Thermodynamic Calculation and Experimental Determination of the Equation of State of Oxide Fuels Up to 5000 K

摘要

The safety analysis of fast reactors requires the knowledge of the thermodynamic data of state of the nuclear fuel materials up to 5000 K. Based on the law of mass action, the saturation vapor pressure curves p(T) have been calculated for uranium dioxide and stoichiometric and hypostoichiometric (U,Pu) mixed oxide up to 5000 K. The functions used of the free energies of formation and of the oxygen potentials and the resulting partial vapor pressures are represented. The present scatter of the input data leads to a tolerable uncertainty of the calculated equations of state of delta p/p approx. = +-50%. Vapor pressure measurements at very high temperatures require the application of dynamic measuring methods with pulse heating. The potential is discussed of the various experimental techniques: electrical resistive hating, electron beam heating, neutron pulse heating, and laser beam heating. A measuring method using a laser heating technique is described. Vapor pressure measurements with liquid UO sub 2 up to 4200 K are reported. The resulting vapor pressure data fairly well agree with the calculated equation of state of UO sub 2 sub 00 . For pyrometric measurements of liquid fuel the exact value of the spectral emissivity of the fuel surface is needed which depends on temperature. Measurements of the emissivity of liquid UO sub 2 at 0.65 mu m are shortly described. (ERA citation 04:046647)