Testing of 304L Stainless Steel in Nitric Acid Environments with Fluorides and Chlorides

Nitric acid solutions containing fluorides is a typical solution for processing nuclear materials.  Some materials contain residual chlorides from previous processing, creating an aggressive environment for 304L stainless steel equipment.  Processing temperature also changes depending on the material to be dissolved.  Coupon immersion and vapor space testing was performed over a range of temperatures and concentrations for nitric acid, fluoride and chloride to characterize the corrosion.  The test set up simulated the dissolver process system as well as the procedure for processing.  Three coupon configurations were used including teardrop-shaped coupons for assessing stress corrosion cracking, creviced coupons, and welded coupons.  Dissolver failures in these environments have typically been near the weld in the heat affected zone with shorter times in the presence of chlorides and at higher temperatures.  An empirical relationship was developed for the corrosion rate as a function of these process parameters.  Mechanistic changes may also be a function of the chloride concentration.