雑固体廃棄物の一括溶融処理に関する高温物理化学的研究(III)(核燃料サイクル開発機構 委託研究成果報告書)

Physico-chemical studies on the disposal of miscellaneous radioactive waste through A single-step process (III)

岩瀬 正則*

Iwase, Masanori*

本研究は、焼却灰を介した溶融金属の酸化反応を制御し、かつそれをスラグ除染に積極的に利用する手段を確立すること最終目的としており、本年は焼却灰の主成分である複数のアルカリ硫酸塩を含む混合溶融塩の物理化学的性質、中でも融体中の酸化物イオンの物理化学的挙動を、溶融塩中のCu2+/Cu+酸化還元平衡によって調査した。2元系、3元系アルカリ金属硫酸塩中のCu2+/Cu+平衡におよぼす諸因子の影響のうち、本年度は特にガス分圧(酸素分圧、SO2分圧)について重点的に調査した。硫酸塩融体中におけるCu2+/Cu+比の酸素分圧、SO2分圧依存の関数形を提示し、その妥当性を熱力学的に検証した。さらに本年度は、高温腐食現象の機構解明の端緒として、複数のアルカリ硫酸塩を含む混合溶融塩中へCr2O3溶解実験を行った。結果から、一定温度および雰囲気において平均イオン半径、換言すれば酸素イオン活量が同じ融体は、同様の酸化物溶解挙動を示すという重要な知見が得られた。

This study is aimed at controlling oxidation reaction of molten metal by ash in incineration systems, and at positively utilizing the oxidation reaction for decontamination of slag. In this year, in order to investigate physico-chemical properties of mixed fused salt containing alkali sulfates, with special focus on the behaviour of oxygen anion in the melts, Cu / Cu redox equilibrium experiments were carried out. Among the effect of various parameters on Cu / Cu ratio in binary and ternary alkali sulfate melts, the effect of partial pressures of oxygen and SO was mainly investigated in the study. Variation in Cu / Cu ratio were presented as the function of partial pressures of oxygen and SO, respectively. Possible thermodynamic interpretation were made on the experimental results. In addition, the dissolution of CrO in mixed alkali sulfates were also investigated as a first step to elucidate the mechanism of hot corrosion. With this investigation, an important finding was obtained that the solubility of CrO for melts with same average ionic radius, in other words, oxygen ion activity, were essentially identical under constant temperature and atmosphere.