The behaviour of stoichiometric U1-yPuyO2compounds used as nuclear fuel is relatively well understood. Conversely, the effects of stoichiometry deviation on fuel performance and fuel stability are intricate and poorly studied. In order to investigate what affect these have on the thermophysical properties of hypo-stoichiometric U1-yPuyO2-xmixed oxide fuel, new interaction parameters based on the many-body CRG (Cooper-Rushton-Grimes) potential formalism were optimized. The new potential has been fitted to match experimental lattice parameters of U0.7Pu0.3O1.99(O/M = 1.99) and U0.7Pu0.3O1.97(O/M = 1.97), where M represents the total amount of metallic cations, through a rigorous procedure combining classical molecular dynamic and classical molecular Monte Carlo simulation methods. This new potential provides an excellent description of the U1-yPuyO2-x system. Concerning lattice parameter, although fitted on only one Pu content (30%) and two stoichiometries (1.99 and 1.97), our potential allows good predictions compared to available experimental results as well as to available recommendations in wide ranges of O/M ratio, Pu content and temperature. For the U0.7Pu0.3O2-xhypo-stoichiometric system (30% Pu content and O/M ratio ranging from 1.94 to 2.00), some direct properties (lattice parameter and enthalpy) and some derivative properties (linear thermal expansion coefficient and specific heat) were systematically investigated from room temperature up to the expected melting temperatures and a good agreement with experiments is found. Moreover, our potential shows a good transferability to the plutonium sesquioxide Pu2O3system.

中文翻译：

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优化新的原子间势以研究亚化学计量混合氧化物燃料 U1-yPuyO2-x 的热力学性质

用作核燃料的化学计量 U1-yPuyO2 化合物的行为相对较好。相反，化学计量偏差对燃料性能和燃料稳定性的影响错综复杂且研究不足。为了研究这些对亚化学计量 U1-yPuyO2-x 混合氧化物燃料的热物理性质有何影响，优化了基于多体 CRG（Cooper-Rushton-Grimes）势形式的新相互作用参数。新的电势已被拟合以匹配 U0.7Pu0.3O1.99(O/M = 1.99) 和 U0.7Pu0.3O1.97(O/M = 1.97) 的实验晶格参数，其中 M 代表金属的总量阳离子，通过结合经典分子动力学和经典分子蒙特卡罗模拟方法的严格程序。这种新的潜力很好地描述了 U1-yPuyO2-x 系统。关于晶格参数，虽然仅适用于一种 Pu 含量（30%）和两种化学计量（1.99 和 1.97），但与可用的实验结果相比，我们的潜力允许良好的预测以及在广泛的 O/M 比率范围内的可用建议，Pu含量和温度。对于 U0.7Pu0.3O2-xhypo-stoichiometric 体系（30% Pu 含量和 O/M 比范围从 1.94 到 2.00），一些直接性质（晶格参数和焓）和一些衍生性质（线性热膨胀系数和比热） ) 从室温到预期的熔化温度进行了系统研究，发现与实验有很好的一致性。而且，