Measurement of Iodine, Iodide, and Iodate in Hanford Tank Waste: Technology Transfer from PNNL to Hanford 222-S Laboratory (2021)

This report describes the chemical separations used to measure the amount and chemical forms of inorganic iodine in Hanford tank waste and provides the technical basis and recommendations for transferring and implementing this new inorganic iodine analytical technique at Hanford's 222-S Laboratory.Part of the iodine in the tanks is fission product iodine-129, a long-lived beta emitter.Iodine is known to exist in the tanks in the forms of iodide and iodate, and perhaps periodate.The tanks may also have organic iodides, but their measurement is outside the scope of this report.When the tank waste is converted into its final waste forms (such as glass or grout), it will undergo various unit operations such as filtration, cesium ion exchange, evaporation, and vitrification.Secondary waste streams are subjected to many other separation and conversion processes (adsorption, oxidation, reduction).The behavior of iodine in these processes depends on its chemical forms, which have not been previously measured.The various inorganic chemical forms of iodine are chemically reactive and will dissolve, precipitate, undergo redox reactions, evaporate, and condense in parts of the waste treatment process.Iodine-129 is radiotoxic, and its behavior must be known in the waste treatment process.Iodine-129 is regulated for air emissions and problematic for disposal.Because tank waste is strongly basic, only a few inorganic chemical forms of iodine can be present, and the analyte list is short.At pH 12 to 14, iodine can exist as iodide, iodate, and periodate.All of the other oxidation states convert into one of these forms at the high pH of tank waste.Several iodides are insoluble in water and could conceivably exist as suspended solids in tank waste (AgI, PdI 2 , CuI, Hg 2 I 2 ), but this is unlikely because the concentrations of silver, palladium, copper, and mercury in the tank wastes are quite low, probably too low to materially affect the concentration of iodine in the tank waste supernatant liquid.Several iodates are sparingly soluble, but the concentration of iodate is quite low, almost certainty too low to form a precipitate.Inorganic iodine compounds may be mechanically occluded in tank waste solids.The water-insoluble sludge is believed to have only about 1% of the iodine in the tanks. 1 Traces of a silver-iodine compound have been found in the water-insoluble sludge from tank 241-C-105, 2 which the authors attributed to a silver reactor for offgas treatment that was flushed into this tank.In a simple aqueous solution, iodate and iodide are straightforward to measure, but the raw tank waste has several oxidizing agents that could seriously interfere with the iodine redox chemistry, primarily nitrite and chromate.The iodide and iodate separation chemistry described in this report is designed to accommodate the tank waste composition.To measure iodine, each chemical form of iodine is separated, in sequence, by a series of solvent extractions and redox reactions.Once isolated, the iodine is measured using inductively couple plasma mass spectrometry (ICP-MS).Both 127 I (stable iodine) and 129 I (long-lived beta emitter) are reported by the ICP-MS.Because stable iodine is an analyte, no iodine carrier can be used.The concentration of iodine in the raw tank waste is on the order of 1 ppm, which is high enough to comfortably separate and measure without using an iodine carrier.Analysis of the chemical form of iodine in Hanford tank wastes was developed at Pacific Northwest National Laboratory and will be transferred to the Department of Energy's 222-S Laboratory on the Hanford Site, in Washington State, for implementation during waste processing operations.1 Asmussen RM, TG Levitskaia, CL Bottenus, and MS Fountain.