STUDY OF THERMAL HISTORY EFFECT ON WATER MOVEMENT IN UNSATURATED BENTONITE

Abstract

 Bentonite buffer in disposal project for high-level radioactive waste is expected to delay migration of radioactive nuclides, because it has low water permeability and can fill up the technical gaps between overpack and bedrock by swelling during saturation. However, high-level radioactive waste generates decay heat and it is concerned that bentonite buffer may experience functional decline in terms of swelling property and low water permeability because of the thermal history of the buffer. To address this problem, this study measured swelling pressure and water absorption of bentonite that experienced thermal history. The following conclusions are obtained based on this study: i) Effect of thermal history on swelling pressure may not be significant. ii) Diffusivity and water absorption rate of compacted bentonite specimen with dry density less than 1.6 Mg/m³ may increase for cases when temperature equals or higher than 160℃ and thermal history equals or longer than 30 days. iii) It is expected that thermal history effect on water movement in buffer would be minor for properly designed maximum temperature in disposal site and dry density of the buffer.