Study Of Evolution Mechanism Of Irradiation-Temperature Thermal Aging On Mechanical Properties Of The GMZ Sodium Bentonite

With the development of the utilization of nuclear energy in China,the safe disposal of nuclear waste is increasingly conspicuous and pressing.The deep geological disposal of high-level radioactive waste is widely accepted by the world.The bentonite from Gaomiaozi(GMZ),Inner Mongolia,has been selected as the buffer/backfilling material for the geological disposal of high-level radioactive waste in China.Researches on the mechanical properties of soil,the swelling characteristics and the mineral structure evolution have positive effects on the studies on the fitness of the repository.In this paper,the microstructure analysis test,the axial shear test and the swelling test are performed and combined with theoretical analysis.The change of microstructure,mineralogical composition,and mechanical character of the bentonite has been discussed,after treated by Different cumulative dose irradiation and thermal sequential aging of irradiation-temperature.These data provide a reliable theoretical guidance for the later period Construction of deep geological disposal repository.Through comparison and analysis,the following conclusions are obtained:(i)After treated by only cumulative dose irradiation and thermal sequential aging of irradiation-temperature,the montmorillonite content of high pressure natural Na-bentonite decreases.Compared with the Thermal aging temperature,the irradiation dose and thermal aging time have a greater impact on the change of montmorillonite content.The irradiation dose affects the microstructure obtained by scanning electron microscopy more than the effect of temperature.The pore structure of the bentonite is much more complicated after treated by irradiation dose and thermal aging.Meanwhile,the pore size distribution has greatly changed,mainly in the transformation of micropores to fine pores and ultramicropores to micropores.(ii)The shear strength of the bentonite is affected by the different cumulative dose irradiation and thermal sequential aging of irradiation-defferent temperature,the peak strength and the elasticity m odulus increase.The effect of irradiation and thermal sequential aging of irradiation-temperature on the shear strength of the bentonite is suppressed by the confining pressure.(iii)The swelling character of the high pressure natural sodium Na-bentonite decreases after irradiation aging.The swelling force and swelling rate of the bentonite decrease with increasing irradiation dose.The swelling character of the bentonite will not change when the irradiation dose is increased to a certain value.After thermal sequential aging of irradiation-different temperature,swelling force has increased in a certain time range,and then turn to be stable.The load-free swelling rate did not show a regular change,but the Load swelling rate has a lightly decrease with the increase of temperature,and the swelling performance has been weakened.