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 or
700°C for 100 and 400 h as a screening test for
compatibility. Using weight change, tensile testing, and
metallographic analysis, HT-UPS and 316L were found to
be largely immune to changes resulting from sodium
exposure, but NF-616 was found 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.
Changes in specimen appearance, weight, and tensile
properties were observed to be very minor in all cases,
and there was no metallographic evidence of
microstructure 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 exposure conditions.