Vaporization and thermodynamics of the Cs₂O–MoO₃ system studied using high‐temperature mass spectrometry

Abstract

Rationale Cesium and molybdenum are fission products of uranium dioxide fuel in nuclear reactors, which interact with each other depending on the oxygen potential of the fuel. This leads to formation of various compounds of the Cs2O–MoO3 system, which are exposed to high temperatures during operation of a reactor or a severe accident at a nuclear power plant. This is why the study of the vaporization and thermodynamics of compounds in the Cs2O–MoO3 system is important. Methods Synthesis of the compounds in the Cs2O–MoO3 system was carried out by sintering Cs2MoO4 and MoO3. Characterization of the samples was accomplished with the use of XRD, TGA/DSC/DTA, IR spectroscopy, and ICP emission spectroscopy. Vaporization of the samples under study was carried out from a platinum effusion cell using an MS‐1301 mass spectrometer developed for high‐temperature studies of low‐volatility substances. Results The temperature dependences of partial pressures of vapor species were determined over pure MoO3 and Cs2MoO4 in the ranges 870–1000 K and 1030–1198 K, respectively. MoO3, Mo2O6, Mo3O9, Mo4O12, and Mo5O15 were shown to be the main vapor species over the Cs2O–MoO3 system in the temperature range 850–1020 K. The component activities, Gibbs energies of mixing, and excess Gibbs energies were obtained as functions of the component concentration at 900, 950, and 1000 K. Conclusions The thermodynamic properties of the Cs2O–MoO3 system found in the study evidenced negative deviations from ideality. The MoO3 and Cs2MoO4 partial molar enthalpies of mixing, the Cs2MoO4 partial vaporization enthalpy, and the total enthalpy of mixing in the Cs2O–MoO3 system at 1000 K were obtained for the first time.

Knudsen effusion mass spectrometry: Current and future approaches

“…It should be mentioned that, although not included in the reviews discussed earlier, recent experimental data obtained using KEMS at high temperatures on oxide systems and materials for nuclear applications such as the UO 2 ‐ZrO 2 , 67,210 Cs 2 O‐B 2 O 3 , 211 Cs 2 O‐MoO 3 , 212 and SrO‐Al 2 O 3 213,214 systems are available. Recent KEMS data on ceramics and glass ceramics with the special unique physicochemical properties such as the ZnO‐Nb 2 O 5 , 215 TiO 2 ‐Al 2 O 3 ‐SiO 2 , 216,217 and Al 2 O 3 ‐SiO 2 ‐ZrO 2 systems 218 as well as ultrahigh refractory ceramics based on the binary and multicomponent systems containing rare‐earth and hafnium oxides 219–221 have also been reported.…”

“…Understanding the interaction of materials in a reactor is another area in which KEMS can play a crucial role. Regarding the interaction of fission products with their environment during severe accidents, Stolyarova and colleagues have published thermodynamic studies on the Cs 2 O‐B 2 O 3 211 and Cs 2 O‐MoO 3 212 systems. Nakajima published a KEMS study on CsBO 2.…”