Development and application of novel detection methods for aqueous radioactive iodine

Novel detection and analysis methods for radioactive iodine concentration and speciation were investigated for aqueous samples. Radioactive iodine is one of the primary risk-drivers at nuclear waste facilities, and regulations for the presence of radioactive iodine in drinking water are stringent. The first phase of this investigation described the development and characterization of a scintillating anion-exchange resin preferential for aqueous iodine in the form of iodide (I-). The resin was incorporated into a radiochromatography flow-cell scintillation detection system that allowed for simultaneous separation, concentration, and detection of aqueous 129I. The performance of this analytical method was characterized with both on-line and off-line measurements of synthetic groundwater samples spiked with 129I as I-. Parameters of interest included loading efficiency, detection efficiency, capacity, column elution, sorption kinetics, and interferences. It was determined that this detection system was suitable for the measurement of aqueous radioactive I - in the presence of potentially interfering analytes at typical groundwater concentrations. However, this method was insufficient for the determination of multiple aqueous radioactive iodine species.;The developed and characterized flow-cell method for I- was incorporated into a larger analytical technique suitable for the determination of multiple aqueous radioactive iodine species including I-, molecular iodine (I2), and iodate (IO 3-) at environmental concentrations. The redox-active nature of iodine makes its mobility and fate in the environment difficult to predict, thus underscoring the importance of species-specific determination of iodine concentrations. The expanded method coupled solid phase extraction and liquid scintillation counting with the radiochromatography method for a sequential measurement of each of the three iodine species. Solid phase extraction disks (SDB-XC) were impregnated with polyvinylpyrrolidone (PVP) for the selective extraction and stabilization of I2 with subsequent analysis by liquid scintillation counting. Aqueous I- was then concentrated and measured using the radiochromatography system. A subsequent chemical reduction of IO3- to I - in the effluent was then used to quantify IO3 - by the same flow-cell system. Nearly quantitative results were found for standardized single-species samples of I2 (92%), I- (102%), and IO3- (91%), respectively, while consistent results were obtained for aqueous samples containing a mixture of the three iodine species.;The aqueous radioactive iodine speciation method was subsequently applied to the analysis of aqueous radioactive iodine speciation in the presence of hausmannite (Mn3O4). Other manganese minerals such as birnessite have been shown to affect iodine speciation in the subsurface. Batch contact studies were completed with 129I (as I -) in synthetic groundwater over a range of pH values and contact times. Samples were analyzed and iodine speciation was determined by the application of the novel method. An additional step involving the dissolution of the solid phase with subsequent analysis by liquid scintillation counting was included to determine iodine sorption to the mineral. Results for samples at pH 3 indicated initially rapid oxidation of I- to I2 followed by subsequent slower oxidation of I2 to IO3- . Increased sorption of iodine was also observed with increasing IO 3- concentrations. The redox and sorption behavior was observed to be highly pH dependent. The data were also used to model the kinetics of the observed oxidation and sorption with first-order Bateman equations.