ADVANCED SOLUTIONS FOR BERYLLIUM AND TUNGSTEN PLASMA-FACING COMPONENTS

Beryllium and tungsten are candidate plasma-facing armour materials fo r the International Thermonuclear Experimental Reactor (ITER). These a rmours are proposed for areas with low heat flux (less than or equal t o 5 MW m(-2)); however, in the divertor, surface melting during abnorm al events may occur. This paper reports the progress made in developin g novel approaches to solving the difficulties posed in designing with these armours. A Be monoblock brazed to an oxygen free high conductiv ity (OFHC) 10 mm ID Cu tube using InCuSil 'ABA' braze alloy has surviv ed 130 cycles of 10-11 MW m(-2) for 6 s, with surface temperatures of 1250 degrees C. No visible surface cracking occurred. The same monoblo ck was then exposed to several cycles of 20-22 MW m(-2) for 8 s, creat ing a 2 mm deep molten layer. High cycle fatigue was then performed. T he test results are detailed in this paper. Comparison between experim ental 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 'brush'-like struct ure with rectangular fibres set in a Cu substrate using the 'active me tal casting' (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 analys es show that both solutions are theoretically viable (similar to 10(4) cycles). A 'brush' mock-up has been manufactured and progress on its testing is reported. Results of all tests and their relevance to the I TER design are discussed. (C) 1998 Published by Elsevier Science S.A. All rights reserved.