High‐temperature mass spectrometric study of thermodynamic properties in the UO₂–ZrO₂ system

Abstract

Rationale The UO2–ZrO2 solid solution at high temperatures is the key system of modern nuclear science and technology in the context of the safety operation of nuclear cycles, the consequences of severe accidents, and the incorporation of nuclear waste. Urgent needs of the continuation of experimental studies of this system at temperatures up to 3000 K are aimed at preventing severe accidents similar to Chernobyl and Fukushima when the thermodynamic approach is used for the prediction of high‐temperature behavior of materials. Methods This investigation was carried out using the Knudsen effusion mass spectrometric method using the MS‐1301 magnetic sector mass spectrometer. The samples in the UO2–ZrO2 system were vaporized from a tungsten effusion cell. Vapor species effusing from the cell were ionized at an electron ionization energy of 70 eV. Results The vaporization and thermodynamics of pure UO2 and ZrO2 as well as of the samples in the UO2–ZrO2 system were studied in the range 2000–2730 K. The temperature dependences of the partial vapor pressures of UO and UO2 over pure UO2 were obtained at 2060–2456 K, which agreed with the literature results. The partial vapor pressures of UO, UO2, ZrO, and ZrO2, the vaporization rates, and the UO2 and ZrO2 activities in the UO2–ZrO2 solid solutions were determined at 2370, 2490, 2570, and 2730 K. Conclusions The component activities and excess Gibbs energies of the UO2–ZrO2 system indicated a change in deviations from the ideal behavior from positive to negative with the temperature increase from 2370 to 2730 K. The thermodynamic functions of formation from the oxides of the solid solutions in the UO2–ZrO2 system such as Gibbs energies as well as the enthalpies and entropies of formation were obtained for the first time at 2550 K in the composition range 0.89–1.00 ZrO2 mole fraction.

Knudsen effusion mass spectrometry: Current and future approaches

“…Refractory ceramic oxides are also important for other nuclear issues such as nuclear waste immobilization, fuel cladding, and severe accident containment. KEMS studies on the following relevant systems have recently been reported: Sm 2 O 3 ‐ZrO 2, 67,305 UO 2 ‐ZrO 2, 306 and Sm 2 O 3 ‐ZrO 2 ‐HfO 2. 244,307 …”

Mass spectrometric study of ceramics in the Sm2O3‐ZrO2‐HfO2 system at high temperatures

“…The ZrO 2 and HfO 2 vaporization processes were examined thoroughly by various methods including high‐temperature mass spectrometry 39 . Recently, the ZrO 2 and HfO 2 vaporization processes were studied by Stolyarova et al 40 and Kablov et al, 41 respectively. The transitions of ZrO 2 and HfO 2 into the gaseous phase are known to proceed with dissociation into the monoxides and atomic oxygen, with ZrO 2 also vaporizing without dissociation: where Me is Zr or Hf.…”