A Study on Fabrication Technology of Ceramic Overpack - A Conceptual Design and Fabrication of a Full-Scale Ceramic Over
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A STUDY ON FABRICATION TECHNOLOGY OF CERAMIC OVERPACK - A CONCEPTUAL DESIGN ANDFABRICATION OF A FULL-SCALE CERAMIC OVERPACK
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T. TESHIMA' , Y. KARITA' , K. Katsumoto" , H. ISHIKAWA "" AND N. SASAKI " NGKInsulators, Ltd., Suda-cho, Mizuho-ku, Nagoya, Aichi-ken, JAPAN "*Power Reactor and Nuclear Fuel Development Corporation, Tokai-mura, Ibaraki-ken, JAPAN ABSTRACT The conceptual design and fabrication test of a full-scale ceramic overpack were performed from the viewpoint of structural barriers as a part of program to evaluate their potential use as overpack under conditions of deep geological disposal. Materials investigated were porcelain (used for insulators) and A1203 with high purity of 99.7 %. The selected design consisted of a cylindrical body with hemispherical heads at each end. The design thickness of overpack is the sum of the structural thickness and corrosion allowance. The thickness required to resist the lithostatic pressure was estimated by the basic cylinder buckling formulas and finite element stress analyses in both case of uniform and non-unifom external pressure conditions. These analyses showed that structural thickness of 119 mmwas necessary for overpack of porcelain and 40 - for A1203 under the predicted maximum uniform pressure. In addition, fracture probability of delayed failure, one of significant degradation mode, was estimated for overpack of porcelain. A full-scale overpack of porcelain, of dimensions 800 mmouter diameter x 2200 mmlength x 150mm wall thickness, was fabricated under the ordinary level of fabrication technology. INTRODUCTION One of the significant subjects in geological disposal of high-level radioactive waste is to assure the long term reliability and integrity of overpack. The overpack is expected to isolate the waste from the disposal environment for more than several hundreds years. In the disposal system in Japan, the primary candidate materials for overpack are carbon steel and titanium (and its alloy) [1], selected on the basis of the preliminary survey on literatures from many countries and various corrosion tests. Ceramic materials are being considered as possible alternatives to metallic materials for long-term containment because of their high chemical stability and strength. Limited studies, however, have been performed on ceramic materials for applications to overpack [2,3,4,5,6,7], which focused mainly on corrosion behaviors in the predicted repository conditions. Recently for industrial use, ceramic materials are applied widely to the structural components because of improvements in the reliability of ceramic components and its excellent properties (for example gas turbine engines and ceramic turbo-charger rotors). These wide applications depend on the progress of optimized design method, studies on behaviors of significant failure modes and life time prediction method, and establishment of fabrication process. The similar progress should be carried out to apply ceramic materials to overpack. This paper describes the conceptual design, life time predicito
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