Effect of Americium and Simulated Fission Products Addition on Oxygen Potential of Uranium-Plutonium Mixed Oxide Fuels
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1215-V12-04
Effect of americium and simulated fission products addition on oxygen potential of uranium-plutonium mixed oxide fuels Kosuke Tanaka1, Masahiko Osaka1, Ken Kurosaki2, Hiroaki Muta2, Masayoshi Uno3 and Shinsuke Yamanaka2, 3 1 Japan Atomic Energy Agency, 4002 Narita-cho, Oarai-machi, Higashiibaraki-gun, Ibaraki, 311-1393, Japan 2 Division of Sustainable Energy and Environmental Engineering, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka, 565-0871, Japan 3 Research Institute of Nuclear Engineering, Fukui University, 3-9-1 Bunkyo, Fukui, 910-8507, Japan.
ABSTRACT The oxygen potentials at 1273 K of mixed oxide (MOX) fuels with Am and 26 kinds of fission product elements (FPs), simulating low-decontaminated MOX fuel and high burn-up of up to 250 GWd/t, have been measured by using thermogravimetric analysis (TGA). The oxygen potentials for simulated low-decontaminated MOX fuels were higher than the fuels without FPs and increased with increasing simulated burn-up. INTRODUCTION Low-decontaminated mixed oxide (MOX) fuel, which contains several percent of minor actinides (MAs) and fission products (FPs), is a promising candidate for a closed nuclear fuel cycle system based on a fast reactor [1]. Extending burn-up of the fuel has been identified as a practical means of improving the economics of the system. In high burn-up oxide fuels, some FPs dissolve in the fuel matrix and others form oxide or metallic precipitates, which will affect the physical and chemical properties of the fuels [2]. It is, therefore, crucial to understand the effect of FPs accumulation on the fuel performance. Among the thermodynamic properties, the oxygen potential is one of the concerns for oxide fuels [3]. The oxygen potential greatly affects thermochemical and thermophysical properties of non-stoichiometric nuclear fuel via variation of the oxygen-to-metal (O/M) ratio. This means that effects of the oxygen potential should be considered with great care for the thermal design of the fuel. The quality of fabricated fuel pellets is also influenced by the oxygen potential in their sintering atmosphere [4, 5]. Besides, it is an indispensable property for interpreting migration behavior of the fuel constituent elements under a temperature gradient, especially in the initial stage of the irradiation. During the irradiation, effects of the oxygen potential become more critical as it has direct influences on the oxidation of the cladding material, which may eventually lead to cladding failure due to the reduction of the effective loadbearing thickness. Oxygen potential is also closely related to various aspects of the fuel during the long term irradiation.
There are some experimental data for oxygen potentials of the oxides containing americium (Am) which is representative of MAs. Chikalla and Eyring [6] measured the oxygen potentials of AmO2−x as a function of the O/M ratio at several temperatures. Their study showed that AmO2−x has very high oxygen potentials, compared with other related actinide oxides such
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