ИСТИНА

Fuel-cladding interaction in course of severe accident at Chernobyl NPP Fuel-cladding interaction in real nuclear accidents demonstrate remarkable complexity. In course of our detailed investigation of wide range of materials from accident at Chernobyl NPP in 1986 we were able to observed various stages of the materials transformation. Early stages of fuel-cladding interaction are preserved in “hot” particles expelled from the reactor into the environment and in unique samples collected in under-reactor room; some of the samples also show evidence for reactions between corium and steel. Prolonged contact between pieces of damaged fuel rods with construction materials led to formation of Chernobyl “lava”: silicate-based glassy ceramics with numerous inclusions of U-bearing phases. Investigation of solid phases in “lava” gives unique opportunity to constrain conditions in the melts produced in real nuclear accidents. In particular, formation of an abundant phase - U-rich zircon - remains poorly constrained. We will discuss structural and compositional peculiarities of the samples collected in the under-reactor room. These materials record processes of the fuel-cladding-steel interaction at stages preceding explosion of the reactor. Sub-micron particles comprising PGE, Tc, Te are encountered in the samples. Remarkably, they are devoid of Mo. We also report new spectroscopic and structural data on unique collection of the U-rich zircon crystals extracted from the “lava”. Complex internal structure of zircon reveals domains with widely different concentration of uranium and presence of numerous inclusions represented by (Zr,U)O2, UO2, steel and lava droplets (silicate glass). Detailed examination of textural relationships between the phases unambiguously proves that U-rich zircon was formed during interaction of (Zr,U)O2 with the silicate melt. Polymorphic modification of relic zirconia (monoclinic, tetragonal or even cubic) depends on U content. Concentration of U in zircon depends on concentration of this element in the precursor zirconia.