimum Tf for all the radionuclides concerned were determined on the "Experimental Field" ground, followed by the determined ones in the "plumes" of radioactive fallout and in the conditionally "background" territories analysed. The highest transfer factors were characteristic of zones of radioactive streamflows and places of warfare radioactive agent (WRA) tests. On the other hand, ordering the radionuclide transferring factors in descending order, the following sequence was obtained: 90Sr Tf > Cs Tf > 239+240Pu Tf > 241Am Tf, with the 90Sr Tf, on the average, exceeding the 137Cs Tf by 8 times and exceeding the 239+240Pu Tf by up 16 times. 239+240Pu Tf values were up to 3 times higher than the 241Am Tf. The exception to the indicated radionuclide Tf descending order corresponded to places of WRA tests where Tf of radionuclides of interest by plants follows the sequence 90Sr > 239+240Pu > 137Cs.

Distribution of artificial radionuclides in particle-size fractions of soil on fallout plumes of nuclear explosions.

In this paper are analyzed the artificial radionuclide distributions (137Cs, 90Sr, 241Am, 239+240Pu) in particle-size fractions of soils from two radioactive fallout plumes at the Semipalatinsk Test Site. These plumes were generated by a low-yield surface nuclear test and a surface non-nuclear experiment with insignificant nuclear energy release, respectively, and their lengths are approximately 3 and 0,65 km. In contrast with the great majority of similar studies performed in areas affected mainly by global fallout where adsorbing radionuclides such as Pu are mainly associated with the finest soil fractions, in this study it was observed that along both analyzed plumes the highest activity concentrations are concentrated in the coarse soil fractions. At the plume generated by the surface nuclear test, the radionuclides are concentrated mainly in the 1000-500 µm soil fraction (enrichment factor values ranging from 1.2 to 3.8), while at the plume corresponding to the surface non-nuclear test is the 500-250 µm soil fraction the enriched one by technogenic radionuclides (enrichment factor values ranging from 1.1 to 5.1). In addition, the activity concentration distributions among the different soil size fractions are similar for all radionuclides in both plumes. All the obtained data are in agreement with the hypothesis indicating that enrichment observed in the coarse fractions is caused by the presence of radioactive particles resulted from the indicated nuclear tests.