Investigation on performance of bentonite as engineered barrier for geological disposal facility of high-level radioactive wastes

It is planned to place buffer material between high level radioactive wastes and host rock in a disposal facility. This buffer material must keep off migration of nuclides into geology. Items of this barrier capacity are low hydraulic conductivity and good thermal conductivity. A candidate of buffer material is compacted bentonite. The aim of this report is to survey previous studies on barrier capacity of bentonite. The major results are as follows: (1) Hydraulic conductivity of compacted bentonite is about 1012cm/s. On this condition, nuclide migration is mainly due to dispersion rather than advection. (2) Thermal conductivity of compacted bentonite is less than that of rock and sand. Just after disposal, compacted bentonite will become very hot, and hydraulic conductivity increase. Therefore it is necessary to design the buffer material with low hydraulic conductivity and high thermal conductivity by mixing with material which has good thermal conductivity. (author)