[en] To detect interrelations between boltwoodite and weeksite from the regions of their joint segregation an attempt has been made to study the above uranium silicates by means of scanning electron microscopy. Investigations have been carried out with the Phillips 501-B device comprising the adax 91-00 microanalysing adapter. Large plate and columnar crystals and their growths of boltwoodite, where bunched weeksite concentrations precipitate, are distictly traced. A lot of bolt woodite crystals represent only a coating filled with weeksite formed due to its destruction. Data on boltwoodite and weeksite composition are obtained. Coincidence of mineral microsegregation visualization with their analysis turns out well for the ferst time

[en] Radioactive carbonaceous matter, possibly of organic origin, with coffinite inclusions (U(SiO₄)_I-x(OH)_4x) are reported for the first time in the fractures within the core samples of highly deformed Bundelkhand granitoids in the Gwalior basin. Intense hydrothermal alterations along these fractures are manifested in the form of silicification, argillic alteration (clay formation), chloritisation, ferruginisation and by sulphide formation. The globular radioactive cabonaceous matter is of organic origin and generally associated with silica rich veins. Globular nature of this cabonaceous matter indicates their formation from coagulation of smaller colloids in a low temperature hydrotherm. Mixing of descending oxidizing hydrotherm derived from basinal fluid rich in heavy metals, uranium, organic matter and ascending reducing fluid (hydrotherm) rich in H₂S and Si in these fracture zones has resulted in the precipitation of sulphides, secondary quartz, carbonaceous material and coffinite. (author)

[en] Present article is devoted to industrial opportunities of processing of uranium ores of Tajikistan. The mineral content of uranium ores was defined.

[en] Eight phases (U, U₃Si, U₃Si₂, USi, U₂Si₃, USi₂, USi₃ and Si) are reported to occur in the uranium-silicon system. This report describes the preparation of samples corresponding in composition to these phases, and the identification of each phase using the electron microprobe. The phases were characterized with respect to distribution, etching behaviour and microhardness. The results permit identification of the phases without using the electron microprobe. (author)

[en] Studied are relations of oxides and silicate phases of uranium mineralization in ores of stratiform manifestation of a new genetic type formed by deposition with endogenic source of ore substance. The ore manifestation is localized in the upper volcanogenic sedimentary structural stage of intermountain late orogenic basin with Caledonian folded base. Uranium-arsenide mineralization is localized in lacustrine deposits of Famennian stage and are controlled by consedimentational dislocations. It represents the mixture of oxide-silicate uranium minerals containing coffinite and pitchblende. X-ray analysis of samples has confirmed the presence of uraninite fine dispersion phase, native lead and amorphous silica formed as a result of coffinite metamict decomposition as well as coffinite recrystallization phenomenon due to oxide-silicate uranium ore mass. Such intertransformations of oxide and silicate phases were determined earlier at hydrothermal uranium deposits. Their investigation permits to determine genetic, geochemical and technological features of uranium ores

[en] The effects of fabrication and heat treatment variables on the structure of a uranium -- 3.96 wt% silicon alloy have been studied using optical microscopy, quantitative metallography and hardness determinations. It has been shown that an optimum temperature exists below the peritectoid temperature where the maximum amount of transformation to U₃Si occurs in a given period of time. The time required to fully transform an as-cast alloy at this optimum temperature is affected by the size of the primary U₃Si₂ dendrites. With a U₃Si₂ particle size of <12 μm complete transformation can be achieved in four hours. (author)

[en] Published in summary form only

[en] Analysis on microstructure and hardness of U₃Si₂-AI fuel element plate of 3.6 g/cm3 have been carried out using SEM/EDS hardness tester respectively. The fuel plates of 3.6 g/cm3 uranium loading were heated respectively at 600 ^oC, 900 ^oC, and 1400 ^oC in DITA furnace with in the argon atmosphere. Selection of those temperatures were based on the occurring thermic reaction and the fuel plate that causes phase transformation and new compound formation. Presumably the new compound will affect microstructure and hardness of fuel plate. Therefore it will be analyzed under this experiment the effect of heating temperature against the change of microstructure and hardness of the fuel element. Metallographic preparation was conducted on samples which have been heated in DTA and followed later with analysis on its microstructure and hardness. The result show that in heating temperature of 600 ^oC interaction between molten AI-matrix and AIMg2 cladding with U₃Si₂ meat occurred. Molten AI-matrix enclosed U₃Si₂ meat to from small agglomeration. The higher rise of the heating temperature the bigger agglomeration was formed. While from the hardness analysis, it was shown that the higher rise of heating temperature the lower hardness of fuel plate was found. This microstructure and hardness data of fuel plate is hoped could be used in studying phenomena happened in U₃Si₂ fuel plate caused by thermic reaction and as an input or manufacturer of research reactor fuel element and manufacturing silicide fuel elements with higher uranium loading. Key words : U₃Si₂-AI fuel element plate, temperature changes, microstructure, and hardness

No abstract available

[en] Coffinite, USiO₄, is the second most abundant U⁴⁺ mineral on Earth, and its formation by the alteration of the UO₂ in spent nuclear fuel in a geologic repository may control the release of radionuclides to the environment. Despite its abundance in nature, the synthesis and characterization of coffinite have eluded researchers for decades. On the basis of the recent synthesis of USiO₄, we can now define the experimental conditions under which coffinite is most efficiently formed. Optimal formation conditions are defined for four parameters: pH, T, heating time, and U/Si molar ratio. The adjustment of pH between 10 and 12 leads probably to the formation of a uranium(IV) hydroxo-silicate complex that acts as a precursor of uranium(IV) silicate colloids and then of coffinite. Moreover, in this pH range, the largest yield of coffinite formation (as compared with those of the two competing byproduct phases, nanometer-scale UO₂ and amorphous SiO₂) is obtained for 250 C, 7 days, and 100% excess silica. (authors)