Laser-Pulse Melting of Nuclear Refractory Ceramics.

Abstract not availableJRC.E-Institute for Transuranium Elements (Karlsruhe

Melting Point of MgO.

Abstract not availableJRC.E-Institute for Transuranium Elements (Karlsruhe

Advances in Measurements of Melting Transition in Non-Stoichiometric UO2.

Abstract not availableJRC.E-Institute for Transuranium Elements (Karlsruhe

Advances in the Experimental Determination of the Uranium–Oxygen Phase Diagram at High Temperature

International audienceDue to its complex phase diagram and the employment of UO2 as a nuclear fuel, the binary system U–O is of great interest both scientific and technological. Numerous experimental and theoretical studies have been carried out in the last 45 years in order to determine the properties of this system, leading to a precise definition of a considerable part of the state diagram in the region ranging from pure uranium to stoichiometric UO2, and at temperatures lower than 1500 K, up to the oxide U4O9. However, due to the poor chemical stability of O–U compounds with high oxygen content at high temperature (O/U > 2, T > 2000 K), an important part of the phase diagram still lacks experimental data. In this work measurements are presented on the melting transition of the stoichiometric and hyperstoichiometric dioxide UO2+x up to x=0.21, and on the melting point of the higher oxide U3O8. These measurements were performed under buffer gas pressures varying between 10 and 250 MPa, using a method based on subsecond laser heating developed to overcome experimental difficulties encountered by previous researchers

Advances in the Experimental Determination of the Uranium¿Oxygen Phase Diagram at High Temperature

Due to its complex phase diagram and the employment of UO2 as a nuclear fuel, the binary system U¿O is of great interest both scientific and technological. Numerous experimental and theoretical studies have been carried out in the last 45 years in order to determine the properties of this system, leading to a precise definition of a considerable part of the state diagram in the region ranging from pure uranium to stoichiometric UO2, and at temperatures lower than 1500 K, up to the oxide U4O9. However, due to the poor chemical stability of O¿U compounds with high oxygen content at high temperature (O/U>2,T >2000 K), an important part of the phase diagram still lacks experimental data. In this work measurements are presented on the melting transition of the stoichiometric and hyperstoichiometric dioxide UO2+x up to x = 0.21, and on the melting point of the higher oxide U3O8. These measurements were performed under buffer gas pressures varying between 10 and 250MPa, using a method based on subsecond laser heating developed to overcome experimental difficulties encountered by previous researchers.JRC.DG.E.3-Materials researc

Dependence of the Melting Temperature on Pressure up to 2000 Bar in Uranium Dioxide, Tungsten and Graphite.

The melting point of uranium dioxide, tungsten and graphite was measured as a function of the isostatic pressure up to 2000 bar, in a laser-heated autoclave filled with inert gas. The measured melting curves and their slopes were compared with the predictions obtained from the Clausius-Clapeyron equation and the existing thermochemical data of these substances. Whilst for tungsten and graphite the results show a reasonable agreement with the equilibrium thermodynamic calculation, the melting point of UO2 increases with the equilibrium thermodynamic calculation, the melting point of UO2 increases with pressure with a slope more than three times larger than expected.JRC.E-Institute for Transuranium Elements (Karlsruhe

The Molten State of Graphite. An Experimental Study.

Sub-second laser heating technique has been succesfully applied for graphite melting under controlled isobaric conditions. During the applied pulses, relatively large amounts of graphite were melted and subsequently solidified under good stability conditions of the liquid mass. The SLV triple point was determined. From metallographic analysis of the quenched liquid, the expansion upon melting could be estimated. A mathematical model was then applied to deduce the thermal conductivity of liquid carbon. Both experimental observations and calculation results indicate a non-metallic nature of liquid carbon in the pressure range of 110-2500 bar. Finally, an analysis of the melting line Tm(p) based on Simpon's empirical equation of state confirms the self-consistency of all results obtained.JRC.E-Institute for Transuranium Elements (Karlsruhe

Advances in the Mass Spectrometry Study of the Laser Vaporisation of Graphite

Reliable experimental data on graphite vaporization and especially on carbon vapor composition exist only up to 2500¿3000 K. Data measured at higher temperatures are questionable due to several experimental limitations, such as the difficult temperature determination and the not straightforward correlation of measured temperatures and intensities of signals in mass spectra. That is why a new method of high-temperature mass spectrometry with laser vaporization was developed, in order to extend the accessible temperature range while overcoming these limitations and to shed more light on the still poorly known behavior of carbon at high temperatures. Thus, carbon sublimation relative partial pressures of the species C1, C2, C3, C4, and C5 were measured up to 4100 K. Moreover, the values of the relative vaporization coefficients of C1, C2, C3, C4, and C5, estimated by comparison of the experimentally obtained partial pressures with the predicted equilibrium ones, are proposed.JRC.E.3-Materials researc

Advances in the Use of Laser-Flash Techniques for Thermal Diffusivity Measurement.

A laser-flash apparatus has been constructed, and is here presented, for the measurement of thermal diffusivity. The apparatus is specially designed to operate under the stringent conditions imposed by the requirement to measure the thermal diffusivity of highly radioactive reactor-irradiated nuclear fuels. These materials require the adaption of mechanical, optical and electrical technologies for use in a alpha-gamma hot-cell environment.JRC.E-Institute for Transuranium Elements (Karlsruhe