Secondary Phases on the Surface of Real Vitrified Radioactive Waste Disposed in a Loamy Soil
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6HFRQGDU\3KDVHVRQWKH6XUIDFHRI5HDO9LWULILHG5DGLRDFWLYH:DVWH 'LVSRVHGLQD/RDP\6RLO Natalie V. Ojovan1, Irene V. Sartceva1, Alexander S. Barinov1, Andrew V. Mokhov2, Michael I. Ojovan3, Günter Möbus3 1 Scientific and Industrial Association “Radon”, Moscow, Russia. 2 Institute of Geology of Ore Deposits of Russian Academy of Science (IGEM), Moscow, Russia. 3 Immobilisation Science Laboratory, Department of Engineering Materials, University of Sheffield, UK. $%675$&7 This work examines secondary phases formed on the surface of radioactive borosilicate glass K-26 during 12 years of testing in the loamy soil. This glass has been produced to immobilise intermediate level operational nuclear power plant (NPP) radioactive waste. An altered layer has been formed at the glass surface that had been contacting with the repository environment. The layer is morphologically following the bulk waste glass. The layer is chemically inhomogeneous and non-uniform in thickness and structure. It contains in addition to the major vitreous phase, alpha quartz, calcite, aluminium hydrochlorides, and molybdenum compounds. ,1752'8&7,21 Secondary phases on the surface of vitrified radioactive waste play a crucial role in the redistribution and consequent migration of radionuclides into the environment. These are formed during long term disposal of vitrified radioactive waste resulting from the interaction of water with glass. Some of the secondary phases can act as retention media for radionuclides thus being protective for vitrified waste, other retard chemical contaminants [1]. Identification of secondary phases is important for performance assessment models to predict the release and migration of radionuclides [2]. Due to high corrosion durability of glasses, formation of secondary phases on the surface of glasses is a very slow process requiring a long time. Thus many studies dealt with formation of secondary phases in accelerated conditions, e.g. vapour hydration conditions, which are far from real even theoretically envisaged disposal conditions. Moreover in many investigations simulated glasses were studied, and in many cases these were glasses prepared under laboratory conditions. These glasses drastically differ from real ones not only in the structure (e.g. having a higher homogenisation) but even in composition due to volatilisation and carry over of certain components during the re-melting of initial batches of glasses. Actual vitrified radioactive waste really contains not only a homogeneous vitreous phase but also a significant volume fraction of impurities, flaws, unmelted inclusions, inhomogeneities. In addition to that there are radiation fields intrinsic to radioactive waste. These can significantly change the behaviour of real vitrified waste in the repository in comparison with almost perfect and non radioactive glass samples prepared under laboratory conditions and used to predict the behaviour of materials which are quite different. Hence there is challenge on studying real vitrified radioactive waste in
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