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Formation and properties of Chernobyl "lava": new data on glass matrix and inclusions.

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Title: Formation and properties of Chernobyl "lava": new data on glass matrix and inclusions.
Authors: Shiryaev, Andrey A.1 (AUTHOR) a_shiryaev@mail.ru, Yapaskurt, Vasily O.2 (AUTHOR), Burakov, Boris E.3 (AUTHOR), Averin, Alexey A.1 (AUTHOR), Pavlushin, Anton D.4 (AUTHOR)
Source: Progress in Nuclear Energy. May2026, Vol. 195, pN.PAG-N.PAG. 1p.
Subjects: Electron microscopy, Uranium oxides, Oxidation-reduction potential, Chernobyl Nuclear Accident, Chornobyl, Ukraine, 1986, Spectrometry, Zirconium oxide
Geographic Terms: Chornobyl (Ukraine)
Abstract: Polished samples of Chernobyl "lava" and rich variety of trapped inclusions were studied using complementary spectroscopic methods and by electron microscopy. Spectroscopic properties of the brown "lava" variety in infra-red and visible range are dominated by contribution of nearly stoichiometric (U,Zr)O 2+x (x ≤ 0.05-0.1). At the same time, abundant inclusions of strongly hyperstoichiometric urania are detected using electron microscopy. Their morphology, internal structure (when present) and textural relationships with other included phases indicates partial oxidation of fuel from degraded bundles. Melting and/or liquefaction of hyperstoichiometric urania occur at much lower temperatures than for ideal UO 2 , explaining "molten" appearance of many inclusions. Fuel-cladding interaction prior to the explosion led to formation of monoclinic and tetragonal polymorphs of ZrO 2 with markedly different crystalline quality; the high temperature modifications are stabilized by uranium admixture. These phases were formed on the saturation stage of the interaction. At later stages of the accident, uranium-rich zircon crystals were formed as a result of reaction of the zirconia-based pieces with molten construction materials. Dynamic conditions in the melt pool explain remarkably complex internal structure of some zircon crystals: some of them experienced several growth-dissolution-regrowth events with clear compositional differences between the "growth"-related and "secondary" generations. Partitioning of Nb and Si between droplets of former steel and the surrounding melt allowed estimation of oxygen fugacity in the pool. Strongly reducing conditions down to IW-3.6, where IW – iron-wustite buffer, were present. Implications for the accident scenario are presented. [ABSTRACT FROM AUTHOR]
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Database: Engineering Source
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Abstract:Polished samples of Chernobyl "lava" and rich variety of trapped inclusions were studied using complementary spectroscopic methods and by electron microscopy. Spectroscopic properties of the brown "lava" variety in infra-red and visible range are dominated by contribution of nearly stoichiometric (U,Zr)O 2+x (x ≤ 0.05-0.1). At the same time, abundant inclusions of strongly hyperstoichiometric urania are detected using electron microscopy. Their morphology, internal structure (when present) and textural relationships with other included phases indicates partial oxidation of fuel from degraded bundles. Melting and/or liquefaction of hyperstoichiometric urania occur at much lower temperatures than for ideal UO 2 , explaining "molten" appearance of many inclusions. Fuel-cladding interaction prior to the explosion led to formation of monoclinic and tetragonal polymorphs of ZrO 2 with markedly different crystalline quality; the high temperature modifications are stabilized by uranium admixture. These phases were formed on the saturation stage of the interaction. At later stages of the accident, uranium-rich zircon crystals were formed as a result of reaction of the zirconia-based pieces with molten construction materials. Dynamic conditions in the melt pool explain remarkably complex internal structure of some zircon crystals: some of them experienced several growth-dissolution-regrowth events with clear compositional differences between the "growth"-related and "secondary" generations. Partitioning of Nb and Si between droplets of former steel and the surrounding melt allowed estimation of oxygen fugacity in the pool. Strongly reducing conditions down to IW-3.6, where IW – iron-wustite buffer, were present. Implications for the accident scenario are presented. [ABSTRACT FROM AUTHOR]
ISSN:01491970
DOI:10.1016/j.pnucene.2026.106318