Evolutions On Mechanical Properties Of Borosilicate Glass Induced By Ions And Electrons

Several issues are challenging the energy development of China,such as the imbalance of quality and structure of the energy resources,increasing environmental pressures and severe energy security situation,etc.It is significant to develop the nuclear power for optimizing the energy structure and protecting national energy security.Although the nuclear power is a 'clean'and efficient energy,a large number of radioactive wastes will be produced,and the high level waste(HLW)should to be isolated from biosphere and disposed permanently.According to the development plan of the Chinese government,the HLW will be vitrified in glass and then be settled in the underground disposal repository.As the first engineering protation of the underground disposal repository of HLW,nuclear waste glass will suffer irradiations caused by a decay and ? decay of radionuclide in HLW,which will change the micro structions and macro properties of nuclear waste glass,finally result in more leaching of radioactive nuclide.Therefore,the stability of nuclear waste glass under irradiation affects the success of the disposal of HLW,it is necessary to study the irradiation effect of nuclear waste glass.Nowadays,the most widespread accepted nuclear waste glass base material for HLW in the world is the borosilicate glass.As the leaching performance of radioactive nuclide is influencd by the mechanical properties of nuclear waste glass,it is necessary to study the evolutions of the mechanical properties of borosilicate glass with irradiation.It will contribute to the prediction of the behaviors of nuclear waste glass in disposal repository and prevent the possible leaching accident of radioactive nuclide.To study the evolutions of mechanical properties of nuclear waste glass caused by irradiation during disposal,light ions,heavy ions and electrons were employed to simulate the irradiation environment in this work.Three types of borosilicate glass were irradiated by ions and electrons in a external irradiation way,the mechanical properties of glass were investigated by nano-indentation test.The irradiation dose was set in accordance with the irradiation dose of the nuclear waste glass disposed for one million years.In addition,to analyze the physical mechanism evolutions of irradiated borosilicate glass,glass samples were also measured with Raman spectroscopy,electron paramagnetic resonance and optical absorption spectrum.By analyzing the evolutions of irradiated glass samples,several conclusions were obtained in this work as flowed:1).The nano-hardness curves of borosilicate glasses irradiated by He ions and heavy ions are shown as two regions with the increase of penetration depth and increasing region,the former region is caused by irradiation damage in glass,in which the ratio of incident ion range to the deepest depth of plateau region K1 is about 1.3.The increasing region,converged with the un-irradiated glass,in which the ratio of the end of this region to the range of incident ion K2 is about 1.8.This indicates that the ranges of incident ions is 1.8 times of the plastic interaction zone in irradiated glass and the plastic effects on the hardness of irradiated glasse expands to about 1.3 times the range of incident ions.2).The nano-hardness of borosilicate glasses irradiated by He ions and heavy ions begin to decrease when nuclear energy deposition is about 5×1019 keV/cm3,and reach stabilization as the nuclear energy deposition get about 1×1021 keV/cm3,the decrease of mean hardness of irradiated glass is about 11-16%.The evolutions of mechanical properties of glass irradiated by He ions and heavy ions might be induced by the density variation or swelling of volume after irradiation.3).Comparing with the pristine glass,the nano-hardness curve of electron-irradiated glass decreases in the whole penetration depth.A slight decrease of about 6%is observed in the mean hardness of the electron-irradiated glasses with the irradiation dose of 109 Gy.With electron irradiation,some changes have been observed in microstructure of borosilicate glass,such as the increase of the polymerization of silica network,formation of defects,and evolutions of ring structures.4).By He ions,heavy ions and electrons irradiation,the hardness of borosilicate glass decreases.However,there is no evident change is observed in the elastic modulus of irradiated glasses,which indicates that the recovery resistance of glass improved,the brittleness of glass decreased,and the mechanical properties of borosilicate glasses are improved after irradiation.5).The nuclear energy deposition is the major factor for the evolution in the plastic response of the borosilicate glass,while the electronic energy deposition influences the silicate network and migration of alkaline,which causes sight variation of the mechanical properties.The structural origins of modifications on mechanical properties of borosilicate have not been clearly confirmed,especially considering the effects of electronic and nuclear process,respectively.For this reason,the physical mechanism of evolutions of irradiated borosilicate glass caused by energy depositon during irradiation was also discussed in this work.