(U,Pu)O系燃料の固・液相線温度の解析的評価

Analytical evaluation of solidus and liquidus temperature on (U,Pu)O fuel

長井 修一朗

Nagai, Shuichiro

(1)定温・定圧での平衡の基準"Gibbs自由エネルギーは極小"の原理に基づいた、2相2成分及び2相3成分系状態図計算プログラムを作成した。(2)このプログラムを用いて、理想溶液モデルで記述されるUO-PuO系、正則溶液モデルで記述したAg-Au-Cu系状態図の計算結果を評価し、解析プログラムの妥当性を確認した(3)U-O及びPu-O系の固・液相線を最も良く再現するように設定したパラメータを用いたU-Pu-O系状態図は、O/Mの低下に従い小さな極大を持つPu-O系と類似の固・液相線となり、Aitken等及び森本の測定結果と良く一致した。(4)Aitken等によるU-Pu-O系の固・液相線の測定結果は測定精度向上を図る必要があるが、Pu-O系の固・液相線と自己矛盾のない優れた測定データであることが確認できた。

Phase diagram calculation code PD32 for 2 phases-2components and 2 phases-3components systems was developed based on Gibbs Free Energy Minimum Principal under equilibrium condition. Phase diagram calculation of UO-PuO system described by ideal solution model and Ag-Au-Cu system described by regular solution model showed that PD32 gave the reasonable results, that was, the chemical potential of each component had good agreement between two phases. Free energy of solid U-O, Pu-O and (U,Pu)O systems was calculated based on Blackburn's oxygen potential model. For the calculation of free energy of liquid systems, three parameters which modified the equilibrium constants between the metal ions and oxygen pressure in Blackburn model was introduced, and was established to fit the solidus and liquidus line in U-O and Pu-O systems. Calculated solidus and liquidus line and their O/M dependence in (U,Pu)O system agreed well with measured data by Aitken et al. It was confirmed that the solidus and liquidus line between Pu-O and (U,Pu)O systems by Aitken et al was self-consistent.