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Flow cell detectors were developed for simultaneous concentration and scintillation detection of technetium-99 in water. Evaluated flow cell geometries consisted of a coil and a fountain flow cell design; the latter is based on radial solution flow through a resin bed interfaced with a photomultiplier tube through a polycarbonate window. The sorptive scintillating media investigated were (1) an extractive scintillator combining a porous polystyrene resin with the extractant Aliquat-336 and fluor 2-(1-naphthyl)-5-phenyloxazole, (2) a mixed bed of organic scintillator (BC-400) and Tc-selective resin (TEVA), and (3) a mixed bed of inorganic scintillator particles (Ca[F.sub.2]-Eu) with either TEVA resin or strong base anion-exchange resin (Dowex 1 x 8-400(C1)). Depending on flow cell geometry and medium, the detection efficiencies for [sup.99]Tc ranged from 7.26 (BC-400/TEVA in coil geometry) to 50.20% (Ca[F.sub.2](Eu)/Dowex 1 x 8-400(C1) in fountain flow cell geometry). The configuration with the highest sensitivity, Ca[F.sub.2](Eu)/Dowex 1 x 8--400(C1) in coil geometry, can detect [sup.99]Tc as low as 3.78 Bq [L.sup.-1] for a 100-s count interval and a 200-mL sample, which is below the current regulatory level of 33 Bq [L.sup.-1]. The issue of sensor reusability was addressed in this research, and its potential application at near neutral pH was demonstrated. The optimal sensor design was evaluated with a [sup.99]Tc-spiked synthetic groundwater matrix.

The objective of this research was to develop a method suitable for the determination of aqueous concentrations of radioactive iodine as I2, I-, and IO3-. As one of the primary risk-drivers and contaminants of concern at nuclear waste repositories, the accurate determination of 129I in aqueous systems is of significant concern. 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 developed method couples solid phase extraction with liquid scintillation counting, and scintillating anion exchange with a flow-cell detection system for a sequential measurement of each iodine species. Solid phase extraction disks were impregnated with polyvinylpyrrolidone for the selective extraction and stabilization of I2 with subsequent analysis by liquid scintillation counting. Aqueous I- was concentrated and measured by a previously developed flow-cell system utilizing scintillating anion-exchange resin. A subsequent chemical reduction of IO3- to I- in the effluent was used to quantify IO3- by the same flow-cell system. Nearly quantitative results were found for standardized single-species samples of I2 (95%), I- (101%), and IO3- (91%), respectively, while consistent measurements were obtained for multispecies samples using the developed method and algorithm. [ABSTRACT FROM AUTHOR]

The objective of this research was to develop a scintillating anion exchange resin selective for monitoring 129I at concentrations at or below ~0.4 Bq/L. One of the primary long-term risk-drivers and contaminants associated with nuclear waste sites is 129I. Synthesis of scintillating anion exchange resin consisted of diffusing a fluor, 2-(1-naphthyl)-5-phenyloxazole (α-NPO), into a polymeric resin. The resultant scintillating resin was further modified by amination with N-methyldi-n-octylamine (MDOA) to serve as an anion exchange group. Radiochromatography columns were prepared with the synthesized resin for use in a variety of flow-cell experiments utilizing a standard 129I solution in a synthetic groundwater to determine the properties (selectivity, interferences, loading efficiency, kinetics, capacity, and detection efficiency) of the resin. Column effluents were quantified by liquid scintillation. Average loading and detection efficiencies have been measured at 91 ± 9% and 50 ± 4%, respectively. Finally, batch sorption studies indicated fast iodide sorption rates (90% loading in ~10 min) for the resin, and dynamic sorption tracer studies indicated an iodide capacity of approximately 7800 μg/g at 10% breakthrough. [ABSTRACT FROM AUTHOR]