Molecular Dynamics Of Coulomb Explosion In Nuclear Reactor Material

In the strong radiation field,the structure and properties of nuclear reactor material will be changed.The resistance of irradiation and performance changing in harsh environment,which is important properties of nuclear fuel directly determines the safety of nuclear reactors.Different from the light particles,the interaction between heavy ion with high energy and material will produce some special effects,one of them is the Coulomb explosion effect.By understanding Coulomb explosion effect,it has not only vital significance to study radiation damage for accelerator simulation,but also has an important significance to the irradiation damage effect for realistic reactor,due to the fission fragments in the fission reactors are mostly heavy ions with high energy.Due to the Coulomb explosion effects complete in nanoseconds,so the developing process cannot be observed with the current experimental conditions.Over the past few decades,with the rapid development of computer server technology,the nanometer scale atomic system can be simulated using molecular dynamics(MD)method in picoseconds time scale.The aim of the present work is to understand the Coulomb explosion effect and descript the changes in microstructure of the materials in nanometers spatial scale and in time scale nanoseconds during Coulomb explosion effect,and find the main factors which influence the Coulomb explosion effect.In this study,monocrystal silicon material and monocrystal silicon carbide material and monocrystal U02 material were selected as research objects.Monocrystalline silicon material consists components serving as nuclear sensitive detector,which has been widely used in nuclear engineering detection,also is a kind of important semiconductor materials;In the new inert matrix fuels,silicon carbide material as matrix material was sintered together with Pu02 and form new nuclear fuel;Uranium dioxide material as the nuclear fuel has been widely used in light water nuclear reactors.These materials will be bombarded by high energy heavy ion inevitably in the nuclear engineering application,in which the Coulomb explosion effect will occur.In order to study the Coulomb explosion effect,molecular dynamics code LAMMPS(Large-scale Atomic Molecular Massively Parallel Simulator)was used to simulate the microstructure change after swift and heavy ion irradiation.It is an open source software,which is mainly used for the calculation and simulation of molecular dynamics.The simulation works include:Building a model based on the theoretical data of the material,selecting a suitable potential energy function used to describe the interaction among atoms,relaxing the models to the corresponding initial temperature,selecting 50%atoms in local area as ionization atoms and ionizing them,combining the ionized atoms as cooling stage.Using the results of LAMMPS program output,combining with visualization software VMD and OVITO,we can get the information of atoms movement in the material.In addition,the energy information and the relative position information among the atoms in the material could be obtained by using the code developed by ourselves and assistant software.The results indicate that:The pulsed ionization of cylindrical cores can lead to localized melting,disorder of atoms and amorphization by the Coulomb Explosion effect.The longer ionization time,the larger melting/amorphization radius.The melting radius is larger at higher substrate temperatures.Shock waves can be generated by Coulomb explosion,whose propagation exhibit anisotropy,the transfer is also different by different mass atoms in the materials.Sputtering atoms can be produced from the free surface by Coulomb explosion,there is a close relationship between the sputtering phenomenon and ionization time.Comparing the damage produced by Coulomb explosion in Si and UO2 materials,it can be inferred that:for Si material,the initial temperature influence is more obvious;and for U02 material,the ionization time influence is more obvious.The research results provide not only a theoretical reference for the experimental study on the damage effect of heavy ion irradiation,but also provide a theoretical reference for the development of advanced nuclear reactor materials.