Peculiarities of radioactive soil contamination in places of underground nuclear tests in the Semipalatinsk test site.

The article highlights the results of a radioecological survey of the surface areas of combat boreholes at the Sary-Uzen site located on the territory of the Semipalatinsk Test Site (STS), where underground nuclear tests in these boreholes were conducted earlier. The surface areas of boreholes were examined the levels of radioactive contamination of the soil were determined. A total of 2 main groups were identified. The first group includes boreholes with radioactive contamination of the soil on the surface area. The second group includes boreholes with no radioactive contamination of the surface soil layer. The first group can be divided into boreholes with a deformation of the ground surface and without it. For each variety, depending on the specifics of the nuclear test, the characteristic features of radioactive contamination were determined. Based on the results of the survey, the ranges of specific activity values were established.

Assessment of the tritium distribution in the vegetation cover in the areas of underground nuclear explosions at the Semipalatinsk test site.

This paper provides results of assessment of the tritium distribution in the vegetation cover in the areas of underground nuclear explosions at the Semipalatinsk Test Site (STS). The research was conducted at the former "Degelen" test site along the streams that are one of the main channels of tritium migration from underground nuclear explosions epicenters. The dominant plant species Carex supine and Achnatherum splendens that belong to different ecological groups in relation to humidity were selected as representatives of the vegetation cover. The TFWT (tissue free water tritium) and OBT (organically bound tritium) activity concentrations in the vegetation cover were measurement. TFWT activity concentration in the samples of both plant species had high values with an average of up to 30 kBq kg-1. The OBT activity concentration was 1-2 orders of magnitude lower than the TFWT in all plant samples. The TFWT and OBT activity concentrations in vegetation samples are closely correlated (r = 0.75, p < 0.05). No statistically significant difference was found between the content of tritium in the samples of Carex supine and those of Achnatherum splendens taken at the same locations. OBT/HTO ratios for vegetation samples of both species were close to equilibrium ratio used in environmental transfer models. In some cases, OBT/HTO ratios were significantly lower than one, which indicates that simple environmental transfer models may not accurately predict the behavior of HTO and OBT in different environmental compartments. The average OBT/HTO ratio for soil samples (0.6 ± 0.1) close to the equilibrium value indicates the equilibrium condition at the research area. The obtained [OBT]plant/[OBT]soil ratios indicate that soil organic matter accumulates tritium from year to year. However, in some locations with high tritium contamination ratios [OBT]plant/[OBT]soil were more than one due to OBT activity in soils is almost the same as OBT activity in plants. It was found that the nature of the spatial distribution of tritium in the vegetation cover in the areas of underground nuclear explosions is complex, and obviously depends on the location of the tunnels in which nuclear tests were conducted, as well as on the peculiarities of the hydrological regime of underground and surface waters, which are the main channels of tritium migration in the research area. Thus, the vegetation cover reflects the spatial distribution of tritium contamination in the sites of underground nuclear explosions and can be used as an indicator of the radiation situation when monitoring radiation-hazardous areas.

Development of measures for limiting negative impacts of the «Atomic¼ lake on population and environment.

In arid climate, economic activities at the territory of the "Atomic" lake is one of the topical issues for the Semipalatinsk test site (STS). Hence, the boundaries of areas with radionuclides contamination, which correspond to the level of radioactive wastes at the territory adjacent to the "Atomic" lake of STS, are to be determined. The territory around the lake is used for cattle breeding and the water of the "Atomic" lake that is the one large water source is used for livestock watering. It is important to develop measures that will limit possible negative impact on population and environment. In results of the conducted research were developed measures consisting of remediation and access limitation to the stockpile of soils with contamination level corresponding to the level of radioactive waste (RW).

Mechanisms for surface contamination of soils and bottom sediments in the Shagan River zone within former Semipalatinsk Nuclear Test Site.

The Shagan River is the only surface watercourse within the former Semipalatinsk Test Site (STS). Research in the valley of the Shagan River was carried out to study the possible migration of artificial radionuclides with surface waters over considerable distances, with the possibility these radionuclides may have entered the Irtysh River. The investigations revealed that radioactive contamination of soil was primarily caused by the first underground nuclear test with soil outburst conducted at the "Balapan" site in Borehole 1004. The surface nuclear tests carried out at the "Experimental Field" site and global fallout made insignificant contributions to contamination. The most polluted is the area in the immediate vicinity of the "Atomic" Lake crater. Contamination at the site is spatial. The total area of contamination is limited to 10-12 km from the crater piles. The ratio of plutonium isotopes was useful to determine the source of soil contamination. There was virtual absence of artificial radionuclide migration with surface waters, and possible cross-border transfer of radionuclides with the waters of Shagan and Irtysh rivers was not confirmed.