Oxidation and volatilization from tungsten brush high heat flux armor during steam exposure

Tungsten brush accommodates thermal stresses and high heat flux in fusion r eactor components such as plasma facing surfaces or armor. However, inheren tly higher surface areas are introduced with the brush design. We have test ed a specific design of tungsten brush in steam between 500 and 1100 degree sC. Hydrogen generation and tungsten volatilization rates were determined t o address fusion safety issues. The brush design prepared from 3.2-mm diame ter welding rods had a packing density of 85%. We found that both hydrogen generation and tungsten volatilization from brush, fixtured to represent a unit within a larger component, were less than projections based upon the i ntegrated total surface area (TSA). Steam access and the escape of hydrogen and volatile oxide from void spaces within the brush are restricted compar ed with specimens with more direct diffusion pathways to the test environme nt. Hydrogen generation rates from restrained specimens based on normal sur face area (NSA) remain about five times higher than historic rates based on total surface area. Volatilization rates from restrained specimens based u pon normal surface area (NSA) were only 50% higher than our historic cumula tive maximum flux plot (CMFP) for tungsten. This study has shown that hydro gen generation and tungsten volatilization from brush do not scale accordin g to predictions with earlier determined rates. Volatilization rates from b rush with higher packing density could, in fact, approach those from flat s urfaces. (C) 2001 Elsevier Science B.V. All rights reserved.