ISSN 1066-3622, Radiochemistry, 2011, Vol. 53, No. 1, pp. 13–18. © Pleiades Publishing, Inc., 2011. Original Russian Text © V.I. Almjashev, M. Barrachin, S.V. Bechta, D. Bottomley, S.A. Vitol, V.V. Gusarov, F. Defoort, E.V. Krushinov, D.B. Lopukh, A.V. Lysenko, A.P. Martynov, L.P. Mezentseva, A. Miassoedov, Yu.B. Petrov, M. Fisсher, V.B. Khabensky, S. Hellmann, 2011, published in Radiokhimiya, 2011, Vol. 53, No. 1, pp. 14–19. 13 Ternary Eutectics in the Systems FeO–UO 2 –ZrO 2 and Fe 2 O 3 –U 3 O 8 –ZrO 2 1 V. I. Almjashev* a , M. Barrachin b , S. V. Bechta c , D. Bottomley d , S. A. Vitol c , V. V. Gusarov a,e , F. Defoort f , E. V. Krushinov c , D. B. Lopukh a , A. V. Lysenko c , A. P. Martynov a , L. P. Mezentseva g , A. Miassoedov h , Yu. B. Petrov а† , M. Fisсher i , V. B. Khabensky c , and S. Hellmann i a St. Petersburg Electrotechnical University (LETI), St. Petersburg, Russia; * e-mail: vac@mail.ru b Institute for Radiological Protection and Nuclear Safety (IRSN), Paris, France c Alexandrov Research Institute of Technology, Federal State Unitary Enterprise, Sosnovy Bor, Leningrad oblast, 188540 Russia d EC Joint Research Centre, Institute for Transuranium Elements, Kalsruhe, Germany e St. Petersburg State Institute of Technology (Technical University), St. Petersburg, Russia f French Alternative Energies and Atomic Energy Commission (CEA), Grenoble, France g Grebenshchikov Institute of Silicate Chemistry, Russian Academy of Sciences, St. Petersburg, Russia h Institute for Nuclear and Energy Technologies, Forschungszentrum Karlsruhe (FZK, IKET), Karlsruhe, Germany i AREVA NP GmbH, Erlangen, Germany Received July 2, 2010 Abstract—The systems FeO–UO 2 –ZrO 2 (in inert atmosphere) and Fe 2 O 3 –U 3 O 8 –ZrO 2 (in air) were studied. For the FeO–UO 2 –ZrO 2 system, the eutectic temperature was found to be 1310°С, with the following component concentrations (mol %): 91.8 FeO, 3.8 UO 2 , and 4.4 ZrO 2 . For the Fe 2 O 3 –U 3 O 8 –ZrO 2 system, the eutectic temperature was found to be 1323°С, with the following component concentrations (mol %): 67.4 FeO 1.5 , 30.5 UO 2.67 , and 2.1 ZrO 2 . The solubility limits of iron oxides in the phases based on UO 2 (ZrO 2 ,FeO) and UO 2.67 (ZrO 2 ,FeO 1.5 ) were determined. Keywords: eutectics, iron oxides, uranium oxides, zirconium dioxide, phase analysis Data on phase equilibria in the U–Zr–Fe–O system are important for understanding physicochemical proc- esses that occur in severe NPP accidents with melting of the reactor core and operation of protective safety systems. The extent to which the data on phase equilib- ria are reliable and detailed largely determines the quality of predicting the progress of severe accidents [1] and the adequacy of measures developed for their control. For the description of the fuel melt behavior and of its interaction with structural materials, of most practi- cal interest are characteristic points (binary and ternary eutectics), the positions of the liquidus surfaces, and the solubility limits of the components in the coexist- ing phases in the systems FeO–UO 2 –ZrO 2 (corresponds to the melt after full oxidation of metallic Zr in it [2]) and Fe 2 O 3 –U 3 O 8 –ZrO 2 (formed after oxi- dation of the remaining melt components in an ex- vessel accident in the steam–air medium [3, 4]). However, the volume of the experimental data on these ternary systems is apparently insufficient to con- struct their phase diagrams. Only one paper can be men- tioned [3], in which the liquidus temperature (1946 ± 20°C) was determined for the composition (mol %) 55.0 FeO–23.6 UO 2 –21.4 ZrO 2 [3]. Actually all the in- formation on ternary systems is concentrated in binary sections. A detailed review of them is given in [5, 6]. DOI: 10.1134/S1066362211010024 1 To 40th Anniversary of the Department of Chemical-Engineer- ing and Materials-Science Studies of the Alexandrov Research Institute of Technology. † Deceased.