Two thermal convection loops (TCLs) fabricated from 316L stainless steel and containing mercury and a variety of 316L coupons representing variable surface conditions and heat treatments have been operated continuously for 2000 h. Surface conditions included surface ground, polished, gold-coated, chemically etched, bombarded with Fe to simulate radiation damage, and oxidized. Heat treatments included solution treated, welded, and sensitized. In addition, a nitrogen doped 316L material, termed 316LN, was also examined in the solution treated condition. Duplicate TCLs were operated in this experiment - both were operated with a 305 deg. C peak temperature, a 65 deg.C temperature gradient, and mercury velocity of 1.2 m/min - but only one included a 36 h soak in Hg at 310 deg. C just prior to operation to encourage wetting. Results indicate that the soak in Hg at 310 deg. C had no lasting effect on wetting or compatibility with Hg. Further, based on examination of post-test wetting and coupon weight loss, only the gold-coated surfaces revealed significant interaction with Hg. In areas wetted significantly by Hg, the extreme surface of the stainless steel (ca 10 micrometers) was depleted in Ni and Cr compared to the bulk composition.
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