PRINCIPAL FEATURES OF CHERNOBYL HOT PARTICLES: PHASE, CHEMICAL AND RADIONUCLIDE COMPOSITIONS

摘要

1) Most hot particles (from 60 to 80 %) in highly contaminated Chernobyl areas have matrices consisted of multi-grain aggregates or single grains of UO_x phase, probably, U_4O_9. The mechanical durability of relatively large (50-150 μm) particles is not high, and they might be degraded in the environment over time to single grains 5-30 μm in size. Five years after Chernobyl accident no evidences of essential alteration of single-grain fuel particles by the environment were observed. 2) Although, some fuel hot particles are characterized by unusual radionuclide ratios, in general, their radionuclide and chemical composition can be considered as the same to initial irradiated Chernobyl fuel. 3) Fuel-constructional hot particles represent up to 40 % of all hot particles in highly contaminated Chernobyl areas. These particles are characterized by complex phase and chemical composition what should be taken into account for modeling of radionuclide migration from their matrices. Bulk radionuclide composition of fuel- constructional particles is similar to initial irradiated Chernobyl fuel but the radionuclide ratios of single particles are significantly different. 4) The following main phases were identified in the matrices of fuel-constructional hot particles: UO_x (the same to U-oxide phase in fuel particles); UO_x with Zr (contained from 60 to 80 wt.% U and from 22 to 5 wt.% Zr); Zr-U-O (contained from 33 to 51 wt. % Zr and from 47 to 29 wt.% U) and metallic alloy Fe-Cr-Ni (molten stainless steel). 5) Metallic phase Fe-Cr-Ni in fuel-constructional hot particles is responsible for accumulation of such radionulcides as: ~(106)Ru, ~(125)Sb and ~(60)Co. 6) Chemical durability of Zr-bearing phases and Fe-Cr-Ni-alloy found in the matrices fuel-constructional hot particles are essentially higher then UO_x phase.