بازنگری در فعالیت های "تحقیق و توسعه" مواد در ژاپن در رابطه با ساخت و ساز ITER و بهره برداری

This paper presents an overview of ITER-supporting materials R&D activities and major achievements in Japan during the period from the Co-ordinated Technical Activities to date. In view of the completed engineering design of ITER during the Engineering Design Activities period, R&D efforts since then have been focused on: those for reduction of component fabrication cost; those in support of domestic preparations of a structural technical code for construction; and those necessary for operation, and been extended to component-level testing rather than pure material testing. They cover materials R&D for in-vessel components, vacuum vessel, cryogenic steels of superconducting magnets and diagnostics components. Major achievements in each R&D area are highlighted and their impact or implication to the design, construction and operation of ITER is presented.

Extensive R&D had been conducted in Japan during the ITER Engineering Design Activities (EDA) mainly for selecting design choices and completing the engineering design. During the subsequent phases, in view of the progress of international negotiations towards construction and operation, R&D in this area has been extended to: those for reduction of component fabrication cost; those in support of domestic preparations of a structural technical code for construction; and those necessary for operation of the machine. From the viewpoint of reduction of component fabrication cost, cost-effective fabrication routes have been pursued for the divertor, and their performance under ITER relevant conditions has been examined. For the jacket material of the central solenoid conductor, alternate materials have been explored with a view to relaxing the constraints on the design and fabrication processes. As the vacuum vessel forms an essential part of the physical barrier to contain radioactive materials, its mechanical integrity, in particular, T-welded joints with a partial penetration, has been examined in support of domestic preparations of a structural technical code for construction. Towards ITER operation, a new approach to remove co-deposited layers of tritium and carbon by means of laser irradiation has been explored, and neutron irradiation testing of key diagnostics components has continued. In the following sections, outline and major achievements on ITER-supporting materials R&D activities in Japan after the EDA to date are described in a system-wise manner from internal to external components.

ITER-supporting materials R&D activities and major achievements in Japan during the period after the EDA to date are overviewed. R&D efforts during this period have been oriented to: those for reduction of component fabrication cost; those in support of domestic preparations of a structural technical code for construction; and those necessary for operation of the machine, and the following results have been obtained: (1) Two options, `rod-shaped tungsten armor' and `screw tube', have been proposed for the divertor, mainly for reducing the fabrication cost, and their adequate thermo-mechanical performance has been demonstrated under ITER heat load conditions. (2) An excimer laser irradiation technique has been proposed as a rapid and effective means to remove co-deposited layers of tritium and carbon retained inside the vacuum vessel, and effectiveness of this method has been demonstrated by applying to the carbon tiles with co-deposited layers as used in JT-60 and TFTR. (3) As a course of domestic preparations of a structural technical code for construction, a series of mechanical tests have been performed for the T-welded joints with a partial penetration to be applied in the vacuum vessel fabrication. It could be concluded that this type of welded joints are acceptable from the structural integrity viewpoints. (4) A new cryogenic steel, grade JK2LB, has been successfully developed for the jacket material of the central solenoid conductor, and it has been selected as the reference material, instead of Incoloy 908, due to improved mechanical properties even after the aging process. (5) Irradiation testing has been conducted for key diagnostics components (bolometer, optical fibers and magnetic coils), and critical issues to be examined further have been addressed.