After discovery of failed Viton™ B Fluoroelastomer gaskets at the Salt Waste Processing Facility (SWPF) in early calendar 2021, a short-term (27 day) compatibility test was conducted between SWPF process solutions including Average Salt Simulant, 1 mM nitric acid, 10 mM boric acid, Caustic-Side Solvent Extraction (CSSX) solvent, and Next Generation Solvent (NGS) and the following four polymers: Viton™ B, Viton™ Extreme™ ETP-600S, expanded polytetrafluoroethylene (ePTFE), and Garlock ® Blue-Gard

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... ® 3700. To the aqueous solutions, 20 mg/L of the following organics were added to represent impurities: Dibutyl phosphate, n-butanol, 2butanone, ethyl acetate, 4-secbutyl phenol, and N-(3,7-dimethyloctyl) amine. The 1 mM nitric acid, 10 mM boric acid, NGS, and CSSX solvent exposure tests were performed at 35 °C, with NGS, CSSX, and Average Salt Simulant Solution tests also performed at ambient temperature. The physical characteristics of the polymeric gaskets, their surface chemistry and the chemistry of the solutions were monitored. The gasket material behavior is summarized. Viton™ B Fluoroelastomer showed low swelling (less than 2%) with the test solutions due to the presence of a surface treatment or barrier layer, presumed talc (magnesium silicate hydroxide). However, if the talc layer was removed, Viton™ B is susceptible to fast caustic hydrolysis as noted in the literature (expect significant swelling). The talc surface treatment is generally applied by gasket manufacturers to reduce friction during gasket installation and to prevent sticking between materials, not for chemical protection. It is possible that a combination of over-torquing the gaskets and breaking of the protective talc layer led to gasket degradation in the facility. The degree to which each factor contributed to the failure cannot be determined based on the data available at this time. It is noted that reliance on a surface treatment for chemical resistance is less desirable than having sufficient inherent resistance. Fourier Transform Hydrogen Nuclear Magnetic Resonance (FT-HNMR) indicated that Viton™ B did not absorb 2butanone, dibutyl phosphate, and secbutylphenol in 1 mM nitric acid and in10 mM boric acid. The ETP-600S Fluoroelastomer gained weight and volume during testing (swelling less than 5%), with some hardness loss in Average salt simulant, 10 mM boric acid and 1 mM nitric acid solutions. This was expected based on the literature and information provided by the polymer manufacturer (The Chemours Company). The free volume available in this polymer explains the rate of mass gain in such a short period (27 days of contact) and it should be considered for long-term performance of this gasket. The extent of the swelling in Average salt simulant, in 1mM nitric acid, and in 10 mM borica was less than 5% which is considered as "little effect" by the manufacturer (The Chemours Company). Longer-term exposures are recommended to better assess this behavior. The ETP-600S did better when exposed to CSSX or NGS solvent with a volume swelling of 2% or less. FT-HNMR showed that ETP-600 did not absorb 2-butanone, dibutyl phosphate, and secbutylphenol in1 mM nitric acid and in 10 mM boric acid. The Garlock ® Blue-Gard ® 3700 material gained significant mass and volume in Average salt solution, NGS and CSSX solvent, but it showed resistance against 1 mM nitric acid and 10 mM boric acid. The material density gradually dropped from 1.62 to 1.49 g/mL in 27 days. Garlock ® Blue-Gard ® 3700 is a composite material (fiber-reinforced rubber) where the fibers (Aramid fibers) provide strong mechanical properties to the composite and in applications where it is compressed between two metallic flanges, it can be resilient to the SWPF process solutions. FT-HNMR indicated Garlock ® leached methyl acetate in Average Salt Solution and acetone in 1 mM nitric acid and in 10 mM boric acid. SRNL-STI-2021-00461 Revision 0 vi The ePTFE polymer only gained mass and volume in NGS and CSSX solvents because of its high porosity at the polymer surface. ePTFE is chemically compatible with all the SWPF liquids. However, the radiation resistance of ePTFE is known to be lower than that of most other polymers. This aspect may be reviewed in more detail if other sealing options do not show adequate compatibility. However, ePTFE is not recommended for high gamma radiation fields due to polymer scission and the production of F2 (or HF in the presence of water) gas.