This review summarizes the results of the joint Japanese (Central Research Institute of Electric Power Industry, CRIEPI, Tokyo), Swiss (National Cooperative for the Storage of Radioactive Waste, NAGRA, Baden), Swedish (Swedish Nuclear Fuel and Waste Management Company, SKB, Stockholm) international 'JSS' project on the determination of the chemical durability of the French nuclear waste borosilicate glass, which was completed in 1988. Radioactive and nonradioactive glass specimens were investigated. A data base was created with results from glass corrosion tests performed with different water compositions, pH values, temperatures, sample surface areas (S), solution volumes (V), and flow rates. Glass corrosion tests were performed with and without bentonite and/or steel corrosion products present. Variation of the glass composition was taken into account by including the borosilicate glass 'MW in the investigations, formulated by British Nuclear Fuels, pic. An understanding was achieved of the glass corrosion process in general, and of the performance of the French glass under various potential disposal conditions in particular. A special effort was made to establish a corrosion data base, using high S/V ratios in the experiments in order to understand the glass durability in the long term.A computer program, GLASSOL, was developed, based on a dissolution-precipitation model, to calculate the glass water reaction. Fair agreement between observations and the model calculations was achieved. Use of a constant (time-independent) long-term rate was justified by observations on naturally altered basaltic glasses of great age, which were compatible with what was inferred from experiments with nuclear waste glasses in the laboratory. A fractured glass block would not be altered within 10 000 years at 90 °C (flow rate <100 L/year). It is unlikely, however, that for long-term contact with groundwater the glass block would remain intact for time periods longer than one million years under repository conditions. The long-term rate controls the release of soluble elements, whereas that of sparingly soluble glass constituents was lower and was controlled by the groundwater flow rate. The chemical effect of bentonite on glass durability was minor, but sorption of specific elements such as Cs reduced their concentrations in groundwater. The effect of magnetite depended on the corrosion rate of the steel canister and/or the rate of iron silicate formation or multi-layer silica sorption.

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Metal-oxide interfaces of three different materials irradiated in a pressurized water reactor have been analyzed by TEM and AEM. Standard Zircaloy-4, low-tin Zircaloy-4, and Zr-2.5%Nb were used for this study. The microstructure of the material on the two sides of the metal-oxide interface, the geometry of the interface, the distribution of different alloying elements, and the oxygen profile have been examined in each material. Results of the examinations showed that the three materials had different microstructure and oxygen distribution on the two sides of the metal-oxide interface. In particular, the following parameters were noticed: a) the geometry of the interface seems to be of a different nature in the case of Zr-2.5%Nb alloy. Unlike the Zircaloy-4 alloys, which show an undulated interface, this material has a "jigsaw" type interface. This point is discussed, and its role on the oxidation is considered. b) Hydrides are observed and analyzed in the vicinity of the interface in the case of low-tin Zircaloy-4, and it is shown that they can have an influence on the occurrence of cracks in this material. c) The origins of stress are discussed, and it is shown that it can have different sources. The crystal structure of the oxides is mainly monoclinic. A tetragonal oxide is observed at some regions, in particular in the standard Zircaloy-4.

Since 1982, the corrosion behaviour of radioactive high level waste glass and of inactive glasses of the same composition has been studied in the framework of a Japanese-Swedish-Swiss (JSS) project. In addition to granite and backfilling material, the influence of steel corrosion products on glass corrosion has been investigated in experiments of up to one year at 90°C with a sample surface area to leachant volume ratio of 10 m−1. Leachant and steel corrosion products were separated from each other by filtration and analyzed by atomic absorption spectroscopy and γ-spectroscopy. The glass corrosion layers were characterized by optical and scanning electron microscopy and by secondary ion mass spectrometry.It could be shown, that glass corrosion is enhanced by steel corrosion products. The quantity of corroded glass seems to be dependent on the surface area and not on the total amount of steel corrosion products in the system, suggesting a mechanism controlled by silica sorption on the steel corrosion product. If lead oxide is added to the system, glass corrosion is almost to- tally suppressed.

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