Natural analogue studies of engineered barrier materials at PNC TOKAI, JAPAN; Their framework and recent activities

Kamei, Gento ; Yusa, Yasuhisa; Yamagata, Junji*; Inoue, K.*

Long-term extrapolations concerning the safety of a nuclear waste repository cannot be satisfactorily made on the sole basis of short-term laboratory tests. Natural analogues, which are the only means by which very slow mechanisms can be identified and by which long-term predictions of models can be tested for pertinence. Our studies for the assessment of long-term durability of engineered barrier materials are outlined. Materials of young age and with simple history are the most suitable for these studies as: (1)properties of the materials tend to deteriorate over the longer term; and (2)detailed quantitative data on the term and on the environmental conditions can be obtained. The framework of our studies includes: (1)clarification of alteration phenomena,(2)examination or the environmental conditions, and (3)support experiments. The following four materials and their alteration phenomena were selected: (1)Weathering alteration of basaltic glass (as vitrified waste form) : Basaltic glasses within 2800 years, from the Fuji and the Izu-Ohshima, were studied. (2)Corrosion of iron in soil (as overpack): corrosion of Industrial materials, gas/water service pipes of carbon steel or cast iron embedded in soil for the range from 20 to 110 years, were studied as analogy of alteration of iron in bentonite. (3)Illitization of smectite associated with contact metamorphism (as buffer material): A lateral variation of smectite to smectite/illite mixed-layer minerals, found in the aureole of the rhyolite intrusion, were studied. (4)Alteration of cement (as buffer or backfill material): Concrete components of fabrications with a known age were studied.