Molecular Simulation Of Composition And Irradiation Effects On Borosilicate Glasses

The nuclear energy industry has developed rapidly in recent years.Borosilicate glass?NBS glass?has been paid attention and researched due to its important application in the nuclear industry.On the one hand,NBS glass is an important immobilization material for high-level nuclear waste?HLW?,which is the first barrier to shield radioactive waste.In the long-term geological disposal process,it will inevitably suffer radiation from the decay of radioactive waste;On the other hand,NBS glass is also the main component of hollow glass microspheres?HGM?in inertial confinement fusion?ICF?.In the fusion experiment,the target gas is filled with D,T as reacted gas and argon as diagnostic gas to diagnose the density and temperature of the plasma.At present,ion beam irradiation modification method is a widely used method of filling gas.Based on the important application of NBS glass in nuclear fission and fusion,the molecular dynamics?MD?simulation was used to study NBS glass in two aspects in this work.It is hoped that NBS glass can be studied in micro level,so it can make up for the inadequacy of experimental method and have a guidance for experiments.1.Composition effects on NBS glassIn this part of work,the mechanical properties of a series of unirradiated glass samples named SNBS1-8 were tested by MD simulation and experimental methods.Both simulated and experimental results showed that the hardness and modulus of the glass increased with augment of the sodium to boron ratio?R?.Through the statistical analysis of the glasses'microstructure,it was found that the[BO₃]units were converted to[BO₄]with R increase,while the Si-O-Si structure was also increased consistently,but the non-bridging oxygen?NBO?remained almostly unchanged,which reflected the polymerization process of glass system.We believed that the increase of the mechanical properties should be mainly attributed to the polymerization of glass system.Through the study of component effects,it can be explained that MD simulation is feasible in predicting the mechanical properties of NBS glass,and the mechanical properties of NBS glass are greatly affected by the polymerized degree of glass system.2.Irradiation effects on NBS glassThe components of glass samples in this part were based on the experimental composition of HGM.The Au particles with energy of 1 keV were injected into the glass system by external irradiation.As the irradiation dose increases,more and more defects were generated in glass system,and finally a distinct diffusion channel was produced,indicating that the particles irradiation can enhance the diffusion ability in glass microspheres.Then after a period of relaxation under high temperature and high pressure,it was found that the defects caused by irradiation can be repaired to some extent,and the particle channel was gradually closed.We also found that the repaired effects becomed better with a higher temperature.The results could serve as a guidance to experiments:argon gas can diffuse into the microsphere through the microchannels generated by irradiation,and after a period of thermal relaxation,the defects are repaired and the purpose of inflating gas is finally achieved.The elevated temperature is beneficial to the repair process of the microspheres.