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

Solidus and liquidus of plutonium and uranium mixed oxide

“…Fig. 5 compares the melting point of UO 2 observed in previous studies [6,7,9,12,[20][21][22][23][24][25][26]. The melting point of UO 2.00 observed in the present work was 3128 ± 35 K which is in good agreement with the average of those earlier works.…”

Melting behavior of (Th,U)O2 and (Th,Pu)O2 mixed oxides

“…Experimentally reported melting temperatures of UO2 vary from 3050 K to 3138 K ( Table 2) [11][12][13][14][15][16][17][18]. The melting point of UO2 given in MATPRO [15] is 3113.15 K, based on the equations for the solids and liquids boundaries of the UO2-PuO2 phase diagram given by Lyon et al [11].…”

“…The melting point of UO2 given in MATPRO [15] is 3113.15 K, based on the equations for the solids and liquids boundaries of the UO2-PuO2 phase diagram given by Lyon et al [11]. The recommended value by ORNL [17] for UO2.00 is 3120 ± 30 K. In recent experimental measurements of the heat capacity of liquid UO2, using laser heating of a UO2 sphere, Ronchi et al [13] made several measurements of the freezing temperature of UO2 on different samples. For specimens in an inert gas atmosphere with up to 0.1 bar of oxygen, they obtained melting points in the interval 3070 ± 20 K.…”

“…The variation in melting temperature is in accordance with the expected lower oxygento-uranium (O/U) ratio in the latter samples. The melting point of UO2 drops on variation of the O/M ratio away from stoichiometry: for example, if the melting point of stoichiometric UO2 is 3138 K, its value drops to 2698 K at an O/U ratio of 1.68 and to 2773 K at an O/U ratio of 2.25 [13]. Thus, our MD calculated melting temperature, which lies between 3050 K and 3075 K, is in fairly consistent with experimental data available in the literature for stoichiometric UO2.…”

“…ThO2 3650-3675 3663 ± 100 Benz et al [6] 3643 ± 30 Rand et al [7] 3573 ± 100 Lambertson et al [8] 3651 ± 17 Ronchi et al [9] 3624 ± 108 Bohler et al [10] UO2 3050-3075 3113 ± 20 Lyon et al [11] 3138 ± 15 Latta et al [12] 3075 ± 30 Ronchi et al [13] 3120 ± 30 Adamson et al [14] 3,113.15 MATPRO [15] 3138 ± 15 Komatsu et al [16] 3120 ± 30 ORNL [17] 3050 ± 55 Böhler et al [18] PuO2 2800-2825 2663 ± 20 Lyon et al [11] 2701 ± 35 Adamson et al [14] 2647 MATPRO [15] 2718 Komatsu et al [16] 2701 ± 35 ORNL [17] 2843 Kato et al [19] Table 4: MD calculated enthalpy increments (in J/mole) of solid and liquid phases of (Th,U)O2 and (Th,Pu)O2 MOX are fitted to equation (7) and (8), respectively and coefficients are enlisted.…”