STUDY ON THERMODYNAMIC PROPERTIES OF OXIDE FUELS SIMULATED FOR TRANSMUTATION

ThO_2、uo_2、Np O_2和PuO_2样品的晶格参数用绝对温度的三阶多项式方程表示。在1200k时计算的二氧化锕系元素的线性热膨胀系数（alpha）与其熔点成反比。在室温下，UO_2的α值高于NpO_2和PuO_2，这可能是由于UO_2的德拜温度较低所致。Np_yU_<1-y>O_<2+x> （y=0、0.1、0.3、0.5、0.7、1.0）、Np_yPu_<1-y>O_<2+x> （y=0、0.05、0.1、0.2、0.5）和（Pu_yU_<1-y>）O_<2 > （y=0、0.02、0.03、0.05、0.08、0.10）固溶体的晶格参数均表示为三阶多项式方程，且随绝对温度的升高而平稳增加，无相变。根据测量的热膨胀数据和估计的力学性能，根据热力学关系C_p = (beta V)/(kappa_3 γ)计算了它们固溶体的比热容。UO_<2 >的热容误差在实验值的*5%以内。本课题计算的所有固溶体的C_p值与文献中的温度依赖性相同。已有文献报道了化学计量（Pu_yU_<1-y>）O_<2.00>在y=0.04和化学计量（Th_yU_<1-y>）O_<2.00>在y=0.02时偏离维加德定律，但在本研究中没有观察到掺杂阳离子浓度的异常行为，并且化学计量（M_yU_<1-y>）O_<2.00> (M=Pu, Th，在小y处，随着掺杂阳离子的增加，La)固溶体呈线性变化。通过假设二氧化铀中掺杂阳离子的随机分布和每个阳离子和阴离子形成刚性球体的离子模型，从阳离子浓度与晶格常数的依赖关系计算了掺杂阳离子的价态。通过理论值与实验数据的比较，认为固溶体中的钚、钍和镧离子以Pu^<4+>（或Pu^<3+>）、Th^<4+>和La^<3+>的形式存在。少

The lattice parameters of ThO_2, U O_2, Np O_2 and PuO_2 samples were expressed in terms of the third order polynomial equation of the absolute temperature. The linear thermal expansion coefficients(alpha) of the actinide dioxides calculated at 1200 K were in reverse relation to their melting points. At room temperature, on the other hand, the alpha value of UO_2 was found to be higher than those of NpO_2 and PuO_2, probably due to lower Debye temperature of UO_2.The lattice parameters of Np_yU_<1-y>O_<2+x> (y=0, 0.1, 0.3, 0.5, 0.7, 1.0), Np_yPu_<1-y>O_<2+x> (y=0, 0.05, 0.1, 0.2, 0.5) and (Pu_yU_<1-y>)O_<2 > (y=O, 0.02, 0.03, 0.05, 0.08, 0.10) solid solutions were expressed as the third order polynomial equation and smoothly increased with increasing the absolute temperature without any phase transitions. The specific heat capacities of their solid solutions were calculated from the thermodynamic relation C_p = (beta V)/( kappa_3 gamma) using measured thermal expansion data and estimat … More ed mechanical properties. The errors for heat capacities of UO_<2 > were within *5% of the experimental values. The calculated C_p values for all solid solutions in this project showed the same temperature dependence as the literature ones.Deviation from Vegard's law had been reported at y=0.04 for stoichiometric (Pu_yU_<1-y>)O_<2.00> and at y=0.02 for stoichiometric (Th_yU_<1-y>)O_<2.00> in the literatures, However, in this study no abnormal behavior was observed for doped cation concentrations, and the lattice parameters of the stoichiometric (M_yU_<1-y>)O_<2.00> (M=Pu, Th, La) solid solutions changed linearly with increasing doped cation at small y. The valence of the doped cations was calculated from the dependence of the cation concentrations on the lattice constants by assuming a random distribution of doped cations in uranium dioxide and an ionic model where every cation and anion form a rigid sphere. By comparing the theoretical values with the experimental data, plutonium, thorium and lanthanum ions in solid solution are considered to exist as Pu^<4+> (orPu^<3+>), Th^<4+> and La^<3+>. Less