Study On The Mechanism Of Leaching Property Changes In Ion Irradiated Borosilicate Glass

With the rapid development of human society,the level of industrialization and the improvement of social production and life require a lot of energy.Among them,nuclear energy is regarded as the most ideal energy because of its clean,reliable and sustainable characteristics,which can make an important contribution to reducing global greenhouse gas emissions.However,with the development of the nuclear energy,how to safely dispose these highly toxic and radioactive nuclear waste caused by the production and use of nuclear fuel has also become a serious issue.At present,the mainstream treatment method in the world is"vitrification-deep geological disposal".The high-level radioactive waste and the glass matrix material are melted into a glass solidified body and placed in the ground for burial.However,in the process of underground burial,the glass solid body may come into contact with groundwater,resulting in the leaching of radionuclides and flowing into the biosphere through the groundwater,which will bring great harm to the survival and development of the earth’s ecosystem.Therefore,the"anti-leaching performance"of the glass solidified body has become an important indicator to measure the actual performance of the glass solidified body.In this paper,the change of leaching properties of borosilicate glass caused by ion irradiation was discussed.In the real geological disposal process,there are many kinds of radionuclides in the high-level radioactive waste in the borosilicate glasses.These highly radioactive nuclides produce alpha decay accompanied by recoil nuclei of 70～100 ke V and associated gamma rays.And beta decay produces electrons and accompanying gamma rays.In order to study the influence of the mixed radiation field on the leaching performance of the glasses during real geological disposal,in this paper,15 Me V Si⁵⁺irradiation experiment was used to simulate the radiation damage caused by the mixed radiation field to the borosilicate glasses.The irradiation doses were 10¹⁴,5×10¹⁴and 10¹⁵ions/cm~2,respectively.The self-made glass samples were leached by the MCC-1 static immersion method.The leaching time was 1,3,7,14,and 28 days,respectively.The leaching temperatures were 50°C,70°C,and90°C,respectively.By using Inductively Coupled Plasma Optical Emission Spectrometer,Scanning Electron microscope and Raman spectrometer,the leaching rate of different elements and the surface structure and morphology of the altered layer were measured before and after irradiation of glass samples.In summary,the main conclusions are described as follows.1.The leaching rate of the boron element and sodium element in glass samples decrease with the increase of leaching time,and finally reaches saturation.The surface of the glass samples peeled off during the leaching process and formed an altered layer after 28 days of leaching process.The boron and sodium elements in the altered layer are almost depleted,the Danburite structure disappears,and the transformation from[BO₄]unit to[BO₃]unit happens,accompanied by the hydrolysis of Si O₂network（Si O₂+2H₂O→H₄Si O₄）,Q~3and Q~4structure almost disappeared,Si-OH bonds increased,and metasilicate and disilicate structures were formed.2.After the irradiation of silicon ions,the leaching rate of glass samples increased in the early stage of the leaching process,and the leaching rate was positively correlated with the irradiation dose.However,the irradiation effect disappeared in the later stage of the leaching process.Comparing with the non-irradiation glass samples which the leaching process is controlled by the single ion diffusion mechanism,the leaching process of irradiated glass sample is controlled by the combination of network dissolution mechanism and ion diffusion mechanism.3.With the increase of temperature,the leaching rate of borosilicate glass samples also increases a lot.The reaction activation energy of unirradiated glass is obviously affected by temperature.The reaction activation energy between 50℃and70℃is 245.93 KJ/mol,and the reaction activation energy between 70℃and 90℃is27.86 KJ/mol.In contrast,after the irradiation of silicon ions,the reaction activation energies of the glass samples between 50℃and 90℃are similar,almost around 100KJ/mol.This indicates that the leaching mechanism of glass samples after irradiation is relatively less affected by temperature.