MANUFACTURING AND TESTING OF A BE OFHC-CU DIVERTOR MODULE/

Beryllium, carbon-based materials and tungsten are considered as plasm a facing materials for the next generation of fusion machines such as the international thermonuclear experimental reactor (ITER). Beryllium is one of the primary candidate materials because of its low atomic n umber and lack of tritium codeposition. However, Joining of a berylliu m armor to a copper heat sink remains a critical problem due to the fo rmation of brittle intermetallics at the interface. To address this co ncern, the Japan Atomic Energy Research Institute manufactured a beryl lium/Cu divertor module with Cr and Ni diffusion barriers. This Be/Cu module was tested in the electron beam test system of Sandia National Laboratories in the framework of the US-Japan Fusion Collaboration. Th e divertor module consisted of four beryllium tiles, 25 mm x 25 mm, an d a square copper heat sink with convolutions like a screw nut inside the coolant channel. To evaluate the integrity of the brazed bonds und er various heat fluxes, beryllium tiles of two different thicknesses, 2 and 10 mm, were bonded to the copper heat sink. Cooling conditions o f 10 m/s water flow velocity at 1 MPa, and a water inlet temperature o f 20 degrees C were selected based on the thermal analysis, During hig h heat flux testing the 10 mm. thick Be tiles detached at an absorbed heat flux around 5 MW/m(2) for several shots due to flaws al the braze joint confirmed by optical observation after manufacturing. One of th e 2 mm thick Be tiles failed after 550 cycles at the steady state heat flux of 6.5 MW/m(2). Most likely the failure was caused by brittlenes s at the interface caused by the presence of Be-Cu intermetallics.