Abstract
A test to determine the lithium compatibility and impurity gettering capabilities of various materials including yttrium was performed in Beryllium-7 Experimental Lithium Loop (7BELL) at 270°C. Yttrium coupons were exposed in liquid lithium for a total of 3,718 hours. X-ray diffraction and bulk chemical analysis data indicated that yttrium absorbs hydrogen from liquid lithium at 270°C and transforms to yttrium dihydride (YH 2). The transformation of yttrium to YH 2 resulted in embrittlement of the coupons and subsequent fragmentation to small pieces. Additional analysis, based on the equilibrium hydrogen pressures for the transition of yttrium to YH 2, and Sievert's relationship for hydrogen in equilibrium with hydrogen in lithium, indicates that the temperature of yttrium cannot exceed 280°C to control the hydrogen concentration in lithium at below 1 wt ppm. It is concluded in general that yttrium in sponge form is a good getter for removal of hydrogen isotopes from the lithium blanket of a fusion reactor at or below 280°C, which is in excellent agreement with the results of previous authors.
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