Corrosion of Steel Drums Containing Cemented Ion-Exchange Resins as Intermediate Level Nuclear Waste
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Corrosion of Steel Drums Containing Cemented Ion-Exchange Resins as Intermediate Level Nuclear Waste Gustavo S. Duffó1, 2, 3, Silvia B. Farina1, 2 and Fátima M. Schulz1 1 Consejo Nacional de Investigaciones Científicas y Técnicas, Argentina. 2 Universidad Nacional de San Martín, Argentina. 3 Comisión Nacional de Energía Atómica, Depto. Materiales, Av Gral Paz 1499, (1650) San Martín, Buenos Aires, Argentina. ABSTRACT Ion-exchange resins are used for purification of radioactive liquid waste from nuclear reactors. After exhaustion, resins become intermediate level radioactive waste to be managed. They have to be immobilized before being stored to improve the leach resistance of the waste matrix and to maintain mechanical stability for safety requirements. The immobilized resins are thus contained in steel drums that can undergo internal corrosion depending on the presence of certain contaminants. This work shows an study of the corrosion susceptibility of steel drums in contact with cemented ion-exchange resins with different types and contents of aggressive species. Results show that the corrosion depth of the steel drums after a period of 300 years (foreseen life-span of the radioactive waste disposal facility), in the most unfavorable case (high chloride contamination), will be considerably lower than the thickness of the wall of the drums. INTRODUCTION Intermediate level radioactive solid wastes originated in the operation and maintenance activities of the two nuclear power plants operating in Argentina, consist mainly of mechanical filters from the primary circuit of the reactor and of spent ionic exchange resin beds. Such intermediate level radioactive solid wastes are stored at the facilities of each power plant awaiting treatment and conditioning. Treatment of these wastes is necessary for long term storage and disposal. The design of the Intermediate Level Radioactive Waste (ILW) repository foresees a period of 300 years of institutional post-closure control. In this model, wastes are immobilized in cement matrixes and packed in 200 litre drums that, in turn, may undergo internal corrosion depending on the presence of contaminants in the waste. An extra enclosure made of concrete is required to guarantee the radionuclides containment. As a consequence of a conservative approach to the safety analysis, the steel drums are not considered to be physical barriers, with the concrete assumed to be the sole barrier to prevent radionuclide release during the life-span of the facility. However, if the durability of the steel drums could be guaranteed, an extra security period could be claimed. The present work is a study of the corrosion susceptibility of steel drums in contact with cemented ion-exchange resins contaminated with different types and concentrations of aggressive species. To achieve this aim, a special type of specimen was manufactured to simulate the cemented ion-exchange resins in the drum [1]. The evolution of the corrosion potential (Ecorr) and the corrosion rate (CR) of the steel, as well as the ele
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