Release of radioactive species from activated metallic blanket structures during fusion reactor accident conditions. Final report

The release and transport of activated materials-of-construction in a fusion reactor during an accident scenario involving overheating and ingress of oxidants is an important area of safety research. This investigation quantified material release characteristics that result from surface oxide spallation and vaporization from the steel alloys PCA and HT-9 in impure helium and air environments. Flowing air and helium, each containing specific quantities of O/sub 2/ and H/sub 2/O, were used to oxidize test sample surfaces at temperatures of 800/sup 0/ and 1000/sup 0/C for exposure times of <200 h. The changes and features observed are described and include: weight, oxide scale morphology, adherence and composition; alloy composition (including decarburization); and vaporization as fractional loss of alloying elements. Oxide scales formed were dominant in Mn and Cr but minor in Fe. The dominant volatilized elements detected were Mo, W, Cr, As, Mn, Sb, and Co. The implications of these data for safety analyses of activated material release are that following an accidental temperature excursion to 800/sup 0/C in an oxidizing environment, material transport by scale spallation and/or volatilization should be minor. Furthermore, the potential material release fractions at 1000/sup 0/C appear to be significantly lower than the release fractions used more » in early fusion safety analyses. « less