Laboratory Measurement of the Heat Capacity of Urania up to 8000 K: I. Experiment

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Abstract
The heat capacity Cp of UO2 was measured in a laboratory experiment where sintered 0.5-to 1-mm-diam microspheres were heated by four tetrahedrally oriented laser beams in an inert-gas-filled autoclave at pressures up to ∼1000 bar. The sample, suspended by a tungsten needle, was heated to 8000 K during pulses of a few milliseconds duration. The experimental technique, the instrumentation, and the analytical method used to deduce Cp from the experimental pulse-heating curves are described. Between the melting point Tm and ∼4000 K, the heat capacity decreases to a value close to that given by the Neumann-Kopp rule for a triatomic, harmonic lattice, i.e., 9R. Near 5000 K, however, the heat capacity again increases, and it appears to saturate at a value ∼30% higher by 8000 K. The new results are compared with published Cp values for molten UO2 (and other relevant materials) and are briefly discussed in light of the established temperature dependence of Cp at T < Tm and the high-energy electronic structure of UO2.

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