Technology Transfer of Ultra-Trace Mercury Speciation Analytical Methods Developed at PNNL to a DOE Analytical Laboratory - 23534

Having a capability at the Hanford Site's 222-S Laboratory to independently measure key mercury species in both liquid and slurry samples offers important risk mitigation for Direct Feed Low-Activity Waste and future high-level waste processing flowsheets relative to waste feed acceptance and waste disposal. Understanding where and how mercury appears throughout the flowsheet will reduce risk to mission success by identifying when the transport, speciation, retention, or interactions with other tank waste constituents can impact regulatory compliance and/or operational performance. During fiscal years 2018 through 2020, staff at Pacific Northwest National Laboratory (PNNL) developed and demonstrated the novel application of an ultra-trace mercury analytical method to speciate and quantify total, elemental, and total methyl mercury in supernatant tank waste. Method development and analysis was conducted on 12 unique sample types stemming from three Hanford waste tanks and included samples collected from various process steps in the PNNL Radioactive Waste Test Platform sequence (e.g., raw feed, raw filter feed, aged diluted feed, particle filtered, post-cesium decontaminated, and lab-scale melter offgas condensate). Results demonstrated that both mercury concentrations and speciation could vary dramatically depending on the sample type. As such, understanding the movement of mercury and its speciation, chemical consequences, and fate is important for the Hanford flowsheet. This new analytical method intends to provide necessary information to evaluate the impact and management of these mercury species, including the magnitude and speciation of the constituent in feed inventory, how this inventory and speciation are distributed throughout the tank farms, how the tank-by-tank inventory is distributed and speciated by waste phases (i.e., sludge, salt cake, and supernatant), the expected speciation and concentrations during waste processing, and the degree of uncertainty in this information. In fiscal year 2021, this technique was transferred to the Hanford 222-S Laboratory to allow for future routine mercury speciation measurements as the Hanford Site moves into production operations. This technology transfer is discussed relative to four key aspects: (1) the motivation or need for mercury speciation and quantification, (2) assessment of existing capabilities versus future equipment needs at the 222-S Laboratory, (3) implementation guidance based on the analytical methods developed at PNNL, and (4) opportunistic additions and extensions to the methodology to quantify and speciate additional mercury species. (authors)