Measurement of oxygen potential of (UPu)O at 1773 and 1873 K, and its analysis based on point defect chemistry

1773K及び1873Kにおける(UPu)Oの酸素ポテンシャル測定と点欠陥化学による解析

加藤 正人   ; 中道 晋哉  ; 武内 健太郎 ; 砂押 剛雄*

Kato, Masato; Nakamichi, Shinya; Takeuchi, Kentaro; Sunaoshi, Takeo*

ウラン・プルトニウム混合酸化物は、高速炉の燃料として用いられる。MOXは、蛍石構造を持つ酸素不定比性化合物であり、ハイパー,ハイポストイキオメトリの両方の組成で安定な酸化物である。MOXの酸素量は、基礎特性に大きく影響するため、酸素量と酸素ポテンシャルの関係を評価することは大変重要である。本研究では、(UPu)Oの酸素ポテンシャル測定を1773K及び1873Kで行った。測定は熱重量計を用いて気相平衡法で行った。酸素ポテンシャルを温度,O/Mの関数として決定し、点欠陥モデル用いて定比組成の酸素ポテンシャルを1773K及び1873Kにおいて、それぞれ-311kJ/mol及び-299kJ/molと得た。

Uranium and plutonium mixed oxide (MOX) has been used as fuels of fast reactors. The MOX having fluorite structure is an oxygen nonstoichiometric compound which is stable in hyper- and hypo-stoichiometric composition range. The stoichiometry of MOX significantly affects their properties. So, it is essential to know the relation between stoichiometry and oxygen potential to develop MOX fuels. In this work, the oxygen potentials of (UPu)O were measured at high temperatures of 1773, and 1873K. The measurements were carried out by gas equilibrium method using thermo-gravimetry. Th The oxygen partial pressure was adjusted by controlling the ratio of H/HO in the flowing gas atmosphere, and the oxygen potential was determined. The oxygen potentials were determined as functions of O/M ratio, and temperature. The data at stoichiometric composition were estimated to be -311kJ/mol and -299kJ/mol at 1773K, and 1873K based on point defect model.