[en] Fuel-bearing masses (FBM) of the 4-th unit of the Chernobyl NPP represent products of nuclear fuel interaction with structural materials formed as peculiar longwalls during active part of the accident in the southeastern quadrant of the reactor vault bottom. All longwalls are divided into 4 modifications: reddish-brown and black glassy ceramic one; pumiceous one; slaggy granular one; up to 15 cm thickness melted and solidified metal. Fuel content in FBM varies from 2 uo to 18 %, average value of burnup constitutes 11.8 MW·24 hours/kg U. Density of FBM - from 2.2 up to 3.2 g/cm³. Processes of secondary uranium mineral formation which destroy longwalls with formation of water-soluble unstable minerals, occurs in the unit

[en] During the 1979 and 1980 inservice inspections of a Swedish BWR, two indications were detected, which because of their size, position and extent required an accurate mapping. A technically refined examination was performed using lens focused search units with P-scan equipment. The new examination resulted in an accurate determination of the position of the indications, which was one of the stated objectives. Reliable values of the height of the indications were also determined. The extent of one indication, i.e. if the indication consisted of several small, closely adjacent defects, could not be verified. An additional focused sound field was required in this case. (author)

[en] Data obtained using screen electron microscopy and X-ray spectral microanalysis and linked with investigation into hot particles from soil samples of red forest (the nearest zone of right of way of the Chernobyl NPP) collected in 1986-1990. Three main types of hot particles: fuel particles or fuel element fragments (dispersed uranium oxide); fuel and structural particles (fuel element uranium oxide with metallic zirconium, stainless steel, graphite); structural particles, are extracted on the basis of chemical analysis of the composition

[en] Short communication

[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] 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] Active interaction of nuclear fuel and structural metallic zirconium with formation of Zr-U-O melt and of uranium oxide with zirconium impurity occurred due to the accidental process at the Chernobyl NPP. A part of varied nuclear fuel from the accidental unit in the form of uranium oxides with zirconium impurity melted at 2500-2600 deg C. Now no melted stoichiometric uranium dioxide is detected at the 4th unit and it does not allow to prove the temperature excess equal to 2860 deg C

[en] The state of the uranium-lead system in uranium minerals is the determining factor in their use as geological chronometers. X-ray microprobe analysis of uranium minerals was used by the authors to establish that pitchblende differs from brannerite and coffinite in its ability to retain radiogenic lead. In coffinite and bramnerite, active diffusion of the lead takes place regardless of geochemical conditions. Radiogenic lead that leaves the confines of the grains of uranium minerals is sorbed by sulphides. Pitchblende retains radiogenic lead in its lattice for hundreds and thousands of million years. This peculiarity of pitchblende is caused, apparently, by the radiogenic lead entering into chemical combination with the pitchblende lattice. The secondary processes of change in pitchblende cause a redistribution of radiogenic lead and its partial expulsion. When pitchblende is hydrated, uranium is expelled preferentially to lead. (V.Ya.)

[en] Among the geological and geochemical methods for prospecting and searching the nuclear raw material, the isotope-dating methods determine the most important search criterion - the time of the ore-forming. The elaboration and use of these methods in uranium-ore regions reveal a series of geochemical epochs of uranium and thorium accumulation connected naturally with the history of geological evolution of the earth crust. The isotope-dating methods enable with confidence to establish the stages of tectono-magmatic activity resulting in the redistribution and the local concentration of uranium. The wide use of isotopic methods is a necessary condition for reasonable trends of the modern geological exploration