Hisanori Okamura

High heat load tests of a graphite armor first wall with a water cooling jacket

Heat load tests are performed on actively cooled graphite/stainless steel laminated structures, for the simulation of steady-state first wall operations in nuclear fusion reactors. Graphite armor tiles (40 mm × 40 mm × 10 mm) are brazed to stainless steel substrates (1 mm thick, 68 mm diameter) with the insertion of copper-carbon fiber composite (Cu-C) compliant layers (1.7 mm thick). Ag-28 wt%Cu-5wt%Ti solder and Ag-28wt%Cu solder are used for brazing the graphite/ Cu-C interface and Cu-C/stainless steel interface, respectively. Fine grain isotropic graphite and carbon fiber felt reinforced carbon composite (felt C-C) are chosen for armor tile materials. Thermal conductivities of these graphite materials, being measured through a laser flashing method, are 109 and 170 W/mK at room temperature, respectively. Heat load tests are carried out by using a 40 kW DC power source (maximum current: 1000 A). Pulsed thermal loads at heat fluxes ranging from 1 to 6 MW/m2 are realized either through resistance heating of a carbon felt heater on test specimens (1–4 MW/m2) or through electric arcing between a cathode graphite rod and graphite tiles of test specimens (> 4 MW/m2). Surface temperatures of graphite tiles are found to reach equilibrium temperatures at around 20 s after the start of heating. The equilibrium temperatures are higher by 30–40% for isotropic graphite tiles as compared to felt C-C tiles: 1800 °C for isotropic graphite and 1300 °C for felt C-C, at 6 MW/m2. The equilibrium temperature at the Cu-C layer for a 6 MW/m2 heat flux is measured to be around 600 °C.

Development and material testing of OF-Cu /DS-Cu/OF-Cu triplex tube (dispersion strengthened copper clad with oxygen free-copper) and trial fabrication of a vertical target mock-up for ITER divertor

Abstract For the divertor target of the International Thermonuclear Experimental Reactor (ITER), an OF-Cu/DS-Cu/OF-Cu triplex-structured cooling tube has been newly fabricated through powder metallurgy and drawing. The triplex structure comprised an aluminium oxide (0.5 mass%) - dispersion strengthened copper core (DS-Cu) clad with oxygen free copper (OF-Cu), a compliant layer for joining to the carbon fiber composite (CFC) tiles, and with an inner skin which tightly grasps a twisted INCONEL tape to assist heat transfer. Physical and mechanical properties of the DS-Cu core after heat treatment at 850°C for 600 s were investigated. Also, CFC brazability, fabricability and feasibility of the triplex tube for cooling channels for the divertor target were studied: A large scale vertical target mock-up of a 1500 mm length, 35 mm width and 3000 mm radius curved front face, has been fabricated with nearly 50 pieces of “saddle”-shaped one-dimensional (1D)-CFC tiles were brazed on to 1500 mm long triplex tubes set in grooves of OF-Cu heat sink blocks joined to a stainless-steel back plate. The mock-up was tested under 20 MW/m 2 for 15 s for 1000 cycle thermal loadings, which simulated transient heat loadings of a vertical target of an ITER divertor.