Phillip E. Warwick

A new ground-level fallout record of uranium and plutonium isotopes for northern temperate latitudes

Plutonium and uranium isotope ratios can be used to differentiate the sources of nuclear contamination from nuclear weapon establishments (Environ. Sci. Technol. 34 (2000) 4496; Internal Report for AWRE Aldermaston, UK (1961)), weapon fallout (Geochim. Cosmochim. Acta 51 (1987) 2623; Earth Planet. Sci. Lett. 63 (1983) 202; Earth Planet. Sci. Lett. 22 (1974) 111; Geochim. Cosmochim. Acta 64 (2000) 989), reprocessing plants, reactor or satellite accidents (Science 105 (1979) 583; Science 238 (1987) 512) and in addition they provide markers for post-1952 geochronology of environmental systems. A good record of plutonium and uranium isotope ratios of the background resulting from atmospheric nuclear testing is essential for source characterisation studies. Using recently developed mass spectrometric techniques (J. Anal. At. Spectrom. 16 (2001) 279) we present here the first complete records between 1952 and the present day of northern temperate latitude 240Pu/239Pu and 238U/235U atom ratios for atmospheric deposition. Such information was not derived directly during the period of atmospheric testing because suitable mass spectrometric capability was not available. The currently derived records are based on an annual herbage archive and a core from an Alpine glacier. These studies reveal hitherto unseen fluctuations in the 238U/235U atmospheric fallout record, some of which are directly related to nuclear testing. In addition, they also provide the first evidence that plutonium contamination originating from Nevada Desert atmospheric weapon tests in 1952 and 1953 extended eastwards as far as northwestern Europe. The results presented here demonstrate that we now have the capability to detect and precisely identify sources of plutonium in the environment with implications for the development of atmospheric transport models, recent geochronology and environmental studies.

Rapid procedure for plutonium and uranium determination in soils using a borate fusion followed by ion-exchange and extraction chromatography

A rapid and highly precise method, which uses a borate fusion, of U and Pu determination in soils, sediments and other materials is described. The chemical separation steps are optimised by using an anion resin column stacked on an extraction chromatography column (Eichrom Industries UTEVA resin). The whole procedure was streamlined to measure 700 soil samples in 10 weeks as part of an urgent environmental monitoring programme. Uranium was measured using thermal ionisation mass spectrometry with a precision of 0.2% at the 95% uncertainty level. Pu was measured using alpha spectrometry with a precision of approximately 10% at the 95% uncertainty level. The method can be applied successfully to a wide range of sample types and other actinide elements (Th, Am, etc.) can also be effectively included in the analytical scheme. The whole method has been critically evaluated by measuring a range of international reference samples.

ADSORPTION OF RADIOACTIVE METALS BY STRONGLY MAGNETIC IRON SULFIDE NANOPARTICLES PRODUCED BY SULFATE-REDUCING BACTERIA

The adsorption of a number of radioactive ions from solution by a strongly magnetic iron sulfide material was studied. The material was produced by sulfate-reducing bacteria in a novel bioreactor. The uptake was rapid and loading on the adsorbent was high due to the high surface area of the adsorbent and because many of the ions were chemisorbed. The structural properties were examined with high-resolution imaging and electron diffraction by transmission electron microscopy. The adsorbent surface area was determined to be 400–500m2/g by adsorption of heavy metals, the magnetic properties, neutron scattering, and transmission electron microscopy. The adsorption of a number of radionuclides was examined at considerably lower concentration than in previous work with these adsorbent materials. A number of ions studied are of interest to the nuclear industry, particularly the pertechnetate ion (TcO4 −). 99Tc is a radionuclide thought to determine the long-term environmental impact of the nuclear fuel cycle because of its long half-life and because it occurs normally in the form of the highly soluble pertechnetate ion, which can enter the food chain. This bacteria-generated iron sulfide may provide a suitable matrix for the long-term safe storage of the pertechnetate ion. Also, because of the prevalence of the anaerobic sulfate-reducing bacteria worldwide and, in particular, in sediments, the release of radioactive heavy metals or toxic heavy metals into the environment could be engineered so that they are immobilized by sulfate-reducing bacteria or the adsorbents that they produce and removed from the food chain.

Multiple ion counting determination of plutonium isotope ratios using multi-collector ICP-MS

Sector-field multi-collector inductively coupled plasma mass spectrometers, commonly referred to as MC-ICP-MS, can now be fitted with multiple ion counting detectors in tandem with the array of Faraday detectors. In this paper, for the first time, we utilise such an array to measure plutonium isotopes. The chief advantage of multiple ion counting is that it obviates the need to cycle a number of small ion beams through a single collector, and hence increases the efficiency of ion beam usage. This increase in efficiency, combined with the elimination of effects produced by ion beam instability, makes multi-channel analysis an ideal method for low-level plutonium isotope analysis. Mass bias and inter-detector bias can be corrected using an external standard solution, which can be uranium or plutonium based. Using minimised analytical times and desolvating nebulisation, 240Pu/239Pu can be reproduced to better than 3% 2s with less than 10 fg of Pu.

Continuous radionuclide recovery from wastewater using magnetotactic bacteria

Magnetotactic bacteria (MTB) can be magnetically removed and harvested from samples collected from ponds and streams. This is achieved by placing a permanent magnet at the sediment/water interface of a sample container. The bacteria swim along field lines, accumulating at regions close to the pole of the magnet. This is the basic principle of Orientation Magnetic Separation (OMS), where the applied magnetic field is utilised to orientate the bacteria to swim in a specific direction. This paper describes the use of MTB for bioaccumulation and radionucleide removal from wastewater using an OMS system.

Precise and rapid determination of 238U/235U and uranium concentration in soil samples using thermal ionisation mass spectrometry

Abstract Uranium isotopic composition and concentration have been determined on over 500 soil samples from the Greenham Common Air Base and surrounding Berkshire, UK, to detect potential contamination from nuclear sources. Due to the large number of samples involved in this study and the potentially subtle nature of the contamination a new method of analysis was developed which is both rapid and highly precise. Data are presented for international standard reference materials and soil samples for uranium content and 238U/235U measured by thermal ionisation mass spectrometry (TIMS) using a dynamic combination of Faraday and ion-counting detectors. Precision of the 238U/235U ratio was enhanced by correcting for mass bias as a function of ion beam intensity. In-run mass fractionation was controlled without recourse to double spiking by ensuring that sample loads were always in excess of 350 ng U. The resulting reproducibility for standards and soil samples was better than 0.2% at 2 standard deviations (sd). This precision means that an addition of ≥0.4 ng of enriched uranium (93 at% 235U) per gram of typical soil can be reliably identified. Subtle deviations from natural uranium composition have been recognised in a number of soil samples in the Aldermaston area.

Evidence for the Preservation of Technogenic Tritiated Organic Compounds in an Estuarine Sedimentary Environment

The macrotidal Severn Estuary (southwestern UK) has received a broad range of industrial discharges since the beginning of the Industrial Revolution. A more recent anthropogenic input to the estuary has been technogenic tritium (specifically organically bound tritium, OBT). This was derived from a specialized industrial laboratory producing custom radiolabeled compounds for life science research and diagnostic testing from 1980 until 2008. While it was generally acknowledged that the radiological impact of the tritium discharges into the Estuary was small, public concern motivated the company and regulatory agencies to commission several research studies from 1998 to 2005 to better understand their environmental impact. This study examined OBT interaction with estuarine sediment by acquiring a broad range of geochemical and sedimentological data from a suite of sediment cores collected from the northern side of the Estuary. Two important observations are that the OBT compounds are strongly bound to the clay/silt fraction of sediment and that the down-core OBT profiles in intertidal and subtidal sediments are broadly similar to the discharge record. Geochemical and chronometric methods (Cu, Pb and Zn elemental profiles, (210)Pb, (137)Cs) provide important corroboration of the OBT record. A key additional piece of evidence that firmly authenticated the established chronology was the discovery of a previously unreported sedimentary marker layer that was generated by a major storm surge that occurred on December 13, 1981. Although this study has provided clear evidence of systematic accumulation of OBT in sedimentary sinks of the region, an estimation of its depositional inventory shows it represents only a small fraction of the total discharge. This modest retention in the principal sedimentary sinks of the Severn Estuary system reflects the particular dynamics of this highly macrotidal sediment starved estuary.

Effective desorption of tritium from diverse solid matrices and its application to routine analysis of decommissioning materials

Tritium extraction from materials is most commonly carried out using oxidative thermal desorption in purpose-built furnace systems and typically involves trapping the product in a water bubbler which is sampled for measurement using liquid scintillation counting (LSC). The performance of perhaps the most widely used commercial system, the Raddec Pyrolyser, has been evaluated for a broad range of sample types. Several parameters that were expected to affect tritium desorption and recovery were systematically studied. These included sample heating rates and end-point temperatures, carrier/oxidant gas flows, catalyst temperature, bubbler trapping and carry-over/memory effects. A catalyst such as platinised-alumina is used to ensure the quantitative oxidation of volatile combustion products to HTO and CO(2). This also ensures that the trapped decomposition products do not colourise the bubbler solutions that are subsequently sampled for LSC. Tritium evolution profiles were determined for a range of sample types and were obtained by systematically changing bubblers at a set of progressively increasing temperatures. These experiments showed the maximum heating temperature and total combustion time required for the complete recovery of tritium from samples was dependent on the sample matrix types and the (3)H form. These evolution profiles need only be determined once and are readily transferable to other Pyrolyser systems. For example tritiated water is rapidly liberated from samples at temperature around 100 degrees C whereas (3)H substituted for structural H in organic species can require a temperature in excess of 300 degrees C to be released. Higher temperatures (up to 900 degrees C) are needed to liberate (3)H originating from neutron capture reactions on trace Li or B within a material (e.g. reactor graphite or concrete). The furnace system investigated is highly effective at extracting tritium and (14)C from all sample types studied (soil, sediment, biota, wood, metal, plastic, concrete, graphite, etc.) and overall it demonstrates high and reproducible recoveries.

AN OPTIMISED AND ROBUST METHOD FOR THE DETERMINATION OF URANIUM AND PLUTONIUM IN AQUEOUS SAMPLES

Abstract The paper describes a method for the separation of uranium and plutonium isotopes using anion exchange resin and UTEVA ™ resin in stacked sequential columns for routine analysis of river water and liquid effluent samples. The optimisation of the UTEVA ™ column for separation of U is described and compared with the conventional anion exchange technique for the separation of U from Fe. The stacked anion exchange and UTEVA ™ column configuration facilitates a more rapid and efficient separation of Pu and U and also reduces the quantity of reagents required for the separation.

Review of analytical techniques for the determination of Americium-241 in soils and sediments

Abstract This paper reviews the literature on the separation and quantitative determination of 241 Am in soils and sediments. It identifies a range of separation techniques that have been employed by various investigators and assesses the merits of each technique to determine a preferred method for the separation of 241 Am in a complex matrix such as soil or sediment. The paper also presents the experiences of two U.K. laboratories dealing with the separation of 241 Am from sediments revealing problems encountered with unpredictable behaviour of the separation chemistry. Suggestions are offered as to the cause of these problems along with possible solutions to the difficulties.