Corrosion impact of reductant on DWPF and downstream facilities

Abstract

Pitting corrosion, nitrite concentration fell outside that specified in the corrosion control program for HLW 30 A537SRNL-STI-2014-00281 Revision 0 design basis, but in the regions with cracking and cavitation the K-3 corrosion rate is at or greater than the DWPF design basis.5. The cavitation is likely due to the proximity of the refractory coupon to the bubbler orifice but the cracking is related to the Fe° depletion caused by excessive nitric acid used in the glycolic acid CEF campaign.The expected performance of the materials of construction within the CPC, specifically C276, Ultimet® and Stellite® at boiling temperatures, is questionable due to the susceptibility to localized corrosion identified during this testing. Since the glycolate anion concentration is at the highest in the CPC for the whole HLW processing system, determining operating limits where localized corrosion is not a concern is stressed. Additional testing for these materials is recommended to better understand the limits of these results and identify conditions for acceptable performance in service.These proposed tests would include performing electrochemical testing with formic acid based SRAT/SME supernates, which would provide a correlation between accelerated electrochemical test results and observed performance of components within the CPC and with glycolic acid based SRAT/SME supernates at levels of aggressive species (chloride, sulfate and mercury) where localized corrosion does not occur. Similar simulants would be used in hot-wall tests to verify that localized corrosion also does not occur under heat transfer conditions. Finally, a coupon immersion test is recommended to verify that the accelerated results of the electrochemical test occur with time during an extended exposure in the coupon test.Additional testing was also recommended for other materials where the presence of the glycolate anion impacted test results. These tests were recommended to better identify the temperature and glycolic acid limits for acceptable performance of the materials of construction, especially those susceptible to localized corrosion.1. Coupon immersion test with 304L in 70% glycolic acid at actual service temperature to determine if pitting occurs.2. Hot-wall testing for G30 and G3 in waste stream simulants without glycolic acid present for comparison to results with glycolate anion present, where pitting and crevice corrosion was observed.3. Metallurgical examination of the inner diameter of I690 pipe used in fabrication of melter bubbler to determine presence of cracks, which would reduce effective thickness and act as stress concentrators.4. Perform modified ASTM C621 tests in glycolic acid feeds to determine impact of glycolic acid vs. formic acid with and without the impact of Ar bubbling, i.e. all the formic acid flowsheet corrosion data has been derived in non-bubbled pilot scale melters except for the CEF glycolic acid campaign. This testing should suffice to get more precise comparative corrosion data for the K-3.viii Revision TABLE OF CO...

Influence of Glycolate Anion on Aqueous Corrosion in DWPF and Downstream Facilities – SCC Testing

“…The glycolate-based solutions were able to maintain more elements in solutions such as Fe, Ni, and Mn. Neither glycolate-or formate-based solutions were able to maintain Hg in boiling solutions, which has been noted in previous testing [2,3].…”

“…These more electronegative values are believed to be a function of solution chemistry. Previously, the concentration of soluble mercury was found to influence both Ecorr and the measured corrosion rate [2]. A higher soluble mercury concentration results in more electropositive Ecorr and higher corrosion rates, which can be seen in the data in Table 3-1.…”

“…The solutions used in this testing were like those used in previous testing [2,3]. The formate-and glycolatebased solutions were formulated from CPC simulants determined during flowsheet development testing to support processing of Sludge Batch #8 waste and Sludge Batch #7 waste, respectively.…”

“…DWPF requested a corrosion assessment from the Savannah River National Laboratory (SRNL) for the components of the DWPF facility and the other High Level Waste and Low Level Waste processing facilities that would be exposed to glycolic acid or the glycolate anion [1]. Testing was conducted in both aqueous and glass environments [2]. Follow on testing was required to further investigate several issues for aqueous environments: 1) several results where localized corrosion was observed on test samples; 2) the influence of glycolic acid for all the different waste compositions covered by the Tank Farm Corrosion Control Program; and 3) a new chloride corrosion limit for the DWPF Waste Acceptance Criteria (WAC), which was established at 800 ppm [3,4].…”

Impact of Permanganate Oxidation of Glycolate on Corrosion of the Defense Waste Processing Facility (DWPF) Recycle Collection Tank (RCT), Transfer-line and Waste Tank Materials of Construction (MoC)

“…Laboratory studies performed at Savannah River National Laboratory (SRNL) indicated that the replacement to glycolic acid allows the reduction and removal of mercury in the Sludge Receipt and Adjustment Tank (SRAT) without significant hydrogen generation [2]. Due to the many advantages that glycolic acid can have over formic acid, testing was performed to evaluate the materials that can be in direct contact and the associated corrosion mechanisms compared with exposure to formic acid [3]. Glycolate, which is the product that may remain after using glycolic acid, can also be carried downstream to High-Level Waste and Low-Level Waste facilities.…”