| 1. |
- Chamizo, E., et al.
(författare)
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Performance of the 1 MV Accelerator Mass Spectrometry system at the Centro Nacional de Aceleradores for the analysis of U-233 at environmental levels
- 2022
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Ingår i: Nuclear Instruments and Methods in Physics Research Section B. - : ELSEVIER. - 0168-583X .- 1872-9584. ; 533, s. 81-89
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Tidskriftsartikel (refereegranskat)abstract
- U-233 (T-1/2 = 0.159 My) has aroused much interest in the last few years because of the potential of U-233/U-236 to inform about anthropogenic U sources. The reported U-233/U-238 atom ratios in general environmental samples are in the 10(-12)-10(-6) range. We demonstrate that U-233/U-238 abundance sensitivities at the 5 x 10(-11) level can be achieved at the 1 MV Accelerator Mass Spectrometry system at the Centro Nacional de Aceleradores (CNA, Seville, Spain). Unresolved U-234, U-235 and Th-232 molecular fragments are identified as the main U-233 background contributors and procedures to subtract them are proposed. U-233/U-238 and U-236/U-238 atom ratios were analysed in the IAEA reference materials coded Soil-6, 300, 385, 410, and 412 at the CNA and at the 600 kV ETH AMS system for intercomparison. U-233/U-238 atom ratios for samples 412 and 385 were only reported by the ETH.
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| 2. |
- Chamizo, E., et al.
(författare)
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The Potential of U-233/U-236 as a Water Mass Tracer in the Arctic Ocean
- 2022
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Ingår i: Journal of Geophysical Research - Oceans. - : Wiley-Blackwell Publishing, Inc.. - 2169-9275 .- 2169-9291. ; 127:3
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Tidskriftsartikel (refereegranskat)abstract
- This study explores for the first time the possibilities that the U-233/U-236 atom ratio offers to distinguish waters of Atlantic or Pacific origin in the Arctic Ocean. Atlantic waters entering the Arctic Ocean often carry an isotopic signature dominantly originating from European reprocessing facilities with some smaller contribution from global fallout nuclides, whereas northern Pacific waters are labeled with nuclides released during the atmospheric nuclear testing period only. In the Arctic Ocean, U-233 originates from global fallout while U-236 carries both, a global fallout and a prominent nuclear reprocessing signal. Thus, the U-233/U-236 ratio provides a tool to identify water masses with distinct U sources. In this work, U-233 and U-236 were analyzed in samples from the GN01 GEOTRACES expedition to the western Arctic Ocean in 2015. The study of depth profiles and surface seawater samples shows that: (a) Pacific and Atlantic waters show enhanced signals of both radionuclides, which can be unraveled based on their U-233/U-236 signature; and (b) Deep and Bottom Waters show extremely low U-233 and U-236 concentrations close to or below analytical detection limits with isotopic ratios distinct from known anthropogenic U sources. The comparably high U-233/U-236 ratios are interpreted as a relative increase of naturally occurring U-233 and U-236 and thus for gradually reaching natural U-233/U-236 levels in the deep Arctic Ocean. Our results set the basis for future studies using the U-233/U-236 ratio to distinguish anthropogenic and pre-anthropogenic U in the Arctic Ocean and beyond.
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| 3. |
- López Lora, Mercedes, et al.
(författare)
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Plutonium Signatures in a Dated Sediment Core as a Tool to Reveal Nuclear Sources in the Baltic Sea
- 2023
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Ingår i: Environmental Science and Technology. - : AMER CHEMICAL SOC. - 0013-936X .- 1520-5851. ; 57:5, s. 1959-1969
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Tidskriftsartikel (refereegranskat)abstract
- Plutonium distribution was studied in an undisturbed sediment core sampled from the Tvaren bay in the vicinity of the Studsvik nuclear facility in Sweden. The complete analysis, including minor isotopes, of the Pu isotope composition (238Pu, 239Pu, oPu, 241Pu, 242Pu, and 244Pu) allowed us to establish the Pu origin in this area of the Baltic Sea and to reconstruct the Studsvik aquatic release history. The results show highly enriched 239Pu, probably originating from the Swedish nuclear program in the 1960s and 1970s and the handling of high burn-up nuclear fuel in the later years. In addition, the 244Pu/239Pu atomic ratio for the global fallout period between 1958 and 1965 is suggested to be (7.94 +/- 0.31)center dot 10-5. In the bottom layer of the sediment, dated 1953-1957, we detected a higher average 244Pu/239Pu ratio of (1.51 +/- 0.11)center dot 10-4, indicating the possible impact of the first US thermonuclear tests (1952-1958).
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| 4. |
- López Lora, Mercedes, et al.
(författare)
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U-236, Np-237 and Pu-239,Pu-240 as complementary fingerprints of radioactive effluents in the western Mediterranean Sea and in the Canada Basin (Arctic Ocean)
- 2021
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Ingår i: Science of the Total Environment. - : ELSEVIER. - 0048-9697 .- 1879-1026. ; 765
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to assess the potential of combining the conservatively behaving anthropogenic radionuclides U-236 and Np-237 to gain information on the origin of water masses tagged with liquid effluents from Nuclear Reprocessing Plants. This work includes samples collected from three full-depth water columns in two areas: i) the Arctic Ocean, where Atlantic waters carry the signal of Sellafield (United Kingdom) and La Hague (France) nuclear reprocessing facilities; and ii) the western Mediterranean Sea, directly impacted by Marcoule reprocessing plant (France). This work is complemented by the study of the particle-reactive Pu isotopes as an additional fingerprint of the source region. In the Canada Basin, Atlantic waters showed the highest concentrations and Np-237/U-236 ratios in agreement with the estimated values for North Atlantic waters entering the Arctic Ocean and tagged with the signal of European Nuclear Reprocessing Plants. These results may reflect the impact of the documented releases for the 1990s. In the Mediterranean Sea, an excess of U-236 presumably caused by Marcoule is reflected in the lower Np-237/U-236 ratios compared to the Global Fallout signal in all the studied samples. On the contrary, the Pu-239,Pu-240 profiles were mainly governed by the Global Fallout. The impact of Marcoule as a local source is further corroborated when comparing the temporal evolution of these ratios between 2001 and 2013. The lowest Np-237/U-236 ratios observed in 2001 at the surface reflect a previous local input that is no longer observed in 2013 as it had been homogenized through the whole water column. This work presents the use of Np-237 as a new ocean tracer. A more accurate characterization of the main sources is still needed to optimize the use of U-236-Np-237 as a new tool to understand transient oceanographic processes. (C) 2020 Elsevier B.V. All rights reserved.
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| 5. |
- Rozmaric, M., et al.
(författare)
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Fate of anthropogenic radionuclides (Sr-90, Cs-137, Pu-238, Pu-239, Pu-240, 241Am) in seawater in the northern Benguela upwelling system off Namibia
- 2022
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Ingår i: Chemosphere. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0045-6535 .- 1879-1298. ; 286
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Tidskriftsartikel (refereegranskat)abstract
- A baseline study on anthropogenic radioactivity in the Namibian marine ecosystem, which is part of the northern Benguela upwelling system, known as one of the most productive ocean areas in the world, has been performed. A scientific cruise carried out in 2014 covering inshore and offshore areas, exhibiting different oceanographic features, has provided a basis for better understanding the distributions, ratios and inventories of six anthropogenic radionuclides (90Sr, 137Cs, 238Pu, 239Pu, 240Pu and 241Am) in seawater. Although 3H was also measured, due to extremely low levels, its behaviour was not studied. The main source of 90Sr, 137Cs, 239Pu, 240Pu and 241Am in the samples analysed was proven to be global fallout, a finding further confirmed by 240Pu/239Pu and 90Sr/137Cs ratios. Furthermore, the 238Pu SNAP-9A satellite accident signal was confirmed once again through the determination of the 238Pu/239+240Pu activity ratio. Inshore and offshore samples showed different patterns due to the unique oceanographic features of this upwelling system. The levels of anthropogenic radionuclides, comprehensively assessed for the first time in this region, are comparable with the few existing data and filled a critical gap for the Southern Atlantic Ocean.
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| 6. |
- Törnquist, Per, et al.
(författare)
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On the use of dated sediments to investigate historical nuclear discharges
- 2023
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Ingår i: Marine Pollution Bulletin. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0025-326X .- 1879-3363. ; 188
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Forskningsöversikt (refereegranskat)abstract
- Studsvik, a Swedish nuclear research facility, has been releasing aquatic radioactive discharges in the Baltic Sea, through the bay Tva center dot ren, since 1959. The permissible discharge levels are regulated by the Swedish Radiation Safety Authority (SSM) but only information about 60Co, 137Cs, 152Eu, total alpha and beta activities were re-ported up to 2002. Since then, the reports cover most a more comprehensive set of radionuclides. In this context, the seabed can be utilized as a chronological archive to investigate historical Studsvik releases. To this end, 23 sediment cores covering the whole area of the bay were studied and 5 of them were dated using 210Pb-dating methods. Since the discharges from Studsvik contain both plutonium and caesium, neither can be used to validate the 210Pb-dating method. Instead, stable lead with maximum deposition, known to be dated to 1970, was used. Cobalt-60, 137Cs, and 152Eu depth distributions were studied from the dated sediment cores and compared with reported levels of aquatic discharges. The expected sediment 137Cs-peak from the fallout from the Chornobyl accident was however smeared out, indicating an ongoing inflow of 137Cs with the Baltic seawater. Our findings show that reported releases of aquatic discharges of 60Co and 152Eu are consistent with measured sediment activity distribution. The sediments from the deepest parts of Tva center dot ren, with intact chronology and with a high time resolution, are ideal for investigating historical nuclear discharges and can be a tool to investigate unreported radionuclide releases. Dated sediment can in this way be a tool for nuclear safeguards to evaluate past and present activities in nuclear facilities.
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