Search

In this work, a comparative study of two popular radiochemical procedures for 90Sr determination in biological and sediment samples via Cerenkov counting was performed. Comparative tests were carried out with a Liquid Scintillation Counter (LSC) and several key factors related to green analytical chemistry were considered. Chemical yields, time of analysis, cost per sample, hazardous reagents used (H-factor), wastes generated (E-factor) and energy consumed (Q-factor) were calculated. The separation methods are based on two contrasted extraction mechanisms: chromatographic extraction (using Sr resin, a crown-ether diluted in octanol) and liquid-liquid solvent extraction (using HDEHP, an organophosphorus compound), where the chromatographic extraction method was optimized. The developed analytical procedure based on HDEHP was cheaper and faster than the analytical procedure based on Sr resin, according to the green chemistry. On the other hand, the Sr resin method provided a minimum detectable activity (MDA) of 1.1 Bq kg−1, lower than 1.5 Bq kg−1 corresponding to HDEHP method, due to the higher capacity of sample that can be loaded into the resin. The accuracy and reproducibility of both methods was confirmed in the analysis of certified reference materials provided by the International Atomic Energy Agency (IAEA). [ABSTRACT FROM AUTHOR]

Abstract: The simultaneous estimation of particulate organic carbon (POC), particulate inorganic carbon (PIC) and biogenic silica (BSi) export fluxes is key to the study of carbon export due to the hypothesized role of biominerals in the sinking of organic particles. This paper presents of the first attempts to measure downward fluxes of POC, PIC and BSi from the surface ocean using both the 234Th-238U and the 210Po-210Pb disequilibria and drifting sediments trap synchronously at the Porcupine Abyssal Plain in summer 2009. The combined use of the three techniques allowed us to analyze their suitability not only for POC flux estimates, but also as tracers of PIC and BSi fluxes. POC and biomineral/radionuclide ratios were measured in two size fractions to better understand differences between 234Th derived export and 210Po derived export. 210Po derived POC and biomineral fluxes were unexpectedly closer to POC and biomineral fluxes recorded by sediment traps than 234Th derived POC and biomineral fluxes which were higher than obtained from the other two approaches. We suggest that 210Po, because of its biogeochemical behavior, is a better proxy for POC and mineral fluxes than is 234Th in post bloom conditions. The contribution of smaller (1–53μm) particles to flux is also considered in order to explain the differences in derived fluxes. [Copyright &y& Elsevier]

234Th measurements are widely used to estimate the downward carbon flux of particles via the oceanic Biological Pump. Carbon export is evaluated from 234Th‐238U disequilibrium assuming either steady state (SS) conditions, or including a non‐SS (NSS) correction. We use a novel stochastic simulation to quantify the temporal variation of vertical carbon and 234Th (dissolved and particulate) concentration profiles with high temporal resolution. We calculate seasonal export as if in situ measured with sediment trap and SS‐ and NSS‐234Th approaches and quantify the periods of validity for SS/NSS conditions defined in previous works. The SS approach is valid throughout the entire season in oligotrophic regions. In temperate regions, the SS introduces a bias in the export if sampling takes place outside specific temporal windows. Windows of validity range from days in short blooms of ~15‐day duration to weeks in blooms longer than ~30 days. Plain Language Summary: Climate change driven by anthropogenic CO2 emissions has a significant impact on mankind. An important component of Earth's carbon cycle is the ocean's biological carbon pump (BCP), which buffers the air‐sea balance of CO2. It starts with production of organic matter in the surface ocean, continues with its sinking into the dark ocean, and finishes with the storage of a small fraction below 1,000 m. Without the BCP, atmospheric CO2 concentration would be 50% higher than it currently is. Understanding the BCP helps to predict the future CO2 that will be stored by the oceans and how that will affect the global carbon cycle. The photosynthetically fixed carbon is mainly transferred as large particles. Among the methods currently used to estimate the downward flux of particles, sediment traps, and 234Th‐238U radioactive pair are the most accepted ones. However, the simultaneous use of these two techniques does not always provide comparable flux estimates. This questions the consistency of our current calculations of the magnitude of the carbon flux and the accuracy of the global predictions. In this study, we assess the accuracy of the 234Th method in relation to the traps and explain the source of the discrepancies between them. Key Points: We assess downward carbon flux temporal evolution along the season from simulated sinking carbon and dissolved and particulate 234Th depth profilesWe analyze the accuracy of the steady/non‐steady state approaches to calculate the 234Th‐derived carbon flux in relation to the trap fluxWe quantify temporal windows during which the steady state approach results accurate and introduce the concept of "window of success" [ABSTRACT FROM AUTHOR]

A Lagrangian transport model for the North Atlantic has been applied to simulate the historical releases of 137 Cs, 129 I and 236 U from the European nuclear fuel reprocessing plants. Advection by currents, mixing and decay are included, as radionuclide interactions between water, sediments and suspended matter. The model was validated comparing predictions with measured radionuclide concentrations in water and sediments in several areas. 129 I and 236 U signals entering the Arctic Ocean have been compared with the input terms: the 236 U signal is distorted, but the 129 I signal preserves its shape. In the first moments after the releases, the sediments act as sinks for 236 U, but not significantly for 129 I and ultimately they become sources of 236 U to the open sea. This results in a weaker correlation between input and output signals for 236 U than for 129 I. The same effects as for 236 U have been found for 137 Cs signal into the Arctic., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier Ltd.. All rights reserved.)

The development of Deep Geological Repositories (DGP) to the storage of high-level radioactive waste (HLRW) is mainly focused in systems of multiple barriers based on the use of clays, and particularly bentonites, as natural and engineered barriers in nuclear waste isolation due to their remarkable properties. Due to the fact that uranium is the major component of HLRW, it is required to go in depth in the analysis of the chemistry of the reaction of this element within bentonites. The determination of uranium under the conditions of HLRW, including the analysis of silicate matrices before and after the uranium-bentonite reaction, was investigated. The performances of a state-of-the-art and widespread radiochemical method based on chromatographic UTEVA resins, and a well-known and traditional method based on solvent extraction with tri-n-butyl phosphate (TBP), for the analysis of uranium and thorium isotopes in solid matrices with high concentrations of uranium were analysed in detail. In the development of this comparison, both radiochemical approaches have an overall excellent performance in order to analyse uranium concentration in HLRW samples. However, due to the high uranium concentration in the samples, the chromatographic resin is not able to avoid completely the uranium contamination in the thorium fraction., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

A numerical model, previously validated with other radionuclides, was applied to simulate the dispersion of 236 U released from European nuclear fuel reprocessing plants in the North Atlantic and Shelf Seas using a published reconstruction of Sellafield and La Hague releases. Model results are in better agreement with observations if the lowest estimation of such releases are used. This implies that approximately 40kg of 236 U has been discharged from Sellafield. It was found that adsorption of 236 U on bed sediments of the shallow European Shelf Seas plays an essential role in its dispersion patterns. This contrasts strongly with the more conservative behaviour of 129 I in the same area. This has two important implications in the use of 236 U as oceanographic tracer; i) special care must be taken in coastal areas, as sediments might act as sinks and sources of 236 U; ii) the annual input function of 236 U into the Arctic is not directly controlled by the annual discharges from Sellafield and La Hague, since sediments from the Irish, Celtic and North Sea modulate and smooth the signal. Only 52% of the total releases enter into the Arctic Ocean., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Most of the anthropogenic radionuclide 129 I released to the marine environment from the nuclear fuel reprocessing plants (NFRP) at Sellafield (England) and La Hague (France) is transported to the Arctic Ocean via the North Atlantic Current and the Norwegian Coastal Current. 129 I concentrations in seawater provides a powerful and well-established radiotracer technique to provide information about the mechanisms which govern water mass transport in the Nordic Seas and the Arctic Ocean and is gaining importance when coupled with other tracers (e.g. CFC, 236 U). In this work, 129 I concentrations in surface and depth profiles from the Nordic Seas and the North Atlantic (NA) Ocean collected from four different cruises between 2011 and 2012 are presented. This work allowed us to i) update information on 129 I concentrations in these areas, required for the accurate use of 129 I as a tracer of water masses; and ii) investigate the formation of deep water currents in the eastern part of the Nordic Seas, by the analysis of 129 I concentrations and temperature-salinity (T-S) diagrams from locations within the Greenland Sea Gyre. In the Nordic Seas, 129 I concentrations in seawater are of the order of 10 9 at·kg -1 , one or two orders of magnitude higher than those measured at the NA Ocean, not so importantly affected by the releases from the NFRP. 129 I concentrations of the order of 10 8 atoms·kg -1 at the Ellet Line and the PAP suggest a direct contribution from the NFRP in the NA Ocean. An increase in the concentrations in the Nordic Seas between 2002 and 2012 has been detected, which agrees with the temporal evolution of the 129 I liquid discharges from the NFRPs in years prior to this. Finally, 129 I profile concentrations, 129 I inventories and T-S diagrams suggest that deep water formation occurred in the easternmost area of the Nordic Seas during 2012., (Copyright © 2017 Elsevier B.V. All rights reserved.)

In this work we present and evaluate a radiochemical procedure optimised for the analysis of 236 U and 239,240 Pu in seawater samples by Accelerator Mass Spectrometry (AMS). The method is based on Fe(OH) 3 co-precipitation of actinides and uses TEVA® and UTEVA® extraction chromatography resins in a simplified way for the final U and Pu purification. In order to improve the performance of the method, the radiochemical yields are analysed in 1 to 10L seawater volumes using alpha spectrometry (AS) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Robust 80% plutonium recoveries are obtained; however, it is found that Fe(III) concentration in the precipitation solution and sample volume are the two critical and correlated parameters influencing the initial uranium extraction through Fe(OH) 3 co-precipitation. Therefore, we propose an expression that optimises the sample volume and Fe(III) amounts according to both the 236 U and 239,240 Pu concentrations in the samples and the performance parameters of the AMS facility. The method is validated for the current setup of the 1MV AMS system (CNA, Sevilla, Spain), where He gas is used as a stripper, by analysing a set of intercomparison seawater samples, together with the Laboratory of Ion Beam Physics (ETH, Zürich, Switzerland)., (Copyright © 2017 Elsevier B.V. All rights reserved.)