Abstract
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.
Highlights
The Semipalatinsk Test Site (STS), located in the North-East of Re public of Kazakhstan, was the first and the main proving grounds for the testing of nuclear weapons by the former Soviet Union
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, identified at epicenters of detonations, 3) Particles with visually unchanged structure, containing micro-inclusions of fissile materials associated with soil components, 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
Focus has been put radioactive particles produced by a number of nuclear tests, and the potential mobility and bioavailability of particle associated ra dionuclides of relevance for radiation impact assessments
Summary
The Semipalatinsk Test Site (STS), located in the North-East of Re public of Kazakhstan, was the first and the main proving grounds for the testing of nuclear weapons by the former Soviet Union. The test site, situated 150 km west of Semey city, extends over an area of 18,300 km i.e., a territory comparable in size to Slovenia. A total of 456 nuclear weapon tests (616 nuclear devices) were performed from 1949 until 1989, including atmospheric air-drop or tower shots and underground shots in boreholes and tunnels. The first bomb was con ducted in 1949 from a tower at the “Experimental field” at STS. The majority of tests was performed before 1963 (Test ban treaty), when the atmospheric tests were replaced by underground nuclear explosions (Lukashenko et al, 2017, Nazarbayev et al, 2016)
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