Compaction Properties Of Gmz Bentonite-sand Mixture As Buffer Material For Hlw Disposal

High-level radioactive waste which contains strong radioactive,heat,toxicity,and long half-life nuclides must be long-term and reliably isolated with the living environment of the human.The deep geological disposal is currently believed to be the best feasible disposition.Due to its very low permeability and excellent retardation of nuclides from migration,the bentonite is selected as base material of the backfill/buffer material in HLW repositories.However the pure bentonite as the backfill/buffer material has two limitations.One is that low thermal conductivity properties is not helpful to conducting the heat of radiation into the surrounding rock in the cavern, that causes the buffer layer temperature raise to more than 100℃and water vapor pressure. Anther is that it has bad workability,which is difficult to compact to the maximum dry density.As a modern trend in backfill/buffer material development,bentonite is optimized by addition of certain content of quart sand to improve the strength and heat conductivity without obvious lowering of permeability.Since 1985,GMZ bentonite was preliminary confirmed as the backfill/buffer materials for high-level radioactive waste disposal.The expected methods for the construction of backfill/buffer materials included In-situ compaction and prefabricated masonry block law.For this reason,Dynamic compaction and Static compaction tests were carried out in laboratory on the mixture of GMZ bentonite and artificial quart sand to illustrate the effects of sand mixing ratio and compaction pressure and to show the relationship of the max dry densities and the optimum water content.Test results show that the relationship between maximum dry density and optimum water content follow the same power function for all of the mixture specimens prepared,while there is a linear correlations between mixture specimens prepared in different compaction methods and compaction efforts.These correlation functions provide useful tools for convenient selection of compaction methods in practice.It is concluded that addition of 10-30%quartz sand to GMZ bentonite can improve the compaction quality with no altering the impermeability of the backfill/buffer material.