ARTICLE | doi:10.20944/preprints201711.0032.v1
Subject: Earth Sciences, Environmental Sciences Keywords: geology; radioactivity; uranium; sampling; Stara Planina
Online: 6 November 2017 (05:13:50 CET)
Stara Planina is known for numerous occurrences and deposits of uranium and associated radionuclides. It is also famous for its geodiversity. The geologic framework is highly complex. The mountain is situated between the latitudes of 43° and 44° N and the longitudes from 22°16′ to 23°00′ E. Uranium exploration and radioactivity testing on Stara Planina began back in 1948. Uranium has also been mined in the zone of Kalna, within the Janja granite intrusive. The naturally-radioactive geologic units of Stara Planina are presented in detail in the paper.
ARTICLE | doi:10.20944/preprints202208.0077.v2
Subject: Earth Sciences, Environmental Sciences Keywords: Uranium; Groundwater; Colorado Plateau; Navajo Nation; Chinle Formation
Online: 23 September 2022 (03:38:21 CEST)
Uranium (U) is enriched in the waters of the southern Colorado Plateau, including waters of the Navajo Nation. The region has naturally occurring U in rocks and a history of U mining which may increase U concentrations in waters. Despite prior research into the concentration of U in the waters of the Navajo Nation, a framework has not been established to understand the variation of U in the region’s groundwater. To this end, we examined data from six studies to establish where and why U is likely to be enriched in waters of the southern Colorado Plateau. We show that U concentrations are related to the presence of U-rich rock bodies, elevation, and local aquifer salinity. Additionally, we show that U concentrations in waters downstream from abandoned U mines are higher than in waters that are not downstream from mines, and that the area around mines has an elevated U concentration relative to background U concentrations. Our work can act as a guide for local water withdrawal, regional water remediation and mitigation efforts, and provides a means for understanding the geographical patterns of U concentration in waters of the southern Colorado Plateau.
ARTICLE | doi:10.20944/preprints201911.0110.v1
Subject: Earth Sciences, Environmental Sciences Keywords: partial extraction; mineral phases; uranium; disequilibrium; retardation factor
Online: 10 November 2019 (13:26:04 CET)
A partial extraction procedure was used to study the distribution of uranium in the mineral phases of rocks of an aquifer of sandy-clay deposits of the Vendian in the northwest of Russia. This work is a part of a research project to develop a method for combined radiocarbon and uranium-isotope dating of groundwater. Representative aliquots of each core sample were subjected to five "partial" extractions by treatment with: distilled water, low mineralized fresh natural groundwater, minopolycarboxylic acid chelating agent (0.05M EDTA), 0.5M HCl, 15M HNO3, and a total digestion, with U isotopes reported in this study for each procedure. The following mineral phases of core samples: adsorbed material, carbonate minerals, amorphous iron oxides, aluminosilicates partial digestion and a crystalline iron oxides, aluminosilicates total digestion and a clay/quartz resistate were characterized. Red-colored siltstones depleted in uranium in relatively readily soluble mineral phases. The concentration of adsorbed uranium was established in the amount of 15.8±2.1 - 30.5±3.9 μg/kg. Carbonate minerals contain even less of this element. In iron hydroxides and the most readily soluble aluminosilicates, its concentrations are in the range 168±24 - 212±28 μg/kg. The most insoluble fraction contains 1.65±0.21 - 4.32±0.45 mg/kg of uranium. In green-colored siltstones, the concentration of adsorbed uranium is much higher: 106±14 - 364±43 μg/kg. Carbonate minerals and amorphous iron oxides contain 1.91±0.21 - 2.34±0.26 mg/kg of uranium. In aluminosilicates and a clay/quartz resistate, uranium concentrations are 5.6±0.5 - 16.8±1.4 mg/kg. Elevated values of 234U:238U activity ratio prevail in the adsorbed material and iron hydroxides. In aluminosilicates and clay/quartz resistate, the values decrease. This indicates the replacement of primary sedimentogenic uranium by secondary hydrogenic uranium adsorbed on the surface of minerals and coprecipitated with iron hydroxides. The results obtained made it possible to carry out preliminary quantitative estimates of the retardation factor and recoil loss factor of uranium in the groundwater of siltstones of the studied Vendian aquifer.
ARTICLE | doi:10.20944/preprints202105.0743.v1
Subject: Physical Sciences, Acoustics Keywords: PERALS; alpha spectrometry; Polonium; Radon; Radium; Radiostrontium; Thorium; Uranium; Actinides
Online: 31 May 2021 (11:16:23 CEST)
In this paper, experiences of the last 20 years with the PERALS-technique are described. PERALS stands for Photo Electron Rejecting Alpha Liquid Scintillation. This LSC-technique was developed by Jack McDowell in the 70ies and is a powerful technique for the analyses of many natural alpha nuclides. The principle is based on a selective extraction of the radionuclide from the water phase by means of a complexing or ion pair reagent. The extractant contains also a suitable cocktail for the scintillation counting. Therefore, the extract can be analysed directly after the extraction step. After removing quenchers, such as oxygen, and the proper setting of a pulse shape discriminator, alpha pulses can be counted with a photomultiplier. The paper describes the development of robust analysis schemes for the determination of traces of polonium, radon, radium, strontium, thorium, uranium and other actinides in water samples (groundwater, rain water, river water, drinking water, mineral water, sea water).
ARTICLE | doi:10.20944/preprints201805.0255.v1
Subject: Chemistry, Other Keywords: magnesium potassium phosphate compound; actinides; rare earth elements; uranium; plutonium; americium; lanthanum; neodymium; immobilization; leaching
Online: 18 May 2018 (06:13:11 CEST)
The problem of effective immobilization of liquid radioactive waste (LRW) is key to the successful development of nuclear energy. The possibility of using magnesium potassium phosphate (MKP) compound for LRW immobilization on the example of nitric acid solutions containing actinides and rare earth elements (REE), including high level waste (HLW) surrogate solution is considered in the research work. Under the study of phase composition and structure of the MKP compounds obtained by the XRD and SEM methods, it was established that the compounds are composed of crystalline phases - analogues of natural phosphate minerals (struvite, metaankoleite). The hydrolytic stability of the compounds was determined according to the semi-dynamic test GOST R 52126-2003. Low leaching rates of radionuclides from the compound are established, including a differential leaching rate of 239Pu and 241Am - 3.5 × 10-7 and 5.3 × 10-7 g/(cm2∙day). As a result of the research work it was concluded that the MKP compound is promising for LRW immobilization and can become an alternative material combining the advantages of easy implementation of the technology like cementation and the high physical and chemical stability corresponding to a glass-like compound.