A search for the thermodynamics integrating the crystal phases formed in the nuclear fuel waste glasses and their aqueous ions

2023 Fiscal Year Final Research Report

• Project/Area Number: 20K05183
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 26060:Metals production and resources production-related
• Research Institution: University of Hyogo
• Principal Investigator: Morishita Masao 兵庫県立大学, 工学研究科, 教授 (60244696)
• Project Period (FY): 2020-04-01 – 2024-03-31
• Keywords: 熱力学 / 固相 / 水溶液中イオン / 使用済核燃料 / 放射光 / リートベルト解析 / 磁性 / 飽和溶解度

Outline of Final Research Achievements

α-ZrMo2O8 is one of the yellow phase-group composed of Mo as a fission product of U and Zr as the main component of nuclear fuel cladding tubes. In the present study, the thermodynamic values for α-ZrMo2O8 were determined. Due to its lattice instability, the ionic configurations from room to very low tempearature were precisely explored using synchrotron radiation XRD with SPring 8 followed by the Reatveld analysis. Change in the magnetic properties to very low temperature were clarified in complementary with the ionic configurations. Having knowledge of the lattice instability, the heat capacity from room to near absolute zero and the saturation solubility into water at room temperature were measured. Namely, the thermodynamic values were determined by consolidating the solid and aqueous ionic states.

Free Research Field

金属生産工学

Academic Significance and Societal Importance of the Research Achievements

原子力発電による使用済み核燃料は、硝酸水溶液に溶解して煆焼後ホウ珪酸融体に混合、ガラス固化体に成型することが試みられている。しかしながら、ガラス固化体中、Uの核分裂生成元素Moからなる水溶性の有害相イエローフェーズ群が形成される。イエローフェーズ結晶群のうち、核燃料被覆管成分Zrに由来するα-ZrMo2O8は特に熱力学的性質の全容解明が待たれている。本研究において、α-ZrMo2O8の格子不安定性を、放射光XRDとリートベルト解析、および磁化測定によって明らかにした。また、水溶液への溶出過程を熱力学的に定量評価した。得られた成果は核燃料廃棄物の安全管理に役立てることができる。