Advanced solutions for beryllium and tungsten plasma-facing components

Beryllium and tungsten are candidate plasma-facing armour materials for the International Thermonuclear Experimental Reactor (ITER). These armours are proposed for areas with low heat flux (⩽5 MW m−2); however, in the divertor, surface melting during abnormal events may occur. This paper reports the progress made in developing novel approaches to solving the difficulties posed in designing with these armours. A Be monoblock brazed to an oxygen free high conductivity (OFHC) 10 mm ID Cu tube using InCuSil `ABAʹ braze alloy has survived 130 cycles of 10–11 MW m−2 for 6 s, with surface temperatures of 1250°C. No visible surface cracking occurred. The same monoblock was then exposed to several cycles of 20–22 MW m−2 for 8 s, creating a 2 mm deep molten layer. High cycle fatigue was then performed. The test results are detailed in this paper. Comparison between experimental and theoretical results are made. W and Cu have a large mismatch in their thermal expansion coefficients and two designs are proposed that minimise the interface stresses. These are: a `brushʹ-like structure with rectangular fibres set in a Cu substrate using the `active metal castingʹ (AMC) technique; and thin monoblocks (or lamellae) brazed or active metal cast onto a Cu tube. Analyses of the lamellae concept for steady-state heat loads of 5 MW m−2 are presented. Fatigue analyses show that both solutions are theoretically viable (∼104 cycles). A `brushʹ mock-up has been manufactured and progress on its testing is reported. Results of all tests and their relevance to the ITER design are discussed.