EXPERIMENTAL STUDY TO EVALUATE CORROSION OF THE F-CANYON DISSOLVER DURING THEUNIRRADIATED MARK-42 CAMPAIGN

Unirradiated Mark 42 fuel tubes are to be dissolved in an upcoming campaign in F-canyon. Savannah River Technology Center (SRTC)/Chemical & Hydrogen Technology Section (CHTS) identified a flow sheet for the dissolution of these Mark 42 fuel tubes which required a more aggressive dissolver solution than previously required for irradiated Mark 42 fuel tubes. Subsequently, SRTC/MTS was requested to develop and perform a corrosion testing program to assess the impact of new flow sheets on corrosion of the dissolver wall. The two primary variables evaluated were the fluoride and aluminum concentrations of the dissolver solution. Fluoride was added as Calcium Fluoride (CaF{sub 2}) while the aluminum was added either as metallic aluminum, which was subsequently dissolved, or as the chemical aluminum nitrate (Al(NO{sub 3}){sub 3}). The dissolved aluminum metal was used to simulate the dissolution of the aluminum from the Mark 42 cladding and fuel matrix. Solution composition for the corrosion tests bracketed the flow sheet for the Mark 42. Corrosion rates of AISI Type 304 stainless steel coupons, both welded and non-welded coupons, were calculated from measured weight losses and post-test concentrations of soluble Fe, Cr and Ni. The corrosion rates, which ranged between 2.7 and 32.5 mpy, were calculated from both the one day and the one week weight losses. These corrosion rates indicated a relatively mild corrosion on the dissolver vessel. The welded coupons consistently had a higher corrosion rate than the non-welded coupons. The difference between the two decreased as the solution aggressiveness decreased. In these test solutions, aggressiveness corresponded with the fluoride concentration. Based on the results of this study, any corrosion occurring during the Mark 42 Campaign is not expected to have a deleterious effect on the dissolver vessel