Radioanalysis of ultra-low level radionuclides for environmental tracer studies and decommissioning of nuclear facilities

Suitability of 210Pbex, 137Cs and 239+240Pu as soil erosion tracers in western Kenya

Land degradation resulting from soil erosion is a global concern, with the greatest risk in developing countries where food and land resources can be limited. The use of fallout radionuclides (FRNs) is a proven method for determining short and medium-term rates of soil erosion, to help improve our understanding of soil erosion processes. There has been limited use of these methods in tropical Africa due to the analytical challenges associated with 137Cs, where inventories are an order of magnitude lower than in the Europe. This research aimed to demonstrate the usability of 239+240Pu as a soil erosion tracer in western Kenya compared to conventional isotopes 210Pbex and 137Cs through the determination of FRN depth profiles at reference sites. Across six reference sites 239+240Pu showed the greatest potential, with the lowest coefficient of variation and the greatest peak-to-detection limit ratio of 640 compared to 5 and 1 for 210Pbex and 137Cs respectively. Additionally, 239+240Pu was the only radionuclide to meet the 'allowable error' threshold, demonstrating applicability to large scale studies in Western Kenya where the selection of suitable reference sites presents a significant challenge. The depth profile of 239+240Pu followed a polynomial function, with the maximum areal activities found between depths 3 and 12 cm, where thereafter areal activities decreased exponentially. As a result, 239+240Pu is presented as a robust tracer to evaluate soil erosion patterns and amounts in western Kenya, providing a powerful tool to inform and validate mitigation strategies with improved understanding of land degradation.

Optimisation of plutonium separations using TEVA cartridges and ICP-MS/MS analysis for applicability to large-scale studies in tropical soils

The analysis of plutonium (Pu) in soil samples can inform the understanding of soil erosion processes globally. However, there are specific challenges associated for analysis in tropical soils and so an optimal analytical methodology ensuring best sensitivity is critical. This method aimed to demonstrate the feasibility of sample preparation and analysis of Pu isotopes in African soils, considering the environmental and cost implications applicable to low-resource laboratories. The separation procedure builds upon previous work using TEVA columns, further demonstrating their usefulness for the reduction of uranium (U) interference in ICP-MS analysis with enhanced selectivity for Pu. Here several steps were optimised to enhance Pu recovery, reducing method blank concentration, and improving the separation efficiency through the determination of the elution profiles of U and Pu. The elimination of the complexing agent in the eluent, increased the spike recovery by improving matrix tolerance of the plasma, and simplified the separation procedure, improving throughput by 20%. The subsequent method was validated through the analysis of Certified Reference Material IAEA-384, where high accuracy and improved precision of measurement were demonstrated (measured value 114 ± 12 versus certified value 108 ± 13 Bq kg-1). Optimisation of the column separation, along with the analysis of the samples using O2 gas in ICP-MS/MS mode to mass shift Pu isotopes away from interfering molecular U ions provided a simple, robust, and cost-effective method with low achievable method detection limits of 0.18 pg kg-1 239+240Pu, applicable to the detection of ultra-trace fallout Pu in African soils.

Sequential Separation of Iodine Species in Nitric Acid Media for Speciation Analysis of 129I in a PUREX Process of Spent Nuclear Fuel Reprocessing

For efficient and accurate speciation analysis of ¹²⁹I in the nitric acid solution of spent nuclear fuel in its reprocessing process, a sequential procedure for stepwise separation of different iodine species in 3 mol/L HNO₃ was proposed based on the solvent extraction using CCl₄ and mesitylene. Molecular iodine (I₂) was first separated by solvent extraction using CCl₄, and iodide (I^-) remaining in the aqueous phase was oxidized to I₂ by adding NaNO₂ and then extracted to mesitylene. Finally, iodate (IO₃^-) was reduced to I₂ using NH₂OH·HCl and extracted to mesitylene. The separation efficiency of 98-99% for tracer amounts of ¹²⁹I₂, ¹²⁹I^-, and ¹²⁹IO₃^- in 3 mol/L HNO₃ and less than 2% crossover among different iodine species were achieved. The extraction process and mechanism of different iodine species in CCl₄ and mesitylene were investigated, and the problem of crossover of different iodine species due to the low extraction efficiency of low concentration of iodine in nitric acid solution was solved. A direct transfer of IO₃^- from HNO₃ to the mesitylene phase without conversion to I₂ was observed, which was attributed to the iodination of mesitylene in the HNO₃ medium. Addition of a stable iodine species carrier and repeated extraction significantly improved the separation efficiency of iodine species, making their quantitative separation achievable. This method provides an approach for speciation analysis of ¹²⁹I in the acidic spent nuclear fuel solution, enabling us to investigate and control the behavior of volatile ¹²⁹I in the spent nuclear fuel reprocessing process.

Rapid radionuclide specific screening procedures in drinking water: alternative options to replace inaccurate gross activity measurements

It was concluded from two European wide proficiency tests that the gross alpha/beta methods used for drinking water analysis have fundamental pitfalls regardless of the specific gross-counting methods. The majority of gross-counting methods suffer from serious trueness and repeatability issues. To replace inaccurate gross activity measurements an alternative rapid radionuclide specific screening procedure for water analysis is proposed. This procedure considers liquid scintillation counting, alpha-particle- and gamma-ray spectrometry. The proposed procedure is more robust and can achieve lower uncertainties than gross-counting methods. Furthermore, qualitative and quantitative analytical data can be obtained with turnaround times comparable to the gross-counting methods.

An effective method for the determination of 106Ru in seawater by γ-spectrometry

¹⁰⁶Ru is a product originating from the fission reactions of uranium (²³⁵U) and plutonium (²³⁹Pu). ¹⁰⁶Ru represents a potential source of radioactive marine contamination since it makes up 70-90% of the total radioactivity of liquid effluents from fuel reprocessing plants; thus, it is important to effectively determine the quantity of ¹⁰⁶Ru in the natural environment. In this study, a simple and effective method was developed for the determination of ¹⁰⁶Ru in seawater by γ-spectrometry using NiS coprecipitation. In addition, the amounts of S^2- and Ni²⁺ added, Ru³⁺ carrier addition, pH, salinity, and sample volume were tested, and accordingly, optimal conditions were proposed. With the optimized conditions, the recovery of ¹⁰⁶Ru in seawater ranged from 85.3% to 92.3%, with an average of 88.1 ± 4.2%. The method proposed in the present study can also be applied to seawater samples with various salinities and volumes. For 20 L seawater and 24 h counting time on a γ-spectrometer, the limit of detection for ¹⁰⁶Ru in seawater was 5.74 mBq/L. In contrast to the traditional CoS method, the usage of NiS does not require any heating process; thus, the pretreatment time is substantially reduced. In addition, by using our method, ¹⁰⁶Ru can be determined in the presence of other radionuclides, further enhancing processing efficiency.

Towards the application of electrokinetic remediation for nuclear site decommissioning

Contamination encountered on nuclear sites includes radionuclides as well as a range of non-radioactive co-contaminants, often in low-permeability substrates such as concretes or clays. However, many commercial remediation techniques are ineffective in these substrates. By contrast, electrokinetic remediation (EKR), where an electric current is applied to remove contaminants from the treated media, retains high removal efficiencies in low permeability substrates. Here, we evaluate recent developments in EKR for the removal of radionuclides in contaminated substrates, including caesium, uranium and others, and the current benefits and limitations of this technology. Further, we assess the present state of EKR for nuclear site applications using real-world examples, and outline key areas for future application.

Dynamic Flow Approaches for Automated Radiochemical Analysis in Environmental, Nuclear and Medical Applications

Automated sample processing techniques are desirable in radiochemical analysis for environmental radioactivity monitoring, nuclear emergency preparedness, nuclear waste characterization and management during operation and decommissioning of nuclear facilities, as well as medical isotope production, to achieve fast and cost-effective analysis. Dynamic flow based approaches including flow injection (FI), sequential injection (SI), multi-commuted flow injection (MCFI), multi-syringe flow injection (MSFI), multi-pumping flow system (MPFS), lab-on-valve (LOV) and lab-in-syringe (LIS) techniques have been developed and applied to meet the analytical criteria under different situations. Herein an overall review and discussion on these techniques and methodologies developed for radiochemical separation and measurement of various radionuclides is presented. Different designs of flow systems with combinations of radiochemical separation techniques, such as liquid-liquid extraction (LLE), liquid-liquid microextraction (LLME), solid phase extraction chromatography (SPEC), ion exchange chromatography (IEC), electrochemically modulated separations (EMS), capillary electrophoresis (CE), molecularly imprinted polymer (MIP) separation and online sensing and detection systems, are summarized and reviewed systematically.

An Automated SeaFAST ICP-DRC-MS Method for the Determination of 90Sr in Spent Nuclear Fuel Leachates

To reduce uncertainties in determining the source term and evolving condition of spent nuclear fuel is fundamental to the safety assessment. ß-emitting nuclides pose a challenging task for reliable, quantitative determination because both radiometric and mass spectrometric methodologies require prior chemical purification for the removal of interfering activity and isobars, respectively. A method for the determination of ⁹⁰Sr at trace levels in nuclear spent fuel leachate samples without sophisticated and time-consuming procedures has been established. The analytical approach uses a commercially available automated pre-concentration device (SeaFAST) coupled to an ICP-DRC-MS. The method shows good performances with regard to reproducibility, precision, and LOD reducing the total time of analysis for each sample to 12.5 min. The comparison between the developed method and the classical radiochemical method shows a good agreement when taking into account the associated uncertainties.