Re-evaluation of SiC permeation coefficients at high temperatures

Abstract

Since 2007, our group has studied the deuterium permeation and diffusion coefficients for SiC materials at temperatures above 600°C as a means of evaluating the tritium inventory and permeation in fusion blankets. During such measurements, control and evaluation of the wraparound flow through the sample holder are important, and so the heated sample holder is enclosed by a glass tube and kept under vacuum during experimental trials. However, detailed studies regarding the required degree of vacuum based on model calculations have shown that the wraparound flow is much larger than expected, and so can affect measurements at high temperatures. We therefore modified the measurement apparatus based on calculations involving reduced pressure in the glass tube, and are now confident that the measurement error is only several percent, even at 950°C. In this paper, recent experimental results obtained with a chemical vapor deposition (CVD)-SiC sample over the temperature range of 600–950°C are presented, showing that the permeation coefficient for CVD-SiC is more than three orders of magnitude smaller than that for stainless steel (SS316) at 600°C, and that at 950°C, the coefficient for CVD-SiC is almost equal to that for SUS316 at 550°C.