Automated radioanalytical system incorporating microwave-assisted sample preparation, chemical separation, and online radiometric detection for the monitoring of total 99Tc in nuclear waste processing streams.

An automated fluidic instrument is described that rapidly determines the total (99)Tc content of aged nuclear waste samples, where the matrix is chemically and radiologically complex and the existing speciation of the (99)Tc is variable. The monitor links microwave-assisted sample preparation with an automated anion exchange column separation and detection using a flow-through solid scintillator detector. The sample preparation steps acidify the sample, decompose organics, and convert all Tc species to the pertechnetate anion. The column-based anion exchange procedure separates the pertechnetate from the complex sample matrix, so that radiometric detection can provide accurate measurement of (99)Tc. We developed a preprogrammed spike addition procedure to automatically determine matrix-matched calibration. The overall measurement efficiency that is determined simultaneously provides a self-diagnostic parameter for the radiochemical separation and overall instrument function. Continuous, automated operation was demonstrated over the course of 54 h, which resulted in the analysis of 215 samples plus 54 hly spike-addition samples, with consistent overall measurement efficiency for the operation of the monitor. A sample can be processed and measured automatically in just 12.5 min with a detection limit of 23.5 Bq/mL of (99)Tc in low activity waste (0.495 mL sample volume), with better than 10% RSD precision at concentrations above the quantification limit. This rapid automated analysis method was developed to support nuclear waste processing operations planned for the Hanford nuclear site.

Direct spectrophotometric analysis of Cr(VI) using a liquid waveguide capillary cell.

Hexavalent chromium Cr(VI) is a notorious ground water contaminant toxic to humans and animals. Assessment of an exposure risk for aquatic receptors necessitates frequent Cr(VI) concentration data from a range of surface and groundwater locations at Cr(VI) contamination sites. In this work, we demonstrate that enhanced ultraviolet-visible (UV-vis) spectroscopy using a liquid waveguide capillary cell (LWCC) offers an easy-to-use and economical methodology for the determination of chromate anion CrO(4)(2-) in Hanford natural waters without chemical pretreatment and generation of hazardous waste. Direct determination of CrO(4)(2-) in actual surface and ground water samples with the complexities of competing ions, dissolved organics, and other potential interfering agents was achieved by measuring the chromate optical absorbance at 372 nm. For a 100 cm path length LWCC, the detection limit for chromate was found to be as low as 0.073 ppb. A quantitative relationship between the intensity of the absorbance signal and water pH allowed for the straightforward calculation of total Cr(VI) content in natural water. The described method is applicable for in-field monitoring of Cr(VI) in environmental water samples at trace levels.

Equilibration-based preconcentrating minicolumn sensors for trace level monitoring of radionuclides and metal ions in water without consumable reagents.

A sensor technique is described that captures analyte species on a preconcentrating minicolumn containing a selective solid-phase sorbent. In this approach, the sample is pumped through the column until the sorbent phase is fully equilibrated with the sample concentration, and the exit concentration equals the inlet concentration. On-column detection of the captured analytes using radiometric and spectroscopic methods is demonstrated. In trace level detection applications, this sensor provides a steady-state signal that is proportional to sample analyte concentration and is reversible. The method is demonstrated for the detection of Tc-99 using anion-exchange beads mixed with scintillating beads and light detection, Sr-90 using SuperLig 620 beads mixed with scintillating beads and light detection; and hexavalent chromium detection using anion-exchange beads with spectroscopic detection. Theory has been developed to describe the signal at equilibration and to describe analyte uptake as a function of volume and concentration, using parameters and concepts from frontal chromatography. It is shown that experimental sensor behavior closely matches theoretical predictions and that effective sensors can be prepared using low plate number columns. This sensor modality has many desirable characteristics for in situ sensors for trace level contaminant long-term monitoring where the use of consumable reagents for sensor regeneration would be undesirable. Initial experiments in groundwater matrixes demonstrated the detection of Tc-99 at drinking water level standards (activity of 0.033 Bq/mL) and detection of hexavalent chromium to levels below drinking water standards of 50 ppb.

Microwave-assisted sample treatment in a fully automated flow-based instrument: oxidation of reduced technetium species in the analysis of total technetium-99 in caustic aged nuclear waste samples.

An automated flow-based instrument for microwave-assisted treatment of liquid samples has been developed and characterized. The instrument utilizes a flow-through reaction vessel design that facilitates the addition of multiple reagents during sample treatment and removal of the gaseous reaction products and enables quantitative removal of liquids from the reaction vessel for carryover-free operations. Matrix modification and speciation control chemistries that are required for the radiochemical determination of total (99)Tc in caustic aged nuclear waste samples have been investigated. A rapid and quantitative oxidation procedure using peroxydisulfate in acidic solution was developed to convert reduced technetium species to pertechnetate in samples with high content of reducing organics. The effectiveness of the automated sample treatment procedures has been validated in the radiochemical analysis of total (99)Tc in caustic aged nuclear waste matrixes from the Hanford site.