[en] Two independent criteria for evaluation of stability constants of complex compounds calculated from solubility curves are proposed. As a practical example, the complex formation of thorium in oxalate solutions is examined. The reason for the change in the shape of the solubility curve of thorium oxalate hexahydrate in solutions with log (OX) ≥ -2 is suggested to be the polymerization of thorium in solution. The polymerized form is determined to have the composition Th₂(XO)₅^2- with an instability constant of K_2.5 = 8.03·10^-41

[en] A review of existing data reveals that fuel-containing masses (FCM) are reaction products of nuclear fuel and construction materials of the destroyed fourth block of the Chernobyl NPP. They were formed as unique lavas during the active stage of the accident mainly in the southeastern quadrant of the bottom reactor shaft (room 305/2). From here, they took various paths into the subreactor rooms and cooled there. Thus, secondary U mineralization processes that destroy the Chernobyl lavas occur in the Shelter. These phenomena are not connected with any specific conditions of the Shelter (for example, high radiation fields) but are a natural course of geologic processes that occur continuously in the Shelter. The secondary U minerals (epijanthinite, studtite, rutherfordine, etc.) are very unstable chemical compounds. They are soluble in water. This forces a re-examination of the nuclear safety of the Shelter

[en] Results are presented from a study of hot particles in ground samples of the red forest (Chernobyl NPP exclusion zone) that were collected in 1986 and 1990. Scanning electron microscopy and x-ray microprobe analysis were used. The data enable the hot particles to be classified according to their morphology and chemical composition

[en] During an analysis of samples from elephant foot (room 217/2) in 1989, the authors first observed Chernobyl zircon, a unique synthetic crystalline Zr silicate (1) generated through the reaction of Zr from fuel elements, U oxide, and silicate materials. It has an anomalously high U content within the crystal matrix, 6-12 mass % (besides particles of U oxide mechanically captured during its growth). This may possibly be due to isomorphous inclusion of U into the mineral structure after replacing Zr. Natural crystalline zircon with such a high U content is unknown. Impurities of U in them rarely exceed hundredths of a percent. Further study of this mineral enables important information on aspects of the accident processes to obtained. The mineral is typical of all lavas. The brown ceramic contains the maximal amounts

[en] The paper gives the algorithm and the results from computer treatment of data on the solubility of a thorium oxalate hexahydrate precipitate in solutions with various compositions. A new method is proposed for the determination of the solubility product of the precipitate by means of the solubility curve. The stability constants were calculated. The calculations were made on an Elektronika-60 computer

[en] We present the results of investigations of the dependence of the size and shape of americium oxalate crystals on the precipitation conditions (nitric acid content, precipitation temperature, manner in which the precipitating agent is added). We have observed five varieties of americium oxalate crystals. We present the conditions for obtaining americium oxalate crystals which are homogeneous in shape and size

[en] The precipitation of thorium as a poorly soluble oxalate was investigated. An equation relating the concentrations of the metal and nitric acid in the initial solution and the amount of precipitant required to minimize the product losses was derived. A graphical solution of the equation is presented for the case where the precipitant is oxalic acid at a concentration of 0.78 M

[en] In this paper we give the results of investigations on the effect of precipitation conditions on the size and shape of thorium oxalate crystals (concentration of thorium and nitric acid in the solution, precipitation temperature, method of adding the precipitating agent). We show that with an increase in the concentration of nitric acid in the solution from 0.5 to 2.0 moles/liter, the size of the thorium oxalate crystals increases for all the investigated thorium concentrations. Thorium oxalate crystals which are homogeneous in shape and size are obtained at elevated temperature (→90 degree C) when the entire volume of oxalic acid solution is added all at once

[en] Short note

[en] The precipitation of metals in the form of poorly soluble oxalates was investigated. A program which was written for the Elektronika-60 computer makes it possible to calculate the process parameters to minimize the product losses. The obtained relationships were checked for the case of thorium oxalate. The experimental data agreed well with the calculations