Experimental measurements of some thermophysical properties of molten nuclear core materials according to their level of oxidation

Caroline Denier1^{1}, Jules Delacroix1,^{1,\star}, Pascal Piluso1^{1}, Emmanuel De Bilbao2^{2}
^{\star} : jules.delacroix@cea.fr
1^{1} CEA, DES, IRESNE, DTN, SMTA, LEAG, Cadarache F-13108 Saint-Paul-Lez-Durance
2^{2} CNRS, CEMHTI UPR3079 Univ. Orléans, F-45071 Orléans, France.
Mots clés : Suboxidized corium, Surface tension, Density, VITI, Maximum bubble pressure, High temperature.
Résumé :

During a severe accident in a nuclear reactor, many complex phenomena, such as Fuel-Coolant Interaction (FCI) can occur. They involve a variety of fundamental mechanisms that are still partially understood.

Among them, the oxidation of liquid corium is expected to impact the so-called steam explosion risk, by altering the thermophysical properties of corium. To compute FCI phenomena, such liquid corium thermophysical properties as density ρ\rho, surface tension σ and viscosity η at high temperatures, are indeed required to feed severe accident codes. To our best knowledge, such data are not available in the existing literature.

As the composition of the corium varies depending on the accident progression, we focus in this study on in-vessel corium, composed mainly of U, and O. To be representative of real in-vessel corium, the U/ ratio is constant and taken equal to 1.2, corresponding to pressurized water reactors (PWR). The stoichiometry in oxygen of the corium depends on the considered severe accident scenario. It is represented by the oxidation degree of corium, obtained by the ratio /(+). The compositions considered in this work have an oxidation degree varying from 0 to 100, which is representative of different severe accident scenarios.

The VITI test facility has been designed to implement Maximum Bubble Pressure (MBP) technique in refractory crucibles at high temperatures. In this configuration, once the sample is melted by induction heating above 2000^{\circ}C, a capillary tube is immersed in the liquid corium pool, and the continuous gas bubbling is monitored. The application of Laplace-Young law, which governs liquid/gas interface equilibrium, gives access to original correlations (and related uncertainties) for both ρ\rho and γ as functions of the temperature for compositions of interest.

This original data constitutes to our knowledge the first systematic measurements ever performed for in-vessel suboxidized liquid corium compositions according to corium stoichiometry.

Work In Progress