Iron corrosion products (CP) impact on the long term alteration of fractured nuclear glass: effects of transport and CP stability

摘要

In the context of long term nuclear waste repository, the reference system is based on a multi-barriers concept: nuclear glass is placed in a low-alloy iron steel overpack stored in clay media saturated by water. The water will in time corrode the overpack and alter the fractured glass. In order to accurately simulate the storage analogues of long term alteration, archaeological artefacts buried under similar conditions, were used. Representative corrosion products (RCP) were extracted from 450 year old archaeological iron nail corroded in clay media saturated with anoxic carbonated water at Glinet reference site.The interactions between glass and iron can have a catalytic effect the glass alteration mechanisms as iron-rich phases possess a strong affinity for silicon. Laboratory experiments under anoxic conditions have shown an increase in the glass alteration rate when in contact with iron and/or its corrosion products. The extent of the alteration and the underlying mechanisms depend on the phase nature and its specific surface area. Affinity to silicon will also differ between synthesized corrosion products and RCP, due to their porosity limiting or enhancing the transport through the iron corrosion layer and the stability of iron corrosion products which will impact on the availability of iron in solution.For this study, the fractured glass system is simulated by a model-fissure of SON68 glass (the inactive surrogate of French nuclear R7T7 glass) in contact with iron, iron RCP or iron CP synthetized in storage conditions. Experiments were conducted in cell at 50℃ in contact with synthetic groundwater solution. The analyses of the resulting samples were conducted through systematic multi-scale and multi-instrumental analyses: optic microscopy, scattering and transmission electronic microscopy, μRAMAN spectrometry, μXRD and STXM at the Fe and Si-edge.The results will provide information on the transport of silicon in the system, migration through the porous material and retention due to affinity with iron. The distance between the glass-solution interface and the source of iron will impact on the rate of alteration as well as on the nature of the secondary products formed.