Current Assessment of Integrated Content of Long-Lived Radionuclides in Soils of the Head Part of the East Ural Radioactive Trace - Current Assessment of Integrated Stocks of Long-Lived Radionuclides in Soils of the Head Part of the East-Ural Radioactive Trace

The East Ural Radioactive Trace is a result of the accident at the Production Association Mayak in 1957(the Kyshtym accident). The 90Sr was the main contaminant among long-lived radionuclides. Most of it was concentrated in the zone closest to the accident epicentre to the north-west (a narrow sector of about 15 deg., 35 km long). Later, in 1967, the EURT area was contaminated again with air-borne radioactive sediments from Lake Karachay, which had been used by the PA Mayak for storage of liquid radioactive waste. At this case the primary contaminant was 137Cs most of which was spread within 60 deg. sector oriented in the same direction (Aarkrog et al., 1997; Romanov et al., 1990). Our earlier radioecological studies included the assessment of integrated quantities of 90Sr, 137Cs, and 239,240Pu within the central axis of the trace (Pozolotina et al., 2008; Molchanova et al., 2009). The aim of this investigation was the current assessment of integrated stocks of 90Sr, 137Cs, and 239,240Pu in soils of the head part of the EURT along the central axis and the adjacent areas, to map the contamination data of the studied area using established geostatistical models by ArcGIS 9.3 (ESRI, USA). An inventory of the existing data (38 sampling locations) was performed earlier (Molchanova et al., 2009). Currently the database has information on 102 soil profile cuts. Taking into account the presence of global trends and anisotropy in the source data, ordinary kriging interpolation method was used. Geostatistical data analysis was performed for the determination of the basic parameters of spatial dependencies and the integral assessment of long-lived radionuclides in soils of the central, east peripheral, and west one parts of the trace. This analysis employed simplified geometric models (sector- and rectangle-shaped areas). The Monte Carlo technique was used for quantitatively assesses the uncertainty of the integrated stocks to resulting from statistical source data approximation errors. The high values of the stocks of the radionuclides are concentrated in the central part of the trace. They are decreased at west and east from the central axis about hundred times. The radionuclide stocks in soils of the west peripheral area of the trace are 2 to 5 times lower than those in soils of the east one. Mapping of the data we obtained clearly illustrates the spatial distribution of the contamination density of 90Sr, 137Cs, and 239,240Pu within the study area. This research was funded by the Scientific and Technical Program in support of leading scientific schools (SS-5325.2012.4), by the Ural Branch of the RAS (12-?-24-2016). (authors)