A Study of disposal concept for TRU waste, 5; A Study on the mechanical properties of engineered barrier materials

Tanaka, M.*; Yamamoto, H.*; Fujisawa, O.*; Okutsu, Kazuo*; Miura, K.*; Takamura, Hisashi*

TRU waste should be isolated from biosphere for a long period of time as it includes long lived nuclides. In this study, (1) data were conected on the mechanical properties of engineered barrier materials, (2) affection on the mechanical properties of Na bentonito by salt water was studied and (3) soundness of the disposal system against changes in the volume of engineered banier was evaluated, to examine critical events related to the long-term soundness of the disposal system. Described below are the results of the studies. (1) The swelling pressure, swelling amount and permeability were obtained for a material consisting of NaCa-exchanged bentonito and silica sand with a relative weight of 30% (with a dry density of 1.6 Mgm) by supplying saturated calcium hydroxide aqeous solution. As a result, it was confirmed that the swelling pressure and permeability were approximately estimated from the relation between these properties and the effective dry density of bentonito. (2) The swelling pressure, swelling amount and permeability were obtained for a material consisting of salty Na bentonito and silica sand with a relative weight of 30% (with a dry density of 1.6 Mgm) by supplying artifical salt water. As a result, it was confirmed that these properties were approximately these properties of NaCa-bentonito. (3) Tests were conducted as a part of the evaluation of system soundness against changes in the volume of engineered barrier. Development of a void around bentonito was assumed. Self sealing of Na and NaCa-exchanged bentonito, and theirs water cut-off capability and swelling pressure were investigated.As a result, it was confirmed that the change of permeability and swelling pressure under self sealing of bentonito. Based on the test results (i.e. the both relations between the swelling pressure and dry density, and the permeability and dry density), soundness of the system was verified against changes of the volume of engineered barrier materials.