Based on machine learning,the high-dimensional fitting of potential energy surfaces under the framework of first principles provides density-functional accuracy of atomic interaction potential for high-precision and l...Based on machine learning,the high-dimensional fitting of potential energy surfaces under the framework of first principles provides density-functional accuracy of atomic interaction potential for high-precision and large-scale simulation of alloy materials.In this paper,we obtained the high-dimensional neural network(NN)potential function of uranium metal by training a large amount of first-principles calculated data.The lattice constants of uranium metal with different crystal structures,the elastic constants,and the anisotropy of lattice expansion of alpha-uranium obtained based on this potential function are highly consistent with first-principles calculation or experimental data.In addition,the calculated formation energy of vacancies in alpha-and beta-uranium also matches the first-principles calculation.The calculated site of the most stable self-interstitial and its formation energy is in good agreement with the findings from density functional theory(DFT)calculations.These results show that our potential function can be used for further large-scale molecular dynamics simulation studies of uranium metal at low pressures,and provides the basis for further construction of potential model suitable for a wide range of pressures.展开更多
Using the experimental results given in literatures about the contact angle, θ and the work of adhesion, W, for nonreactive liquid metal / solid UO_2 systems, the validity and feasibility of the different existing mo...Using the experimental results given in literatures about the contact angle, θ and the work of adhesion, W, for nonreactive liquid metal / solid UO_2 systems, the validity and feasibility of the different existing models for calculating W in the metal /ox- ide systems are discussed. It can be shown that the models assuming that only metal atom-oxygen ion interactions existing at the interfaces are unable to explain the experimental results for W. More reasonable model should take into account both metal atom-oxygen ion and metal atom-oxide metal cation interactions, the proportion of the latter is balanced by the stoichiometry of the oxide. By applying the model recently set up by the authors for binary alloy / oxide systems, one can use the experimental and calculated values of θ and W for various metal / UO_2 systems to predict the influence of metallic additions on the contact angle and the work of adhesion of a given metal / UO_2 system.展开更多
This paper shows a methodology to obtain metallic uranium through a magnesiothermy process. Chile has two experimental reactors operated by the “Chilean Nuclear Energy Commission” (CCHEN). One is 5 MW and the other ...This paper shows a methodology to obtain metallic uranium through a magnesiothermy process. Chile has two experimental reactors operated by the “Chilean Nuclear Energy Commission” (CCHEN). One is 5 MW and the other is 10 MW. In order to fulfill international agreements about nuclear energy for testing purposes of these reactors, CChEN purchased 19.9% enriched uranium hexafluoride, also known as the limit of Low Enriched Uranium (LEU). Due to the capacity of these reactors, they need high-density uranium compounds for their fuel, in order to work with LEU. For this reason, the uranium needs a previous conversion into metallic uranium. The conversion laboratory carried out experiences for reduction of UF4 with Mg. The main purpose of this study was to analyze the operating conditions under which the reduction reaction takes place, the designed method and the equipment and materials used. The raw material used was dehydrated UF4, prepared by electrolytic reduction and commercial purity Magnesium. The reaction took place in a cylindrical reactor made of low alloy steel, with a conic section in the lower part. The internal zone was coated with a 2.5 cm thick layer of CaF2. The process started by applying external heating, according to a heating program, developed specially for this purpose. The reduction reaction took place starting at 650°C. The result was a cylinder of uranium metal and MgF2 slag. The crossed cut uranium cylinder showed a smooth and homogeneous surface without inclusions of slag, pores or blisters. The yield of the reaction was of the order of 75% with respect to the expected theoretical value. The uranium cone obtained fulfilled the required conditions for source material for nuclear fuel fabrication, with a uranium content of 97.5%.展开更多
扬子地台寒武系下统存在富含V、Ni、Mo和铂族元素(platinum group element, PGE)等的黑色页岩,局部地区有U或者Ba、Hg、As等的富集,研究这些元素富集机理有利于寻找相关矿产或者探究地质事件。6 500万年前的小行星撞击地球产生了高PGE...扬子地台寒武系下统存在富含V、Ni、Mo和铂族元素(platinum group element, PGE)等的黑色页岩,局部地区有U或者Ba、Hg、As等的富集,研究这些元素富集机理有利于寻找相关矿产或者探究地质事件。6 500万年前的小行星撞击地球产生了高PGE含量的地层或者化石,依据这一事实和陨石的特征及其他地质地球化学证据,推断下寒武统黑色页岩中Ni-Mo-PGE富集是陨石撞击结果,PGE中的Ir、Os富集最明显是因为二者最抗淋滤。U在康滇地轴东侧黑色页岩中最高可达480×10^(-6),因康滇地轴本身就存在混合型铀矿,推测黑色页岩中U来自它的风化。据V和Ba-Hg-As等的地化特性,认为V富集是受生物活动影响,但因V易于在热泉水中富集,故寒武纪早期泛非运动的构造-热事件可导致V富集成矿,Ba、Hg、As也因该事件产生构造裂隙后,它们优先随热液沿裂隙上升富集,并在海底局部成矿。此外,5.65亿年前的埃迪卡拉动物群发生地基本上就是5.8亿年前小行星撞击地点,提出此次行星撞击可能与埃迪卡拉生物群出现存在因果关系。由于在中国存在寒武纪澄江生物群大爆发事件,推测该次生物大爆发之前存在的下寒武统黑色页岩也存在陨石撞击痕迹。寒武系下统的含岩屑细砂岩夹黑色页岩甚至砾岩,反映了黑色页岩沉积时存在的突变沉积环境,加上其他地球化学特征也支持小行星撞击说。展开更多
基金Beijing Computational Science Research Center(CSRC)the National Natural Science Foundation of China(Grant Nos.52161160330 and U2230402)。
文摘Based on machine learning,the high-dimensional fitting of potential energy surfaces under the framework of first principles provides density-functional accuracy of atomic interaction potential for high-precision and large-scale simulation of alloy materials.In this paper,we obtained the high-dimensional neural network(NN)potential function of uranium metal by training a large amount of first-principles calculated data.The lattice constants of uranium metal with different crystal structures,the elastic constants,and the anisotropy of lattice expansion of alpha-uranium obtained based on this potential function are highly consistent with first-principles calculation or experimental data.In addition,the calculated formation energy of vacancies in alpha-and beta-uranium also matches the first-principles calculation.The calculated site of the most stable self-interstitial and its formation energy is in good agreement with the findings from density functional theory(DFT)calculations.These results show that our potential function can be used for further large-scale molecular dynamics simulation studies of uranium metal at low pressures,and provides the basis for further construction of potential model suitable for a wide range of pressures.
文摘Using the experimental results given in literatures about the contact angle, θ and the work of adhesion, W, for nonreactive liquid metal / solid UO_2 systems, the validity and feasibility of the different existing models for calculating W in the metal /ox- ide systems are discussed. It can be shown that the models assuming that only metal atom-oxygen ion interactions existing at the interfaces are unable to explain the experimental results for W. More reasonable model should take into account both metal atom-oxygen ion and metal atom-oxide metal cation interactions, the proportion of the latter is balanced by the stoichiometry of the oxide. By applying the model recently set up by the authors for binary alloy / oxide systems, one can use the experimental and calculated values of θ and W for various metal / UO_2 systems to predict the influence of metallic additions on the contact angle and the work of adhesion of a given metal / UO_2 system.
文摘This paper shows a methodology to obtain metallic uranium through a magnesiothermy process. Chile has two experimental reactors operated by the “Chilean Nuclear Energy Commission” (CCHEN). One is 5 MW and the other is 10 MW. In order to fulfill international agreements about nuclear energy for testing purposes of these reactors, CChEN purchased 19.9% enriched uranium hexafluoride, also known as the limit of Low Enriched Uranium (LEU). Due to the capacity of these reactors, they need high-density uranium compounds for their fuel, in order to work with LEU. For this reason, the uranium needs a previous conversion into metallic uranium. The conversion laboratory carried out experiences for reduction of UF4 with Mg. The main purpose of this study was to analyze the operating conditions under which the reduction reaction takes place, the designed method and the equipment and materials used. The raw material used was dehydrated UF4, prepared by electrolytic reduction and commercial purity Magnesium. The reaction took place in a cylindrical reactor made of low alloy steel, with a conic section in the lower part. The internal zone was coated with a 2.5 cm thick layer of CaF2. The process started by applying external heating, according to a heating program, developed specially for this purpose. The reduction reaction took place starting at 650°C. The result was a cylinder of uranium metal and MgF2 slag. The crossed cut uranium cylinder showed a smooth and homogeneous surface without inclusions of slag, pores or blisters. The yield of the reaction was of the order of 75% with respect to the expected theoretical value. The uranium cone obtained fulfilled the required conditions for source material for nuclear fuel fabrication, with a uranium content of 97.5%.
文摘扬子地台寒武系下统存在富含V、Ni、Mo和铂族元素(platinum group element, PGE)等的黑色页岩,局部地区有U或者Ba、Hg、As等的富集,研究这些元素富集机理有利于寻找相关矿产或者探究地质事件。6 500万年前的小行星撞击地球产生了高PGE含量的地层或者化石,依据这一事实和陨石的特征及其他地质地球化学证据,推断下寒武统黑色页岩中Ni-Mo-PGE富集是陨石撞击结果,PGE中的Ir、Os富集最明显是因为二者最抗淋滤。U在康滇地轴东侧黑色页岩中最高可达480×10^(-6),因康滇地轴本身就存在混合型铀矿,推测黑色页岩中U来自它的风化。据V和Ba-Hg-As等的地化特性,认为V富集是受生物活动影响,但因V易于在热泉水中富集,故寒武纪早期泛非运动的构造-热事件可导致V富集成矿,Ba、Hg、As也因该事件产生构造裂隙后,它们优先随热液沿裂隙上升富集,并在海底局部成矿。此外,5.65亿年前的埃迪卡拉动物群发生地基本上就是5.8亿年前小行星撞击地点,提出此次行星撞击可能与埃迪卡拉生物群出现存在因果关系。由于在中国存在寒武纪澄江生物群大爆发事件,推测该次生物大爆发之前存在的下寒武统黑色页岩也存在陨石撞击痕迹。寒武系下统的含岩屑细砂岩夹黑色页岩甚至砾岩,反映了黑色页岩沉积时存在的突变沉积环境,加上其他地球化学特征也支持小行星撞击说。
