The determination of pure beta-emitters and their behaviour in a salt-marsh environment

The thesis describes the development of analytical procedures for the isolation and measurement of anthropogenic pure beta-emitting radioisotopes in low-level radioactive wastes and environmental samples. The research focussed on three key pure beta-emitting radioisotopes, namely 63Ni, 90Sr and 99Tc. Iron-55, which decays by electron capture, was also investigated. Source preparation and measurement techniques based on liquid scintillationcounting were developed and optimised to permit the low-level measurement of all four radioisotopes. In particular, a technique was developed for increasing the amount of stable Fe that may be loaded into scintillant, reducing the limit of detection achievable for 55Fe measurement and increasing the sensitivity of analysis for 55Fe in Fe-rich materials such assediments and steels. Chemistries for the isolation of the four radioisotopes were studied and optimised. Solvent extraction was chosen for the specificity offered by the technique. In most instances, improvements in separation efficiency were achieved by adsorbing the extractant onto an inert support producing an extraction chromatographic material. Key separation techniqueswere then combined to produce a sequential separation scheme that permitted a more rapid analysis of the four radioisotopes on a single sample. The sequential separation technique was then optimised for the analysis of 55Fe, 63Ni, 90Sr and 99Tc in both low-level wastes and environmental matrices (mainly sediments). Such separation schemes are crucial to the efficient analysis of samples in limited time spans and are vital when the amount of sample available is restricted.The optimised methods were used to investigate levels of anthropogenic pure beta-emitters in a saltmarsh sediment core collected from the Esk Estuary in Cumbria. Analysis of the four beta emitting radioisotopes was complemented by the analysis of major elements, trace elements and gamma emitting radioisotopes. This information was used to determine the behaviour of the beta emitters following deposition within the saltmarsh environment.Although all four beta emitters were detected in the core, only 90Sr and 99Tc were at sufficiently high levels to permit a more thorough investigation. The combination of geochemica! analysis and radiochemical analysis of this range of radioisotopes with widely varying chemistries has allowed a range of possible pre- and post-depositional processes to be investigated as well as providing data on the levels of previously unmeasured beta emitters inthe saltmarsh environment. Such information is essential in assessing the long-term retention and potential re-release of these radioisotopes and their importance in radiological dose assessment. The information also has wider implications to the behaviour of inorganic pollutants in coastal waters

Isolation and quantification of 55Fe and 63Ni in reactor effluents using extraction chromatography and liquid scintillation analysis

A novel extraction chromatographic resin based on diisobutyl ketone has been developed for the isolation of 55Fe. This material has been used in conjunction with a dimethylglyoxime-based resin for the sequential separation of 55Fe and 63Ni and isolation of these radionuclides from associated contaminants. The preparation and characterisation of these resins is described along with an assessment of their performance for the isolation of 55Fe and 63Ni from a mixture of nuclear activation products. In addition, a refined approach for the measurement of these nuclides by liquid scintillation counting is discussed. The findings of these studies have been combined to develop a robust procedure for the analysis of 55Fe and 63Ni in reactor effluents which is now the preferred method for a number of UK analytical laboratories

A novel approach for the rapid decomposition of Actinide resin and its application to measurement of uranium and plutonium in natural waters

A rapid and robust procedure is described for the decomposition of Actinide™ resin permitting the routine application of this resin as a preconcentrator. Although the classical Fe(OH)3 precipitation is effective in scavenging actinides, the need for careful handling to recover the sticky precipitate makes the new method much more attractive. The known difficulty of decomposing Actinide™ resin, which is required prior to the subsequent separation of adsorbed actinides, is innovatively overcome by using a borate fusion attack. This procedure effectively solves the normally encountered problem by safely and speedily decomposing the resin in minutes rather than hours. The alternative and apparently simpler technique of direct ashing of the Actinide™ resin is not used since it leads to a residue that is not readily leachable. The new technique has been incorporated into a procedure for the isolation of Pu and U from natural water samples and their subsequent quantification by alpha spectrometry. The efficiency of loading of the elements onto Actinide™ resin has been tested using both batch and column-based approaches. The integrated method involving Actinide™ resin preconcentration, borate fusion, anion and UTEVA chromatography and electrodeposition provides limits of detection of 0.001 Bq L?1 and chemical recoveries in excess of 80% from groundwater and seawater samples as large as 5 L. Comparative data, presented for the analysis of independently analysed river, borehole and surface run-off waters using both the described procedure and other competing techniques, show very good agreement

A suite of robust radioanalytical techniques for the determination of tritium and other volatile radionuclides in decommissioning wastes and environmental matrices

Tritium is ubiquitous in and around nuclear plants, being formed via neutron capture by 2H, 6Li, 10B and 14N and via ternary fission. The highly mobile nature of 3H species results in widespread distribution of the radionuclide. Predictive modeling of 3H activity concentrations is challenging and direct measurement of 3H activities in materials is the preferred approach to underpin waste and environmental assessments. For well over a decade, the UK nuclear industry has engaged in a significant program of site decommissioning of its first generation reactors. This has resulted in a high demand for the rapid characterization of 3H in a diverse range of matrices, including concretes, metals, plastics, sludges, resins, soils and biota. To support such assessments, it has been necessary to develop dedicated instrumentation in parallel with robust radioanalytical methodologies; namely a multi-tube furnace and a high-capacity, closed (pressurized) oxygen combustion system. Data are presented on the development and validation of these instruments, designed specifically to enable the quantitative extraction of 3H (and other volatile radionuclides) from diverse sample types. Furthermore the furnace system has been employed as a tool to gain insights into the 3H association in decommissioning and environmental matrices exposed to 3H arising from nuclear power plant operations through tritium evolution with temperature profiling. The impact of the chemical speciation of 3H on analytical strategy is discussed. A major benefit of the multi-sample furnace is its ease of use and applicability to 3H determination in virtually any sample type. The complementary HBO2 oxygen combustion system has been developed for the quantitative oxidation of organic-rich samples (e.g. wood, plastic, oil, biota) and analytical data prove its effectiveness

Variations in the gross alpha and beta activity in surface waters at the Atomic Weapons Establishment Aldermaston (UK)

Statistical analysis has been performed on thegross alpha- and beta-activity measurements of surfacewaters collected at the Atomic Weapons Establishment atAldermaston (UK) during the period January 2002–September2005. The results have been found to follow alognormal distribution and this has important applicationswhen considering gross activity exemption thresholds. Thisimplies that the gross activity is the multiplicative productof many small independent factors, such as meteorology,flow conditions and site operations. The influence ofmeteorological parameters has been investigated usinglinear regression, and some correlation has been identifiedbetween gross beta-activity and parameters indicative offine weather. Variations in gross activity have been consideredon monthly, weekly and daily timescales andcharacterised using the geometric mean and geometricstandard deviation in accordance with the properties of thelognormal probability density function

Pre-concentration of naturally occurring radionuclides and the determination of 212Pb from fresh waters

A novel technique has been developed for determining the 212Pb activity of fresh waters. This is of interest to environmental monitoring programmes that utilise gross ?-activity methods to screen for anthropogenic radionuclides. The contribution from 212Pb varies, and is difficult to experimentally measure due to its relatively short half-life (t½ = 10.6 h) and low environmental activity (<0.1 Bq l?1). The use of a three-stage technique that encompasses a unique form of pre-concentration, separation and analysis by liquid scintillation counting allows a lower detection limit of 0.006 Bq l?1 with a chemical yield of 92.5 ± 5.6%. The measurement can be obtained within 7 h of sample collection, and is calculated using the radioactive decay of 212Bi. Other naturally occurring radionuclides may also be extracted using the pre-concentration stage of the technique, with efficiencies above 90% at a range of pH values

Effective Determination of the Long-lived Nuclide 41Ca in Nuclear Reactor Bioshield Concretes: Comparison of Liquid Scintillation Counting and Accelerator Mass Spectrometry

The routine application of liquid scintillation counting to 41Ca determination has been hindered by the absence of traceable calibration standards of known 41Ca activity concentrations. The introduction of the new IRMM 41Ca mass-spectrometric standards with sufficiently high 41Ca activities for radiometric detection has partly overcome this although accurate measurement of stable Ca concentrations coupled with precise half-life data are still required to correct the certified 41Ca:40Ca ratios to 41Ca activity concentrations. In this study, 41Ca efficiency versus quench curves have been produced using the IRMM standard, and their accuracy validated by comparison with theoretical calculations of 41Ca efficiencies. Further verification of the technique was achieved through the analysis of 41Ca in a reactor bioshield core that had been previously investigated for other radionuclide variations. Calcium-41 activity concentrations of up to 25 Bq/g were detected. Accelerator mass spectrometry (AMS) measurements of the same suite of samples showed a very good agreement, providing validation of the procedure. Calcium-41 activity concentrations declined exponentially with distance from the core of the nuclear reactor and correlated well with the predicted neutron flux.<br/