Improvement of the European thermodynamic database NUCLEA

Mass spectrometric study and modeling of the thermodynamic properties of SrO-Al2 O3 melts at high temperatures

RATIONALE

The SrO-Al₂ O₃ system holds promise as a base for a wide spectrum of advanced materials, which may be synthesized or applied at high temperatures. Therefore, studying vaporization and high-temperature thermodynamic properties of this system is of great practical importance.

METHODS

Samples of the SrO-Al₂ O₃ system were obtained by solid-state synthesis and identified by X-ray fluorescence analysis, X-ray phase analysis, scanning electron microscopy, electron probe microanalysis, simultaneous thermal analysis, and thermogravimetric analysis. The thermodynamic properties of the SrO-Al₂ O₃ system were studied by the Knudsen effusion mass spectrometric (KEMS) method and were fitted by the Redlich-Kister and Wilson polynomials. The thermodynamic values obtained were also optimized within the generalized lattice theory of associated solutions (GLTAS).

RESULTS

The vapor composition, temperature, and concentration dependences of the partial vapor pressures over the samples under study as well as the SrO activities in melts of the SrO-Al₂ O₃ system were determined by the KEMS method. Usage of the Redlich-Kister and Wilson polynomials allowed calculation of the excess Gibbs energies, enthalpies of mixing, and excess entropies in the concentration range 0-33 mol% of SrO at temperatures of 2450 and 2550 K.

CONCLUSIONS

Significant negative deviations from the ideality were observed in the melts of the SrO-Al₂ O₃ system at 2450, 2550, and 2650 K. The Wilson polynomial was found to be the optimal approach to describe the thermodynamic properties in the system studied. Optimization of the experimental data using the GLTAS approach allowed the characteristic features of the thermodynamic description of the SrO-Al₂ O₃ system to be elucidated and explained.

High-temperature mass spectrometric study and modeling of ceramics based on the Al2 O3 -SiO2 -ZrO2 system

RATIONALE

Materials based on the Al₂ O₃ -SiO₂ -ZrO₂ system are promising for a wide range of high-temperature technological applications, such as thermal barrier coatings in the aviation and space industry or advanced materials in nuclear power reactors. Experimental studies of the ceramics based on this system by the Knudsen effusion mass spectrometric (KEMS) method are of significant interest in designing technological processes for the synthesis and exploitation of the Al₂ O₃ -SiO₂ -ZrO₂ materials.

METHODS

Samples of ceramics in the Al₂ O₃ -SiO₂ -ZrO₂ system, including the Al₂ O₃ -ZrO₂ and SiO₂ -ZrO₂ binaries, were prepared by solid-state synthesis. Analysis of the samples was performed by X-ray fluorescence and diffraction techniques. The vapor composition and thermodynamic properties of the components in this system were determined by KEMS. The derived thermodynamic functions were optimized within the generalized lattice theory of associated solutions (GLTAS).

RESULTS

In the temperature range 1900-2600 K, the SiO, Al, AlO, Al₂ O, ZrO, ZrO₂ , and O vapor species were identified over the samples in the systems under study. For the thermodynamic properties to be determined correctly, the samples of the Al₂ O₃ -SiO₂ -ZrO₂ system had to be vaporized at temperatures less than 2000 K, where data could be obtained only for the SiO species. The SiO₂ activities obtained were taken as the experimental basis for the modeling within the GLTAS approach. This allowed evaluation of the component activities and excess Gibbs energy, and assessment of the relative number of bonds of different types.

CONCLUSIONS

At 1920 K, the Al₂ O₃ -SiO₂ -ZrO₂ system is characterized by negative deviations of its thermodynamic properties from the ideal behavior. The consistency of the obtained modeling results was illustrated by comparison of the values derived from the data for the ternary and the boundary binary systems and thereby indicates the reasonable uniformity of the energy parameters of the lattice model derived in the calculations, which may be used in further modeling of multicomponent systems.

The European Research on Severe Accidents in Generation-II and -III Nuclear Power Plants

Forty-three organisations from 22 countries network their capacities of research in SARNET (Severe Accident Research NETwork of excellence) to resolve the most important remaining uncertainties and safety issues on severe accidents in existing and future water-cooled nuclear power plants (NPP). After a first project in the 6th Framework Programme (FP6) of the European Commission, the SARNET2 project, coordinated by IRSN, started in April 2009 for 4 years in the FP7 frame. After 2,5 years, some main outcomes of joint research (modelling and experiments) by the network members on the highest priority issues are presented: in-vessel degraded core coolability, molten-corium-concrete-interaction, containment phenomena (water spray, hydrogen combustion…), source term issues (mainly iodine behaviour). The ASTEC integral computer code, jointly developed by IRSN and GRS to predict the NPP SA behaviour, capitalizes in terms of models the knowledge produced in the network: a few validation results are presented. For dissemination of knowledge, an educational 1-week course was organized for young researchers or students in January 2011, and a two-day course is planned mid-2012 for senior staff. Mobility of young researchers or students between the European partners is being promoted. The ERMSAR conference is becoming the major worldwide conference on SA research.