PHYSICAL PROPERTY OF CHINA′S BUFFER MATERIAL FOR HIGH-LEVEL RADIOACTIVE WASTE REPOSITORIES

The deep geological disposal is regarded as the most reasonable and effective way to safely dispose high-level radioactive wastes(HLW) in the world. The conceptual model of HLW geological disposal in China is based on a multi-barrier system that combines an isolating geological environment with an engineered barrier system including the vitrified HLW, canister, overpack and buffer/backfill material. The bentonite is selected as base material of the buffer/backfill material in HLW repositories,due to the very low permeability and excellent retardation of nuclides from migration,etc. GMZ deposit is selected as the candidate supplier for buffer material of HLW repositories in China. Since 2000,systematic study was conducted on GMZ–1 that is Na-bentonite produced from GMZ deposit and selected as reference material for Chinese buffer material study. The mineral composition,basic parameters of GMZ–1 bentonite and thermal conductivity,hydraulic conductivity,unconfined compression strength as function of dry density and water content are presented. The swelling stress of GMZ–1 bentonite as function of dry density is also reported. GMZ–1 bentonite is characterized by high content of montmorillonite(about 75%) and less impurities. The adequacy understanding of property and long-term behavior in deep geological condition of GMZ–1 is essential to safe dispose the high-level radioactive wastes in China.