Development of evaluation methodology on hydraulic performance of bentonite with long-term degradation

Mukai, Masayuki ; Sawaguchi, Takuma ; Kataoka, Masaharu; Tsukada, Manabu; Maeda, Toshikatsu; Tanaka, Tadao 

In the Japanese HLW disposal program, vitrified HLW is encapsulated in a steel container called overpack, and placed in a repository surrounded with bentonite clay material in an underground site. Bentonite is planed to be used as buffer material to prevent from contacting overpack with huge volume of groundwater for extended period of post-closure. Cementinious material affects on surrounding groundwater to alkalize and that probably deteriorates the low hydraulic conductivity of bentonite. JAEA, therefore, has been developed evaluation methodology to calculate long-term performance of bentonite in alkaline groundwater condition by means of concurrent calculations of chemical-reaction and mass-transport, combining with key models formulated mainly on experimentally basis.