Speciation of actinide ions in aqueous solution by laser-induced pulsed photoacoustic spectroscopy

Laser Photoacoustic Spectroscopy for Trace Level Detection of Actinides in Groundwater

The Basalt Waste Isolation Project (Rockwell Hanford Operations- BWIP) is investigating the feasibility of building a repository in the Columbia River Basalts for the permanent disposal of high-level nuclear waste. One aspect of this effort is to develop an understanding of the chemical behavior of radionuclides in the near-field environment of the waste container. Such information is needed to determine radionuclide release rates from the waste package and to make long-term projections of repository performance. To accomplish this task, ultrasensitive laser- based techniques, such as laser photoacoustic spectroscopy (LPAS) and laser induced fluorescence (LIF), are being developed as analytical methods for the trace-level detection and speciation of actinides in solutions typical of those encountered in groundwaters near the BWIP repository.

Padiolytically Induced Oxidation Reactions of Actinide Ions in Concentrated Salt Solutions

The autoradiolytic oxidation of Pu(IV) and Am(III) has been investigated in saline solution of different NaCl concentrations, pH and specific α-activities. The high linear energy transfer (LET) property of α-radiation in solution enhances the oxidation of the Cl ion and thus increases the redox potential (Eh) of the NaCI solution system to a value of more than +1000 mV vs. NHE. Radiolytic reaction products are found as being comparable with those from the Cl2 saturated NaCl solution 'and create a metastable system consisting of C12/HCl0/Cl0−/Cl−. The oxidation of Pu(IV) and Am(III) in such solutions is dependent on the NaCl concentration, pH and specific a-activity involved. The quantitative oxidation to Pu(VI) and Am(V) is ob- served in the concentrated NaCl solution at pH > 7 with a moderately high specific activity (> 1 Ci/L).

Humic Colloid Generation of Transuranic Elements in Groundwater and Their Migration Behaviour

The generation of humic colloids of Am(III) has been investigated in Gorleben groundwaters containing different amounts of humic substances. Dissolved organic carbon (DOC) in these groundwaters consists mainly of humic acid and fulvic acid, which is present in a colloidal form through aggregation with trace heavy metal ions of groundwater constituents. Concentrations of these heavy metal ions are proportional to the DOC concentration. The generation of Am(III) pseudocolloids through geochemical interactions with humic colloids in different groundwaters is quantified by ultrafiltration as well as ultracentrifugation by the aid of radiometric concentration measurements. The speciation of dissolved Am(III) species in groundwaters is carried out by laser induced photoacoustic spectroscopy (LPAS).

Migration of Radionuclides in Geologic Media: Fundamental Research Needs

An assessment of the fundamental research needs in understanding and predicting the migration of radionuclides in the subsurface is provided. Emphasis is on the following three technical areas: (1) aqueous speciation of radionuclides, (2) the interaction of radionuclides with substrates, and (3) intermediate-scale interaction studies. This research relates to important issues associated with environmental restoration and remediation of DOE sites contaminated with mixed radionuclide-organic wastes.

Speciation of Transuranic Ions in Groundwater by Laser-Induced Photoacoustic Spectroscopy (LPAS)

The speciation of the Am(III) ion in various chemical states is illustrated using laser-induced photoacoustic spectroscopy (LPAS). Based on these reference LPAS spectra, the actual chemical states of Am(III) in one of Gorleben groundwaters are systematically verified. The a-radiolytic oxidation of Am(III) to Am(V) in the concentrated NaCl solution and their carbonate complexation are also speciated for the purpose of demonstration.

Solubility and Colloid Generation of Plutonium from Leaching of a HLW Glass in Salt Solutions

Solubilities of Pu from leaching of a simulated HLW glass (C31–3-EC) spiked with 5 wt % Pu and from PuO2 are determined in salt solutions of different NaCl concentration and in groundwaters which are representative for the Gorleben area. Th.e leaching experiment is carried out either in an autoclave at 200 °C or under normal conditions (1 atm, 25°C). Solubilities of Pu in all investigated solutions are observed to be considerably higher than the values known from theoretical estimates. The predominant Pu species in solutions are found to be microcolloids, which are characterized by means of ultrafiltration and pulsed laser-induced photoacoustic spectroscopy.

Speciation of the oxidation states of plutonium in aqueous solutions by UV/Vis spectroscopy, CE-ICP-MS and CE-RIMS

For the speciation of the plutonium oxidation states in aqueous solutions, the online coupling of capillary electrophoresis (CE) with inductively coupled plasma mass spectrometry (ICP-MS) has been developed. Depending on the radius/electrical charge ratio, the oxidation states III, IV, V, and VI of plutonium are separated by CE, based on the different migration times through the capillary and are detected by ICP-MS. The detection limit is 20 ppb,i.e.109–1010atoms (10-12–10-13g) for one oxidation state with an uncertainty of the reproducibility of the migration times of ≤1% and ≤5% for the peak area. The redox kinetics of the different plutonium oxidation states in the presence of humic substances (humic and fulvic acid) have been studied. A relatively rapid reduction of Pu(VI) (10 to 1000 h) in contact with Gorleben fulvic or Aldrich humic acid could be observed, depending on the pH of the solution. Furthermore, at pH=1, a reduction to Pu(III) and Pu(IV) in a mixture of all four oxidation states in contact with Gorleben fulvic acid after one month has been observed. In order to improve the sensitivity of the CE method, the offline coupling of CE to resonance ionization mass spectrometry (RIMS) has been explored. First applications of this new speciation method are presented.

Laser-based non-fluorescence detection techniques for liquid separation systems

Over the last two decades, the possibility to use lasers for detection purposes in column liquid chromatography (LC) and capillary electrophoresis (CE) received much attention in the analytical chemistry literature. Most attention has been devoted to laser-induced fluorescence. The present review covers developments on non-fluorescence techniques for LC and CE. The techniques considered are thermal lens spectrometry, photoacoustic detection, refractive index detection including refractive index backscattering, Raman spectroscopy and degenerate four-wave mixing (a special mode of transientholographic spectroscopy). The paper starts with an outline of the characteristics of lasers; it ends with an overall evaluation and a discussion of the perspectives of the techniques dealt with.

The Chemical Behavior of Transuranium Elements and Barrier Functions in Natural Aquifer Systems

The chemical behavior of transuranium elements in natural aquifer systems is governed by a variety of geochemical reactions, such as dissolution reaction (solubility), hydrolysis, complexation with inorganics or organics, redox reaction, colloid formation, geochemical interaction with surfaces of various minerals, coprecipitation, mineralization, etc. This paper reviews the present state of knowledge on some of these particular reactions. The emphasis here is on how the individual reactions can be appraised for long-term prediction of the geochemical behavior of transuranium elements in the natural environment. of the various possible reactions, the primary thermodynamic processes are discussed with notable examples: dissolution of transuranium compounds in aquatic solution; complexation with important anions present in groundwater; and colloid generation. Various laser spectroscopic methods in use for chemical speciation are mentioned briefly for their spectroscopic capability, as well as for their applicability. The present paper attempts to better understand the migration behavior of transuranium elements in natural aquifer systems.