Analysis of spatial distribution and inventory of radioactivity within the uranium mill tailings impoundment

Abstract

ANALYSIS OF SPATIAL DISTRIBUTION AND INVENTORY OF RADIOACTIVITY WITHIN THE URANIUM MILL TAILINGS IMPOUNDMENTResults are presented of the characterization of radioactivity inventory of Zapadnoe uranium mill tailings impoundment situated at Pridneprovsky Chemical Plant (PChP; Dneprodzerginsk, Ukraine). Analyses of radioactivity data set based on analytical studies of core material from 15 characterization boreholes allowed significantly refining waste volume and radioactivity inventory estimates. Geostatistical analyses using variogram function have established that radioactivity distribution in Zapadnoe tailings is characterized by regular spatial correlation patterns. Ordinary kriging method was applied to assess distribution of radioactivity in 3D. Results of statistical analyses suggest significant redistribution of uranium in the dissolved form in the residues (presumably due to water infiltration process). The developed structural model for radioactivity distribution is used for further risk assessment analyses. Derived radioactivity correlation scales can be used for optimization of sample collection when characterizing the PChP Site and similar contaminated sites elsewhere.

Speciation and mobility of uranium in tailings materials at the U-production legacy site in Ukraine

“…The tailings material from the CY is almost homogeneous with respect to the grain size distribution and represented by sandy-silt fractions with a mean particle size of about 0.03 mm. This is a loose material with a bulk density of 0.75 -0.92 g/cm 3 and an effective porosity of 50 -58 %. The density of the solid phase is practically uniform over the whole profile of the body of the tailings dump and equal to 2 g/cm 3 .…”

“…This is a loose material with a bulk density of 0.75 -0.92 g/cm 3 and an effective porosity of 50 -58 %. The density of the solid phase is practically uniform over the whole profile of the body of the tailings dump and equal to 2 g/cm 3 . Such parameters fully correspond to the material that remains after a technological cycle of the uranium processing.…”

“…The results of the modeling shown in Fig. 6 show that at low pH conditions the uranium predominantly migrates in the form of sulfate UO 2 SO 4 and uranyl carbonate compounds UO 2 CO 3 , UO 2 (CO 3 ) 2 2and UO 2 (CO 3 ) 3 4that occur in a neutral and slightly alkaline pH range. The oxidation-reduction potential (Eh) is one of the key limitation factors of the uranium mobility.…”

“…The main constituent anions in the hydrochemical composition of porewater and ground water within the CY tailings are sulfate-ion (up to 2.6 g/L of SO 4 2-) and hydro-carbonate ion (up to 0.9 g/L of HCO 3 -) The mean composition of rainwater, pore water and Quaternary aquifer is listed in Table 2. Precipitation is the only surface water source within the territory of CY tailings, rainwater does not contain such high values of sulfate-ion compared to ground waters.…”

“…Next drilling companies carried out during 2009 and 2012. The results of studies of this material reported in [1,3,4] allowed to preliminary estimate the vertical profiles of radionuclide distribution in the tailings bodies and consequently to present more accurate radionuclide inventory assessment for the tailings. Physical and chemical speciation of the radionuclides of U/Th series in the tailings materials from this site have also been studied by Protsak and Kashparov [5] and by Marynych et al [6,7].…”