Ion And Electron Beam Irradiation Induced Microstructure Evolution In Borosilicate Glass

Currently,rapid development of nuclear power is the basic national policy of energy strategy in China.However,a lot of high level waste(HLW)will be produced at the meantime.According to the plan of Chinese government,these high level wastes will be solidified into the glass and then disposed into geological repository.However,the materials properties(e.g.,leach rate,stored energy,and volume expansion)of glasses can be very sensitive to interactions with a radiation field caused by the decay of the incorporated fission products and actinides.Such radiation effects could potentially impact the long term performance and environmental risk of glasses for HLW immobilization and disposal.However,in China,very few studies have been carried on the irradiation stability of HLW glass.The micromechanism of radiation induced modifications on the glass is still not yet well understood.Thus,it is very necessary to study the radiation effects of HLW glass and develop the related assessment system.In this thesis,we introduced:the source and characteristic of HLW;the vitrifaction and geological disposal of HLW;the types and characteristic of HLW glass;as well as the microstructure of borosilicate glass,which is the main type of HLW glass.The details of irradiation experiments and characterization methods were also presented.In our work,the microstructure evolution of borosilicate glass network induced by ion and electron beam irradiation was studied.In addition,the studies of phase separation induced by electron irradiation was also reported.In the last,the investigation on the changes in the surface morphology of borosilicate glass induced by MeV heavy ion and electron irradiation was presented.1)To simulate the radiation effects induced by a-recoil nuclei,the microstructure e-volutions of sodium aluminoborosilicate glass and high boron-silicate glass induced by 4 MeV Kr17+ ions irradiation were studied by Raman spectroscopy.The shift of Si-O-Si vibration band and changes in the ring structure were evidenced in the irradiated samples.These have been correlated to the densification process of glass.Depolymerization of glass network caused by Kr ion irradiation was also observed.These results indicate that the microstructural modifications caused by Kr ion irradiation are the consequence of ballistic effects.2)To simulate the radiation effects induced by a particles,the microstructure evolutions of sodium borosilicate glass induced by the 400 keV He ion irradiation was studied by infrared reflection spectra.The shift of Si-O-Si vibration band was evidenced,which is corresponded to the densification of glass network.Increase of network polymerization and transition of[BO4]to[BO3]were also observed,which were correlated to the diffusion of sodium ions caused by ionization.3)To simulate the radiation effect induced by ? particles,the microstructure evolutions of sodium aluminoborosilicate glass induced by 1.2 MeV electron irradiation were studied by X-ray photoelectron spectroscopy and Raman spectroscopy.A sodium depleted layer with thickness of a few tens of nanometers and corresponding increase of network polymerization on the top surface were observed after electron bombardment,while the polymerization in the subsurface region had a negligible variation with the irradiation dose.Moreover,the formation of molecular oxygen after electron irradiation was evidenced,which was mainly aggregated on the first two microns of the irradiated glass surface.These modifications have been correlated to the network relaxation processes as a consequence of diffusion and desorption of sodium species during electron irradiation.4)The phase separation induced by electron irradiation was studied in situ by transmission electron microscope.Under electron beam,the phase separation was occurred very soon in both glass,which was correlated to diffusion and desorption of sodium species.A simple structural model was introduced to explain the difference in separated phase in two different glass,which indicates that the phase separation induced by electron irradiation is closely related to the sodium contents in the glass sample.5)The changes in the surface morphology of borosilicate glass induced by MeV heavy ion and electron irradiation was initially presented.The formation of bumps was observed.These bumps have inhomogeneous size and height,and were randomly arranged on the glass surface.The roughness was significantly increased after irradiation.The formation of bumps might correlate to the formation of Si-O-O-Si bonds after network relaxation processes caused by migration of alkali ions.