Heat capacity measurement of U1−yGdyO2 (0.00 ≦ y ≦ 0.142) from 310 to 1500 K

Inaba, Hideaki; Naito, Kunihiko; Oguma, Masaomi

doi:10.1016/0022-3115(87)90536-8

Cited by 52 publications

(16 citation statements)

References 18 publications

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“…This indicates that the heat capacity can be determined precisely (i2-3%) up to 1500 K, even for a sample of low thermal conductivity. The heat capacity values for the mixed oxide have almost similar temperature dependence to those of pure U02 up to 1500 K. It should be noted that we observed no thermal anomaly over the temperature region investigated, in contrast to the reported results of Inaba et al (16). Our results are supported by the recent report of the measurements on SIMFUEL( 17).…”

Section: ' 0'supporting

confidence: 89%

High-temperature heat-capacity measurement up to 1500K by the triple-cell DSC

Takahashi¹

1997

Pure and Applied Chemistry

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Although precise heat-capacity data at high temperatures are very important for modern technology such as nuclear engineering, space technology etc, the reliable methods of measurements up to 1000°C are scarce. We developed a new differential scanning calorimeter (DSC) for heatcapacity measurements from room temperature to 1500 K. In order to overcome difficulties encountered in hightemperature heat-capacity measurements with conventional DSC equipment, two new concepts were adopted for the design of this apparatus: a "triple-cell" system and triple-adiabatic temperature control. The heat capacities of several metals were determined from 300 to 1500 K to test the new apparatus. The heat capacities of Ni and Ti, which are known to have phase transitions were also successfully measured. The precision of the apparatus was estimated to be within i3%. Some experimental results on important nuclear fuels are also given.

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Section: ' 0'supporting

confidence: 89%

High-temperature heat-capacity measurement up to 1500K by the triple-cell DSC

Takahashi¹

1997

Pure and Applied Chemistry

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“…Such anomalous increase in the heat capacity is usually observed when UO 2 is doped with an aliovalent cation (in this case Eu +3 , Eu +2 ). This phenomenon was reported earlier [11][12][13][19][20][21][22][23][24][25] and has been ascribed to the formation of oxygen Frenkel defect pairs. An estimate of the temperature dependence of the heat capacity pertaining to the solid solutions (U 1y Eu y )O 2x (y = 0.2, 0.4, 0.6) over the temperature range 298-1800 K was obtained by extrapolating the expression derived through the least squares regression analysis of these data in the temperature range 298-900 K. This would hence forth be termed as baseline heat capacity.…”

Section: Calorimetric Measurementssupporting

confidence: 72%

Thermophysical properties of uranium–europium mixed oxides

et al. 2015

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Uranium-europium mixed oxides (U 1y Eu y )O 2x (y = 0.2-0.8) were prepared by the citrate gel combustion technique and characterized by X-ray diffraction (XRD). Single phase fluorite structure was observed in those solid solutions with y ≤ 0.6. The solid solutions with y > 0.6 were found to be biphasic, with the second phase being cubic Eu 2 O 3 . Heat capacity and enthalpy increment measurements were carried out by using differential scanning calorimeter (DSC) and drop calorimeter in the temperature range 298-800 K and 800-1800 K, respectively. The , p m C values at 298 K for (U 1y Eu y )O 2x (y = 0.2, 0.4, 0.6) are 64.8, 64.6, and 63.5 J·K 1 ·mol 1 , respectively. An anomalous increase was observed in the heat capacity in all of the solid solutions with the onset temperature around 950 K. This could be attributed to the contribution from Frenkel pair oxygen defects. From the excess heat capacity data, the enthalpy for the formation of these defects was computed and found to be in the range of 2.10±0.02 eV.

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“…Numerical calculations show that the difference between the specific heat at constant pressure as calculated from relations (7) and (8) is significantly less than the experimental value at T < 1500 K. Therefore, the difference between the adiabatic and isothermal bulk moduli can be neglected in the calculation of the specific heat at constant pressure from relation (5).…”

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confidence: 85%

“…Models that can be divided into numerical [7,8] and semi-empirical [9][10][11][12] have been developed on the basis of measurements of the specifi c heat of uranium dioxide at constant pressure in the temperature range 5.7-1667 K [2][3][4][5][6]. The former are not suitable for theoretical evaluations of thermophysical quantities and the fuel temperature in asymptotic limits and the latter are incorrect.…”

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Model for the Specific Heat of Uranium Dioxide

et al. 2015

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The existing models of the specifi c heat of uranium dioxide are analyzed. A new physical model of the specifi c heat of uranium dioxide is developed on the basis of experimental phonon spectra by the methods of the theory of solids. The model proposed is applicable in a wide temperature interval and has no adjustable parameters.The temperature distribution in a uranium dioxide pellet is calculated using models with the thermal conductivity and specific heat as parameters. The thermal conductivity of a ceramic is usually measured by the laser flash method [1]. In this method, the thermal conductivity is calculated as the product of the measured thermal diffusivity by the specific heat capacity per unit volume. Thus, it is necessary to know the specific heat capacity of uranium dioxide not only to model the temperature distribution in a pellet of a fuel element but also to process measurements of other thermophysical parameters of this fuel.Models that can be divided into numerical [7,8] and semi-empirical [9-12] have been developed on the basis of measurements of the specifi c heat of uranium dioxide at constant pressure in the temperature range 5.7-1667 K [2-6]. The former are not suitable for theoretical evaluations of thermophysical quantities and the fuel temperature in asymptotic limits and the latter are incorrect.The aim of the present work is to develop a physically valid model for the specific heat of uranium dioxide. Uranium dioxide possesses a crystal lattice of the type found in fluorite CaF 2 ; the lattice parameter a = 547 pm at room temperature. Since the elementary cell contains three types of atoms, viz., one uranium atom and two oxygen atoms, there are nine branches in the spectrum of normal vibrations: three phonon branches are acoustic and six optical.All transverse phonon branches are doubly degenerate. For this reason, six of the nine possible modes are presented in Fig. 1 [13]. It is evident that the longitudinal optical modes not only depend weakly on the quasiwave vector of a phonon but they are also close. The first and second maxima of the phonon density of states correspond to the acoustic doubly degenerate transverse ν TA and longitudinal ν LA frequencies (Fig. 2). The third and fourth peaks correspond to two frequencies ν TO 2 > ν TO 1 of the doubly degenerate transverse optical branches. The frequencies ν LO 1 and ν LO 2 of the longitudinal optical vibrations are indistinguishable from one another.To construct a model of the specific heat C ν of uranium dioxide at constant volume, we shall take account of the contribution of the acoustic branches within the framework of the Debye model and the optical branches by means of Einstein's model [14][15][16].UO 2 Specific Heat at Constant Volume. We shall calculate the Debye frequency ω D of uranium dioxide. For this, we shall calculate the longitudinal and transverse velocity of sound. The isotropic elastic moduli of oxide nuclear fuel at room temperature 298 K as a function of the porosity P of the sample in the interval 0 < P < 0.1 can ...

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Heat capacity measurement of U1−yGdyO2 (0.00 ≦ y ≦ 0.142) from 310 to 1500 K

Cited by 52 publications

References 18 publications

High-temperature heat-capacity measurement up to 1500K by the triple-cell DSC

High-temperature heat-capacity measurement up to 1500K by the triple-cell DSC

Thermophysical properties of uranium–europium mixed oxides

Model for the Specific Heat of Uranium Dioxide

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