Aluminosilicate-Phosphate Model of Polyphase Matrices for Immobilization of Sr-Cs-fractions of Nuclear Fuel Cycle HLW
R. V. Bogdanov, R. A. Kuznetsov, V. N. Epimahov, A. V. Titov and E. E. Prudnikov
Affiliation: Saint Petersburg State University, Radiochemistry Department, University quay 7-9, St. Petersburg, 199034, Russia.
The paper presents new polyphase ceramic waste forms (matrices) of aluminosilicate-phosphate type synthesized
from natural bauxites and apatite ore tailings. This ceramic material is named “geoceramics” by the authors. The optimum
composition of the waste matrix is selected (Cs2O, P2O5, SiO2, and Al2O3) and a cost-saving method for synthesis
of matrices capable to accommodate up to 12 wt. % of cesium and 6 wt. % of strontium isotopes is developed. Phases
which immobilize cesium isotopes are identified. It is shown that waste forms which are close in stoichiometric composition
to pollucite (CsAlSi2O6) have the best resistance to water. The rate of cesium leaching (R) from these waste forms is
2.10-6 g/cm2day in the kinetic region. Heat treatment and cooling of the matrix material does not affect the immobilization
performance of the proposed waste forms. In some cases, a positive effect is achieved by using the sol-gel method which
can reduce the grain sizes, resulting in a decrease in the leach rate of cesium to 1.10-6 g/cm2 day. The leach rate of strontium
is below the detection limit of atomic absorption spectrophotometers (0.3 .10-6 g/cm2day).
Keywords: Aluminosilicate-phosphate polyphase ceramics, apatite ore tailings, bauxite, Cs-Sr-fraction of HLW, corrosion
resistance of matrices, geoceramic matrices (geoceramics), high level radioactive waste (HLW), immobilization of HLW.
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