35 D16. Recent Advances in Mineralogy/Crystallography (Posters)

Sunday, 22 September 2019
9:00 AM - 5:30 PM
Hall AB, North Building

PHASES IN THE SYSTEM LN2O3 – TIO2 AS MATRICES FOR ACTINIDE WASTE IMMOBILIZATION

Paper number: 35-7
Program: Technical Sessions
Time: 9:00 AM – 5:30 PM

Authors

  • Sergey V. Yudintsev Presenting Author
    Institute of geology of ore deposits, petrography, mineralogy and geochemistry, Moscow
  • Sergey V. Yudintsev Presenting Author
    Institute of physical chemistry and electrochemistry, Moscow

Abstract

Toxic transuranic actinides (An) generated in a closed nuclear fuel cycle must be isolated from the biosphere for a very long period of time. This term is equal to ten of half-life periods and can vary from a few thousands (Am-241) to tens millions of years (Np-237). Optimal way of management with the radionuclides is their incorporation into durable ceramic compounds (actinides host phases) and disposal in a deep geological repository. New extraction technologies are developed for separation Ln-An fraction from the high level waste (HLW) produced at spent nuclear fuel reprocessing. Here symbol Ln denotes cerium group lanthanides (La, Ce, Nd, Sm, Pr), and An – minor actinides, americium (Am) and curium (Cm), value of mass ratio Ln : An in the waste is close to 30. All these elements predominantly exist as trivalent cations with close radii. So they have similar crystal-chemical, mineralogical, and geochemical properties and can be jointly incorporated into the same host phases. In this work we have analysed properties of the phases produced in the system Ln2O3-TiO2 by sintering or melting-crystallization as possible host for immobilization of the Ln-An fraction. The main attention is paid to the compounds with nominal formulae: Ln2TiO5 (orthorhombic symmetry, space group Pnma), Ln2Ti2O7 (monoclinic, P21), and Ln4Ti9O24 (orthorhombic, Fddd). The results of study of limits of U incorporation into the phases, their response to irradiation and corrosion stability in a hot water are discussed. Taking the data obtained into considiration optimal compounds for immobilization of lanthanide - actinide waste are suggested. This study is supported by the Russian Foundation for Basic Research (project #18-29-12032 mk).

Geological Society of America Abstracts with Programs. Vol. 51, No. 5

doi: 10.1130/abs/2019AM-331248

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