Geological repository of high-level nuclear waste(HLNW),the most feasible approach for the safe and permanent treatment of HLNW without human intervention,has been investigated for years by many researchers.In some co...Geological repository of high-level nuclear waste(HLNW),the most feasible approach for the safe and permanent treatment of HLNW without human intervention,has been investigated for years by many researchers.In some countries,real facilities for the geo-logical repository are already under construction.In Japan,however,due to complicated geologic conditions,especially underground water and fractured rock masses,and the high risk of natural disasters,ensuring the long-term stability of the method remains a struggle.The influential factors include underground water,heat generation from radioactive waste,and thermal and chemical weathering of the surrounding rock mass as a natural barrier.It is difficult to estimate and verify the long-term stability for up to one hundred thousand years,a complicated thermal-hydraulic-mechanical-chemical coupling behavior,via any field test.The objective of the study is to develop a numerical method for predicting the long-term stability of geological repositories.As the first step toward realizing this objec-tive,heating and loading tests on cave model made of man-made rock specimens that are composed of diatoms,gypsum,and water,which are viscoplastic materials,were conducted,based on which a newly proposed numerical method with finite element method(FEM)was used to describe the thermal,mechanical,and time-dependent behavior of the model tests for a geological repository.To ensure the accuracy of the numerical calculations,all the material parameters in the thermoelasto-viscoplastic model with consideration of overconsolidation,the structure,and the influence of intermediate stress were determined via triaxial compression/creep tests under various temperatures,confining stresses,and loading rates.Finally,the validity of the numerical method was demonstrated by model tests over a limited time span.展开更多
基金substantially supported by financial support from Grant-in-Aid Scientific Research(B)(Grant No.17H03304)JSPS,and JSPS KAKENHI(Grant No.JP20K14823).
文摘Geological repository of high-level nuclear waste(HLNW),the most feasible approach for the safe and permanent treatment of HLNW without human intervention,has been investigated for years by many researchers.In some countries,real facilities for the geo-logical repository are already under construction.In Japan,however,due to complicated geologic conditions,especially underground water and fractured rock masses,and the high risk of natural disasters,ensuring the long-term stability of the method remains a struggle.The influential factors include underground water,heat generation from radioactive waste,and thermal and chemical weathering of the surrounding rock mass as a natural barrier.It is difficult to estimate and verify the long-term stability for up to one hundred thousand years,a complicated thermal-hydraulic-mechanical-chemical coupling behavior,via any field test.The objective of the study is to develop a numerical method for predicting the long-term stability of geological repositories.As the first step toward realizing this objec-tive,heating and loading tests on cave model made of man-made rock specimens that are composed of diatoms,gypsum,and water,which are viscoplastic materials,were conducted,based on which a newly proposed numerical method with finite element method(FEM)was used to describe the thermal,mechanical,and time-dependent behavior of the model tests for a geological repository.To ensure the accuracy of the numerical calculations,all the material parameters in the thermoelasto-viscoplastic model with consideration of overconsolidation,the structure,and the influence of intermediate stress were determined via triaxial compression/creep tests under various temperatures,confining stresses,and loading rates.Finally,the validity of the numerical method was demonstrated by model tests over a limited time span.
