Effect of an electron gas on a neutron-rich nuclear pasta

We studied the role that electron gas has on the formation of nuclear structures at subsaturation densities and low temperatures(T1 Me V).Using a classical molecular dynamics model we studied isospin symmetric and asymmetric matter at subsaturation densities and low temperatures varying the Coulomb interaction strength.The effect of such variation was quantified on the fragment size multiplicity,the inter-particle distance,the isospin content of the clusters,the nucleon mobility and cluster persistence,and on the nuclear structure shapes.We found that the presence of an electron gas distributes matter more evenly,disrupts the formation of larger objects,reduces the isospin content,and modifies the nucleon average displacement,but does not affect the inter-nucleon distance in clusters.The nuclear structures are also found to change shapes by different degrees depending on their isospin content,temperature and density.     

Basic quantities of the equation of state in isospin asymmetric nuclear matter

Based on the Hugenholtz-Van Hove theorem,six basic quantities of the EoS in isospin asymmetric nuclear matter are expressed in terms of the nucleon kinetic energy t(k),the isospin symmetric and asymmetric parts of the single-nucleon potentials U0(ρ,k)and Usym,i(ρ,k).The six basic quantities include the quadratic symmetry energy Esym,2(ρ),the quartic symmetry energy Esym,4(ρ),their corresponding density slopes L2(ρ)and L4(ρ),and the incompressibility coefficients K2(ρ)and K4(ρ).By using four types of well-known effective nucleon-nucleon interaction models,namely the BGBD,MDI,Skyrme,and Gogny forces,the density-and isospin-dependent proper-ties of these basic quantities are systematically calculated and their values at the saturation density ρ0 are explicitly given.The contributions to these quantities from t(k),U0(ρ,k),and Usym,i(ρ,k)are also analyzed at the normal nuclear density ρ0.It is clearly shown that the first-order asymmetric term U/sym,1(ρ,k)(also known as the symmetry potential in the Lane potential)plays a vital role in deter-mining the density dependence of the quadratic symmetry energy Esym,2(ρ).It is also shown that the contributions from the high-order asymmetric parts of the single-nucleon potentials(Usym,i(ρ,k)with i＞1)cannot be neglected in the calculations of the other five basic quantities.Moreover,by analyzing the properties of asymmetric nuclear matter at the exact saturation density ρsat(δ),the corresponding quadratic incompressibility coefficient is found to have a simple empirical relation Ksat,2 = K2(ρ0)-4.14L2(ρ0).     

基于傅里叶级数展开的裂变位能曲面与碎片质量分布计算

裂变位能曲面是裂变核结构性质和裂变动力学研究的基础。本文使用傅里叶级数展开方法描述裂变过程中原子核的形状,采用基于Lublin Strasbourg Drop(LSD)宏观模型和Yukawa Folded微观模型计算了236U多维裂变位能曲面,研究了位能曲面随不同集体自由度(原子核拉长形变、左右碎片质量不对称度以及颈部宽度)的变化情况以及温度对位能曲面的影响。在位能曲面基础上采用基于Born Oppenheimer近似的三维集体模型描述原子核裂变过程,计算了236U裂变碎片质量分布,计算结果与实验数据符合较好,特别是质量分布的峰位,同时分析了核温度、零点能和颈部断裂概率半宽度对裂变碎片质量分布计算结果的影响。     

利用12C+96Zr弹性散射角分布研究96Zr的中子皮

中子皮是原子核的关键物理参数之一,对非对称核物质状态方程有重要的约束作用。本工作主要利用¹²C+⁹⁶Zr弹性散射角分布研究⁹⁶Zr的中子皮,首先采用Woods-Saxon势,通过改变实部势参数得到与实验数据拟合最优的1组光学势参数,然后利用双折叠势模型（DFM）计算⁹⁶Zr在不同中子密度分布下与¹²C的相互作用势,通过比较两组相互作用势,找出与最佳光学势对应的⁹⁶Zr核的中子分布均方根半径,从而得到⁹⁶Zr的中子皮厚度为0.087 fm,此结果与其他研究结果在误差范围内符合很好。     

234U裂变的五维势能曲面计算

本工作基于连接二次曲面的形状描述+LSD(Lublin Strasbourg drop)公式+折叠汤川势建立了宏观 微观模型。对234U裂变,计算了具有5 906 250个格点的五维势能曲面,然后通过搜索势能曲面得到了对称裂变和非对称裂变两个裂变通道,给出了裂变势垒高度以及鞍点和断点等特殊位置的原子核形状。     

The asymmetry of nuclear fission

One of the essential characteristics of nuclear fission and of processes occuring in nuclear reactors is the distribution of fission fragments by mass. According to the drop model of the nucleus, a symmetrical mass distribution of the fragments is most probable, but this, however, is contrary to experiment.To find the mass distribution of the fragments, in this work we calculated the energy of the fissionable nucleus before rapture of the neck, taking into account shell effects, for several nuclei. It was shown that the energy minimum corresponds to asymmetric fission.     

New features of the Monte-Carlo code MOCADI

MOCADI, the Monte-Carlo code for tracking of ions in ion-optical systems with non-Liouvillian elements, has been extended. Accurate atomic and nuclear interactions are taken into account when ions penetrate gaseous and solid matter placed within the ion-optical system. The new features of MOCADI are described in this article with practical examples which demonstrate the new possibilities, such as new event-generators for targets and spontaneous nuclear decay, the option of atomic-charge state fluctuation in matter, loops for multi-turn ion-optical systems and a graphical user interface for easier operating and control of the program. Experiments for investigation of nuclear structure and reactions with ions circulating in a storage ring can now be ideally studied with MOCADI.     

Modeling the nonlinear dynamic temperature and power oscillations in VVER

The nonlinear dynamic auto-oscillatory regimes of the temperature at the exit from the core and of the power of nuclear reactors are investigated and the quantitative features of the regimes are determined. A physical-mathematical model of the dynamics of a VVER-type nuclear reactor is examined, taking account of the inertial (temperature) and instantaneous (power) feedbacks in the reactor but neglecting the delayed neutrons. Analytical solutions characterizing the auto-oscillatory real-time behavior of the temperature at the exit from the core and of the reactor power are obtained. The period of these oscillations is determined. The model constructed for the dynamics of a reactor is used as a basis to simulate, using the RELAP5/Mod3.2 computer code, certain nonlinear auto-oscillatory processes occurring in the first and second loops of a nuclear power plant with a VVER-440 reactor. It is found that the oscillations of the temperature at the exit from the core and power of the nuclear reactor generate the same period for processes which were calculated.     

核分析相关技术用于上海市大气污染特征研究

本文研究了近年来上海市区和郊区大气气溶胶颗粒物的污染状况,采用的多种核分析方法及相关技术有质子激发X荧光分析(PIXE)、激光粒径谱仪(LPS)、同步辐射X射线吸收精细结构(XAFS)和扩展X射线吸收谱精细结构(EXAFS)分析等先进技术.充分发挥核分析技术高灵敏度、快速无损、多元素微量微区同时分析的优势,从大气颗粒物的形貌特征、粒径分布、质量浓度、元素浓度、化学价态等入手,对上海大气可吸入颗粒物PM23和PM1o展开多方位的综合研究.     

Transient processes induced by heavy projectiles in silicon

The thermal spike model developed for the electronic stopping power regime is extended to consider both ionization and nuclear energy loss processes of the projectile as electronic and atomic heat distinct sources. The time and space dependencies of the lattice and electron temperatures near the projectile trajectory are calculated and discussed for different ions in silicon, at room and cryogenic temperatures, taking into account the peculiarities of electron-phonon interaction in both domains. The model developed contributes to the understanding of transient microscopic processes immediately after the projectile interaction in the target.     

非对称压水室对CAP1400主泵性能影响的分析研究

压水室作为主泵的边界,不仅承担着压力而且还是周向流出的导叶与单向流动的管路之间的唯一桥梁。为探究压水室对整机性能的影响,以CAP1400的1:2.5缩比模型为目标,提出了一种关于主泵非对称压水室的设计方法,并设计出4种不同几何尺寸的非对称模型。借助计算流体动力学（CFD）数值方法,得到含有口环间隙的核主泵全三维模型的内部流场、外特性及瞬态载荷信息。通过对比分析获得结论:4种非对称压水室模型将上盖板处径向载荷减小60%以上,使叶轮及总径向载荷的主频幅值减小13%以上;在保证径向载荷有明显改善的同时,还能有效提升泵体效率和扬程,前者改善更为明显,提升范围为0.57%~0.83%。      

基于MCNP程序的海洋核动力平台堆芯核设计校核计算研究

海洋核动力平台是小型核反应堆与船舶工程技术的有机结合,具有机动性好、一次性装料运行周期长、功率密度大、运行成本低、节能环保等特点。本文采用蒙特卡罗粒子输运程序(MCNP),建立海洋核动力平台反应堆堆芯几何模型,计算该反应堆首循环初始装料冷态、常压下的堆芯反应性和控制棒价值,并与核设计计算结果进行对比。结果表明:MCNP程序适用于海洋核动力平台反应堆堆芯核设计校核计算,并可与核设计值互相验证。     

Influence of α-clustering nuclear structure on the rotating collision system

In recent years, the collective motion properties of global rotation of the symmetric colliding system in relativistic energies have been investigated. In addition, the initial geometrical shape effects on the collective flows have been explored using a hydrodynamical model, a transport model, etc. In this work, we study the asymmetric ~(12)C+~(197)Au collision at 200 GeV/c and the effect of the exotic nuclear structure on the global rotation using a multi-phase transport model. The global angular momentum and averaged angular speed were calculated and discussed for the collision system at different evolution stages.     

用于缓减UTSG倒流的U型管改进研究

针对自然循环条件下蒸汽发生器部分并联U型管出现的倒流现象,以增强自然循环能力和减少倒流为目的,提出非对称U型管改进方案。基于基本守恒方程,建立了非对称U型管流动传热计算模型和自然循环冷热源位差计算模型。在此基础上,以某型核动力装置U型管为原型,对改进前后U型管倒流临界流量与回路冷热源位差的变化进行了计算分析。计算结果表明：非对称U型管改进使倒流临界流量明显减小,回路冷热源位差明显提升。适当调整U型管上升段与下降段长度比可减少倒流发生,提高自然循环能力。     

Heat Transfer Performance of High Temperature and High Velocity Hydrogen Flow inside Circle Tube

In order to investigate the thermo-hydraulic characteristics of working fluids in the coolant channel of nuclear thermal propulsion reactors, the flow and heat transfer performance of high temperature and high velocity hydrogen in the circle tube was studied by the numerical calculation method. Comparing with the experimental data, it is found that the pressure-based coupled algorithm, SST k-ω turbulence model and hydrogen property model are reasonable and feasible to simulate the flow and heat transfer performance of hydrogen at high temperature and high velocity. The calculated values agree well with the experimental data, and the numerical simulation model is correct. Based on the analysis of flow and temperature field of the base case, the effects of thermal parameters on the flow and heat transfer performance of hydrogen were also studied. The increasing inlet mass flow rate enhances heat transfer performance and the increasing heat flux weakens it. The methods and results can provide some references and guidance for the study of the flow and heat transfer performance of gaseous fluid under high temperature and high heat flux, and thermal design and simulation of nuclear thermal propulsion reactor.     

三维带控制棒反应性温度系数的计算分析

介绍了三维带控制棒计算反应性温度系数的计算方法，对于２００ＭＷ供热堆，在不同棒位下作了三维反应性温度系数的计算，结果表明，慢化剂温度系数的大小和控制棒插入的深度有一定关系。以运行工况临界棒位下的慢化剂温度系数为参考，对二维计算结果作了分析，结果表明第二维无控制棒计算是保守的近似。     

小型核动力装置自然循环运行特性分析

本文以小型一体化自然循环反应堆为研究对象,用RELAP5/MOD3.2对反应堆系统、中间回路及二回路系统进行建模,对反应堆单双环路切换及偏环路运行时反应堆的自然循环运行特性进行数值模拟研究。计算结果表明:在反应堆自然循环运行工况下,进行单双环路切换及偏环路运行时,堆芯能重新建立稳定的自然循环。双环路切换至单环路后,堆芯出口温度降低,堆芯自然循环平衡流量降低但仍大于初始值的1/2;单环路切换至双环路运行时,堆芯流量、温度均与双环路稳定工况的一致;偏环路运行时故障环路循环流量降低,正常环路自然循环流量升高,堆芯总流量降低的数值为二者之差。     

高温、高流速氢气在圆管内流动换热特性研究

为探究工质在核热推进反应堆冷却剂通道内的热工水力行为,基于数值计算方法,开展了圆管内高温、高流速氢气流动换热特性研究。通过与实验数据对比发现,采用压力基耦合算法、SST k-ω湍流模型以及物性模型进行高温、高流速氢气流动换热特性数值模拟是合理可行的,计算值与实验值符合较好,计算模型选择正确。在分析基础工况流场与温度场的基础上,还研究了热工参数对氢气管内流动换热特性的影响,结果表明,随质量流量的增大换热效果增强,随热流密度的增大换热效果变差。研究方法与结果可为高温、高热流密度环境下气体工质流动换热特性研究、核热推进反应堆的热工设计与仿真模拟提供参考。     

Three-dimensional transient thermal stresses of reactor graphite subjected to internal heat generation and asymmetric surface heating

The present paper is concerned with three-dimensional transient thermal stresses of graphite in a nuclear reactor. In analyzing this problem, reactor graphite may be approximated by a transversely isotropic finite circular cylinder subjected to internal heat generation and asymmetric heating on an end surface. Thermal stresses are analyzed by means of the transversely isotropic potential functions method proposed by Takeuti and Noda. Numerical calculations were carried out for a special type of heating conditions, and time variations of temperature and thermal stresses of graphite are shown in figures.     

The growth of gas-bubbles by coalescence in solids during continuous gas generation

In order to get some insight into the mode of gas bubble growth during the high temperature irradiation of solids, we have calculated the distributions of bubbles grown by coalescence. The calculations are based on Gruber's coalescence model for annealing which we have extended to the case of an irradiation induced gas generation. The dominant assumption is that the continuously generated inert gas atoms go into new bubbles distributed around small radii. The results show that the bubble growth rate is markedly increased by the irradiation induced gas generation and that the calculated bubble distribution profile exhibits a double peak as often observed experimentally.