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Abstract
Type 316L stainless steel capsules containing commercially pure sodium and miniature tensile specimens of HT-UPS (austenitic, 14Cr-16Ni), NF-616 (ferritic/martensitic, 9Cr-2W-0.5Mo), or 316L (austenitic, 17Cr-10Ni-2Mo) stainless steel were exposed at 600 and 700°C for 100 and 400 h as a screening test for compatibility. Specimen weight, tensile properties, and microstructure of HT-UPS and 316L were found to be largely immune to changes resulting from sodium exposure, but NF-616 was susceptible to substantial decarburization at 700°C. Subsequently, two thermal convection loops (TCLs) constructed of 316L and loaded with commercially pure sodium and miniature tensile specimens of HT-UPS and 316L were operated for 2000 h each - one between 500 and 650°C, the other between 565 and 725°C - at a flow rate of about 1.5 cm/s. Under these dynamic conditions, changes in specimen appearance, weight, and tensile properties were observed to be very minor in all cases, and there was no metallographic evidence of microstructural changes, composition gradients, or mass transfer resulting from prolonged exposure in a TCL. Thus, it appears that HT-UPS and 316L stainless steels are similarly compatible with commercially pure sodium under these conditions.
