EXPERIMENTAL MANUFACTURE OF A COMPOSITE OVERPACK OF TITANIUM-CARBON STEEL FOR GEOLOGICAL DISPOSAL OF HIGH-LEVEL RADIOACTIVE WASTE

摘要

Long-term stable performance is required for overpacks to be geologically disposed of while being packed with vitrified high-level radioactive waste. A design scheme has been proposed for adopting a composite overpack for this application in which a highly corrosion resistant alloy is used as an outer sheath, and a structural steel constitutes an inner cylindrical container. A composite overpack is designed in the present investigation in which a titanium alloy constitutes the corrosion resistant sheath and carbon steel for a structural cylinder. Necessary qualification tests for various unit technologies employed for manufacturing and testing the composite overpack are conducted. Namely, they are manufacturing technologies of a sheath of a corrosion resistant titanium alloy; tests of insertion methods of a carbon steel structural cylinder into a titanium alloy sheath; verification tests of weldability at sealing edges of the structural steel cylinder; and weldability verification tests and leak tests at sealed edges of the corrosion resistant sheath. A full-scale composite overpack is manufactured based on these test results. Four possible manufacturing methods are tested and compared for manufacturing and insertion methods of corrosion resistant sheaths; an insertion method of a corrosion resistant sheath; a winding method of a corrosion resistant sheath plate; selection of suitable thickness of a corrosion resistant sheath; and effects of machining of an inside surface of a corrosion resistant sheath.